Help with Chemistry calculation?

0mega

Maybe someone's done this before or knows what to do? I'm honestly stumped.

2005 Q10 (a):

An indigestion tablet contains a mass of 0.30 g of magnesium hydroxide [Mg(OH)2] as its only basic ingredient. The balanced chemical equation for the reaction between magnesium hydroxide and
hydrochloric acid (HCl(aq)), the acid produced in the stomach, is as follows:

Mg(OH)2 + 2HCl MgCl2 + 2H2O

(i) Calculate the volume of 1.0 M HCl neutralised by two of these indigestion tablets.

I've tried doing out this question but ended up with an answer of 0.012cm cubed, which is obviously wrong.

Here's the marking scheme, which I can't make heads or tails of at all:

CALC: 20 / 21 cm3:

2 x 0.3 = 0.6 g ÷ 58* 0.01 / 0.0103 mol
0.01 / 0.0103 mol Mg(OH)2 ≡ 0.02 / 0.021 mol HCl
volume of 1.0M HCl = 20 / 21 cm3

If anyone could even help me with the bit of the marking scheme, it'd be much appreciated!

Stalin and rugby

Relative mol mass = 58g/mol

.3 grams* 2 because there are 2 tablets = .6g

0.6g /58 = 0.01 moles

Ratio of reactants is 2 to 1 so you need twice as much Hcl

.02moles

0.02 * 1000cm cubed gives you 20cm cubed

Just out of curiosity what grade are you going for?

reznov

We've got 0.3g per tablet of Mg(OH)2 so multiply it by 2 and get 0.6g in two tablets.

Divide it by 58g, the relative molecular mass and we receive 0.01 moles.

As we have a 1:2 ratio between Mg(OH)2 and HCL, there will be 0.02 moles of HCL.

To get the volume, multiply by 1000 cm^3 and you should have 20 cm^3.

0mega

Stalin and rugby wrote: »

Relative mol mass = 58g/mol

.3 grams* 2 because there are 2 tablets = .6g

0.6g /58 = 0.01 moles

Ratio of reactants is 2 to 1 so you need twice as much Hcl

.02moles

0.02 * 1000cm cubed gives you 20cm cubed

Just out of curiosity what grade are you going for?

An A1/A2 I guess, although I'm only in 5th year and haven't done this chapter since Easter! Revising for Summer exams.

Thanks for your help!