Question

A 0.0250L solution of HCl is neutralized by 0.0780L of an unknown Mg(OH)2 solution. Also 0.050L of this Mg(OH)2 solution is neutralized by 0.0300L of a 0.20 M H3(PO3) solution. What is the concentration of the HCl solution

Answer 1

Answer:

$M_{HCl} = 1.12M$

Explanation:

Hello!

In this case, for the first reaction we need to focus on, the neutralization of magnesium hydroxide by phosphoric acid, we can write up the following equation:

$3Mg(OH)_2+2H_3PO_4\rightarrow Mg_3(PO_4)_2+6H_2O$

Whereas the acid and base react in a 3:2 mole ratio; thus, we can write:

$2M_{Mg(OH)_2}V_{Mg(OH)_2}=3M_{H_3PO_4}V_{H_3PO_4}$

Now, solving for the concentration of the magnesium hydroxide solution we get:

$M_{Mg(OH)_2}=\frac{3M_{H_3PO_4}V_{H_3PO_4}}{2V_{Mg(OH)_2}} \\\\M_{Mg(OH)_2}=\frac{3*0.20M*0.0300L}{2*0.050L}=0.18M$

Now, for the reaction between hydrochloric acid and magnesium hydroxide we have:

$Mg(OH)_2+2HCl\rightarrow MgCl_2+2H_2O$

$2M_{Mg(OH)_2}V_{Mg(OH)_2}=M_{HCl}V_{HCl}$

Therefore, solving for the concentration of the hydrochloric acid solution we get:

$M_{HCl}=\frac{2M_{Mg(OH)_2}V_{Mg(OH)_2}}{V_{HCl}} \\\\M_{HCl}=\frac{2*0.18M*0.078L}{0.025L}\\\\M_{HCl} = 1.12M$

Best regards!