Zn + 2 HCl → ZnCl2 + H2

You are asked the following question: In the chemical reaction above, if you

start with 100 grams of zinc, how many moles of hydrogen will be produced?

What is the logical first step to solving this problem?

O A) Convert grams of zinc to moles of zinc.

OB) Convert moles of zinc to grams of zinc.

Oc) Convert grams of H2 to moles of zinc.

OD) Convert moles of H2

grams of HCI.

A) Convert grams of zinc to moles of zinc.

Explanation:

In the reaction:

Zn + 2 HCl → ZnCl2 + H2

1 mole of Zn produce 1 mole of hydrogen, H₂

As you start with 100g of Zn, you must convert the grams of Zn to moles and, knowing moles of Zn added are equal to moles of hydrogen produced, you can solve the problem. Thus, the first step you must make is:

A) Convert grams of zinc to moles of zinc.

Convert grams of zinc to moles of zinc.

Explanation:

This question has to do with stoichiometry. Usually, when one is solving a stoichiometry question of this sort and you are given a particular mass of reactant and asked to obtain the number of moles of product that it yields, the logical thing to do as a first step is to convert the given mass of reactant to number of moles of reactant.

Secondly, you use the given reaction equation as a standard to obtain what is required.

In the case of the question we have; I can say:

Number of moles of zinc = mass of zinc / molar mass of zinc = 100g/65.4gmol-1

Number of moles of zinc = 1.53 moles of zinc

Since 1 mole of zinc yields 1 mole of hydrogen from the balanced reaction equation;

1.53 moles of zinc will also yield 1.53 moles of hydrogen.