HSC Chemistry Question Thread

[J.B]

Hi,
I really need to practice back titration calculations.
I was wondering if anyone had a bunch of questions they could send me?

I was also wondering for the electrolysis of NaCl school practical, if using a concentrated solution, would 200mL of 6.0mol/L be suitable for a Hoffman's Voltameter on 6 volts?

Thanks.

[winstondarmawan]

Shipwrecks
What are some sources of sulfate in deep ocean wrecks? Not sure if we are required to know this because I can't seem to find it in my notes.
CORE TOPICS
1. Are concentrated and dilute acids defined by >1M and <1M respectively?
2. Also, is there an equation for photochemical smog that we are advised to know?
3. When water is added to a weak acid, does pH increase or decrease?
2012 HSC:
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/22811213_1360059024119617_5363852_n.jpg?oh=30d80c4c98a69709c377d13fc9d5ba6b&oe=59F1FF4E
Not sure how filter funnels are used in the preparation of standard solutions.
TIA.

Bump

[angelahchan]

Bump

1) I don't think there's a definition for a specific concentration that means an acid is concentrated, e.g. concentrated sulfuric acid is around 18M.  Here's a definition I found:  "A dilute acid is that in which the concentration of the water mixed in the acid is higher than the concentration of the acid itself."
2) Not sure, I don't have anything in my notes for this
3) pH increases- even though equilibrium is shifted towards increasing dissociation of the weak acid, the acid is still more dilute than it was before despite this
Filter funnel: i think after you've dissolved the substance to make the solution with water in a beaker, the filter funnel is used to transfer the solution from the beaker to the volumetric flask?

[bridie_2345]

Hi there was just wondering how to figure this out? the answer is B but i got A
thanks!

[mbdtHSC]

Hi there was just wondering how to figure this out? the answer is B but i got A
thanks!

Just missing one step where you divide by the grams you found (answer A) by 0.025 to make it in terms of concentration

[MisterNeo]

Hi there was just wondering how to figure this out? the answer is B but i got A
thanks!

[Shadowfox42]

Hi quick question for Production of Materials, regarding the cyclohexane/cyclohexene prac.

Do you think we need to address the fact that a substitution reaction technically takes place between the cyclohexane and bromine water? But because only one bromine atom takes place in forming the larger molecule, the brown colour still remains. Would we lose marks if we didn't mention that in the actual exam?

Thanks

[bsdfjnlkasn]

Hey there,

Was just wondering if we need to know an example of a saponification reaction? What would be a good one to remember?

[mylinh-nguyen]

you use c1v1=c2v2 right? I got 90ml but the answer is C what did I do wrong??

[Sine]

you use c1v1=c2v2 right? I got 90ml but the answer is C what did I do wrong??

pH = 2 = -log_10([H+])
10^-2 = [H+]
0.01 = [H+]
C1V1 = C2V2
0.1 x 90 = 0.01 x V2
9  = 0.01 x V2
V2 = 900

Water added = V2 - V1 = 900 - 90 = 810mL

[mylinh-nguyen]

pH = 2 = -log_10([H+])
10^-2 = [H+]
0.01 = [H+]
C1V1 = C2V2
0.1 x 90 = 0.01 x V2
9  = 0.01 x V2
V2 = 900

Water added = V2 - V1 = 900 - 90 = 810mL

pH = 2 = -log_10([H+])
10^-2 = [H+]
0.01 = [H+]
C1V1 = C2V2
0.1 x 90 = 0.01 x V2
9  = 0.01 x V2
V2 = 900

Water added = V2 - V1 = 900 - 90 = 810mL

oh that makes sense thanksss!

[kauac]

When going through past papers (since the syllabus update), which year/s had generally the hardest questions??

[bridie_2345]

ah farout completely forgot about converting it to concentration rip haha
thanks

[MisterNeo]

Hi quick question for Production of Materials, regarding the cyclohexane/cyclohexene prac.

Do you think we need to address the fact that a substitution reaction technically takes place between the cyclohexane and bromine water? But because only one bromine atom takes place in forming the larger molecule, the brown colour still remains. Would we lose marks if we didn't mention that in the actual exam?

Thanks

It depends on what the question is. Personally, I would include it if there were enough lines, so I'd definitely know it because it adds much more depth and understanding.

Hey there,

Was just wondering if we need to know an example of a saponification reaction? What would be a good one to remember?

You don't really need to know the specific names of saponification reactions. Usually, they would give you the name and formula of the triglyceride, which you have to draw. It wouldn't hurt to know one anyway, so glyceryl tristearate is the most common one people would use. The rest of the equation would be the same but with a stearate salt.

[liya1234]

Do we need to know anything about back titrations because I have no idea what they are? I can't find anything about them on the syllabus so I'm not sure