Q: Question 7Complete and balance the following chemical equations.(a) KNO3 →heat\xrightarrow{\text{heat}}heat KNO2 + ...............(b) KClO3 →heat\xrightarrow{\text{heat}}heat ............... + O2(c) HgO →heat\xrightarrow{\text{heat}}heat ............... + ...............(d) CaO + H2O ⟶ ...............

(a) 2KNO3 →heat\xrightarrow{\text{heat}}heat 2KNO2 + O2(b) 2KClO3 →heat\xrightarrow{\text{heat}}heat 2KCl + 3O2(c) 2HgO →heat\xrightarrow{\text{heat}}heat 2Hg + O2(d) CaO + H2O ⟶ Ca(OH)2

Question 1

Question 1Give one use for each of the following inert gases:(a) Argon(b) Helium(c) Neon(d) Radon(e) Krypton(f) Xenon

Accepted Answer

(a) Argon is used to fill electric bulbs which improves the quality and life of the bulb.(b) Helium is used for filling up weather observation balloons.(c) Neon is used in making advertising signboards and tube-lights.(d) Radon is used for cancer treatment.(e) Krypton is used for photography.(f) Xenon is used for photography.

Question 2

Question 4"Air is a mixture." Support this statement citing at least three evidences.

Accepted Answer

"Air is a mixture." This statement is supported by following three evidences:The composition of air is not fixed. It varies from place to place and from time to time.The components of air retain their individual properties.No energy exchange occurs when the components of air are mixed with each other.

Question 3

Question 5What is air pollution? What are the harmful effects of sulphur dioxide, nitrogen dioxide and hydrogen sulphide present in the air?

Accepted Answer

When air contains undesirable substances that are harmful to plants and animals, the air is said to be polluted. The harmful effects of sulphur dioxide, nitrogen dioxide and hydrogen sulphide present in the air are:Sulphur dioxide is highly poisonous gas which causes serious respiratory problems.Nitrogen dioxide form a mixture of smoke and fog known as smog which affects our eyes.Both sulphur dioxide and nitrogen dioxide gases cause acid rain which damages crops and buildings and natural resources like water bodies and patches of land.Hydrogen sulphide is highly obnoxious and causes headache.

Question 4

Question 6(a) What are the causes of air pollution?(b) Suggest five measures to prevent air pollution.

Accepted Answer

(a) The causes of air pollution are:Natural process like volcanic eruptions, crop pollination etc.Burning of fuels and fibres.DeforestationEmission of harmful gases from vehicles.Use of chemicals like fertilizers, insecticides and pesticides in agricultural activities.Increase in number of industries.Use of chemical weapons in war.(b) The five measures to prevent air pollution are:By growing more plants and trees.By installing tall chimneys with filters in factories and power plants.By using internal combustion engines in vehicles.By installing catalytic convertors in vehicles.Avoid burning of paper, garbage, dry leaves and other waste materials.

Question 5

Question 2(a) Taking hydrogen peroxide, how would you prepare oxygen in the laboratory?(b) What is the role of manganese dioxide in the preparation of oxygen?(c) Write the balanced chemical equation for the above chemical reaction.(d) Why is hydrogen peroxide preferred in the preparation of oxygen gas?(e) Why is oxygen collected by downward displacement of water?(f) What happens when a glowing splinter is introduced in a jar containing oxygen?(g) What happens when oxygen gas is passed through alkaline pyrogallol solution?

Accepted Answer

(a) Oxygen is prepared from hydrogen peroxide in the laboratory by the following ways-A small quantity of manganese dioxide is taken in a flat bottom flask.Hydrogen peroxide is added drop by drop into the flask by help of thistle funnel as shown in the below figure.Manganese dioxide decomposes hydrogen peroxide very fast and liberates oxygen which passes through the delivery tube and bubbles out through the water in the trough.A gas jar filled with water is inverted over beehive shelf. Oxygen is collected in the jar by downward displacement of water.(b) Manganese dioxide acts as a catalyst, it decomposes hydrogen peroxide very fast and liberates oxygen.(c) 2H2O2 →as catalystMnO2\xrightarrow[	ext{as catalyst}]{	ext{MnO}_2}MnO2​as catalyst​ 2H2O + O2 [g](d) Hydrogen peroxide is preferred in the preparation of oxygen gas because:No heating is required.The rate of evolution of oxygen is moderate and therefore under control.Hydrogen peroxide is a safe chemical.(e) Oxygen is collected by downward displacement of water because:Oxygen is slightly heavier than air, so it cannot be collected over air.Oxygen is only slightly soluble in water i.e. 0.7% only. So it can be collected over water without fear of excessive dissolution.(f) When a glowing splinter is introduced in a jar containing oxygen, the glowing splinter rekindles, but the gas does not catch fire.(g) When oxygen gas is passed through alkaline pyrogallol solution, it turns brown.

Question 6

Question 3(a) What happens when (i) mercuric oxide and (ii) potassium nitrate are heated?(b) Why is potassium chlorate not used for laboratory preparation of oxygen?

Accepted Answer

(a)i. When mercuric oxide is heated, it decomposes to give mercury and oxygen.2HgO →heat\xrightarrow{	ext{heat}}heat​ 2Hg + O2ii. When potassium nitrate is heated, it decomposes to give potassium nitrite and oxygen.2KNO3 →heat\xrightarrow{	ext{heat}}heat​ 2KNO2 + O2(b) Potassium chlorate is heated to a high temperature to obtain oxygen gas which may causecracking of glass apparatus being used.accidents and burn injuries. Thus potassium chlorate is not used for laboratory preparation of oxygen gas.

Question 7

Question 7Complete and balance the following chemical equations.(a) KNO3 →heat\xrightarrow{	ext{heat}}heat​ KNO2 + ...............(b) KClO3 →heat\xrightarrow{	ext{heat}}heat​ ............... + O2(c) HgO →heat\xrightarrow{	ext{heat}}heat​ ............... + ...............(d) CaO + H2O ⟶ ...............

Accepted Answer

(a) 2KNO3 →heat\xrightarrow{	ext{heat}}heat​ 2KNO2 + O2(b) 2KClO3 →heat\xrightarrow{	ext{heat}}heat​ 2KCl + 3O2(c) 2HgO →heat\xrightarrow{	ext{heat}}heat​ 2Hg + O2(d) CaO + H2O ⟶ Ca(OH)2

Question 8

Question 8(a) Give four uses of oxygen.(b) How is oxygen naturally renewed in air?

Accepted Answer

(a) The four uses of oxygen are:RespirationBurningIndustrial uses like welding and cutting metals, removing impurities.In medicines like oxygen cylinders for artificial respiration in patients suffering from breathing problems, a mixture of oxygen and nitrous oxide as local anaesthesia.(b) Oxygen is naturally renewed in air by the process of photosynthesis. Plants use carbon dioxide and water and in presence of sunlight produce glucose and oxygen gas. This oxygen gas is released into air.

Question 9

Question 9State two differences between: Rusting and Burning.

Accepted Answer

RustingBurningRusting is slow oxidation.Burning is fast oxidation.Both air and moisture are necessary for rusting.Only air is necessary for burning.

Air and Atmosphere

Exercise I

Exercise II