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

`V_(HCl)=0.208L=208mL`

Step-by-step 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*(1g)/(1000mg)*(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)=(2*0.00858mol)/(0.0562(mol)/(L) )\\ \\V_(HCl)=0.208L=208mL`

Best regards.