Task

When 7.8 g of a magnesium–aluminium mixture was completely dissolved in excess hydrochloric acid, 8.96 L (STP) of hydrogen was evolved. 1) Determine the masses and mass fractions (%) of the metals in the mixture. 2) What volume (L, STP) of hydrogen is evolved if 7.8 g of the same mixture is placed in excess sodium hydroxide solution? 3) If exactly the stoichiometric amount of 20 % hydrochloric acid (ρ = 1.1 g/mL) was used to dissolve 7.8 g of the mixture, calculate the volume (mL) of the acid solution. 4) For the conditions of part 3, calculate the mass fractions (%) of the salts in the final solution. For every part, show the method (reaction equations, formulas, reasoning) and all calculations step by step.