HSC Chemistry Question Thread

[RuiAce]

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

Which radioisotopes are you studying?

(Jake's notes has info on Tc-99m and Co-60. But not everyone will be studying these radioisotopes.)

[ushna]

Which radioisotopes are you studying?

(Jake's notes has info on Tc-99m and Co-60. But not everyone will be studying these radioisotopes.)

My teacher said that we will need to research by ourselves. We are not going to be learning this at my school.

[RuiAce]

My teacher said that we will need to research by ourselves. We are not going to be learning this at my school.

Then you should pick two that you can find a lot of information on.

The two in Jake's notes tend to appear a lot. I'll start you off with a brief sketch. For Tc-99m the radiation involved is gamma decay, Wikipedia gives quite detailed information regarding its uses, but you can probably find more simplified versions in random websites. (And of course, in Jake's notes.)

Note that Wikipedia also has the nuclear equation for the decay of Tc-99m. I will just provide you the equation for its production myself:
Step 1.  \( ^{98}_{42}Mo + ^1_0n \to ^{99}_{42}Mo \)
Step 2.  \( ^{99}_{42}Mo \to ^{99m}_{43}Tc + ^0_{-1}e \) (Note that beta decay is involved in the production of Tc-99m)

[beeangkah]

Hey again 

1. Just wondering what the key esters are needed to be memorised/familiar with (including their properties e.g. apple smell/flavour)

2. Also, any tips for if given the name of a salt, how you can tell if its acidic/basic/neutral?

Thankss

[RuiAce]

2. Also, any tips for if given the name of a salt, how you can tell if its acidic/basic/neutral?

Thankss

By looking at the cation and anion that make up the salt.
Acidic cation + Neutral anion = Acidic salt
Neutral cation + Neutral anion = Neutral salt
Neutral cation + Basic anion = Basic salt

Acidic cations include ammonium and, really just that for the HSC. (Hydronium doesn't appear in a salt.)
Neutral cations include pretty much all the group 1 metal cations (essentially the cations of a strong base)
Neutral anions include chloride, sulfate and nitrate (essentially the anions of a strong acid)
Basic anions include pretty much every other anion

(Acidic cation + Basic anion is a bit of a hard one. That is usually done on a case-by-case basis. They also tend to appear very very rarely in the course.)

[mxrylyn]

Hello,

I'm just reading, "The oxidation number of an atom in an elementary substance is zero. (e.g in Cl2 the oxidation number of cholrine is zero"


What does elementary substance mean? Does it just mean an atom with a full shell?

[RuiAce]

Hello,

I'm just reading, "The oxidation number of an atom in an elementary substance is zero. (e.g in Cl2 the oxidation number of cholrine is zero"


What does elementary substance mean? Does it just mean an atom with a full shell?

That just means pure elements. These are either single atoms, or molecules that are made up by the same atom. (Cl₂ is an example of this because it's a molecule only made up by chlorine atoms.)

[chloefrecs]

Hello!

I'm having trouble on what to do for the second part of this question (from Conquering Chem):

22. 25 mL of sulfuric acid from a car battery was accurately diluted to 500 mL. 25 mL of the diluted solution was titrated with 0.206 mol/L sodium hydroxide. It required 38.8 mL. Calculate the molarity of the original battery acid and its concentration in grams per litre. If 50 mL of this acid were spilt on the bench, how much anhydrous sodium carbonate would be needed to neutralise it?

I found the molarity of sulfuric acid = 3.2 mol and 314 g/L

Thanks in advance!!! 

[RuiAce]

Hello!

I'm having trouble on what to do for the second part of this question (from Conquering Chem):

22. 25 mL of sulfuric acid from a car battery was accurately diluted to 500 mL. 25 mL of the diluted solution was titrated with 0.206 mol/L sodium hydroxide. It required 38.8 mL. Calculate the molarity of the original battery acid and its concentration in grams per litre. If 50 mL of this acid were spilt on the bench, how much anhydrous sodium carbonate would be needed to neutralise it?

I found the molarity of sulfuric acid = 3.2 mol and 314 g/L

Thanks in advance!!! 

[LaraC]

Hello,

I'm having trouble with the question below. I do Chemistry via DE and have had about 3 actual lessons in the past year and a half....so I'm struggling quite a bit. I don't understand diprotic acids or calculation of acid dissociation constants properly. Can someone please help me??

Carbonic acid is a diprotic acid. Write TWO equations to show its stepwise ionisation in water.

Sorry I know its so basic but I'm pretty stupid! 

[Sine]

Hello,

I'm having trouble with the question below. I do Chemistry via DE and have had about 3 actual lessons in the past year and a half....so I'm struggling quite a bit. I don't understand diprotic acids or calculation of acid dissociation constants properly. Can someone please help me??

Carbonic acid is a diprotic acid. Write TWO equations to show its stepwise ionisation in water.

Sorry I know its so basic but I'm pretty stupid! 

H2CO3 + H20 ---------> HCO3- + H30+
HCO3-  + H20 ---------> CO3(2-)   + H30+

diportic acids have two acidic protons which may be donated from the species.
Each of the equation above will have different acid dissociation constants (Ka) but you will need extra info to calculate them

[RuiAce]

H2CO3 + H20 ---------> HCO3- + H30+
HCO3-  + H20 ---------> CO3(2-)   + H30+

diportic acids have two acidic protons which may be donated from the species.
Each of the equation above will have different acid dissociation constants (Ka) but you will need extra info to calculate them

Just make sure to note that \( K_a\) is not in the HSC course. Also, at times like this, the reversible arrow is preferred (because this is not a strong acid).

Anyway,

Hello,

I'm having trouble with the question below. I do Chemistry via DE and have had about 3 actual lessons in the past year and a half....so I'm struggling quite a bit. I don't understand diprotic acids or calculation of acid dissociation constants properly. Can someone please help me??

Carbonic acid is a diprotic acid. Write TWO equations to show its stepwise ionisation in water.

Sorry I know its so basic but I'm pretty stupid! 

The equations above are correct. Essentially, to demonstrate its diprotic nature, you should be able to demonstrate how it can give away one proton, and then give away another one, so effectively speaking giving away 2 protons. Recall from B-L acid theory that an acid is a proton donor. The "di-" prefix indicates that it should be able to give two away, which is what Sine has shown.

[LaraC]

Thankyou so much Sine and RuiAce!!
Very much appreciated!

[LaraC]

Just while I think of it, I know that Mathematics can include up to 20% of the prelim coursework in the HSC.
What is this percentage for Chemistry? Or is it only the HSC course in the actual HSC exam?

Thanks!

[RuiAce]

Just while I think of it, I know that Mathematics can include up to 20% of the prelim coursework in the HSC.
What is this percentage for Chemistry? Or is it only the HSC course in the actual HSC exam?

Thanks!

0%.

That 20% rule only applies to mathematics