Question

People take antacids, such as milk of magnesia, to reduce the discomfort of acid stomach or heartburn. The recommended dose of milk of magnesia is 1 teaspoon, which contains 500 mg of Mg(OH)2. What volume of HCl solution with a pH of 1.25 can be neutralized by 1 dose of milk of magnesia

Answer 1

Answer:

$V_{HCl}=0.208L=208mL$

Explanation:

Hello,

In this case, since the chemical reaction is:

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

We can see that hydrochloric acid and magnesium hydroxide are in a 2:1 mole ratio, which means that the neutralization point, we can write:

$n_{HCl}=2*n_{Mg(OH)_2}$

In such a way, the moles of magnesium hydroxide (molar mass 58.3 g/mol) in 500 mg are:

$n_{Mg(OH)_2}=500mg*\frac{1g}{1000mg}*\frac{1mol}{58.3g} =0.00858mol$

Next, since the pH of hydrochloric acid is 1.25, the concentration of H⁺ as well as the acid (strong acid) is:

$[H^+]=[HCl]=10^{-pH}=10^{-1.25}=0.0562M$

Then, since the concentration and the volume define the moles, we can write:

$[HCl]*V_{HCl}=2*n_{Mg(OH)_2}$

Therefore, the neutralized volume turns out:

$V_{HCl}=\frac{2*0.00858mol}{0.0562\frac{mol}{L} }\\ \\V_{HCl}=0.208L=208mL$

Best regards.