Answer:
It would take 72.9 mL of milk of magnesia.
Explanation:
First of all we have to think how the compounds react with each other and what are the products formed. In this case, the hydrochloric acid reacts with magnesium hydroxide to generate magnesium chloride and water as a subproduct. Having said that, we have to state the balanced chemical reaction to know the associated stoichiometry:
2 HCl + Mg(OH)2 → MgCl2 + 2 H2O
According to the balanced equation we know that 2 mol of HCl reacts with 1 mol of Mg(OH)2.
Now we calculate the quantity of moles of HCl that we have present in 2.0 lts of 0.10 M solution:
0.1 M HCl = 0.1 moles HCl / 1000 ml Solution
So, in 2 liters of solution we will have 0.2 moles of HCl
This 0.2 moles of acid, as we stated before, will react with 0.1 moles of Mg(OH)2, so we need to calculate the amount of milk of magnesia that has this required quantity of moles.
With the molar mass of Mg(OH)2 we calculate the weight of the compound that represents the 0.1 moles needed to react with all the HCl present in solution:
1 mol Mg(OH)2 = 58.32 g
0.1 mol = 5.832 g
Now we need to determine what volume of the milk of magnesia solution has 5.832 g of Mg(OH)2 to react with the acid:
The concentration of milk of magnesia is 8 % (w/v). This means that we have 8 gr of Mg(OH)2 per 100 ml of solution.
8 gr Mg(OH)2 per 100 mL Solution
5.832 gr Mg(OH)2 = 72.9 mL of Milk of Magnesia
