Question

Problem 1.4. Calculate the total percentage of oxygen in magnesium nitrate crystals :
Mg(NO3)2.6H20 (H = 1, N = 14, Mg = 24)
(I.C.S.E. 1996) [Ans. 75%]​

Answer 1

Molar Mass of Mg(NO₃)₂.6H₂O = 24+2*[14+(16*3)]+6*[(1*2)+16] g

= 24+2*[14+48]+6*[2+16] g

= 24+2*62+6*18 g

= 24+124+108 g

= 256 g

Mass of Oxygen present in the compound = (16*3*2)+(6*16) g

= 96+96 g

= 192 g

Percentage of Oxygen = (192/256)*100 %

= 75 %

I hope this helps.