question for chemistry

Question

Mg + 2 HNO3 ---> Mg(NO3)2 + H2

If I start this reaction with 40.0 grams of magnesium and an excess of nitric acid (HNO3), how many grams of hydrogen gas will I produce?

 

A) 3.3g H2

B) 4.5 g H2

C) 7.8 g H2

D)1.2 g H2

Answer 1

The mass of 40 gram of magnesium gives 1.67 moles of magnesium.40g/24gmol-1

Magnesium to Hydrogen mole ration is 1:1

So 1.67 of Magnesium gives 1.67 moles of Hydrogen

The moles of Hydrogen is then multiplied by its RMM(2gmol-1)

1.67moles*2gmol-1=3.34g