Question
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, find the approximate percentage of oxygen?
(A) 28
(B) 42
(C)58
(D) 68
(E) 84
Solution
Calcium nitrate is an inorganic compound with the formula Ca(NO3)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)/ Total molar mass of Ca(NO3)2
Complete step by step solution:
-Let us see the formula of Calcium nitrate i.e., Ca(NO3)2. Now, let us calculate the molecular mass of Ca(NO3)2
-We know the molecular masses of individual atoms. Let us note it down now.
Calcium is 40g/mol. Nitrogen is 14g/mol. Oxygen is 16g/mol. Then according to the formula Ca(NO3)2, it is 40+2×(14+3(16))=40+2×(62)=164g/mol
-1 mole (164.1 g) of calcium nitrate will contain 6 moles of O atoms.
-The atomic mass of oxygen is 16g/mol. 6 moles of oxygen atoms corresponds to 6×16=96g
-Discussing Option C, The percent of oxygen in calcium nitrate =(96×100)/164 which gives us
58%. Clearly, it is 58%.
Hence, the answer is (C).
Note: As in the formula of calcium nitrate, the percentage of oxygen is 58%. The percentage of calcium in the compound is (40×100)/164 i.e., ,24%. Similarly, let us find out the percentage composition of nitrogen in the compound i.e., 18%. Hence this is the total percentage composition of the elements in calcium nitrate.