Question

Find the percentage of
(a) oxygen in magnesium nitrate crystals $\left[Mg\right(N{O}_3{)}_{2}6H_{2}O]$.
(b) boron in $N{a}_2{B}_4{O}_7.10H_{2}O.[H=1,B=11,O=16,Na=23].$
(c) phosphorus in the fertilizer superphosphate $Ca(H_{2}P{O}_4{)}_2$

Answer 1

(a) The molecular mass of (Mg(NO₃)₂.6H₂O = 256.4 g
% of Oxygen = 12 x 16/256
= 75%

(b) The molecular mass of boron in Na₂B₄O₇.10H₂O = 382 g
% of B = 4 x 11/382 = 11.5%

(c)
Molecular mass of $Ca(H_{2}P{O}_4{)}_2$
is 234g
Atomic mass of phosphorus is 30g

Percentage of phosphorus = (2×30 / 234) × 100 = 25.64%