Could you check my work? Well?

Question

I need to make 100 mL of Mg( NO3)2 and I need to know how much magnesium I need.

I have HNO3 which is 16 M (molarity). I need to know how much Magnesium I need to dissolve in the nitric acid (HNO3) to make 100 mL of Mg(NO3)2, which should have a molarity of .1 M.

1) I wrote out the balanced equation

Mg+ 2HNO3= H2 + Mg( No3)2

2) I calculated the amount of moles of Mg(No3)2

.100 L *.1 M= .01 mol Mg( No3)2

since M1V1=M2V2, there are also .01 mol of HNO3

3) .01 mol HNO3* 1mol Mg/2Mol HNO3*24.31g/1 mol=

.122 grams Mg

ok so my answers is .122 grams. other people though got .24 grams! am i right? or maybe to write out the balanced net ionic equation? i dont know

Answer 1

There's a lot of fancy footwork you don't need, and frankly is getting you in trouble. You want to make a solution which has 0.01 g-atoms (the proper term for elements as opposed to compounds) of Mg. So you multiply 0.01 x 24.3 g/g-mole to get 0.24 grams.

By introducing the nitrate, you are confusing the situation, since a compound which has 0.01 g-atoms of Mg will need 0.02 MOLES of nitrate.

Answer 2

Its a long while since I did Chemistry but I think you are wrong when you say you need 0.01 mol HNO3.
If you are producing 0.01 mol of Mg(NO3)2 from your balanced equation
Mg+ 2HNO3= H2 + Mg( No3)2
you will need to use twice the number of moles of the acid. ie 0.02 mol of HNO3.
Every mole of Mg(NO3)2 produced requires 2 moles of HNO3.
So the other people are right!!

Answer 3

From your equation, you need 2 moles of HNO3 for each mole of Mg(NO3)2, so 0.24 grams is correct.

Answer 4

Mg2+ + 2HNO3-----------> Mg(NO3)2 + 2H+
is the equation
to make 1M Mg(NO3)2 you need 1M Mg2+ and 2M HNO3
lets take basis as 1litre say,
for 100ml , 0.1 M Mg(NO3)2 is produced from 0.1M Mg2+ and 0.2M HNO3, you have 16M HNO3
so you need to use
100ml*0.2/16= 1.25ml 16M HNO3 and 100ml*0.1M/1.25ml=8M i.e. 1.25ml 8M Mg2+
8*24.31g/lit i.e 8*24.31*1.25/1000= 0.2431g for 1.25ml water of Mg2+ is dissolved and used with 1.25ml 16M HNO3