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Atoms and Molecules — Science STD 9 — Question

Maharashtra 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 $50\ g$ of reactant $P$ was heated strongly, than $22\ g$ of a gas $Q $and $28\ g$ 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.
a. What is (i) solid $P$ (ii) gas $Q$, and (iii) solid $R$.
b. What is the total mass of $Q$ and $R$ obtained from $50\ g$ of $P$ ?
c. How does the total mass of $Q$ and $R$ formed compare with the mass of $P$ taken?
d. What conclusion do you get from the comparison of masses of products and reactant?
e. Which law of chemical combination is illustrated by the example given in this problem?
✓

Answer

$\text{P(solid)}\xrightarrow{ \ \ \ \ \ \ \ \ \ \ \ \ }\text{Q(gas)}+\text{R(solid)}\\ \ \ ^{50\text{gm}}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^{22\text{gm}}\ \ \ \ \ \ \ \ \ \ ^{28\text{gm}}$
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 $R (50\ gm)$ is equal to mass of reactant $(50\ gm)$.
  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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