ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: MagicGecko on March 17, 2012, 02:04:05 pm
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Hi
Ok so this is a question that will be related to a SAC I have next week and I would just like to know if my explanations are right…if not can you please explain!!!
A student titrated an aliquot of standard sodium carbonate solution with hydrochloric
acid in a burette. State whether the concentration determined for the hydrochloric acid
would be likely to be higher, lower or unchanged compared with the actual value if
the student had previously washed with water, but not dried, the following apparatus:
a the pipette used to deliver the aliquot of sodium carbonate solution
b the flask containing the aliquot
c the burette.
These are my answers:
a) Well I thought that since the pipette has not been cleansed of water, the volume of Na2CO3 would be smaller than what you thought you had. And since you had a smaller volume of Na2CO3 you would need a much larger amount of HCl to match the volume ratio. --> HIGHER
b) I think that it doesn’t matter how much water there is in the flask, as long as the volume of Na2CO3 is precise, than the concentration of HCl would be normal. -->UNCHANGED
c) …….I had an answer to this but then I scratched it out because I thought that the concentration depends on the volume but I remembered what my teacher said “it doesn’t matter how much of a volume you have, the concentration will always be the same”. So umm….can someone please explain this to me??? :-\
PLEASE THANK YOU!!! :D :D
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Hi
Ok so this is a question that will be related to a SAC I have next week and I would just like to know if my explanations are right…if not can you please explain!!!
A student titrated an aliquot of standard sodium carbonate solution with hydrochloric
acid in a burette. State whether the concentration determined for the hydrochloric acid
would be likely to be higher, lower or unchanged compared with the actual value if
the student had previously washed with water, but not dried, the following apparatus:
a the pipette used to deliver the aliquot of sodium carbonate solution
b the flask containing the aliquot
c the burette.
These are my answers:
a) Well I thought that since the pipette has not been cleansed of water, the volume of Na2CO3 would be smaller than what you thought you had. And since you had a smaller volume of Na2CO3 you would need a much larger amount of HCl to match the volume ratio. --> HIGHER
Yep, your logic works. As you have a lower mol of Na2CO3, you would require less volume of HCl to completely react it, and hence calculated concentration would be higher
b) I think that it doesn’t matter how much water there is in the flask, as long as the volume of Na2CO3 is precise, than the concentration of HCl would be normal. -->UNCHANGED
correct!
c) …….I had an answer to this but then I scratched it out because I thought that the concentration depends on the volume but I remembered what my teacher said “it doesn’t matter how much of a volume you have, the concentration will always be the same”. So umm….can someone please explain this to me??? :-\
If the unknown solution was diluted through the remaining water, you would need a greater volume to react completely with the sodium carbonate. As a result you would end up with lower calculations of concentration of HCl
Just a general thing, remember that the important thing in the standard solution is not necessarily the volume which you use, but more is representative of the exact number of mol of Na2CO3 which you deliver
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THANK YOU SOMYE!!!!!!!!!!! ;D ;D ;D ;D ;D