How many moles of hydrogen gas are needed to produce 20 grams of hydrochloric acid (hcl)?
h2 + cl2 → 2 hcl

0.27 mole

Explanation:

Data given:

mass of hydrochloric acid (HCl) = 20 g

moles of hydrogen (H₂O) = ?

Solution:

First we look to the reaction in which hydrogen react with Chlorine and make hydrochloric acid (HCl)

Reaction:

              H₂ + Cl₂ > 2HCl

Now look at the reaction for mole ratio

              H₂ + Cl₂ > 2HCl

              1 mole                    2 mole

So it is 1:2 mole ratio of hydrogen to hydrochloric acid (HCl)

As we Know

molar mass of H₂ = 2(1) = 2 g/mol

molar mass of HCl = 1 + 35.5 = 36.5 g/mol

Now convert moles to gram

                     H₂         +       Cl₂    >     2HCl

            1 mole (2 g/mol)                             2 mole (36.5 g/mol)

                     2 g                                                 73 g

So,

we come to know that 2 g of hydrogen gives 73 g of hydrochloric acid (HCl) then how many grams of hydrogen will be required to produce 20 grams of hydrochloric acid (HCl).

Apply unity formula

                            2 g of H₂ ≅ 73 g of HCl

                            X g of H₂ ≅ 20 g of HCl

Do cross multiplication

                            X of H₂ = 2 g x 20 g / 73 g

                            X of H₂ = 0.55 g

Now convert grams of H₂ into moles

                    No. of moles = mass in grams/molar mass

Put values in above formula

                   No. of moles = 0.55 g / 2 (g/mol)

                   No. of moles = 0.27 mol

0.27 mole of hydrogen needed to produce 20 gram of hydrochloric acid (HCl).