# How many grams of hydrogen gas (H2) are produced when Zn metal completely replaces hydrogen in 300 mL of?

6. a) How many grams of hydrogen gas (H2) are produced when Zn metal completely replaces hydrogen in 300 mL of a 4.0 M HCl solution (i.e. 4.0 moles/liter)? Zinc chloride (ZnCl2) is the other product.

b) How many grams of ZnCl2 are produced?

### 2 Answers

- PhilippeLv 79 years agoBest Answer
Hi Jared,

I am french (Boulogne sur mer 62200 - FRANCE)

1°/ How many grams of hydrogen gas (H2) are produced when Zn metal completely replaces hydrogen in 300 mL of a 4.0 M HCl solution (i.e. 4.0 moles/liter)? Zinc chloride (ZnCl2) is the other product.

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The equation of the reaction can be written:

. Zn . . . + . . . 2 HCl . . . -----> . . . H2 . . . + . . . ZnCl2

1 mole . . . . . .2 moles . . . . . . . .1 mole . . . . . . 1 mole

M(HCl) = M(H) + M(Cl)

M(HCl) = 1 + 35,5

M(HCl) = 36,5 g/mole

M(H2) = 2M(H)

M(H2) = (2 x 1)

M(H2) = 2 g/mole

M(ZnCl2) = M(Zn) + 2M(Cl)

M(ZnCl2) = 65,4 + (2 x 35,5)

M(ZnCl2) = 136,4 g/mole

Look for the number of moles of HCl in 300 mL of solution :

n(HCl) = C x V

n(HCl) = 4,0 x 0,300

n(HCl) = 1,2 mole

. . . according the equation :

. . . . . . . . . . 2 moles of HCl gives 1 mole of H2

. . . then . . 1,2 mole of HCl gives 1,2 / 2 = 0,6 mole of H2

Finally :

m(H2) = M(H2) x n(H2)

m(H2) = 2 x 0,6

m(H2) = 1,2 g of H2

2°/ How many grams of ZnCl2 are produced ?

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. . . according the equation :

. . . . . . . . . . 2 moles of HCl gives 1 mole of ZnCl2

. . . then . . 1,2 mole of HCl gives 1,2 / 2 = 0,6 mole of ZnCl2

Finally :

m(ZnCl2) = M(ZnCl2) x n(ZnCl2)

m(ZnCl2) = 136,4 x 0,6

m(ZnCl2) = 81,84 g of ZnCl2

I hope to have answered your question.

.

- Trevor HLv 79 years ago
6a) Write a balanced equation:

Zn + 2HCl → ZnCl2 + H2

2mol HCl will produce 1 mol H2

You have 0.3*4.0 = 1.2 mol HCl

This will produce 1.2/2 = 0.6 mol H2

Molar mass H2 = 2g/mol

0.6 mol H2 = 1.2g H2 will be produced.

b) what mass of ZnCl2?

2mol HCl will produce 1 mol ZnCl2

You have 1.2 mol HCl. This will produce 1.2/2 = 0.6 mol ZnCl2

Molar mass ZnCl2 = 136.3158 g/mol

0.6 mol = 0.6*136.3158 = 81.79 g ZnCl2 produced