Question 1 - Case Based Questions (MCQ) - Chapter 1 Class 10 - Chemical Reactions and Equations

Marble’s popularity began in ancient Rome and Greece, where white and off-white marble were used to construct a variety of structures, from hand-held sculptures to massive pillars and buildings.

1.1 The substance not likely to contain CaCO3 is 

a) Dolomite

b) A marble statue 

c) Calcined gypsum 

d) Sea shells

Answer

(c) Calcined Gypsum

Let’s write the Chemical formula for all of them

• Dolomite → (CaMg(CO ₃ ) ₂ )  
• A marble statue → Recrystallized carbonate minerals commonly calcite (CaCO ₃ ) or dolomite (CaMg(CO ₃ ) ₂ )
• Calcined Gypsum →  CaSO ₄ .2H ₂ O;
• Sea shells → CaCO ₃

Thus, we can observe Calcined Gypsum does not contain CaCO 3

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 take place? 

a) 15-20 min 

b) 10-15 min 

c) 5-10 min 

d) 0-5 min 

Answer

(d) 0 - 5 min

This is the Pressure Time Graph

Maximum decomposition is when the pressure is maximum

We see that from 0 to 5 minutes, the pressure increases from 0 to 0.625 atm,

This indicates maximum increase in pressure due to maximum CO 2 formation

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

a) Respiration b) Photosynthesis c) Transpiration d) Photolysis 

Answer

The following reaction takes place when CaCO ₃ is heated;

CaCO ₃ → CaO + CO ₂

Answer is (b) photosynthesis 

CO ₂ is the gas formed and it is utilized in the process of photosynthesis

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. 

Answer

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

Byproducts of air and water pollution are acidic.

Carbon Dioxide contributes to this majorly

When Carbon Dioxide dissolves in water, it forms Carbonic Acid

Similarly other acidic byproducts are formed making polluted water acidic in nature.

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

Answer

Answer is (d) calcium oxide 

Here, Calcium Oxide is losing Oxygen and undergoing reduction

A substance that undergoes reduction is an oxidising agent .

Thus Calcium Oxide is the oxidising agent