Milk of magnesia, which is an aqueous suspension of magnesium hydroxide, is used as an antacid in the reaction below. How many molecules of HCl would have to be present to form 70.84 g of MgCl₂? Mg(OH)₂(s) + 2 HCl(aq) → 2 H₂O(l) + MgCl₂(aq)

8.96×10²³ molecules of HCl are needed

Explanation:

We analyse the reaction:

Mg(OH)₂(s) + 2 HCl(aq) → 2 H₂O(l) + MgCl₂(aq)

1 mol of magnessium hydroxide reacts with 2 moles of hydrochloric acid to produce 2 moles of water and 1 mol of magnessium chloride.

We determine the moles of salt, to know how many moles of it we have formed. → 70.84 g . 1 mol / 95.2g = 0.744 moles

Ratio is 2:1, so let's make a rule of three:

1 mol of chloride can be produced by 2 moles of HCl

Then, 0.744 of chloride were produced by (0.744 m . 2 m) / 1 m = 1.48 moles of HCl

Let's find out the number of molecules.

1.48 moles . 6.02×10²³ molecules / 1 mol = 8.96×10²³ molecules of HCl are needed

We need 8.96*10^23 molecules HCl

Explanation:

Step 1: Data given

Mass of MgCl2 = 70.84 grams

Molar mass of MgCl2 = 95.211 g/mol

Number of Avogadro = 6.022 * 10^23 / mol

Step 2: The balanced equation

Mg(OH)₂(s) + 2 HCl(aq) → 2 H₂O(l) + MgCl₂(aq)

Step 3: Calculate moles MgCl2

Moles MgCl2 = mass MgCl2 / molar mass MgCl2

Moles MgCl2 = 70.84 grams / 95.211 g/mol

Moles MgCl2 = 0.744 moles

Step 4: Calculate moles HCl

For 2 moles H2O and 1 mol MgCl2 produced , we need 1 mol Mg(OH)2 and 2 moles HCl

For 0.744 moles MgCl2 we need 2*0.744 = 1.488 moles HCl

Step 5: Calculate molecules

Molecules = 1.488 moles * 6.022 * 10^23 / mol

Molecules = 8.96*10^23 molecules

We need 8.96*10^23 molecules HCl