VCE Chemistry Question Thread

[TnGn74]

Hey, for combustion reactions and thermochemical equations I was wondering if you give the state of water as (l) or (g)? The answers seem to be inconsistent (for the combustion of octane one gives it as liquid while the other gives it as solid)

Thanks!

I would give H2O(g) for combustion reactions (because hot) in general. Give H2O(l) if it states a specific temperature <373K or SLC, and that includes when giving a dH from the data book in a thermochemical equation as those values are at SLC.

[Arad S]

Hello guys, can anybody help me for writing an aim for an experiment?

This experiment is about the galvanic cell, which there is 6 half cell with 50 ml of their solutions, which we need to determine the voltage produce by each electrochemical cell and determining that which rod is oxidation or reduction.

Thanks!

[biology1234]

Why are ionic substances brittle? Thanks

[bw304]

hi all, could i have some help with this electrolysis question?

An electrolytic cell was constructed using a sodium chloride solution for the electrolyte, a copper electrode and a zinc electrode. Complete the reduction half-equation, oxidation half-equation and overall equation.

based off the electrochemical series i got:

Reduction half-equation: 2H₂O_(l) + 2e^- --> H_{2 (g)} + 2OH^-_aq
Oxidation half-equation: Zn_(s) --> Zn²⁺_(aq) + 2e^-
Overall equation: 2H₂O_(l) + Zn_(s) --> H_{2 (g)} + 2OH^-_aq + Zn²⁺_(aq)

however the solutions say:

Reduction half-equation: 2H₂O_(l) + 2e^- --> H_{2 (g)} + OH^-_aq
Oxidation half-equation: Zn_(s) --> Zn²⁺_(aq) + 2e^-
Overall equation: H₂O_(l) + Zn_(s) --> H_{2 (g)} + Zn²⁺_(aq)

i think there's a balancing error in the solutions for the reduction equation? i'm mainly confused to how they've balanced the final reaction. how come the OH^- disappears without any H⁺ ions being added?
any help would be appreciated!

[user28]

Do Sac marks really matter?

Hello, I was wondering if getting a 40% on my chemistry SACs will impact my study score. Should I be worried about these marks?

I want to aim higher but the content is quite difficult at the moment. What's the mark that I should be aiming for to get a decent study score?

Thanks !

[lm21074]

Why are ionic substances brittle? Thanks

When you apply pressure to an ionic substance, the alignment of the ions change and they often move closer together. When ions with like charges move closer together, there is an electrostatic repulsion between them causing the structure to shatter.

hi all, could i have some help with this electrolysis question?

An electrolytic cell was constructed using a sodium chloride solution for the electrolyte, a copper electrode and a zinc electrode. Complete the reduction half-equation, oxidation half-equation and overall equation.

based off the electrochemical series i got:

Reduction half-equation: 2H₂O_(l) + 2e^- --> H_{2 (g)} + 2OH^-_aq
Oxidation half-equation: Zn_(s) --> Zn²⁺_(aq) + 2e^-
Overall equation: 2H₂O_(l) + Zn_(s) --> H_{2 (g)} + 2OH^-_aq + Zn²⁺_(aq)

however the solutions say:

Reduction half-equation: 2H₂O_(l) + 2e^- --> H_{2 (g)} + OH^-_aq
Oxidation half-equation: Zn_(s) --> Zn²⁺_(aq) + 2e^-
Overall equation: H₂O_(l) + Zn_(s) --> H_{2 (g)} + Zn²⁺_(aq)

i think there's a balancing error in the solutions for the reduction equation? i'm mainly confused to how they've balanced the final reaction. how come the OH^- disappears without any H⁺ ions being added?
any help would be appreciated!

I think the solution would be wrong here. What you've done looks right and I too don't understand why they would remove the hydroxide ion from the final equation. It doesn't seem to be a spectator ion.

Do Sac marks really matter?

Hello, I was wondering if getting a 40% on my chemistry SACs will impact my study score. Should I be worried about these marks?

I want to aim higher but the content is quite difficult at the moment. What's the mark that I should be aiming for to get a decent study score?

Thanks !

I would say yes and no. In short, it's a bit difficult to predict what sort of scores can lead to what study scores. Your SAC marks are moderated so your raw SAC marks don't often end up being your final SAC marks used in the calculation of your study score. A 65 at one school can get scaled up to an A+, and stay the same at another due to factors outside of your control, like how difficult your SACs are. It also depends on what sort of study score you're aiming for. The score that I got in chem was decent to me considering all that happened last year, but for some people, they wouldn't be happy with that study score. If we're looking towards getting the usual prereq score of 25, I reckon you'll be able to based on what you've said. It's one SAC so in essence, it shouldn't impact your study score too much. Keep asking for help and most likely you'll see an improvement in your marks. This is something I wish I did more, especially during the later parts of the year.

HELPPPP!!!!
I DONT GET MOLES/RELATIVE ATOMIC MASS/EVERYTHINGGGGGG

I CANT SEEM TO GRASP THE CONCEPT AT ALL

I don't get N vs n vs m vs M
I need a review over everything

Hi there,


Are you doing Units 1&2 atm? I'm asking just to know in what contexts you would be applying this theory.

Regardless of what year level you're in, I've linked this video on mole calculations (it's a bit long albeit useful) and this video on relative atomic mass which might help you consolidate these concepts. If you have any specific questions, let us know.

Hello guys, can anybody help me for writing an aim for an experiment?

This experiment is about the galvanic cell, which there is 6 half cell with 50 ml of their solutions, which we need to determine the voltage produce by each electrochemical cell and determining that which rod is oxidation or reduction.

Thanks!

The aim should include an action verb like investigate, perform, or explore, your independent variable(s), and dependent variable(s). I would say that the last sentence you've got there in describing the experiment is a pretty decent aim .

[biology1234]

hey, if covalent bond is polar does that make it automatically dipole-dipole interactions/ bonding. For example, ICI how do we know that it uses dipole-dipole forces. Thanks hope that question makes sense.

[biology1234]

hey,
how do you work this question out easily
thank you
ASAP

[lm21074]

hey,
how do you work this question out easily
thank you
ASAP

Look at the size of the molecule and what it contains.

Longer hydrocarbon chains would be less soluble in water than shorter ones due to the dispersion forces between molecules.

Molecules with hydroxyl groups tend to be more soluble in water too due to the formation of intermolecular hydrogen bonds.

hey, if covalent bond is polar does that make it automatically dipole-dipole interactions/ bonding. For example, ICI how do we know that it uses dipole-dipole forces. Thanks hope that question makes sense.

Yep, polar covalent bonds would have a dipole because there is unequal sharing of electrons.

[Chocolatepistachio]

Can someone explain the process of atomic absorption spectroscopy and
explain why separation of the ions is not required when analysing by AAS

[Billuminati]

Can someone explain the process of atomic absorption spectroscopy and
explain why separation of the ions is not required when analysing by AAS

AAS involves a lamp containing the element you want to quantify emitting light of the same wavelength of absorption as your sample, this light source is shined onto a high temperature burner which converts the element of interest in your sample into gaseous, ground state atoms which can absorb this electromagnetic radiation. This absorbance is detected by computers, but not before being wavelength-restricted to the intended wavelength by a monochromator to increase signal:noise ratio. You don't need to separate the species since each ion absorbs a specific wavelength of electromagnetic radiation so there's rarely any interference between 2 different analytes which may cause overestimation of concentration. It's thanks to the fact that all e- transitions are quantised so each transition in different species is represented by a very specific spectral line. Remember that ions are NOT appropriate for AAS since ions have different spectral lines to ground state atoms. You can still analyse ion concentrations in a solution with AAS but they have to be converted to ground state atoms by the burner

[ThomasK12]

Heyy,
If someone has the 2015 TSSM organic chemistry (polymers) key topic test can u plss send??
Thankss

[Chocolatepistachio]

Can someone explain the standard addition method and the difference between the standard addition method and use of a calibration curve and calibration standards 

[Chocolatepistachio]

What are the disadvantages of step wise elution over other elution methods 

[beep boop]

Hi All,

Can someone please help me w/ q13 c and q15d?

Much appreciated,
beep boop