Chemistry Predictions/Thoughts (3 Viewers)

[ninja151]

at the endpoint enough Ag+ has been consumed (to make AgCl precipitate) such that the precipitate Ag2CrO4 dissolves and thus we now see the yellow colour (of potassium chromate) so the colour change would be from red to yellow

is that just in this case? Because the colour starts yellow (also indicated by the q) due to the potassium chromate indicator and then changes to red when chromate ions react with silver to form silver chromate. Wouldn’t that make the indicator pointless if the colour changes back to yellow after endpoint?

 

[cheesynooby]

is that just in this case? Because the colour starts yellow (also indicated by the q) due to the potassium chromate indicator and then changes to red when chromate ions react with silver to form silver chromate. Wouldn’t that make the indicator pointless if the colour changes back to yellow after endpoint?

when the indicator is added, the red silver chromate should immediately precipitate, then at the endpoint this precipitate dissolves leaving a yellow solution of potassium chromate. (thus the indicator is not pointless since it is always red until the endpoint)

 

[ninja151]

when the indicator is added, the red silver chromate should immediately precipitate, then at the endpoint this precipitate dissolves leaving a yellow solution of potassium chromate. (thus the indicator is not pointless since it is always red until the endpoint)

I kind of get what you're saying.. but doesn’t the endpoint occur when the excess silver reacts with the chromate because that only happens once the silver has completely reacted with the halide. And the colour changes from yellow to red when silver reacts with chromate.. Thus shouldn’t the endpoint be yellow -> red. ??

 

[ninja151]

like this??

 

[cheesynooby]

I kind of get what you're saying.. but doesn’t the endpoint occur when the excess silver reacts with the chromate because that only happens once the silver has completely reacted with the halide. And the colour changes from yellow to red when silver reacts with chromate.. Thus shouldn’t the endpoint be yellow -> red. ??

that is the typical Mohr titration but this question is not one of those (hence it is q18 and not a pure memory question)
while in the titration you are referring to, excess silver is added (so it forms the red silver chromate ppt at the endpoint),
in the question, excess chloride ions are added (which undergo a precipitation reaction with the silver ions), so instead of [Ag+] increasing until silver chromate precipitates, it decreases until silver chromate dissolves

 

[C2H6O]

View attachment 50825
I’m actually going to cry. These are the official solutions btw

kill me that’s what I did before erasing it

 

[justletmespeak123]

Why the fuck would they give us small grids if they wanted us to do stupid column graphs?

the HSC is ran on vague questions since the questions are too garbage and piss easy, making poorly worded questions is easier than making unique original questions. fuck them

 

[ninja151]

that is the typical Mohr titration but this question is not one of those (hence it is q18 and not a pure memory question)
while in the titration you are referring to, excess silver is added (so it forms the red silver chromate ppt at the endpoint),
in the question, excess chloride ions are added (which undergo a precipitation reaction with the silver ions), so instead of [Ag+] increasing until silver chromate precipitates, it decreases until silver chromate dissolves

yeah I just figured that out.. thank you though!! AAAHH that’s annoying...

ALSO technically the question doesn’t specify what is added in excess so I guess it really depends on what they started with in the conical flask - which could be either - they haven’t said. From what I know the concentration of silver can still be determined by adding it from the burette which would mean cl- is in the conical flask and thus it would start yellow and change to red. Please correct me if I'm am wrong.