Zinc and magnesium metal each
Zinc and magnesium metal each reacts with hydrochloric acid tomake chloride salts of the respective metals, and hydrogen gas. A12.50-g mixture of zinc and magnesium produces 0.6754 g of hydrogengas upon being mixed with an excess of hydrochloric acid. Determinethe percent magnesium by mass in the original mixture.
Answer:
the reaction of Zinc and magnesium with hydrogen is
Zn+ 2HCl ——–>ZnCl2+ H2(g) and Mg+2HCl———–>MgCl2 + H2
1 mole of Zn reacts with HCl to give 1 mole of H2 as well as 1mole of Mg reacts with HCl to also give 1mole of H2
let x= mass of Zinc in the mixture, mass of Mg in the mixture =12.5-x
moles = mass/atomic weight, atomic weigts ( g/mole) : Zn = 65.38, Mg= 24
moles : Zinc= x/65.3 Mg= (12.5-x)/24
moles of H2 produced due to reaction of Zinc with HCl = x/65.3and Mg with HCl= (12.5-x)/24
total moles of H2 prooduced = x/65.3+(12.5-x)/24=0.015x+(12.5-x)*0.042=0.015x-0.042x+0.525=0.525-0.027x
mass of Hydrogen produced = moles of hydrogen* molar mass =2*(0.525-0.027x)= 1.05-0.054x
mass of hydrogen produced = 0.6754 gm
1.05-0.054x =0.6754
0.054x= 1.05-0.6754
x= 6.93 gm mass of zinv in the mixture = 6.93 gm, mass of Mg =12.5-6.93= 5.57 gm
mass % of Mg in the mixture = 100*5.57/12.5=44.56%
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