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please help with this.

could someone please help me with this.

1.38g of m2c03 was dissolved in water of 100cm3 . the solution was made up to 250cm3. 25.0cm3 samples were titrated against 0.100 mol dm-3 hydrochloric acid. Titres obtained were 25.2 25.4, 25.3 and 25.5.

can someone help me with these questions please.

calucate the amount in moles of hcl in your mean titre
calculate the amount in moles of m2co3 used in the titration.
calculate the amount of m2co3 present in the 250cm3 solution that i prepared.

calcuate the molar mass in g -mol-1 of m2co3
calculate the relvant atomic mass of m
deduce the identity of m in the formula m2c03.

thank you.
i) Amount of moles of HCl in mean titre is 0.1*0.02535=0.002535mol

ii) For the moles of M2CO3 you need a balanced equation, which i presume is M2CO3+2HCl---->H2O+CO2+2MCl. So you'd then divide the moles of HCl by 2 to give moles of M2CO3.

iii) Well you can assume they'l be the same number of moles in each 25cm^3 division of the 250cm^3 sample. So multiply answer for ii) by 10.

iv) You have grams and moles of M2CO3, and units of molar mass are g mol^-1.

v) You have the mass of one mole of M2CO3. Which is numerically equal to the relative formula mass. So find M by substracting 60 from from answer to iv) and dividing by two. The answer i got didnt make sense for this part. :wink:
Reply 2
Avatar for taz321
taz321
OP
i got a bit confused at iv) ne help?
My answers:

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taz321
i got a bit confused at iv) ne help?

It has units grams per mole, so it will be a value in grams divided by a value in moles.
Reply 5
Avatar for taz321
taz321
OP
thank you so much i thought the answer to the last part was potassium carbonate
Np, i may have made a mistake though, probably best to wait for someone else to check as well. If the solution was 'made up' to 250cm^3 using water then the answer should be magnesium, but if it's made up using a solution of the same concentration then you get silver instead. :p:
Reply 7
Avatar for shengoc
shengoc
12
It shouldn't be magnesium, you are told that it is M2CO3, so it must have valence of +1
LearningMath
Np, i may have made a mistake though, probably best to wait for someone else to check as well. If the solution was 'made up' to 250cm^3 using water then the answer should be magnesium, but if it's made up using a solution of the same concentration then you get silver instead. :p:

No, your calculations are correct :yes: - it comes to 24.4 so it must be sodium (maybe experimental error?)

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