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Atoms and Molecules — Science STD 9 — Question

Gujarat BoardEnglish MediumSTD 9ScienceAtoms and Molecules4 Marks
Question
One of the forms of a naturally occurring solid compound P is usually used for making the floors of houses. On adding a few drops of dilute hydrochloric acid to P, brisk effervescence are produced. When 50g of reactant P was heated strongly, than 22g of a gas Q and 28g of a solid R were produced as products. Gas Q is the same which produced brisk effervescence on adding dilute HCl to P. Gas Q is said to cause global warming whereas solid R is used for white-washing.
  1. What is (i) solid P (ii) gas Q, and (iii) solid R.
  2. What is the total mass of Q and R obtained from 50g of P?
  3. How does the total mass of Q and R formed compare with the mass of P taken?
  4. What conclusion do you get from the comparison of masses of products and reactant?
  5. Which law of chemical combination is illustrated by the example given in this problem?
✓

Answer

$\text{P(solid)}\xrightarrow{ \ \ \ \ \ \ \ \ \ \ \ \ }\text{Q(gas)}+\text{R(solid)}\\ \ \ ^{50\text{gm}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^{22\text{gm}}\ \ \ \ \ \ \ \ \ \ ^{28\text{gm}}$

  1. Solid P: Calcium Carbonate (CaCO3)

Gas Q: Carbon dioxide (CO2)

Solid R: Calcium oxide (CaO)

  1. Total mass of Q and R = 22gm + 28gm = 50gm
  2. Total mass of Q and R (50gm) is equal to mass of reactant (50gm).
  3. The law of conservation of mass is followed, i.e. total mass of product is equal to mass of reactant.
  4. Law of conservation of mass is illustrated by the example.

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