Chemistry, 12.01.2020 21:31 xojade

Dissolve 7, 8 grams of mg and al mixture with excess hcl solution. after the reaction, the mass of acid solution increased by 7, 0 grams. determine the mass of each metal in the mix.

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Answer from: martl4175

Mg = 2,5 g; Al = 5,3 g

Explanation:

1) Reactions

Mg + 2HCl ⟶ MgCl₂ + H₂

2Al + 6HCl ⟶ 2AlCl₃ + 3H₂

2) Mass of each metal

If there had been no reaction, the mass of the solution would have increased by 7,8 g.

The mass increased by only 7,0 g.

The missing 0,8 g must represent the mass of the hydrogen generated by the reaction.

We have two relations:

Mass of Mg + mass of Al = 7,8 g

H₂ from Mg + H₂ from Al = 0,8 g

i) Calculate the moles of H₂

$n = \text{0,8 g H}_{2} \times \dfrac{\text{1 mol H}_{2}}{\text{2,016 g H}_{2}} = \text{0.40 mol H}_{2}$

(ii) Solve the relationship

Let x = mass of Mg. Then

7,8 - x = mass of Al

Moles of Mg = x/24.30

Moles of Al = (7,8 - x)/26.98

Moles of H₂ from Mg = (1/1) × moles of Mg = 1 × (x/24,30) = 0,0412x

Moles of H₂ from Al = (3/2) × Moles of Al = 1.5(7,8 - x)/26,98 = (11,7 -1,5x)/26,98

$\begin{array}{rcl}0,0412x + \dfrac{ 11,7 - 1,5x }{26,98} &= &0,40\\\\ 1,11x + 11.7 - 1,5x &=& 10.7\\-0.39x& = &-1.0\\x &=& \text{2.5 g}\\\end{array}$

Mass of Mg = 2,5 g

Mass of Al = 7,8 g - 2,5 g = 5,3 g

The masses of the metals are Mg = 2,5 g; Al = 5,3 g

Answer from: Quest

answer: - 3.) the oxidation state of nitrogen in no changes from +2 to 0, and the oxidation state of carbon in co changes from +2 to +4 as the reaction proceeds.

solution: - as per the rules, oxidation number of oxygen in its compounds is -2. the sum of oxidation numbers of all the elements of a molecule or compound is zero.

also, the oxidation number in elemental form is zero.

in no, the oxidation number of o is -2 so the oxidation number of n is +2 so that the sum is zero.

similarly, the oxidation number of c in co is +2 and o is -2.

on product side the oxidation number of n is 0 as it is in the elemental form( $n_2$ ) .

oxidation number of c in carbon dioxide is +4 as there are two oxygen in it and we know that each oxygen is -2.

so, oxidation number of n is changing from +2 to 0 and the oxidation number of c is changing from +2 to +4.

since nitrogen is reduced and hence no is acting as an oxidizing agent. carbon is oxidized and so co is acting as a reducing agent.

so, the right choice is number 3.)the oxidation state of nitrogen in no changes from +2 to 0, and the oxidation state of carbon in co changes from +2 to +4 as the reaction proceeds.

Answer from: Quest

Nonmetals usually react by gaining electrons

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Dissolve 7, 8 grams of mg and al mixture with excess hcl solution. after the reaction, the mass of a...