# as titration help!!!

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#1
Stuck on some titration questions that I have never even done in class before or encountered.

1.25g of crushed limestone was added to 50.0cm3 of 1.00moldm-3 HCl (in excess). The mixture was left until the bubbling stopped and was then made up carefully to 250cm3 with pure water. A 25.0cm3 sample of this was pipette into a conical flask and some methyl orange indicator was added. Sodium hydroxide solution of concentration 0.100moldm-3 was added from the burette. 30.0cm3 were needed to reach the end-point of the indicator. Calculate the % of calcium carbonate in the limestone.

ANS = 80.0%

How do you get to that answer that's my problem? I have done some titration questions were you need to work out n and I got that. It looks simple but I just can't get 80% any working out would really help please.
0
6 years ago
#2
(Original post by Project Tsukyomi)
Stuck on some titration questions that I have never even done in class before or encountered.

1.25g of crushed limestone was added to 50.0cm3 of 1.00moldm-3 HCl (in excess). The mixture was left until the bubbling stopped and was then made up carefully to 250cm3 with pure water. A 25.0cm3 sample of this was pipette into a conical flask and some methyl orange indicator was added. Sodium hydroxide solution of concentration 0.100moldm-3 was added from the burette. 30.0cm3 were needed to reach the end-point of the indicator. Calculate the % of calcium carbonate in the limestone.

ANS = 80.0%

How do you get to that answer that's my problem? I have done some titration questions were you need to work out n and I got that. It looks simple but I just can't get 80% any working out would really help please.
NaOH + HCl ==> NaCl + H2O

work out how many moles of NaOH

use that to work out how many moles of HCl

then calculate the moles of HCl added to the calcium carbonate

CaCO3 + 2HCl ==> CaCl2 + CO2 + H2O

use the equation to work out how many moles of CaCO3 you have

then you can calculate the percentage composition using the molar mass

hope this helps
0
6 years ago
#3
Would calcium hydroxide by any chance be able to soften sample of tap water. If so how would this be possibly be done in a lab?
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