SCIENCE - Class X Sample Case Studies

1.1 The substance not likely to contain CaCO₃ is

a) Dolomite

b) A marble statue

c) Calcined gypsum

d) Sea shells.

1.2 A student added 10g of calcium carbonate in a rigid container, secured it tightly and started to heat it. After some time, an increase in pressure was observed, the pressure reading was then noted at intervals of 5 mins and plotted against time, in a graph as shown below. During which time interval did maximum decomposition took place?

a) 15-20 min

b) 10-15 min

c) 5-10 min

d) 0-5 min

1.3 Gas A, obtained above is a reactant for a very important biochemical process that occurs in the presence of sunlight. Identify the name of the process -

a) Respiration

b) Photosynthesis

c) Transpiration

d) sphotolysis

1.4 Marble statues are corroded or stained rainwater. Identify the main reason.

a) decomposition of calcium carbonate to calcium oxide

b) polluted water is basic in nature hence it reacts with calcium carbonate

c) polluted water is acidic in nature hence it reacts with calcium carbonate

d) calcium carbonate dissolves in water to give calcium hydroxide.

1.5 Calcium oxide can be reduced to calcium, by heating with sodium metal. Which compound

would act as an oxidizing agent in the above process?

a) Sodium

b) sodium oxide

c) calcium

d) calcium oxide

2. Read the following and answer any four questions from 2.1 to 2.5:

The reaction between MnO₂ with HCl is depicted in the following diagram. It was observed that a gas with bleaching abilities was released

2.1 The chemical reaction between MnO₂ and HCl is an example of:

a) displacement reaction

b) combination reaction

c) redox reaction

d) decomposition reaction.

2.2 Chlorine gas reacts with _ to form bleaching powder.

a) dry Ca(OH)₂

b) dil. solution of Ca(OH)₂

c) conc. solution of Ca(OH)₂

d) dry CaO

2.3 Identify the correct statement from the following:

MnO₂ is getting reduced whereas HCl is getting oxidized

a) MnO₂ is getting oxidized whereas HCl is getting reduced.

b) MnO₂ and HCl both are getting reduced.

c) MnO₂ and HCl both are getting oxidized.

2.4 In the above discussed reaction, what is the nature of MnO₂ ?

a) Acidic oxide

b) Basic oxide

c) Neutral oxide

d) Amphoteric oxide

2.5 What will happen if we take dry HCl gas instead of aqueous solution of HCl?

a) Reaction will occur faster.

b) Reaction will not occur.

c) Reaction rate will be slow

d) Reaction rate will remain the same.

Answer Key

3. Read the following and answer any four questions from 3.1 to 3.5:

Chemistry in Automobiles:

For an internal combustion engine to move a vehicle down the road, it must convert the energy stored in the fuel into mechanical energy to drive the wheels. In your car, the distributor and battery provide this starting energy by creating an electrical "spark", which helps in the combustion of fuels like gasoline. Below is the reaction depicting complete combustion of gasoline in full supply of air:

3.1 Which of the following are the products obtained from the reaction mentioned in the above case?

Product ‘X’Product ‘Y’

a) CO₂ H₂O₂

b) H₂O CO

c) CH₃OH H₂O

d) CO₂ H₂O

3.2 Identify the types of chemical reaction occurring during the combustion of fuel:

a) Oxidation & Endothermic reaction

b) Decomposition & Exothermic reaction

c) Oxidation & Exothermic reaction

d) Combination & Endothermic reaction

3.3 On the basis of evolution/absorption of energy, which of the following processes are similar to combustion of fuel?

a) Photosynthesis in plants

b) Respiration in the human body

c) Decomposition of vegetable matter

d) Decomposition of ferrous sulphate.

(a) (ii) & (iii)

(b) (i) & (ii)

(c) (iii) & (iv)

(d) (ii) & (i)

3.4 ‘A student while walking on the road observed that a cloud of black smoke belched out from the exhaust stack of moving trucks on the road.’ Choose the correct reason for the production of black smoke:

a) Limited supply of air leads to incomplete combustion of fuel.

b) Rich supply of air leads to complete combustion of fuel.

c) Rich supply of air leads to a combination reaction.

d) Limited supply of air leads to complete combustion of fuel.

3.5 ‘Although nitrogen is the most abundant gas in the atmosphere, it does not take part in combustion’. Identify the correct reason for this statement.

a) Nitrogen is a reactive gas

b) Nitrogen is an inert gas

c) Nitrogen is an explosive gas

d) Only hydrocarbons can take part in combustion

Answer Key

3.1-(d)

3.2-(c)

3.3-(a)

3.4-(a)

3.5-(b)

4. Read the following and answer any four questions from 4.1 to 4.5:

Frothing in Yamuna:

The primary reason behind the formation of the toxic foam is high phosphate content in the wastewater because of detergents used in dyeing industries, dhobi ghats and households. Yamuna's pollution level is so bad that parts of it have been labelled 'dead' as there is no oxygen in it for aquatic life to survive.

4.1 Predict the pH value of the water of river Yamuna if the reason for froth is high content of detergents dissolved in it.

a) 10-11

b) 5-7

c) 2-5

d) 7

4.2 Which of the following statements is correct for the water with detergents dissolved in it?

a) low concentration of hydroxide ion (OH^- )and high concentration of hydronium ion (H₃O⁺)

b) high concentration of hydroxide ion (OH^- )and low concentration of hydronium ion (H₃O⁺)

c) high concentration of hydroxide ion (OH^-) as well as hydronium ion (H₃O⁺)

d) equal concentration of both hydroxide ion (OH^-) and hydronium ion (H₃O⁺).

4.3 The table provides the pH value of four solutions P, Q, R and S

Which of the following correctly represents the solutions in increasing order of their hydronium ion concentration?

a) P>Q>R>S

b) P>S>Q>R

c) S<Q<R<P

d) S<P<Q<R

4.4 High content of phosphate ion in river Yamuna may lead to:

a) decreased level of dissolved oxygen and increased growth of algae

b) decreased level of dissolved oxygen and no effect of the growth of algae

c) increased level of dissolved oxygen and increased growth of algae

d) decreased level of dissolved oxygen and decreased growth of algae

4.5 If a sample of water containing detergents is provided to you, which of the following methods will you adopt to neutralize it?

a) Treating the water with baking soda

b) Treating the water with vinegar

c) Treating the water with caustic soda

d) Treating the water with washing soda

Answer Key

4.1 (a)

4.2 (b)

4.3 (c)

4.4 (a)

4.5 (b)