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Atoms and Molecules — Science STD 9 — Question

Gujarat BoardEnglish MediumSTD 9ScienceAtoms and Molecules5 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 $(CaCO_3)$
Gas Q: Carbon dioxide $(CO_2)$
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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