Question

17. Calculate the average percent yield for both trials of your experiment.

17. (a) Write the net ionic equation for this reaction.

(b) Identify the reducing agent in this reaction.

Mg(s)+ 2HCL(aq).  MgCl₂(aq) + H₂(g)

17. The amount of hydrochloric acid added to the reaction was more than enough to consume all of the magnesium. Therefore, the magnesium is the limiting reactant. How many milliliters of 3.0 M hydrochloric acid solution necessary to consume 0.040 grams of magnesium metal?

Data table template:

	Trial 1	Trial 2
Atmospheric pressure (mmHg)	745.9 mm Hg	746.3 mm Hg
Mass of Mg (g)	.0354 g	.0340 g
Volume of gas (mL)	36.05mL	34.10 mL
Water temperature (ºC)	21.0ºC	21.0ºC

Answer 1

1. The balanced chemical reaction:

Mg (s) + 2HCl (aq)   MgCl2 (aq) + H₂ (g)

The ionic equation is:

Mg (s) + 2H⁺ (aq) + 2Cl^- (aq) Mg²⁺ (aq) + 2 Cl^- (aq) + H₂ (g)

The net ionic equation is:

Mg (s) + 2H⁺ (aq) Mg²⁺ (aq) + H₂ (g)

2. Mg (s) + 2HCl (aq)   MgCl2 (aq) + H₂ (g)

Mg has an oxidation state 0 since it is in the elemental state.

In MgCl₂, Mg has an oxidation state of +2.

In HCl, H has an oxidation state of +1.

H₂ has an oxidation state of 0 since it is in the elemental state.

As you can see, the oxidation state of Mg increases from 0 to +2. So it gets oxidised and reduces others. It acts as a reducing agent.

Oxidation state of H increases from +1 to 0. So it gets reduced and oxidises others. It acts as an oxidising agent.

3. As you can see in the reaction, 1 mol Mg is consumed by 2 mol HCl.

1 mol Mg has mass = 24 g

1 mol HCl has mass = 36.5 g

2 mol HCl has mass = 73 g

So, 24g Mg is consumed by 73g HCl

0.040g Mg is consumed by (73/24) * 0.040 = 0.122g

Given that molarity of HCl = 3M

Molarity = Mass / (Molar mass x Volume of solution in L)

Putting the values we get,

3 mol/L = 0.122g / (36.5 g/mol x Volume)

Volume = 0.0011 L = 1.1 mL