6 g of a mixture of copper and aluminum powders were placed in an excess of hydrochloric acid, and 2.8 liters

6 g of a mixture of copper and aluminum powders were placed in an excess of hydrochloric acid, and 2.8 liters of hydrogen were evolved. Calculate the mass fraction (%) of aluminum in the mixture.

Copper does not react with hydrochloric acid under normal conditions.

Metallic aluminum interacts with hydrochloric acid. At the same time, the salt of aluminum chloride is synthesized and bubbles of hydrogen gas are released. The reaction is described by the following equation.

Al + 3HCl = AlCl3 + 3/2 H2;

Let’s calculate the chemical amount of the evolved gaseous hydrogen.

To do this, we find the ratio of its volume to the volume of 1 mole of gas (filling a space with a volume of 22.4 liters).

N H2 = 2.8 / 22.4 = 0.125 mol;

To synthesize such an amount of gaseous hydrogen, it is required to take 0.125 x 2/3 = 0.08333 mol of metallic aluminum.

Let’s determine its weight. To this end, we multiply the amount of substance by the weight of 1 mole of this chemical element.

M Al = 27 grams / mol; m Al = 0.08333 x 27 = 2.25 grams;

Let’s find the mass fraction of metallic aluminum:

K = 2.25 / 6 = 0.375 = 37.5%;