HSC Chemistry 2017

[angelahchan]

C I think?

whoops, i got that one wrong then cuz I forgot to multiply

[mbdtHSC]

whoops, i got that one wrong then cuz I forgot to multiply

not sure though HAHA I never remember the actual letter I put

[Happy Physics Land]

but citric acid is weak, so despite it being triprotic, it doesn't ionise completely in solution so there are less H+ ions dissolved and hence less OH- required to neutralise. Shouldn't the answer be sulfuric acid??

Hey there! Because NaOH is a strong base, it is going to drive one-way reaction and make the citric acid ionise completely even thought it is a weak acid.

[Happy Physics Land]

for 20 I don't remember what answer I picked, but don't you have to divide the moles by the total volume or something to find concentration? (before putting it into the -log calculation I mean)

Absolutely Angela! Thank you for reminding me! Haven't done this for a while and things have been a little rusty! I apologise about the mistake!

[winstondarmawan]

Absolutely Angela! Thank you for reminding me! Haven't done this for a while and things have been a little rusty! I apologise about the mistake!

So, would the answer be C?

[Dylpickle01]

For Q22b, you used the molar mass of Copper instead of Zinc

[MahmoudHassan2017]

Wouldnt question 1 be A - Burette? Burette is more accurate than measuring cylinder and theres no dot point in the syllabus that requires you to use a measuring cylinder (i.e. Measuring cylinder is out of the syllabus and hence cant be the answer)

[lakwas7]

Hey,

When you say, "It delivers anion to the cathode to compensate for the zinc metal that has been oxidised into Zn2+", I thought anions went to the anode and cations went to the cathode (or is this something in physics that I got mixed up with xD).

Take this diagram for example



Any clarification would be appreciated

[mbdtHSC]

For 24b think you should say the Na+ won't react with water but the CH3COO- reacts with water to form acetic acid and hydroxide ions and hydroxide in the solution makes the pH basic

[mbdtHSC]

Hey,

When you say, "It delivers anion to the cathode to compensate for the zinc metal that has been oxidised into Zn2+", I thought anions went to the anode and cations went to the cathode (or is this something in physics that I got mixed up with xD). Any clarification would be appreciated

Think he meant to say that for the salt bridge (say KNO3 or whatever), the K+ cation will migrate to the cathode (through the salt bridge) to mitigate negative build up of charge from reduction and the NO3- will migrate to the anode to mitigate build-up of positive charge from oxidation

[kylesara]

Why isnt q 1 A? and isnt q 3 A as well because of alphabetical order?

[liya1234]

in q24b) is it okay if I talked about how the ch3coo ion is the strong conj base of a weak acid (ch3cooh) and the na ion is the weak conj acid of a strong base (naoh) and therefore ch3coona is a basic salt and thus the pH would be higher than 7?

[angelahchan]

25.a) Cellulose --> (enzymatic hydrolysis, enzyme = cellulase) --> Dissarcharide Sugar (C12H22O11) --> (enzymatic hydrolysis) --> Glucose (C6H12O6) -->
(fermentation reaction, anaerobic condition, 25-30 degrees environment, yeast catalyst) --> ethanol (C2H5OH) --> (dehydration, concentrated sulphuric acid) --> Ethylene

Not entirely sure, but wasn't this q25a  on polyethylene? also can you please explain q 1 and 3? thank you!

[kauac]

Hi!
Is biochemistry of movement interesting? I looked at the syllabus for it and think I would have liked it. My teacher is a bio/chem teacher as well so she would have done it except there are more resources for shipwrecks

Hey... Yes, the lack of resources in the main downside  . But other than that, I really loved the topic! It's mainly about the chemistry of nutrition and food metabolism, energy production and muscle contractions. It would be very helpful for anyone considering studying biochemistry, nutrition and dietetics, sport and exercise sciences, medical or health sciences at uni. Pretty much gives you a good head start on first year uni topics. Would highly recommend!

[Zainbow]

Wouldnt question 1 be A - Burette? Burette is more accurate than measuring cylinder and theres no dot point in the syllabus that requires you to use a measuring cylinder (i.e. Measuring cylinder is out of the syllabus and hence cant be the answer)

Hey!

Technically measuring cylinder IS part of the syllabus just as much as a Bunsen burner is, both not explicitly referenced but an integral component of chemistry nonetheless.

And I disagree with you when you say burettes are more accurate, because with a burette you can accidentally overpour and not have the miniscus sit where you want it to. With a measuring cylinder, however, you can use droppers to gain the most accurate measurement. I'm not saying that burettes aren't accurate, but they're less accurate than measuring cylinders bc too much can go wrong