HSC Chemistry Question Thread

[starkidshani]

Hello! Could someone please help me out with summarising the chemistry of a Dry Cell?

[jakesilove]

Hello! Could someone please help me out with summarising the chemistry of a Dry Cell?

Hey! This is the information I had going into my HSC

[starkidshani]

Hey! This is the information I had going into my HSC

(Image removed from quote.)

Awesome, thank you! What about the overall equation?

[jarin_]

hey, what pracs are the most common for the core topics & industrial and how well should we know them?

[RuiAce]

hey, what pracs are the most common for the core topics & industrial and how well should we know them?

Any prac can be asked whenever BOSTES feels like it and you should know all of them really well. As for how well, you can decide which pracs knowing the method is enough, whereas which pracs you need also some expected results. Discussion questions (especially the classic 3 reliability, accuracy and validity) just need to be known.

Though I only remember these pracs in industrial
- Modelling equilibriums
- Laboratory electrolysis of NaOH
- Laboratory saponification

[jarin_]

Any prac can be asked whenever BOSTES feels like it and you should know all of them really well. As for how well, you can decide which pracs knowing the method is enough, whereas which pracs you need also some expected results. Discussion questions (especially the classic 3 reliability, accuracy and validity) just need to be known.

Though I only remember these pracs in industrial
- Modelling equilibriums
- Laboratory electrolysis of NaOH
- Laboratory saponification

thanks!!
also i'm having trouble with pH calculations
for eg;
A solution was made of mixing 75.00 mL of 0.120M HCL with 25mL of 0.2M NaOH.
What is the pH of the solution?

Is there a particular set of steps in doing these types of questions?

[jakesilove]

thanks!!
also i'm having trouble with pH calculations
for eg;
A solution was made of mixing 75.00 mL of 0.120M HCL with 25mL of 0.2M NaOH.
What is the pH of the solution?

Is there a particular set of steps in doing these types of questions?

There certainly is! Calculate the moles of H+, and the moles of OH-. Figure out the limiting reagent, and then how many left-over moles of acid there are. Then, you can figure out the overall concentration of the left over hydroxide (Left over H+/0.1L), and sub that into the -log(H) formula!

[Potato101]

thanks!!
also i'm having trouble with pH calculations
for eg;
A solution was made of mixing 75.00 mL of 0.120M HCL with 25mL of 0.2M NaOH.
What is the pH of the solution?

Is there a particular set of steps in doing these types of questions?

Writing out the equation and writing the volume and conc. given, underneath the respective acid/base makes it easier

[wesadora]

Hey - for this question, I'm getting two different answers. The conquering chemistry answer correlates to my response when i first answered this question, saying that iron would be forced to act as a cathode and thus reduce.
However, the HSC answers in the past papers book (this is 2008) says that iron acts as a cathodic site and thus isn't reduced??!?! But water /oxygen (presumably from surrounding soil) is instead? I understand the conquering chem answer but idk what the hell the HSC suggested answers are talking about.

thanks!
- probs a Q for Jake. 

[jarin_]

There certainly is! Calculate the moles of H+, and the moles of OH-. Figure out the limiting reagent, and then how many left-over moles of acid there are. Then, you can figure out the overall concentration of the left over hydroxide (Left over H+/0.1L), and sub that into the -log(H) formula!

Writing out the equation and writing the volume and conc. given, underneath the respective acid/base makes it easier

thank u so much guys!!

[WLalex]

Hey! Was wondering if someone could please confirm the correct answers to this question..the paper is too old so I can't find answers

I got 7.6mg but I always struggle with these type of Q's so not sure if it us right

[wesadora]

Hey! Was wondering if someone could please confirm the correct answers to this question..the paper is too old so I can't find answers

I got 7.6mg but I always struggle with these type of Q's so not sure if it us right

You're right just the n=cv, then m=nM and conv g to mg. yay

[IkeaandOfficeworks]

Hi guys, how do you do this question? Thank you. (Btw the answer is C)

[jakesilove]

Hey - for this question, I'm getting two different answers. The conquering chemistry answer correlates to my response when i first answered this question, saying that iron would be forced to act as a cathode and thus reduce.
However, the HSC answers in the past papers book (this is 2008) says that iron acts as a cathodic site and thus isn't reduced??!?! But water /oxygen (presumably from surrounding soil) is instead? I understand the conquering chem answer but idk what the hell the HSC suggested answers are talking about.

thanks!
- probs a Q for Jake. 

Definitely stick with the answer you gave, and the answer in the Chem book. Both answers are technically correct (all it's saying is that it would take less energy to reduce water, rather than reduce iron, so that is more likely to occur and produce some sort of oxide layer). However, the reduction of iron is really what we care about it. Sounds like you understand the topic well, just ignore the HSC answer that has confused you!

[jakesilove]

Hi guys, how do you do this question? Thank you. (Btw the answer is C)

Hey! So we know that



Because the LHS is how ppm works, and the RHS is how fractions work. This gets us an easy answer of



And thus C! Definitely a difficult question conceptually, but once you've seen the method once, you shouldn't have any trouble replicating it