CARBON AND ITS COMPOUND

1. CHEMICAL REACTIONS AND EQUATIONS
1. A Student added few pieces of aluminium metal to two test tubes A and B Containing aqueous
solutions of iron sulphate and copper sulphate. In the second part of her experiment, she added iron
metal to another test tubes C and D containing aqueous solutions of aluminium sulphate and copper
sulphate. In which test tube or test tubes will she observe colour change? On the basis of this
experiment, state which one is the most reactive metal and why.
Ans. 1. Colour change is observed in test tubes A, B and D.
Most reactive metal is aluminium.
This is because it displaces all other metals, i,e., iron and copper from their aqueous salt solutions.
2. What is observed when a solution of sodium sulphate is added to a solution of Barium chloride taken in
a test tube? What is the colour of the precipitate formed, Write equation for the chemical reaction
involved and name the type of reaction in this case.
Ans. 2. White colour precipitate.
BaCl2 +Na2SO4 ----------->BaSO4+2NaCl
Double Displacement reaction.
3. A metal nitrate ’A’ on heating gives yellowish brown coloured metal oxide ‘B’ along with brown
coloured gas ‘C’ is formed.metal present in ‘A’ is used in alloy which is used for soldering purpose.
Identify A,B and C.
Ans. 3. A= Lead Nitrate, 1M
B = Lead Oxide, 1M
C=Nitrogen dioxide 1M
4. About 2g ferrous sulphate crystals are taken in a dry test tube and then is heated the over the flame of a
burner. What was the colour of ferrous sulphate before heating & after strongly heating which is gas
evolved with suffocating odour of burning sulphur ? Write the reaction and name the type of reaction.
Ans. 4. Before heating: light green colour. 1M
After strongly heating: brown colour. 1M
Sulphur dioxide (SO2). 1M
5. Decomposition reactions require energy either in the form of heat or light or electricity for breaking
down the reactants. Write one equation each for decomposition reactions where energy is supplied in
the form of heat,light and electricity.
Ans. 5. 5.CaCO3(s) -----heat----->CaO(s) +CO2(g) 1M
2AgBr(s) -----Light------>2Ag(s) +Br2(g) 1M
2H2O(l) ----Electricity--->2H2(g) +O2(g) 1M

2. 6. a) Explain the following with one example each.
i) Corrosion ii) Rancidity
b) Oil and fats containing food items are flushed with nitrogen. Why ?.
Ans.
a i) Corroision :The process of slowly eating up of the metals due to atmospheric gases such as oxygen,
carbon dioxide, water vapour etc on the surface of metals so as to convert the metal into oxide, carbonate is
known as corrosion.
Eg:-Rusting of iron. When an iron article exposed to moist air for a long time, its surface is covered with
brown flaky substance called rust.
ii ) Rancidty: The oxidation of oils or fats in a food resulting in bad smell and taste is called rancidity.
Eg : stale food.
b) In some food stuffs, the air present around them is replaced by nitrogen because oxidation of the food
stuff is prevented.
7) Explain the following in terms of gain or loss of oxygen with an example each.
a) Oxidation b) Reduction
Ans.
a) Oxidation: The reaction in which oxygen is gained is called oxidation.
2𝐶𝑢 + 𝑂2
∆
→ 2𝐶𝑢𝑂
b) Reduction: The reaction in which oxygen is lost is called reduction.
𝐶𝑢𝑂 + 𝐻2
∆
→ 𝐶𝑢 + 𝐻2 𝑂
CuO gets reduced as oxygen is lost.
8) Sadik’s younger sister was very upset as her silver jewellery had turned black and lost its shine. Sadik
washed and cleaned the jewellery with tooth paste, brought the shine and smile back.
a) How had the toothpaste got the shine of silver back?
b) How had the toothpaste got the shine of silverback.?
c) What value of Sadik is seen in the above act?
Ans.
a) Silver jewellery turns black as it reacts with gases, acids and moisture present due to which it corrodes.
b) Toothpaste reacts with black coating of silver sulphide and removes it.

3. c) Sadik showed the value of responsible behaviour.
9) a) What are redox reactions? Define an oxidising and reducing agent.
b) Give two examples from everyday life situations where redox reactions are taking place.
Ans. a) Reduction and oxidation always go side by side i.e., they occur simultaneously in a reaction. For
this reason they are called redox reactions.
Oxidising agent: It is a substance which i) gives Oxygen or ii)gains hydrogen or a substance which
undergoes reduction acts as an oxidising agent.
Reducing agent: It is a substance which i) gives hydrogen or ii)gains oxygen or a substance which
undergoes oxidation acts as a reducing agent.
b) Combustion, rusting, decay.
10) In the given chemical equation identify the substance oxidised, the substance reduced. Also identify
oxidising agent and reducing agent.
𝐹𝑒2 𝑂3 + 2𝐴𝑙
𝑦𝑖𝑒𝑙𝑑𝑠
→ 𝐴𝑙2 𝑂3 + 2𝐹𝑒
Ans.
a) Al has gained oxygen to form Al2O3.Hence Al has been oxidised
b) Fe2O3 has lost oxygen to form Fe. Hence Fe203 has been reduced.
c) Fe2O3 has given oxygen. Hence Fe2O3 is oxidising agent.
d) Al has gained oxygen. Hence Al is the reducing agent.