Milk of magnesia, a suspension of Mg(OH)2

Question

Milk of magnesia, a suspension of Mg(OH)2

in water, reacts with stomach acid (HCl) in a

neutralization reaction.

Mg(OH)2(s) + 2HCl(aq) −!

2H2O(l) +MgCl2(aq)

What mass of MgCl2 will be produced if

4.55 g of Mg(OH)2 reacts?

Answer in units of g.

 

4.55=0.78 moles

0.78x2=0.156 of HCL

I came up with 0.156 x 34.46=5.47 g of hCL but the answer is not correct. Am I missing something?

021 (part 2 of 2) 10.0 points

What mass of HCl is required to completely

react with 4.55 g of Mg(OH)2?

Answer in units of g.

Answer 1

You are on the right path :)

 

Part 1)

 

4.55 g Mg(OH)₂ = 0.0780 mol Mg(OH)₂ (Molar Mass of Magnesium hydroxide = 58.32 g/mol)

 

What mass of MgCl₂ will be produced for the above amount of magnesium hydroxide to react?

For every one mole of Mg(OH)₂ that reacts, one mole of MgCl₂ is produced.

 

0.0780 mol Mg(OH)₂ = 0.0780 mol MgCl₂

0.0780 mol MgCl₂ = 7.43 g MgCl₂ (Molar Mass of Magnesium chloride = 95.21 g/mol)

 

Part 2)

 

From above, 4.55 g = 0.0780 mol

For every one mold of Mg(OH)₂ that reacts, it needs two moles of HCl

 

0.0780 mol Mg(OH)₂ = 0.1560 mol HCl

0.1560 mol HCl = 5.68 g HCl (molar mass of Hydrochloric acid = 36.46 g/mol)

 

Hope this helps,

Chris