Question

$ 1000g $ aqueous solution of $ CaC{{O}_{3}} $ ​ contains $ 10g $ of calcium carbonate. A concentration of the solution is:
(A) $ 10ppm $
(B) $ 100ppm $
(C) $ 1000ppm $
(D) $ 10000ppm $

Answer 1

Hint : $ CaC{{O}_{3}} $ is known as Calcium carbonate. Calcium carbonate decomposes to form Calcium oxide and emits Carbon dioxide. Calcium oxide has calcium and oxygen; Carbon dioxide has carbon and oxygen. Find the molecular weight of calcium carbonate, the corresponding weight of calcium, oxygen, and carbon of calcium carbonate.

Complete Step By Step Answer:
The molecular formula of Calcium Carbonate is . Calcium Carbonate contains calcium, carbon, and oxygen. Calcium Carbonate on heating decomposes into Calcium Oxide ( $ CaO $ ) and emits Carbon dioxide ( $ C{{O}_{2}} $ ).
 $ CaC{{O}_{3}}\text{ }\xrightarrow{\text{ }\Delta \text{ }}\text{ }CaO+C{{O}_{2}} $
This reaction is a decomposition reaction. The atomic weight of Calcium is $ 40g, $ the atomic weight of Carbon is 12g and the atomic weight of Oxygen is $ 16g. $ Therefore, the molecular weight of Calcium Carbonate is $ \left( 1\times 40 \right)+\left( 1\times 12 \right)+\left( 3\times 16 \right)=40+12+48=100g $
 $ 100 $ grams of Calcium Carbonate contains 40 grams of Calcium, $ 12 $ grams of Carbon and $ ~48 $ grams of oxygen. In the same way, $ 10 $ grams of Calcium Carbonate contain four grams of Calcium, $ 1.2 $ grams of Carbon, and $ 4.8 $ grams of Oxygen.
Here we have given $ 10g $ of $ CaC{{O}_{3}} $ it clears that rest is water,
 $ Concentration(ppm)=\frac{10}{1000}\times {{10}^{6}}=10000ppm $
Therefore the correct answer is option D.

Note :
Do not confuse gram atoms with no. of moles. 1 gram atom is the no. of atoms present in one gram of the substance whereas one mole of a substance has particles and the particles can be atoms, ions or molecules.