On a cold winter day, a stove is heated in the room. In order for the firewood to burn well, the oven door is kept slightly open. If you cover it tightly, the firewood will go out.
From this it can be concluded that combustion requires an influx of air. A tightly closed stove door does not let air through to the wood.
Try this simple experiment. Fix a burning candle at the bottom of the glass jar (Fig. 1) and tightly close the jar with a piece of glass to outdoor air could not penetrate under it (for this, it is best to grease the edges of the jar and glass with lard or petroleum jelly).
A candle closed in this way will soon go out. At first, it will burn with an ordinary, bright flame, but then the flame will dim and go out.
If you now open the lid and put another lit candle in the jar, it will immediately go out!
What's the matter here?
The answer involuntarily suggests itself: it turns out that only fresh air is needed for combustion. In the jar, after a candle burned in it for some time, the air "spoiled", became unfit for combustion.
The correctness of this conclusion can be verified in another way. Have you all noticed, for example, that when in a closed room for a long time there are many people, then a kerosene lamp or a candle burns very dimly. Not enough to burn fresh air, and the air in the room "spoiled".
But what does it mean: the air has "spoiled"?
Remember that air is a mixture of many gases; it includes nitrogen, oxygen, carbon dioxide (a compound of carbon and oxygen), water vapor and the so-called inert gases - helium, argon, neon, krypton and xenon.
Most of all in the air is nitrogen, more than 78 percent of the total volume. Then comes oxygen - it takes about a fifth. Inert gases together occupy less than one hundredth of the volume of air. And the content of water vapor and carbon dioxide in the atmosphere in different places and in different time happens different.
So, when scientists first began to find out the cause of combustion (and this was in the 18th century), it was noticed that a burning body, such as a candle, takes one fifth of it from the air. As soon as this part is used up, the candle will go out.
One fifth of the air is, as already mentioned, oxygen.
So, it is the substance that is necessary for combustion.
And it is really known that in pure oxygen bodies burn very brightly and quickly burn out. You can, for example, fill a jar with oxygen and lower a smoldering splinter into it, the splinter flares up with a bright flame. Even metals burn in oxygen. If an iron wire is red-hot and placed in a jar of oxygen, it will burn, scattering bright sparks (Fig. 2).
Thus, air is necessary for combustion only insofar as it contains oxygen. Oxygen disappears from the air - and the remaining gases are no longer suitable for combustion. This is exactly what happens in a room where there are a lot of people: the oxygen content in the air decreases and the amount of carbon dioxide increases.
Burning down in closed jar, the candle takes all the oxygen from the air and then goes out.
When we tightly close the stove door, burning wood also takes away oxygen from the air in the stove and, if the supply of fresh, oxygen-rich air is stopped, they go out.
Let us now see what happens to oxygen during combustion.
When combustion occurs, oxygen combines with the burning substance. In this case, the so-called oxidation reaction occurs.
Oxygen has a very high chemical activity, it is able to combine with almost all chemical elements. Therefore, oxidation processes are widespread in nature.
Let's take the rusting of iron objects - this is a slow combination of iron with oxygen in the air and water.
The same slow oxidation is the smoldering of animal and plant substances, for example, the smoldering of a tree. In this case, the substance is oxidized and decomposes with the formation of carbon dioxide and water.
There are cases when in old, abandoned and clogged wells or in big caves where there is no influx of fresh air, large amounts of carbon dioxide accumulate from smoldering. In Italy, a cave is known, which is called "Dog". It contains a lot of bones of dead animals - dogs, rabbits, mice. Getting here, the animals die very soon. People walk freely in the cave. In the past, a legend was created about the Dog Cave. An evil “spirit” lives in the cave, superstitious people said. Its heavy poisonous breath spreads along the bottom of the cave; all the animals that get here die from it. When scientists explored the cave, they easily solved its riddle. It turned out that large amounts of heavy carbon dioxide had accumulated at the bottom of the cave; getting into it, small animals suffocate from lack of oxygen and die.
Complex oxidative processes also occur in the human body. Therefore, we need oxygen for breathing, and not any other gas. In a living organism, as in an oven, food is oxidized, “burned out” with the formation of a number of new substances, including carbon dioxide, which is released from the body during breathing.
Oxidation almost always releases heat. That is why our body has an increased temperature compared to the environment (36-37 degrees).
Heat is released during both rusting and smoldering. We do not notice this only because the oxidation here is very slow and the heat released is usually given off to the surrounding air. True, there are cases when the heat generated during slow oxidation is retained. Then we observe an increase in temperature and even spontaneous combustion. So, for example, coal or old, caked hay ignites spontaneously when it begins to smolder and the heat lingers inside the haystack. For the same reason, manure heats up.
But especially much heat is released during combustion, i.e., during the oxidation of combustible substances. In this case, the substances formed from combustion are heated and begin to glow. The flame appears.
Thus, combustion is a rapid oxidation with the release of large amounts of heat and the formation of light.
What substances are included in the composition of combustible bodies? Which substances are oxidized during combustion?
Chemical analysis of various combustible bodies - coal, wood, tallow, oil, stearin, kerosene - shows that they consist mainly of two chemical elements - carbon and hydrogen. When these elements interact with atmospheric oxygen, carbon dioxide and water vapor are formed, and a lot of heat is also released.
If combustion occurs under conditions when there is no fresh air inflow, then the air “spoils”: it becomes less and less oxygen, which goes to oxidize the fuel, and instead of it, water vapor and carbon dioxide are released into the air.
There is a simple experiment that can be used to make sure that these substances are formed during combustion.
The lamp glass is mounted on a stand, as shown in fig. 3, and hung on the scale pan. A candle is placed under the glass. The narrow part of the glass is blocked with a mesh, on which a layer of quicklime and a layer of alkali - caustic soda are placed. These two substances well absorb water vapor and carbon dioxide formed during combustion.
Then weights are placed on the second cup to balance it with the first, and a candle is lit.
As the candle burns out, the weighing pan, on which the lamp glass with the candle stands, will gradually fall down.
The explanation for this seemingly unexpected phenomenon is extremely simple. When burning, a candle takes oxygen from the surrounding air. It combines with carbon and hydrogen, which are part of the stearin candle. Therefore, the carbon dioxide and water vapor formed in this process already weigh more than the burned substances weighed. Under normal conditions, the combustion products of a candle fly into the air and the weighing pan with a candle becomes lighter as it burns. But in our experience they linger quicklime and caustic soda. Therefore, the weight of the candle and the products of its combustion is not less, but more than the weight of the originally taken candle.
From what we have said about combustion, it becomes clear why water does not burn, but coal and other combustible substances do. Water, like carbon dioxide, is already a product of combustion. These are burnt hydrogen and carbon. And coal is basically carbon that has not yet been oxidized, not burned.
1 option
Instruction for students
The test consists of parts A, B and C. It takes 40 minutes to complete. Tasks are recommended to be completed in order. If the task cannot be completed immediately, continue to the next one. If there is time, return to the missed tasks.
Part A
A1. Which of the following are simple non-metal substances?
1) chlorine, nickel, silver 3) iron, phosphorus, mercury
2) diamond, sulfur, calcium 4) oxygen, ozone, nitrogen
A2. chemical element 3rd period of group V periodic system D.I. Mendeleev corresponds to the scheme of distribution of electrons over the layers:
1) 2,8,5 2) 2,3 3) 2,8,3 4) 2,5
A3. For elements of the carbon subgroup with increasing atomic number decreases:
1) atomic radius 3) number of valence electrons in atoms
2) charge of the nucleus of an atom 4) electronegativity
A4. The most durable chemical bond in a molecule
1) F2 2) Cl2 3) O2 4) N2
A5. The interaction of ammonia with hydrogen chloride refers to the reactions:
1) decomposition 2) compounds 3) substitution 4) exchange
A6. Abbreviated ionic reaction equation Ag+ + Cl-◊ AgCl
corresponds to the interaction between solutions:
1) silver carbonate and of hydrochloric acid
2) silver nitrate and sulfuric acid
3) silver nitrate and hydrochloric acid
4) silver sulfate and nitric acid
A7. A burning candle goes out in a corked jar because:
1) there is not enough oxygen 3) the content of nitrogen rises
2) the temperature rises 4) water vapor forms, extinguishing the flame
A8. With the help of a solution of sulfuric acid, transformations can be carried out:
1) copper ◊ copper sulfate (II) 3) sodium carbonate◊ carbon monoxide(IV)
2) carbon ◊ carbon monoxide (IV) 4) silver chloride◊ hydrogen chloride
Part B.
IN 1. Non-metallic properties in the series of elements Si - P - S - Cl from left to right:
1) do not change 3) weaken
2) increase 4) change periodically
IN 2. A shift in the equilibrium of the N2 + 3H2 2 NH3 + Q system towards the reaction product will occur if:
A) an increase in the concentration of ammonia
B) the use of a catalyst
B) pressure reduction
D) reducing the concentration of ammonia
AT 3. What volume (N.S.) of hydrogen chloride can be obtained from 2 mol of chlorine?
Part C.
C1. Find the mass of sulfuric acid required to neutralize 200 g of a 20% sodium hydroxide solution.
C2.
Examination in inorganic chemistry, topic "Non-metals", Grade 9
Option 2
Instruction for students
The test consists of parts A, B and C. It takes 40 minutes to complete. Tasks are recommended to be completed in order. If the task cannot be completed immediately, go to the next one. If there is time, return to the missed tasks.
Part A.
For each task of part A, several answers are given, of which only one is correct. Choose the answer that you think is correct.
A1. How about oxygen simple matter the proposal says:
1) plants, animals and humans breathe oxygen
2) oxygen is part of the water
3) oxides consist of two elements, one of which is oxygen
4) oxygen is included chemical compounds, of which the living
Cell
A2. in the phosphorus atom total number electrons and the number of electron layers, respectively
Equal: 1) 31 and 4 2) 15 and 5 3) 15 and 3 4) 31 and 5
A3. The sum of protons and neutrons in a carbon atom are:
1) 14 2) 12 3) 15 4) 13
A4. A covalent polar chemical bond is characteristic of:
1) KCl 2) HBr 3) P4 4) CaCl2
A5. The reaction, the equation of which is 3N2 + H2 2NH3 + Q, is referred to as the reactions:
1) reversible, exothermic 3) reversible, endothermic
2) irreversible, exothermic 4) irreversible, endothermic
A6. In order to prove that the test tube contains a solution of carbonic acid,
It is necessary to use: 1) hydrochloric acid 3) smoldering splinter
2) ammonia solution 4) sodium hydroxide solution
A7. A sign of the reaction between hydrochloric acid and zinc is:
1) the appearance of an odor 3) the release of gas
2) the formation of a precipitate 4) a change in the color of the solution
A8. abbreviated ionic equation Ba2+ + SO42-◊ BaSO4 corresponds
Interaction between: 1) barium phosphate and sulfuric acid solution
2) solutions of sodium sulfate and barium nitrate
3) solutions of barium hydroxide and sulfuric acid
4) barium carbonate and sulfuric acid solution
Part B.
IN 1. Decreasing serial number in the A (main) subgroups of the periodic system of D.I. Mendeleev, non-metallic properties of chemical elements:
1) do not change 3) change periodically
2) get stronger 4) get weaker
The answer to task B2 is a sequence of letters. Write the selected letters in alphabetical order.
IN 2. Which of the following conditions will not affect the equilibrium shift in the system
H2 + Cl2 2HCl - Q: A) lowering the temperature
B) temperature rise
C) the introduction of a catalyst
D) lowering the concentration of HCl
D) pressure drop
AT 3. What volume of gas (n.c.) will be released during the complete combustion of 600 g of coal?
Part C.
C1. When processing 300 g of wood ash with an excess of hydrochloric acid, 44.8 l (N.O.) of carbon dioxide was obtained. What is mass fraction(%) of potassium carbonate in the original ash sample?
Work instructions
40 minutes are allotted for the performance of the control work in chemistry on the topic "Non-metals". The work consists of three parts (A, B and C) and includes 12 tasks.
Part A contains 8 tasks (A1-A8). Each question has 4 possible answers, of which only one is correct.
Part B contains 3 tasks (B1 - B3). One of them (B1) has 4 possible answers, of which only one is correct. For task B2, you need to write the answer as a sequence of letters, and for task B3 - as a number.
Part C contains one of the most difficult task, to which a full (detailed) answer should be given.
Estimated time to complete the tasks of Part A is 15 minutes, Part B is 15 minutes, and Part C is 10 minutes.
Completion of tasks of various complexity is assessed by 1, 2 or 3 points. Points received for all completed tasks are summed up.
Correct execution of each task of parts A1 -A8 and task B1, i.e. questions with a choice of answers, is estimated by one point.
The maximum score for the correct completion of tasks (B2) with a short answer is two points. A task with a short answer for correspondence or multiple choice is considered to be completed correctly if the student chooses two correct answers out of five proposed answers. In other cases: the correct one is selected; more than two answers are chosen, among which one is correct; among the two selected answers, one is incorrect, the task is evaluated by one point. If there are no correct answers among the selected answers, the task is considered failed. The student gets 0 points. Task (B3) with a short answer in the form calculation problem is considered completed correctly if the student's answer indicates correct sequence digits (number).
The task with a detailed answer provides for the verification of the assimilation of three elements of the content. The presence in the answer of each of these elements is estimated by one point (3-0 points).
Evaluation of work on a five-point scale is determined on the basis of the total number of points received for completing tasks:
"5" - 13-15 points
"4" - 10-12 points
"3" - 7 - 9 points
"2" - 1 - 6 points
Answers and Solutions
No. A1 A2 A3 A4 A5 A6 A7 A8 B1 B2 B3 C1
1 4 1 4 4 2 3 1 3 2 VG 89.6l 49g
2 1 3 2 2 1 1 3 2 2 HP 1120l 92%
1 option (С1)
1) Compiled the reaction equation H2SO4 + 2NaOH = Na2SO4 + 2H2O
2) Calculated mass of sodium hydroxide
M(NaOH)=200*20/100=40(g)
3) The mass of sulfuric acid was found m (H2SO4) \u003d 98 * 40 / 80 \u003d 49 (g)
Option 2 (С1)
1) Compiled the reaction equation K2CO3 + 2HCl= 2KCl + CO2 + H2O
2) Calculated mass of potassium carbonate
M(K2CO3)=138*44.8/22.4=276(g)
3) The mass fraction of potassium carbonate in the ash sample was determined
w(K2CO3)=276*100/300=92(%)
1 option
Instruction for students
The test consists of parts A, B and C. It takes 40 minutes to complete. Tasks are recommended to be completed in order. If the task cannot be completed immediately, continue to the next one. If there is time, return to the missed tasks.
Part A
A1. Which of the following are simple non-metal substances?
1) chlorine, nickel, silver 3) iron, phosphorus, mercury
2) diamond, sulfur, calcium 4) oxygen, ozone, nitrogen
A2. The chemical element of the 3rd period of the V group of the periodic system of D.I. Mendeleev corresponds to the scheme of distribution of electrons over the layers:
1) 2,8,5 2) 2,3 3) 2,8,3 4) 2,5
A3. For elements of the carbon subgroup, with increasing atomic number, the following decreases:
1) atomic radius 3) number of valence electrons in atoms
2) charge of the nucleus of an atom 4) electronegativity
A4. The strongest chemical bond in a molecule
1) F 2 2) Cl 2 3) O 2 4) N 2
A5. The interaction of ammonia with hydrogen chloride refers to the reactions:
1) decomposition 2) compounds 3) substitution 4) exchange
A6. Abbreviated ionic reaction equation Ag + + Cl - AgCl
corresponds to the interaction between solutions:
1) silver carbonate and hydrochloric acid
2) silver nitrate and sulfuric acid
3) silver nitrate and hydrochloric acid
4) silver sulfate and nitric acid
A7. A burning candle goes out in a corked jar because:
1) there is not enough oxygen 3) the content of nitrogen rises
2) the temperature rises 4) water vapor forms, extinguishing the flame
A8. With the help of a solution of sulfuric acid, transformations can be carried out:
1) copper copper sulfate (II) 3) sodium carbonate carbon monoxide (IV)
2) carbon carbon monoxide (IV) 4) silver chloride hydrogen chloride
Part B.
IN 1. Non-metallic properties in the series of elements Si P S Cl from left to right:
1) do not change 3) weaken
2) increase 4) change periodically
IN 2. A shift in the equilibrium of the N 2 + 3H 2 2 NH 3 + Q system towards the reaction product will occur if:
A) an increase in the concentration of ammonia
B) the use of a catalyst
B) pressure reduction
D) reducing the concentration of ammonia
AT 3. What volume (N.S.) of hydrogen chloride can be obtained from 2 mol of chlorine?
Part C.
C1. Find the mass of sulfuric acid required to neutralize 200 g of a 20% sodium hydroxide solution.
Examination in inorganic chemistry, topic "Non-metals", Grade 9
Option 2
Instruction for students
The test consists of parts A, B and C. It takes 40 minutes to complete. Tasks are recommended to be completed in order. If the task cannot be completed immediately, go to the next one. If there is time, return to the missed tasks.
Part A.
For each task of part A, several answers are given, of which only one is correct. Choose the answer that you think is correct.
A1. About oxygen as a simple substance, the sentence says:
1) plants, animals and humans breathe oxygen
2) oxygen is part of the water
3) oxides consist of two elements, one of which is oxygen
4) oxygen is part of the chemical compounds that make up living things
A2. In a phosphorus atom, the total number of electrons and the number of electron layers, respectively
are equal: 1) 31 and 4 2) 15 and 5 3) 15 and 3 4) 31 and 5
A3. The sum of protons and neutrons in a carbon atom are:
1) 14 2) 12 3) 15 4) 13
A4. A covalent polar chemical bond is characteristic of:
1) KCl 2) HBr 3) P 4 4) CaCl 2
A5. The reaction, the equation of which is 3N 2 + H 2 2NH 3 + Q, is referred to as the reactions:
1) reversible, exothermic 3) reversible, endothermic
2) irreversible, exothermic 4) irreversible, endothermic
A6. In order to prove that the test tube contains a solution of carbonic acid,
it is necessary to use: 1) hydrochloric acid 3) smoldering splinter
2) ammonia solution 4) sodium hydroxide solution
A7. A sign of the reaction between hydrochloric acid and zinc is:
1) the appearance of an odor 3) the release of gas
2) the formation of a precipitate 4) a change in the color of the solution
A8. The abbreviated ionic equation Ba 2+ + SO 4 2- BaSO 4 corresponds to
Interaction between: 1) barium phosphate and sulfuric acid solution
2) solutions of sodium sulfate and barium nitrate
3) solutions of barium hydroxide and sulfuric acid
4) barium carbonate and sulfuric acid solution
Part B.
IN 1. With a decrease in the serial number in the A (main) subgroups of the periodic system of D.I. Mendeleev, the non-metallic properties of chemical elements:
1) do not change 3) change periodically
2) get stronger 4) get weaker
The answer to task B2 is a sequence of letters. Write the selected letters in alphabetical order.
IN 2. Which of the following conditions not affect the equilibrium shift in the system
H 2 + Cl 2 2HCl - Q: A) lowering the temperature
B) temperature rise
C) the introduction of a catalyst
D) lowering the concentration of HCl
D) pressure drop
AT 3. What volume of gas (n.c.) will be released during the complete combustion of 600 g of coal?
Part C.
C1. When processing 300 g of wood ash with an excess of hydrochloric acid, 44.8 l (N.O.) of carbon dioxide was obtained. What is the mass fraction (%) of potassium carbonate in the original ash sample?
Work instructions
40 minutes are allotted for the performance of the control work in chemistry on the topic "Non-metals". The work consists of three parts (A, B and C) and includes 12 tasks.
Part A contains 8 tasks (A1-A8). Each question has 4 possible answers, of which only one is correct.
Part B contains 3 tasks (B1 - B3). One of them (B1) has 4 possible answers, of which only one is correct. For task B2, you need to write the answer as a sequence of letters, and for task B3 - as a number.
Part C contains one of the most difficult tasks, which should be given a full (detailed) answer.
Estimated time to complete the tasks of Part A is 15 minutes, Part B is 15 minutes, and Part C is 10 minutes.
Completion of tasks of various complexity is assessed by 1, 2 or 3 points. Points received for all completed tasks are summed up.
Correct execution of each task of parts A1 -A8 and task B1, i.e. questions with a choice of answers, is estimated by one point.
The maximum score for the correct completion of tasks (B2) with a short answer is two points. A task with a short answer for correspondence or multiple choice is considered to be completed correctly if the student chooses two correct answers out of five proposed answers. In other cases: the correct one is selected; more than two answers are chosen, among which one is correct; among the two selected answers, one is incorrect, the task is evaluated by one point. If there are no correct answers among the selected answers, the task is considered failed. The student gets 0 points. Task (B3) with a short answer in the form of a calculation task is considered to be completed correctly if the correct sequence of numbers (number) is indicated in the student's answer.
The task with a detailed answer provides for the verification of the assimilation of three elements of the content. The presence in the answer of each of these elements is estimated by one point (3-0 points).
Evaluation of work on a five-point scale is determined on the basis of the total number of points received for completing tasks:
"5" - 13-15 points
"4" - 10-12 points
"3" - 7 - 9 points
"2" - 1 - 6 points
Answers and Solutions
No. A1 A2 A3 A4 A5 A6 A7 A8 B1 B2 B3 C1
1 4 1 4 4 2 3 1 3 2 VG 89.6l 49g
2 1 3 2 2 1 1 3 2 2 HP 1120l 92%
1 option (C1)
1) The reaction equation H 2 SO 4 + 2NaOH = Na 2 SO 4 + 2H 2 O
2) Calculated mass of sodium hydroxide
m(NaOH)=200*20/100=40(g)
3) The mass of sulfuric acid was found m (H 2 SO 4) \u003d 98 * 40 / 80 \u003d 49 (g)
Option 2 (С1)
1) The equation for the reaction K 2 CO 3 + 2HCl \u003d 2KCl + CO 2 + H 2 O
2) Calculated mass of potassium carbonate
m (K 2 CO 3) \u003d 138 * 44.8 / 22.4 \u003d 276 (g)
3) The mass fraction of potassium carbonate in the ash sample was determined
w(K 2 CO 3) \u003d 276 * 100/300 \u003d 92 (%)
Compiled by a teacher of chemistry MOU secondary school No. 58
Tikhomirova I.P.
Sample plan for a test on the topic "Non-metals" for grade 9
Number Number Content Items to Review Assignment Type Score
Block assignments in points
Part A (I)
1 I Simple and complex substances VO 1
2 I The Periodic Law and the Periodic System
chemical elements DIMendeleeva. Groups
and periods of the periodic system. VO 1
3 I The structure of the atom. The structure of electron shells
atoms of elements No. 1-No. 20 p.s.h.e. VO 1
4 I Chemical bond: ionic, metallic,
covalent (polar, non-polar) VO 1
5 I Classification of chemical reactions according to
various signs. Chemical Equations VO 1
6 I Properties of ions. Qualitative reactions to anions. VO 1
7 I Chemical properties of simple substances: metals and
non-metals VO 1
8 I Relationship inorganic substances various
classes VO 1
Part B (II)
1 II Patterns of changes in the properties of elements and their
compounds in connection with the position in the p.s.h.e. VO 1
2 II Reversible and irreversible reactions. Chemical
equilibrium. KO 2
3 II Calculation of the mass, volume or quantity of one
of the substances involved in the reaction. KO 1
Part C (III)
1 III Calculations according to the equations of chemical reactions with
using solutions with a certain mass
proportion of solute. Finding mass
pure substance using the concept of "impurities" RO 3
Total points 15
Task type designations: IN - choice response
KO - short answer
RO - extended answer
Statistical information on the results of the implementation of k / work on __________ (summary)
School No. ______ class ______ full name teachers __________________________________
Date of completion of the work _________________ No. lesson __________________________
Implemented programs and textbooks on the subject ________________________________________________________________________________
1. Results of the work:
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Number of students completed work |
including those who completed |
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2. The quality of ZUN (number of students who completed the work on "4-5" ______ people _____%
3. Level of training (number of students who completed the work for "3,4,5" ____ people ____%
4. The level of formation of ZUN.
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in general for k / r |
including levels of knowledge |
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coped fully |
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admitted |
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coped |
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proceeded |
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5. Comparison table(data c/r with data for ________________________)
* total wrote the work ______________ people __________%
* Confirmed mark _____________ people __________%
* received a mark below __________ persons. __________%
* received a mark above __________ persons. __________%
6. Of the total number of those absent, they have an assessment for the year:
| Guidelines | ||
- 1. Smoking will occur when there is insufficient oxygen in the combustion atmosphere. I don’t know how to do it, maybe. add water vapor.
2. In a large jar, oxygen did not burn out completely, but some percentage of it remained, so the left candle burned longer than ideally. - Michael,
1. On the first question, an exact solution is needed. The general direction of thought is correct - combustion with a lack of oxygen, but I did not succeed. I tried to just cover the jar with a lid, the flame just gradually goes out, and that's it. There is no smoking.
2. I don't think there will be oxygen left in the big jar. The flame causes strong mixing throughout the volume. Hot carbon dioxide rises - cools from the can - falls down. Plus, its density is 1.5 times greater than that of air, so it will also fall down. - Apparently, part of the carbon dioxide went down from 3 liters. Most likely, the experiment will succeed if the jar is sealed with a piece of plastic lid and turned over before being closed with cardboard.
P.S.
CO2 = 46
Air = 29
Total difference is 1.5 times
For example, you can light a candle chemical reaction potassium permanganate with sulfuric acid
KMnO4 + H2SO4 (conc.)
the resulting oxide, when interacting with paraffin, will ignite it - According to the procedure: I think the answers should have been hidden so that the “second” ones would not see the answers of the “first”, so that there would be no disputes - after all, the competition
Essentially: there is nothing else in the head, there is no way to surf the Internet right now ...
- Michael, openness of comments is normal. The first correct answer still counts.
You don’t need to swear on the Internet, there is more logic and basic knowledge physics and chemistry. And, of course, imagine all the nuances of the experiment in your head. - On the second question: - "Why does the left candle burn for so long?" For some reason, there is still no comment about the burning intensity, if you look at the video it is noticeable that when burning with large quantity carbon dioxide
less gas flame.
On the first question, there is an assumption that perhaps the candle will smoke when the wick is long, that is, the wick burns and burns oxygen around. - Sergei, I agree. It is very difficult to quantify this. Who said that the flame of both candles burns equally intensively? By eye, it seems to be the same, but maybe one consumes more oxygen than the second. And the second is the flame decay processes themselves. As a result, it turns out that we can only give a qualitative assessment (“yes, the left candle burns less”), but not a quantitative assessment.
About burning. The candle "eats" not all the oxygen, but very little. I had a need to organize an oxygen-free atmosphere, and I was just thinking of making it a candle, but I read on the "cavemen" forums that if a candle went out in a closed cave, it means that there is only a couple of percent less oxygen. Well, carbon dioxide there is two or three percent, or what? I do not remember.Andrew August 4, 2010, 06:01
Well, besides, there is such a thing as convection. Carbon dioxide heavier than air and collects from below, and air from above, thus, it turns out somewhat richer in oxygen. This is what allowed the candle to burn out longer.
And how to make her smoke - offhand and I won’t say, you need to play around.- Andrew, did not understand how the thought about convection and about the fact that "Carbon dioxide is heavier than air and collects from below, while air from above is thus somewhat richer in oxygen". If there is strong convection from the flame, as I wrote above, then everything inside the jar is quickly mixed, and there is no role where what is collected.
Anatoly, it is also possible to introduce any object into the middle zone of the flame, where incomplete combustion occurs. Then the soot is deposited on the subject. This is how glass is smoked. You can also watch it here:
Here you can clearly see how the rod and the plastic bag are sooty.
I am still waiting for the last correct answer, where could excess oxygen come from in the closing jar. Hint: think aside thermal expansion gases.
- (hit because the pressure began to decrease in the bank)
- Regarding the first question, I think the answer is already there. It is necessary to do some kind of manipulation so that incomplete oxidation occurs: for example, it can be, for example, an object brought up by a thread - pairs of burning paraffin will cool sharply, not having time to burn out completely (this is still a cold object). If I'm not mistaken, then it seems that it can turn out with the addition of some chemical substances on the wick of the candle.
Regarding the second point:
In general, the burning of a candle in this case can be considered as an inertial link of the nth order. In the simplest case, if the rate of oxygen combustion is directly proportional (although it can be proportional to the square, cube ... concentration). In this case, the less oxygen in the bank, the slower it burns. AT general case VCO2(t)=K1*e^(–k2/t). This non-linear carbon dioxide equation explains why a candle will burn twice as long with "clean" air at 0.5 liters than at 2.5 liters - it's just that the burning will be very intense at first and almost 2 liters of air are used in the first 10 seconds. and only 0.5 liters will remain, as in the second case, which will burn out for another 30 seconds.
Quote: "Wax candles should have a loosely woven wick of thick fibers, for all other candles the wicks are made of tightly woven threads. This is due to the viscosity of the candle mass in the molten state: viscous wax needs wide capillaries, and easily mobile paraffin, stearin and fats require thinner capillaries, otherwise, due to an excess of combustible material, the candle will smoke heavily.esfir January 2, 2014, 06:37
Option: put a piece of loose rope in the melted paraffin near the wick.- I noticed that it starts to smoke when the wick is slightly wet, i.e. the heating temperature of the wick itself is below average when burning dry wicks. The flame itself, of course, has normal temperature, because oxygen burns, and the wick only supports combustion. It is necessary to spit on the finger, draw on the wick and set it on fire - it will smoke
- All this is very interesting. But, "great minds" can you answer another question? While the candle is burning, it does not smell. And that's okay, 'cause pure water and carbon dioxide are odorless. But! It's worth blowing out the candle as you get strong bad smell! Incomplete combustion produces the same water, pure carbon C and CO instead of CO2, but C and CO also have no smell. Then what stinks so strongly when we put out the candle?
Pavel, as I understand it, it smells like products of incomplete combustion of paraffin. That is, at the moment of extinguishing the candle, it should be quite large range any molecular compound.January 5, 2017, 06:15
Lesson format: research with elements of interdisciplinary integration.
You cannot change someone by passing on ready-made experience to him.
You can only create an atmosphere conducive to human development.
K. Rogers
The purpose of the lesson: look at the flame of a candle and at the candle itself through the eyes of a researcher.
Lesson objectives:
To begin the formation of the most important method of knowing chemical phenomena - observation and the ability to describe it;
Show in the course of practical work the significant differences between physical and chemical reactions;
Update basic knowledge about the combustion process, taking into account the material learned in the lessons of other academic disciplines;
Illustrate the dependence of the candle burning reaction on the reaction conditions;
To begin the formation of the simplest methods for conducting qualitative reactions to detect candle combustion products;
Develop cognitive activity, observation, broaden horizons in the field of natural science and artistic and aesthetic knowledge of reality.
Lesson steps:
I Organizing time. Introduction by the teacher.
Candle? - a traditional lighting device, which is most often a cylinder of solid combustible material (wax, stearin, paraffin) serving as a kind of reservoir solid fuel, supplied in molten form to the flame by a wick. The ancestors of candles are lamps; bowls filled with vegetable oil or low-melting fat, with a wick or just a sliver to raise fuel into the combustion zone. Some peoples used wicks inserted into the raw fat (even carcass) of animals, birds or fish as primitive lamps. The first wax candles appeared in the Middle Ages. Candles have been very expensive for a long time. Hundreds of candles were needed to light a large room, they smoked, blackening the ceilings and walls. Candles have come a long way since their inception. People have changed their purpose and today a person has other sources of light in their homes. But, nevertheless, today candles symbolize the holiday, help create a romantic atmosphere in the house, soothe a person, and are an integral part of the decor of our homes, bringing comfort and coziness to the house. A candle can be made from pork or beef fat, oils, beeswax, whale oil, paraffin, which is obtained from oil. Today it is easiest to find candles made from paraffin. With them today we will conduct experiments.
II Actualization of students' knowledge.
Briefing. Safety regulations
Conversation:
Light a candle. You will see how the paraffin near the wick begins to melt, forming a round puddle. What process is taking place here? What happens when a candle burns? After all, the paraffin just melts. But where then heat and light?
What happens when an electric light bulb is on?
Student responses.
Teacher:
When paraffin just melts, there is no heat or light. Most of paraffin burns, turning into carbon dioxide and water vapor. Because of this, heat and light appear. And part of the paraffin melts from heat, because he is afraid of hot. When the candle burns out, there will be less paraffin left than it was at the beginning. But when an electric light bulb burns, heat and light are also released, and the light bulb does not get smaller? Burning a light bulb is not a chemical, but a physical phenomenon. It does not burn by itself, but turns the energy of electricity into light and heat. As soon as the electricity is turned off, the light goes off. A candle should only be lit, then it burns itself.
And now our task is to look at the flame of a candle and at the candle itself through the eyes of a researcher.
III Learning new material.
Experience "The structure of the candle"
| WHAT THEY WERE DOING? | WHAT DID YOU OBSERVE? | CONCLUSIONS |
| 1. Considered a paraffin and wax candle. 2. Separate the wick. |
The candle consists of a rod and a wick of tightly twisted threads in the center of the column. | The basis of the candle is wax or paraffin. A wick is a kind of capillary through which the melt of the candle mass enters the combustion zone. The wicks are woven from cotton threads. Wax candles should have a loosely woven wick of thick fibers; for all other candles, the wicks are made of tightly woven threads. This is due to the viscosity of the candle mass in the molten state: viscous wax requires wide capillaries, and easily mobile paraffin, stearin and fats require thinner capillaries, otherwise, due to an excess of combustible material, the candle will smoke heavily. |
Experience “Study of the physical and chemical processes that occur during the burning of a candle”
| WHAT THEY WERE DOING? | WHAT DID YOU OBSERVE? | CONCLUSIONS |
| 1. Light a candle. | 1. Burning a candle. If you bring your palms to the flame, you feel warmth. | 1. A candle is a source of heat, because the process of combustion of gaseous paraffin is exothermic. |
| 2. We studied the sequence of the candle burning process. Observed phase transformations that occur with a candle. | 2. Paraffin begins to melt near the wick and out solid state turns into a liquid state, forming a round puddle. | 2. When burning a candle, phase transformations of paraffin are observed ( physical phenomena), osmotic phenomenon, chemical transformations. |
| 3. They monitored the cotton wick, found out its role in the burning of a candle. | 3. The candle does not burn along the entire wick. Liquid paraffin wets the wick, ensuring its combustion. Paraffin itself does not burn. The cotton wick stops burning at the level where liquid paraffin appears. | 3. The role of liquid paraffin is to prevent the wick from burning out quickly, to promote its long burning. Liquid paraffin near the fire evaporates, releasing carbon, the vapor of which supports combustion. With enough air near the flame, it burns clearly. Melted paraffin extinguishes the flame, so the candle does not burn along the entire wick. |
Experience “Studying the structure of a candle flame. Detection of combustion products in a flame. Observation of the inhomogeneity of the flame”
| WHAT THEY WERE DOING? | WHAT DID YOU OBSERVE? | CONCLUSIONS |
| 1. Light a candle placed in a candlestick. Let her warm up well. | The flame of a candle has an oblong shape. AT different parts flames are different colors. In a calm candle flame, 3 zones are distinguished. The flame has a somewhat elongated appearance; at the top it is brighter than at the bottom, where the middle part of it is occupied by the wick, and some parts of the flame, due to incomplete combustion, are not as bright as at the top. |
The phenomenon of convention, thermal expansion, Archimedes' law for gases, and the law gravity with the forces of gravity are forced to acquire the characteristic cone-shaped shape of the flame. The ascending current of air gives the flame an oblong shape: because. the flame that we see is drawn out under the influence of this air current to a considerable height. |
| 2. We took a thin long sliver, which we hold horizontally and slowly draw it through the widest part of the flame, not allowing it to catch fire and smoke heavily. | On the chip remains a trace left by the flame. There is more soot above its outer edges, more above the middle. | The part of the flame that is directly adjacent to the wick consists of heavy paraffin vapor - it seems that it is blue-violet in color. This is the coldest part of the flame. The second, the lightest part, is created by hot vapors of paraffin and particles of coal. This is the hottest area. Third, outer layer contains the most oxygen and glows weakly. Its temperature is quite high, but somewhat lower than the temperature of the light part. It is as if cooled by the surrounding air. |
| 3. We took a piece of white thick cardboard, hold it horizontally in our hand, quickly lower it from above onto the flame of a burning candle. | Flame scorch appears on the top side of the cardboard. | A ring-shaped opalina formed on the cardboard, because. the center of the flame is not hot enough to char the cardboard. The flame has different temperature sections. |
| 4. A glass rod was brought into the candle flame. | The candle flame has a yellowish orange color and glows. Soot forms on the surface of the glass rod. |
The luminous nature of the flame is due to the degree of oxygen consumption and the completeness of the combustion of paraffin, the condensation of carbon and the glow of its incandescent particles. Soot indicates incomplete combustion of paraffin and the release of free carbon. |
| 5. A dry test tube was fixed in the holder, turned upside down and held over the flame of an alcohol lamp. | The walls of the test tube were fogged up. Water droplets form on the walls of the test tube. | Water is a product of burning a candle. |
Experience “Studying the dependence of the height of the flame of a candle on the length of the wick”
| WHAT THEY WERE DOING? | WHAT DID YOU OBSERVE? | CONCLUSIONS |
| 1. Light a candle. | The wick of the candle lights up, the flame of the candle is high. | Liquid paraffin wets the wick, ensuring its combustion. Paraffin itself does not burn. The role of liquid paraffin is to prevent the wick from burning out quickly, to promote its long burning. Liquid paraffin near the fire evaporates, releasing carbon, the vapor of which supports combustion. With enough air near the flame, it burns clearly. |
| 2. Cut off part of the burnt wick | The dimensions of the flame have changed, it has decreased in size. The flame descends down the wick to molten paraffin and fades. At the top, it burns longer. The part of the paraffin closer to the wick melts from the heat. | Drops of liquid paraffin are attracted to each other less than to the wick, and are easily drawn into the smallest gaps between the threads. This property of a substance is called capillarity. |
Experience “Proof of burning a candle in the oxygen of the air”
| WHAT THEY WERE DOING? | WHAT DID YOU OBSERVE? | CONCLUSIONS |
| 1. In the middle of the plate they put a burning candle (thin, small, attached with plasticine) Tinted water was added to the plate (to hide the bottom), the candle was covered with a faceted glass. |
Water begins to climb under the glass The candle is gradually extinguished. |
The candle burns as long as there is oxygen in the glass. As oxygen is consumed, the candle goes out. Due to the vacuum that has formed there, the water rises. Combustion is a complex physical and chemical process of interaction of the components of a combustible substance with oxygen, proceeding at a sufficiently high speed, with the release of heat and light. |
Experience “The influence of air on the burning of a candle. Watching the flame of a burning candle
| WHAT THEY WERE DOING? | WHAT DID YOU OBSERVE? | CONCLUSIONS |
| They brought a lit candle to the open door. 1. Put a candle on the floor. 2. Carefully stand on a stool near the ajar door, hold a lit candle at the top of the door. | 1. The flame is deflected towards the room. 2. The flame deviates towards the corridor. |
Warm air upstairs flows out of the room, while downstairs cold flow directed inward. |
| 3. They knocked over the candle so that the fuel flowed onto the wick. | The candle will go out | The flame did not have time to heat the fuel enough to burn, as it happens at the top, where the fuel enters the wick in a small amount and is subjected to full effect flame. |
Experience “Studying the smoke of an extinguished candle”
Experience “Qualitative reaction for the detection of candle combustion products”
| WHAT THEY WERE DOING? | WHAT DID YOU OBSERVE? | CONCLUSIONS |
| 1. Lime water was poured into a glass. The stump of the candle was planted on a wire so that it would be more convenient to lower it into a glass. |
Lime water can be prepared as follows: you need to take a little quicklime, stir it in water and strain it through blotting paper. If the solution turns cloudy, it is necessary to strain it again so that it is completely transparent. | |
| 2. Lit the stub of the candle and lowered it carefully to the bottom of the empty glass. They pulled out the stub, lit it and lowered it back into the jar. |
The cinder burns for a while and then goes out. The flame goes out immediately |
The glass contains a colorless and odorless gas that does not support combustion and prevents the candle from burning. This is carbon dioxide - CO2. |
| 3. Added to a glass of lime water. | The water in the glass becomes cloudy. | When a candle burns, carbon dioxide is produced. Carbon dioxide makes lime water cloudy. |
IV Consolidation of the studied material.
Front poll:
List the sequence of candle burning processes.
What phase transformations are observed when a candle burns?
What is the combustible material of a candle?
What is the cotton wick for?
What phenomenon allows liquid paraffin to rise to a certain height?
Where is the hottest part of the flame?
Why is there a decrease in the length of the candle?
Why does the flame of a candle not go out, although during combustion substances are formed that do not support combustion?
Why does a candle go out when we blow on it?
What conditions are necessary for a longer and better burning of a candle?
How can you extinguish a candle? What properties are these methods based on?
That is qualitative reaction for carbon dioxide?
Teacher:
Consideration of the structure and burning of a candle convincingly illustrates the complexity of the most trivial everyday objects around us, testifies to how inseparable such sciences as chemistry and physics are. A candle is such an interesting object of study that it is impossible to consider the topic exhausted.
In conclusion of our lesson, I want to wish you that you, like a candle, radiate light and warmth to those around you, and that you be beautiful, bright, necessary, like the flame of a candle, which we talked about today.
V Homework.
1. Task for those wishing to carry out research work at home:
Take for experience any thing where there is a zipper. Open and close the zipper several times. Remember your observations. Rub a paraffin candle on a zipper, for example, on a sports jacket. (Don't forget to ask your mom's permission when you take the sweater for the experiment). Has the movement of the zipper changed?
Answer the question: “Why do they sometimes rub zippers with a candle?”
(The substances from which the candlestick is made (stearin, paraffin) are a good lubricant that reduces friction between the links of the fastener.)
2. Task for those wishing to carry out research work at home.
Take 3 candles of different composition, made of paraffin, wax, stearin. Candles can be bought at the store, or you can make your own. (Ask mom or dad to watch the experience with you.) Wait until dusk, place candles close to each other and light them. Complete the table as you observe burning candles.
References.
1. Faraday M .., History of a candle, M., Nauka, 1980.
