HSC Chemistry Question Thread

[IkeaandOfficeworks]

Hi again! Can you explain why the answer is D? Thank you. 

[RuiAce]

Hi again! Can you explain why the answer is D? Thank you. 

That just looks wrong. I would've said C. Going to get Jake's opinion later.

[jakesilove]

Hi again! Can you explain why the answer is D? Thank you. 

Definitely C

[IkeaandOfficeworks]

Hi guys! how do you do this question? Thank you.   

[jakesilove]

Hi guys! how do you do this question? Thank you.   

Hey! The molar heat of combustion of a substance is, by definition, the heat liberated when one mole of the substance is burned. So, you just find the molar mass (44g), and that's your answer! This is kind of just a 'by definition' answer

[Jpw1627]

Hey guys, I have a quick question in regards to calculating the PH of a mixture with a dilution. I have attached the question as a photo if you could have a look. It is from a Ruse Trial. Thanks heaps

[jakesilove]

Hey guys, I have a quick question in regards to calculating the PH of a mixture with a dilution. I have attached the question as a photo if you could have a look. It is from a Ruse Trial. Thanks heaps

Hey! So, we need to figure out the moles of Hydrogen and Hydroxide ions. To do this, we use C=n/V





So, we know we have more moles of Hydrogen than Hydroxide. In fact, we have



of excess hydrogen! We can use C=n/V to thus find the final concentration of Hydrogen ions (the rest have reacted with the base to form Water



Plug that into -Log(H) and you get a pH of 2.85... maybe I messed up my calculations somewhere, but that is the general structure of getting an answer out!

[Jpw1627]

Hey the Answer is B. I think there is something to do with the stoichiometry, as it is a 1:2 ratio.

[jakesilove]

Hey the Answer is B. I think there is something to do with the stoichiometry, as it is a 1:2 ratio.

Absolutely right, I totally ignored that

[karenc.]

Hi I just have 2 questions:
1) How does one answer a 'justify' question? is it similar to evaluate?
2) Why do we not use an indicator for a titration with a weak acid and weak base?

Many thanks

[itsAnuu]

Hi I just have 2 questions:
1) How does one answer a 'justify' question? is it similar to evaluate?
2) Why do we not use an indicator for a titration with a weak acid and weak base?

Many thanks

Justify is supporting an argument or conclusion, whereas evaluate is making a judgment based on criteria

Weak acid and weak base titrations are generally avoided due to no great change in pH, a gradual rise, and the titration curve not being very steep

[karenc.]

Justify is supporting an argument or conclusion, whereas evaluate is making a judgment based on criteria

Weak acid and weak base titrations are generally avoided due to no great change in pH, a gradual rise, and the titration curve not being very steep

Thanks for your help

so just clarifying on the justify question, would someone just write points supporting the statement?
 i really hope they ask something similiar to the 2010 8 marker question

[itsAnuu]

Thanks for your help

so just clarifying on the justify question, would someone just write points supporting the statement?
 i really hope they ask something similiar to the 2010 8 marker question

Yeah suppose there was a question like, justify the conditions used in the Haber process. You would list the conditions of e.g. moderate temperatures and then justify why it is moderate, as high temps shift equilibrium to the left, producing more reactants, and low temperatures shift to right but is extremely slow and not economically viable. <- in more detail of course

[wesadora]

This is from 2009 HSC Chem paper. I thought AAS could only be used for metal ions that can be dissolved in solution? Not like...phosphates (which is phosphorous and oxygen anyway, using AAS wouldn't make sense) or are they just playin wit us

also - for qualitative/quantitative tests regarding eutrophication, in my notes i have the fricken randomest things called the 'Kjeldahl method' and 'colorimetry' (just AAS with colours, as far as i understand) that is kinda complex and ceebs remembering. What do other people have for eutrophication tests.... :|

[WLalex]

Hey, just wanted some clarity regarding this questions.
On my notes I have written that TDS = dissolved solids + suspended solids

SO for the questions I added the mass difference from both evaporating and filtering but on the answers they one did the mass of the dissolved solids (1.14g instead of 1.38 as I did). Is this right?