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Question: In the formula mass of \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2},\) find the approximate percent...

In the formula mass of Ca(NO3)2,\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}, find the approximate percentage of oxygen?
(A) 28
(B) 42
(C)58
(D) 68
(E) 84

Explanation

Solution

Calcium nitrate is an inorganic compound with the formula Ca(NO3)2.\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2} . This colourless salt absorbs moisture from the air and is commonly found as a tetrahydrate. The formula to be used here would be %\% age of oxygen =(=( Weight of OX100)/\mathrm{O} \mathrm{X} 100) / Total molar mass of Ca(NO3)2\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}

Complete step by step solution:
-Let us see the formula of Calcium nitrate i.e., Ca(NO3)2.\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2} . Now, let us calculate the molecular mass of Ca(NO3)2\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}
-We know the molecular masses of individual atoms. Let us note it down now.
Calcium is 40g/mol40 \mathrm{g} / \mathrm{mol}. Nitrogen is 14g/mol14 \mathrm{g} / \mathrm{mol}. Oxygen is 16g/mol16 \mathrm{g} / \mathrm{mol}. Then according to the formula Ca(NO3)2,\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}, it is 40+2×(14+3(16))=40+2×(62)=164g/mol40+2 \times(14+3(16))=40+2 \times(62)=164 \mathrm{g} / \mathrm{mol}
-1 mole (164.1 g) of calcium nitrate will contain 6 moles of O atoms.
-The atomic mass of oxygen is 16g/mol16 \mathrm{g} / \mathrm{mol}. 6 moles of oxygen atoms corresponds to 6×16=96g6 \times 16=96 \mathrm{g}
-Discussing Option C,\mathrm{C}, The percent of oxygen in calcium nitrate =(96×100)/164=(96 \times 100) / 164 which gives us
58%58 \%. Clearly, it is 58%58 \%.

Hence, the answer is (C).

Note: As in the formula of calcium nitrate, the percentage of oxygen is 58%.58 \% . The percentage of calcium in the compound is (40×100)/164(40 \times 100) / 164 i.e., ,24%., 24 \% . Similarly, let us find out the percentage composition of nitrogen in the compound i.e., 18%.18 \% . Hence this is the total percentage composition of the elements in calcium nitrate.