Chemical Reaction & Gases
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Lesson – 15.
Chemical Reaction.
Exercise.
2) Give Reason:
(a) Hydrogen peroxide is not stored in the transparent vessel.
Answer: Because light act as a catalyst which break down the hydrogen peroxide in
so for this reason it is not stored in a transparent vessel.
(b) The rate of Acid/base reaction is also known as neutralization reaction.
Answer: Because, it is neither acidic or base and forms neutral salt when acid reacts with base.
(c) The rate of chemical reaction is different according to type of reaction.
Answer: Because it depends upon different factors like area, temperature and light etc.
3) Difference between.
(a) Single displacement Reaction and Double displacement Reaction
| Single displacement Reaction | Double displacement Reaction |
|---|---|
| In this reaction there is change in color generally and no precipitate formation takes place. | In this reaction precipitate formation takes place. |
| In this metals reacts with the salt solution of another metal. | In this salt, salt solution of two different metals react with each other. |
(b) Combination reaction and Decomposition Reaction
| Combination reaction | Decomposition Reaction |
|---|---|
| The chemical reaction in which two or more reactants combine to forming one product is called combination reaction. | The chemical reaction in which a reactant breaks down in two or more products is called decomposition reaction. |
| Eg: 2Mg + O2 = 2MgO. | Eg: CaCO3 → CaO + CO2. |
4) Balance the following chemical reaction and mention their types.
(a)
Decompose
(b)
Double displacement.
(c)
Combination.
(d)
combination single displacement.
(e)
single displacement.
5) Answer Question.
(a) What do you mean by chemical reaction? Explain with an example?
Answer: The process in which two or more substance is combine, decompose to form a new product by sharing electrons is called chemical reaction.
(b) What is the rate of chemical reaction? Write any four factors which affect the rate of chemical reaction.
Answer: The changes of reactants to products per unit time in any chemical reaction is known as the rate of chemical reaction. The four factors which affect the rate of chemical reaction are:
- catalyst.
- Heat.
- pressure.
- surface area.
- Light.
(c) what do you mean by displacement reaction? write its two examples with their balanced chemical equations.
Answer: The chemical reaction in which an atom or radical of one reactant is displaced by the atom or radical of another reactant is called displacement reaction. Its examples are:
- single displacement.
- Double displacement.
(d) Write two examples of decomposition reactions with balanced chemical equations.
Answer: The two examples of decomposition reactions with balanced chemical equations are:
(e) What is the type of chemical reaction occurring inside the test tube shown in the given figure? Write a balanced chemical equation of that reaction.
Answer: Reaction of copper sulphate with iron is shown in the figure.
Balanced Equation:
(f) Four students A, B, C and D are allowed to carry out decomposition reactions in the laboratory. All of them perform it differently as given below:
(i) Student A burnt magnesium (Mg) ribbon.
(ii) Student B mixed Zn in FeSO4.
(iii) Student C heated KClO3 in a hard glass test tube.
(iv) Student D mixed Zn and HCl.
* Which student followed the correct procedure? Write the balanced chemical reaction of that process.
Answer: Student ‘C’ followed the correct procedure;
(g) Somil burns a magnesium ribbon which is like a small strip of ribbon. It burns brightly and forms white ash ‘A’. Write the name of substance ‘A’ write a balanced chemical reaction of the process.
Answer: The name of the substance ‘A’ is magnesium oxide (MgO). The balanced chemical reaction is given below.
Lesson – 16.
Gases.
Exercise.
2) Give reason.
(a) Carbon dioxide can be collected in an open glass jar.
Answer: Because, carbon dioxide is heavier than air so it stays at the bottom of glass jar.
(b) The bottle of liquid ammonia should be placed in cold water or ice for some time before opening its lid.
Answer: Because when placed in cold water or ice for some time the molecules of ammonia gets contracted. If not done while opening the lid the liquid ammonia will come out of the bottle at a high pressure and gets poured in our mouth, eye or in clothes.
3) Answer the following questions.
(a) Describe the laboratory preparation of carbon dioxide with labelled diagram.
fig: Lab preparation of carbon dioxide.
procedure:
- collect all the required apparatus and chemicals for this gas.
- keep pieces of limestone or marble pieces in woulf’s bottle.
- Connect all the apparatus as shown in the figure by making everything
air tight.
- pour dilute HCl through thistle funnel into woulf’s bottle till it covers the limestone or marble.
- Allow the gas pass through the delivery tube.
- HCl + limestone reacts with dilute HCl and effervescence of CO2 gas can be seen which is collected in the gas jar by upward displacement of air.
(b) study the given figure and answer the following questions:
(i) Which gas is being collected into the gas jar?
Answer: Carbon dioxide (CO2)
(ii) Write a balanced chemical reaction for preparation of this gas.
(iii) Which litmus paper is used to identify the gas?
Answer: moist blue litmus paper.
(iv) Why is this gas collected in the gas jar kept straight upright?
Answer: Because, CO2 is heavier than air, so it can be collected by upward displacement of air.
(c) Write 3 properties of carbon dioxide gas.
Answer: Three properties of carbon dioxide gas are:
- It is 1.5 times heavier than air.
- Slightly soluble in water.
- neither combustible nor is supporter of combustion.
(d) Write any four uses of carbon dioxide gas.
Answer: Following are the four uses of carbon dioxide gas:
- used for the preparation of carbonated drinks.
- Used to prepare Urea (NH2CONH2), washing soda (Na2CO3) and baking soda (NaHCO3).
- Used in bakery products.
- green plants use carbon dioxide for photosynthesis.
- Used to prepare dry ice – used as coolant.
(e) Describe the laboratory preparation of ammonia gas with a labelled diagram.
fig: Lab preparation of ammonia.
Procedure:
- collect all the apparatus and chemicals required for the laboratory preparation of ammonia gas.
- Take a mixture of ammonium chloride and slaked lime (Ca(OH)2) in the ratio of 2:1 in a round bottomed flask.
- Add a little water for making a paste.
- connect all the apparatus as shown in the figure making air tight.
- Gently heat the mixture to generate ammonia gas.
- Lime tower filled with calcium oxide (CaO) is used to obtain dry and pure ammonia. This gas is quite soluble in water so it is not obtained by displacement of water. It is collected by the downward displacement of air as it is lighter than air.
(f) Study the given figure and answer the following questions.
(i) Which gas is being collected in the gas jar?
Answer: Ammonia gas (NH3).
(ii) Write the balanced chemical equation for the preparation of this gas.
(iii) Which litmus paper is used to identify this gas?
Answer: moist red litmus paper.
(iv) Why the hard glass test tube is slightly inclined?
Answer: To pass the gas properly the hard glass test-tube is slightly inclined.
(v) What is the use of lime tower?
Answer: The use of lime is to absorb all the moisture or water and form pure ammonia gas.
(g) Write any four uses of ammonia gas.
Answer: It’s four uses are:
- Liquid ammonia is used as refrigerant.
- Used in blue printing of maps.
- used to make fertilizers.
- Used as reagent in laboratories.
(h) What happens in the following processes. Write with a balanced chemical reaction.
(i) Carbon dioxide is passed through lime water for some time.
The lime water turns milky white due to the formation of insoluble calcium carbonate.
(ii) Carbon dioxide is passed through lime water for long time.
The milky white colour disappears due to the formation of soluble calcium bicarbonate.
(iii) A burning magnesium is inserted into the jar full of carbon dioxide gas.
It burns brightly and produces white powder of magnesium oxide (MgO) and black carbon powder.
(iv) The mixture of ammonium chloride and calcium hydroxide is heated.
Ammonia gas will be formed.
(v) Ammonia is mixed with water.
It forms ammonium hydroxide.
(vi) Ammonia reacts with hydrochloric acid.
It forms Ammonium chloride.
Discussion
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