___1___Zn + __2___HCl → ___1___H2 + 1__ZnCl2 How many grams of hydrogen gas form when 102 grams of hydrochloric acid reacts with 128 grams of zinc?

Mass = 2.8 g

Explanation:

Given data:

Mass of HCl = 102 g

Mass of Zn = 128 g

Mass of H₂ = ?

Solution:

Chemical equation:

2HCl + Zn      →     H₂ + ZnCl₂

Number of moles of Zn:

Number of moles = mass/molar mass

Number of moles = 128 g/ 65.38 g/mol

Number of moles = 2 mol

Number of moles of HCl:

Number of moles = mass/molar mass

Number of moles = 102 g/ 36.5 g/mol

Number of moles = 2.8  mol

Now we will compare the moles of hydrogen gas with HCl and Zn.

                   HCl          :        H₂

                     2            :        1

                     2.8         :       1/2×2.8 = 1.4 mol

                   Zn          :        H₂

                     1            :        1

                     2           :         2

Number of moles of hydrogen formed by HCl are less thus it will limiting reactant.

Mass of Hydrogen:

Mass = number of moles × molar mass

Mass = 1.4 mol ×  2 g/mol

Mass = 2.8 g

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