# Chemical Forums

## Chemistry Forums for Students => High School Chemistry Forum => Chemistry Olympiad and other competitions => Topic started by: CapitalSwine on July 28, 2017, 08:52:48 PM

Title: Relationship between Volumes
Post by: CapitalSwine on July 28, 2017, 08:52:48 PM
I am having trouble with this question:

Consider the following three scenarios:
(i)  2.3 g of pure Na2CO3 reacts completely with a certain volume, V1, of 0.1 mol L–1 hydrochloric acid to give sodium chloride, carbon dioxide and water.

(ii)  2.3 g of a sample containing Na2CO3 but also contaminated with some K2CO3, similarly reacts completely with a certain volume, V2, of 0.1 mol L–1 hydrochloric acid.

(iii) 2.3 g of a sample containing Na2CO3 but contaminated with some NaOH, similarly reacts completely with a certain volume, V3, of 0.1 mol L–1 hydrochloric acid.

What is the relationship between the volumes V1, V2 and V3?
A)  V3>V1>V2
B)  V1>V2>V3
C)  V3>V2>V1
D)  V1>V3>V2
E)  V2>V3>V1

What do they mean by "the relationship between volumes"? How does one go about solving this question? I came up with the balanced equations for all three of the scenarios but am confused as to how much a certain volume of HCl can increase/decrease in a given reaction.
Help with solving the problem would be greatly appreciated!
Title: Re: Relationship between Volumes
Post by: sjb on July 29, 2017, 03:17:38 AM
In your first experiment, you have 2.3g of sodium carbonate only. How much acid is required to completely react? In your second, you have, for instance 2.0g of sodium carbonate and 0.3g of potassium carbonate. How much acid is now required? Similarly for experiment three (2.0g of Na2CO3 and 0.3g of NaOH).

All you need is an order, not necessarily actual figures.
Title: Re: Relationship between Volumes
Post by: Vidya on July 29, 2017, 03:56:01 AM

I came up with the balanced equations for all three of the scenarios but am confused as to how much a certain volume of HCl can increase/decrease in a given reaction.
Help with solving the problem would be greatly appreciated!
Ok you have the balanced equation.So it means that you know that for each mole of Na2CO3 and K2CO3 we need two moles of HCl.However for one mole of NaOH we need only one mole of HCl.If we  analyze number of moles of HCl required in each case without any calculations then  3rd solution needs minimum so its volume should be minimum.If we compare molar of K2CO3 with Na2CO3 then moles of CO3 2- will be less in second solution as compare the first solution so we need less volume for second solution then first one.