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Moles

Volumes of Gases.

Hydrogen is produced in the laboratory
by adding zinc to dilute sulfuric acid.

Example 3.

What volume of hydrogen is produced
by reacting 6·5 g  of zinc with dilute sulfuric acid?

Method.
1) Find how many moles of zinc are present in 6·5 g  of zinc.
RAM of  Zn = 65.

      moles = mass ÷ RAM

moles = 6·5 ÷ 65
                          = 0·1 moles of zinc.

2) Write the equation for the reaction.

zinc    +   sulfuric acid  arrow   zinc sulfate   +   hydrogen.
Zn(s) +    H2SO4(aq)   arrow     ZnSO4(aq)      +        H2(g)

Use the big numbers to find the proportion of reactant to product.

1Zn makes 1H2, the proportion is 1 to 1,
so 0·1 moles of zinc will make 0·1 moles of hydrogen.

3) Convert moles into volume.

   volume  =  moles x 24,000 cm3

volume  =  0·1 x 24,000 cm3
                       = 2,400 cm3 of hydrogen.

So, reacting 6·5 g  of zinc with dilute sulfuric acid
 will produce 2,400 cm3 of hydrogen.

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