Question

Question 13 of 15 Milk of magnesia, which is an aqueous suspension of magnesium hydroxide, is used as an antacid in the reaction below. How many molecules of HCI would have to be present to form 75.82 g of MgCl2? molecules (1 2 3 X 100

Answer 1

Molar mass of MgCl2,
MM = 1*MM(Mg) + 2*MM(Cl)
= 1*24.31 + 2*35.45
= 95.21 g/mol


mass(MgCl2)= 75.82 g

use:
number of mol of MgCl2,
n = mass of MgCl2/molar mass of MgCl2
=(75.82 g)/(95.21 g/mol)
= 0.7963 mol
use:
number of molecules of MgCl2 = number of mol * Avogadro’s number
= 0.7963 * 6.022*10^23 molecules
= 4.796*10^23 molecules

The reaction is:
2 HCl + Mg(OH)2 -> MgCl2 + 2 H2O

So,
Number of HCl required = 2*number of mgCl2 formed
= 2*4.796*10^23 molecules
= 9.592*10^23 molecules

Answer: 9.592*10^23 molecules