[nblu]

Hi, I've just completed one question and I wish to know I've done it correctly;
Thank you in advance for your time to view this post.

Q. Magnesium hydroxide reacts with phosphoric acid to produce magnesium phosphate and water. Find the mass of magnesium hydroxide that will react with 38.2g of acid.

Here is my attempt.

Mg(OH)₂ + H₃PO₄ -----> Mg₃(PO₄)₂ + H₂O
Balancing equation;
3Mg(OH)₂ + 2H₃PO₄ -----> Mg₃(PO₄)₂ + 6H₂O

2H₃PO₄ : 3Mg(OH)₂
2 mol : 3 mol
molar mass of H₃PO₄ = 98.0 g/mol
moles of H₃PO₄ = 38.2 g / 98.0 g/mol = 0.390 mol

Let x=mol of Mg(OH)₂

0.390mol        x mol
2H₃PO₄  ----> 3Mg(OH₄)₂
2mol              3mol

0.390/2 = x/3
x = 0.5850 mol

Molar mass of Mg(OH)₂ = 58.0 g/mol
mass of Mg(OH)₂ produced;
= 0.5850 mol X 58.0 g/mol
= 33.9 g

Therefore the mass of Mg(OH)2 that will react is 33.9 g

[Borek]

Looks OK.