VCE Chemistry Question Thread

[Syedali_]

U know how oxidatipn is the gain of oxygen  and loss of hydrogen, and reduction is the loss of oxygen and gainof hydrogen
What happens if a compound gains both hydrogen and oxygen? Is it oxidation, reduction, both or neither (if you cannot determin the oxidation numbers)

it was 12936 L
answer was 1.29x10^3 :/

[sweetiepi]

it was 12936 L
answer was 1.29x10^3 :/

In that case, I feel that either one could be accepted, however, just to be sure, I'd still put it scientific notation, as if you have too little or too many sigfigs, can lose a mark.
(As it has more than 3 sigfigs )

Edit: I forgot about the sigfigs mark, thanks VanillaRice!

[VanillaRice]

it was 12936 L
answer was 1.29x10^3 :/

The two answers you've given are written to different significant figures. Assuming the answer was to be to 3 sig figs, you would gain the mark for the answer, but however lose the significant figure mark.

[Syedali_]

In that case, I feel that either one could be accepted, however, just to be sure, I'd still put it scientific notation.
(As it has more than 3 sigfigs )

Ok thanks , ill just convert it to scientific from now on, and provide both answers
 

[Phenomenol]

it was 12936 L
answer was 1.29x10^3 :/

As insanipi and VanillaRice have mentioned, your answer is written to different significant figures to the provided answer, however the more important problem is the numerical value is off by a factor of 10. Please check your working once more.

[Syedali_]

As insanipi and VanillaRice have mentioned, your answer is written to different significant figures to the provided answer, however the more important problem is the numerical value is off by a factor of 10. Please check your working once more.

1293.6 i realized it was typed wrong aha

[Phenomenol]

1293.6 i realized it was typed wrong aha

Ah my apologies! Keep studying well

[Butterflygirl]

Hey guys!
What exactly do we need to know about oxidative rancidity??
Because it's quite a complex process so not sure if we need to know the stages of it.

Thanks!

[Phenomenol]

Hey guys!
What exactly do we need to know about oxidative rancidity??
Because it's quite a complex process so not sure if we need to know the stages of it.

Thanks!

With reference to the Heinemann textbook:
- Oxidative rancidity is the formation of unpleasant smelling short-chain aldehydes and ketones from unsaturated fats and oils.
- The double bonds in unsaturated fats and oils are particularly reactive and are susceptible to deterioration by oxygen through a free radical mechanism.
- Antioxidants are used to react with these free radicals before the radicals react with the sensitive triglycerides (interrupting radical propagation). They do not inhibit the formation of the radicals themselves.
- Vitamin C is a natural antioxidant, that operates by being oxidised in favour of unsaturated triglycerides.
- Synthetic antioxidants often contain hydroxyl groups that donate a hydrogen atom to reactive radicals to interrupt propagation.

[Somedudelmaoy]

Can someone explain fully how sig figs work. To my knowledge you just use the amount of sig figs as the lowest number in the question, but what if the question gives an exact number like "10000kg is former", do we still use 1 sig fig?

[sweetiepi]

Can someone explain fully how sig figs work. To my knowledge you just use the amount of sig figs as the lowest number in the question, but what if the question gives an exact number like "10000kg is former", do we still use 1 sig fig?

You're right in saying the lowest amount of sigfigs in a question.
For something like 10000, the zeros are not significant, so it is only only sigfig.

The leading zeros in a decimal number do count as significant, if I remember correctly. (Correct me if wrong, anyone )

[sweetcheeks]

Sig figures are quite difficult to understand. Depending on the situation 10000Kg could either have 1 or 5 sig figures, depending on how precise the measurement is (at 1 significant figure, the measured value could be between 5000Kg and 14999Kg, whilst at 5 sig figs it is restricted to between 10000.49Kg and 9999.5 Kg)

Significant figures gives an indication of precision. Take for example you have a 560mL sample of 1.0000M HCl, the preciseness of amount of moles is restricted by the volume, rather than the concentration. You use the smaller significant figures in your answer, as the preciseness is limited by the the least accurate measurement (560mL in this case). 560mL can have a range between 559.5mL and 560.49mL, whilst the accuracy of the HCl is +-0.00005mL (could be 9.99995 or 1.000049M), you can see that there is much less accuracy with the volume, which is restricting how accurate you can be.

[Willba99]

Hello AN,
I'm writing a set of revision notes (which I'll post when finished) so I'm basically working my way through every for point on the Chem study design. One of the dot points is,
"the comparison of the energy transformations occurring in spontaneous exothermic redox reactions involving direct contact between reactants (transformation of chemical energy to heat energy) compared with those occurring when the reactants are separated in galvanic cells (transformation of chemical energy to electrical energy)"

What are they referring to? Are they simply saying that we have to be aware that galvanic cells produce electricity, but that the same reactions if mixed will produce heat?

[Bri MT]

Hello AN,
I'm writing a set of revision notes (which I'll post when finished) so I'm basically working my way through every for point on the Chem study design. One of the dot points is,
"the comparison of the energy transformations occurring in spontaneous exothermic redox reactions involving direct contact between reactants (transformation of chemical energy to heat energy) compared with those occurring when the reactants are separated in galvanic cells (transformation of chemical energy to electrical energy)"

What are they referring to? Are they simply saying that we have to be aware that galvanic cells produce electricity, but that the same reactions if mixed will produce heat?

Yeah,  and understanding why you need the two different containers

[Willba99]

Yeah,  and understanding why you need the two different containers

Basically just to allow a flow of electrons from one place to another that can be used to power motors etc?