HSC 2012-2015 Chemistry Marathon (archive) (3 Viewers)

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Well when the KNO3 ionizes in water, NO3- is always soluble, no matter what ions join with it.

What about the potassium?

 

[enigma_1]

re: HSC Chemistry Marathon Archive

Ive never done any questions or any theory with solubility rules....

Lol dw I didn't even know my solubility rules

But tbh the answer to the question should be mentioned in all textbooks. It's a pretty common question, so just have a think logically why would you want a certain salt to be used in the salt bridge? Why would you prefer one over several others? (Remember that in the galvanic cell ions are constantly moving and stuff)

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Lol dw I didn't even know my solubility rules

But tbh the answer to the question should be mentioned in all textbooks. It's a pretty common question, so just have a think logically why would you want a certain salt to be used in the salt bridge? Why would you prefer one over several others? (Remember that in the galvanic cell ions are constantly moving and stuff)

Seriously? Did you have to rote learn all of the tests for identifying the presence of ions in unknown solutions in monitoring and management? Wasn't that more difficult in the long run?

 

[Ekman]

re: HSC Chemistry Marathon Archive

What about the potassium?

The potassium ions go into solution.... and don't react with the electrodes....

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

So tempted to answer this, but I will resist the temptation and leave it to the 2015er's

Will start with a simple question:

Describe and evaluate the procedure you used to compare the heat of combustions of various fuels in your first hand investigations. (5 marks)

1) Prepare 100 mL of water for each various fuel
2) Record the weight of the fuel before and after burning it and the temperature before and after
3) Close the cap of the fuel after burning as some is volatile
4) Use the formula to find molar heat of combustion and compair
might need a bit more?

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

The potassium ions go into solution.... and don't react with the electrodes....

What about the solubility of potassium salts (remember it's an alkali metal)

 

[enigma_1]

re: HSC Chemistry Marathon Archive

Seriously? Did you have to rote learn all of the tests for identifying the presence of ions in unknown solutions in monitoring and management? Wasn't that more difficult in the long run?

Yeah, I ended up just roting those ones in CMM. Idk why but solubility rules were so boring to learn haha. I actually found it a little easier that way (wihlth the flowchart and all) ://

The potassium ions go into solution.... and don't react with the electrodes....

Ok, but that wouldn't warrant you 2 marks.

 

[Ekman]

re: HSC Chemistry Marathon Archive

Yeah, I ended up just roting those ones in CMM. Idk why but solubility rules were so boring to learn haha. I actually found it a little easier that way (wihlth the flowchart and all) ://



Ok, but that wouldn't warrant you 2 marks.

Then why is everyone make a big deal about the solubility of the K+ ions, they always stay in solution, whats the problem...

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

write your answer

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Yeah, I ended up just roting those ones in CMM. Idk why but solubility rules were so boring to learn haha. I actually found it a little easier that way (wihlth the flowchart and all) ://

Oh wow, I couldn't have done that hahaha, especially with remembering that you have to exclude some ions beforehand if you're performing some tests.

Though I wrote out my solubility rules really simply and had little mnemonic kind of things to remember them all because just looking at all those rules was daunting lol

 

[Queenroot]

re: HSC Chemistry Marathon Archive

Lol I was trying to make them get it themselves, but I think this whole thread is mostly going to be 14ers answering questions and queen and square derailing hard. Basically the same as the last marathon lol

well we found you didn't we

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Then why is everyone make a big deal about the solubility of the K+ ions, they always stay in solution, whats the problem...

For HSC purposes it's best to explicitly state that as potassium is an alkali (group 1) metal salts of potassium will always be soluble.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Next question:
3 marks

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

well we found you didn't we

I had 200 posts and like three bars of rep when you guys dragged me out of this thread haha

 

[Squar3root]

re: HSC Chemistry Marathon Archive

Next question:

1) get some indicator from the shelf
2) wear safety gear (very important)
3) test it
4) pack equipment away

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Guys pls.

That's actually a really good question since it's one of the pracs that a lot of people forget to study. We need more 15ers here to answer these though. I'll see if I can recruit hawkrider

 

[Librah]

re: HSC Chemistry Marathon Archive

1) Prepare 100 mL of water for each various fuel
2) Record the weight of the fuel before and after burning it and the temperature before and after
3) Close the cap of the fuel after burning as some is volatile
4) Use the formula to find molar heat of combustion and compair
might need a bit more?

The keywords were compare and evaluate.

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

The derails are real!

Yay another 15er! Please answer the indicator question if you can so we can keep the thread going

 

[Ekman]

re: HSC Chemistry Marathon Archive

Yay another 15er! Please answer the indicator question if you can so we can keep the thread going

The pressure is ON!

Ok so:
1-Obtain 2-3 red cabbage leaves and tear them into pieces.
2-Place the torn cabbage leaves into 100mL beaker filled with water.
3-Heat the beaker till the water becomes purple and the leaves become pale in colour.
4-Leave the beaker to cool (Safety first kids!)
5-Decant the beaker to obtain your new red cabbage indicator!
6-Obtain 0.1Molar samples of known household bases and acids.
7-Test by placing a few drops of your red cabbage indicator into your known household substances and record the change in colour

EDIT: They don't have to be at 0.1 Molar concentrations, but I usually say that because Chemistry procedures require numerical measurements.

 

[enoilgam]

re: HSC Chemistry Marathon Archive

Guys, please keep this thread on topic. Also, it would be preferable if past students ask the questions and current ones answer.