chemistry urgent step by step help

i suck with titration cal plz help with this question
Calculate (a) the moles and (b) the mass of magnesium carbonate at the start if 0.2 moles of sulfuric acid is added to the magnesium carbonate and the excess sulfuric acid made up to a 250 cm3 solution. 25 cm3 of this solution required 0.03 moles of sodium hydroxide for neutralisation.
MgCO3 + H2SO4 → MgSO4 + H2O + CO2
H2SO4 + 2 NaOH → NaCl + H2O

Reply 1

thad33

You'll do yourself no favours by asking people for the answer. I'd suggest going onto youtube and watching a few titration videos

Reply 2

yeah1106

Original post by thad33

You'll do yourself no favours by asking people for the answer. I'd suggest going onto youtube and watching a few titration videos

I have already done that still can't get the right answer

the answer is 0.05g

first i found the mol of Naoh- which is 7.5x10-4
then h2s04- 3.75x10-4
as 1/10 is used mol of h2so4 is 3.75x10-3
mol of h2so4 used is 0.19625

i took it away from the initial mol but i get the wrong answer

BTW i always do the question myself before asking people

Reply 3

thad33

a) should be 0.05 mol and b) should be 4.125g

You're already given the moles of 2NaOH, it's 0.03. So the moles of H2SO4 is 0.015 as the ratio is 2:1. Then you scale it up by 10 because 0.015 is the moles in 25cm^3, you want the moles in 250. So you have 0.15 moles of unreacted H2SO4, you started with 0.2 moles of it which means 0.05 must have reacted with MgCO3 as its a 1:1 reaction.

So a) is 0.05

Then you times that by the Mr of MgCO3 for the mass. 84.3 x 0.05 = 4.125

Posted from TSR Mobile

Reply 4

AshvinSeetul

Original post by yeah1106

Hi,
I got the answer to be a)0.05 mol b) 4.22g
Double check your markscheme to see if this correct first then I will post the method

Reply 5

yeah1106

Original post by AshvinSeetul

Hi,
I got the answer to be a)0.05 mol b) 4.22g
Double check your markscheme to see if this correct first then I will post the method

Its right

Reply 6

AshvinSeetul

Original post by yeah1106

Its right

Ok first just think logically, there are two reactions going on here so treat them separately.

1. Find the number of moles in the neutralisation reaction
H2SO4 + 2NaOH.....etc
The ratio is 1:2
So we know the number of moles of NaOH which is 0.03mol, therefore as part of the ratio we need to divide 0.03 by 2 to get the number of moles of H2SO4= 0.015mol.
However this is only in 25cm3 of acid as the question tells us the solution has been diluted to 250cm3. 25cm3------> 250cm3 you need to multiply the number of moles of H2SO4 by x10
This will give you 0.15 mol of acid

2. Find number of moles used in the first reaction
MgSO4 + H2SO4....etc
We are told that the first reaction is in excess( indirectly) which is done using 0.2 moles of acid and we know that 0.15moles which was the left over of the reaction was used to react with the base NaOH. Therefore 0.2-0.15= 0.05mol used in the reaction

3. Find mass of MgSO4
It's a 1:1 ratio so use the equation mass = molecular mass x number of moles

Molecular mass is of MgSO4= 84.3
Number of moles is 0.05mol

Put in the equation and you answer is 4.22g (3 sf)

Hope this helps!!!!

Reply 7

yeah1106

Original post by AshvinSeetul

Thanks so much turn out i read the question wrong i though it said 25cm3 of 0.03moldm-3 such as idiot i am

Reply 8

thad33

Ah yeah 4.215, not 4.125. I mixed the numbers around.

I find it helps to write out and label every piece of information that you're given before even attempting the question

Posted from TSR Mobile