HSC Chemistry Question Thread

[RuiAce]

Oh I see, thanks!

So the mole ratio is irrelevant? Or is that only for fully ionised equations?

It's not needed here because we didn't care about the carbonate ions produced in the ionisation process

Ummmm just to be sure does that mean carbonic acid is a monoprotic acid cause in biology I learnt that as CO2 dissolves in blood it dissolutes into bicarbonate ion and a proton.
And i suppose the mole ratio is still necessary to look at cause it shows only one proton is donated to make hydronium.

The degree of ionisation automatically caters for the diprotic nature of the acid. In general, unless otherwise specified, the degree of ionisation measures how much all of the hydrogen atoms get ionised.

This is also the reason why sulfuric acid has a degree of ionisation OVER 100% (somewhere around 154%)

The stuff you learnt in biology (which is also a good example of a buffer to use in chemistry) is not incorrect. The equation provided just combined two steps into the one, since technically one hydrogen atom comes off at a time, not both at once.

[cnimm2000]

Hi guys,
I was doing this dot point:
T.4.6 Identify amphiprotic substances and construct equations to describe their behaviour in acidic and basic solutions.
I noticed in the textbook some equations use equilibrium arrows and some do not. I wanted to ask if we are required to include equilibrium arrows for writing equations for amphiprotic substances. If so, could you please provide examples of cases where we do include equilibrium arrows?

[RuiAce]

Hi guys,
I was doing this dot point:
T.4.6 Identify amphiprotic substances and construct equations to describe their behaviour in acidic and basic solutions.
I noticed in the textbook some equations use equilibrium arrows and some do not. I wanted to ask if we are required to include equilibrium arrows for writing equations for amphiprotic substances. If so, could you please provide examples of cases where we do include equilibrium arrows?

The equilibrium arrow is used when the reaction does not go to completion. When it does, we use the normal arrow.

For acids, essentially the reaction goes to completion provided we have either a strong acid or a strong base (or both). All the strong acids you need to know in this course are HCl, H2SO4 and HNO3, and a strong base is essentially any group I metal - hydroxide (e.g. NaOH)

[kaustubh.patel]

Hey Ya'll chem lovers need some help
I saw this question on a khan academy quiz and have nooo idea how to solve for it. If anyone know how to o it please lend me a hand i'd deeply appreciate it.
the link to the quiz (https://www.khanacademy.org/test-prep/mcat/chemical-processes/titrations-and-solubility-equilibria/e/titration-questions)

[itssona]

hey guys, is it true that basicity of oxides decreases from left to right as well?

[Natasha.97]

hey guys, is it true that basicity of oxides decreases from left to right as well?

Yep!

Group 1 would form basic oxides, whereas Group 7 would form acidic oxides

[itssona]

the answer is D which makes sense but.. cant it also be C? since its endothermic and increase in temperature will want to shift to the right?
thank you!!

[kiwiberry]

the answer is D which makes sense but.. cant it also be C? since its endothermic and increase in temperature will want to shift to the right?
thank you!!

Delta H is negative which means that the reaction is exothermic, so an increase in temperature will cause a shift to the left

[itssona]

sorry I have a similar question:
so the reaction should shift left since theres a decrease in pressure but how does this yield the answer A since this is exothermic?? thank you so much ahh

[Sine]

sorry I have a similar question:
so the reaction should shift left since theres a decrease in pressure but how does this yield the answer A since this is exothermic?? thank you so much ahh

I think the forward reaction is exothermic so the backward reaction is endothermic

[Rajan_]

Hello!

I was wondering how you are supposed to determine a suitable indicator when doing titrations. I know it's to do with the pH of the salt produced in the reaction, but doesn't the pH of that salt differ depending on the concentration of the unknown solution, and therefore the indicator required will differ too?? Really confused.

Thanks!!

[RuiAce]

Hello!

I was wondering how you are supposed to determine a suitable indicator when doing titrations. I know it's to do with the pH of the salt produced in the reaction, but doesn't the pH of that salt differ depending on the concentration of the unknown solution, and therefore the indicator required will differ too?? Really confused.

Thanks!!

The pH of the salt is primary dependent on whether or not the acid and base are strong or weak. The concentration simply measures just how much acid there is (relative to the volume of water); it has no say in the degree of ionisation of the acid/base.

Strong acid + Strong base -> Neutral salt, and therefore bromothymol blue (or litmus)
Strong acid + Weak base -> Acidic salt, and therefore methyl orange
Weak acid + Strong base -> Basic salt, and therefore phenolphthalein

[beeangkah]

I need help with this question

What volume of 0.99 mol/ L sulphuric acid is required to neutralise 500mL of a solution containing 10.5 g of sodium hydroxide?

[kiwiberry]

I need help with this question

What volume of 0.99 mol/ L sulphuric acid is required to neutralise 500mL of a solution containing 10.5 g of sodium hydroxide?

Hello!! First let’s write out the equation
The number of moles of H+ in H2SO4 must equal the moles of OH- in NaOH for it to be neutralised. We can find the number of moles of NaOH using its mass
n(NaOH)=n(OH-) as there is one OH- ion per NaOH. So n(H+) we need to neutralise the OH- will be 0.2625. However, there are 2 H+ ions per H2SO4 molecule, meaning that n(H+)=2 x n(H2SO4)
Now we can find the volume required using its concentration

[ushna]

Hey. I am a year 11 student. I have an exam coming up and I need help on the question,
Investigate the properties of unstable isotopes using natural and human made radioisotopes as examples, including but not limited to:
-types of radiation
-types of balanced nuclear reactions
-industrial and medical uses