CIE iGCSE Co-Ordinated Science C3.2 Relative masses of atoms and molecules Exam Style Questions Paper 1
Question
What is the mass of hydrogen in 51 g of ammonia, NH₃?
A. 3 g
B. 9 g
C. 14 g
D. 17 g
▶️Answer/Explanation
Answer: B. 9 g
Explanation: The molar mass of NH₃ is 17 g/mol (14 g/mol for nitrogen and 3 g/mol for hydrogen). In 51 g of NH₃, there are 3 moles of NH₃. Since each mole of NH₃ contains 3 g of hydrogen, the total mass of hydrogen in 51 g of NH₃ is 9 g.