HSC Chemistry Question Thread

[Natasha.97]

Hey there!

I was wondering if someone could please help me find the concentration of chloride ions in the original undiluted seawater for the following method? The average titre was found to be 12mL

1.   Dilute estuary water by pipetting a 20 mL sample into a 100 mL volumetric flask and making it up to the mark with distilled water.
2.   Pipette a 10 mL aliquot of diluted estuary water into a conical flask and add about 50 mL distilled water and 1 mL of chromate indicator. The solution should be pale yellow, at this stage.
3.   Titrate the sample with 0.1 mol L−1 silver nitrate solution. The silver chloride that forms will be a white precipitate. The endpoint of the titration is identified as the first appearance of a red-brown colour of silver chromate. It is a good idea to perform a rough titre, so you know what the end point should look like. Your teacher has put colour photos on your lab tray to help.
4.   Repeat the titration with further aliquots of diluted estuary water until concordant results (titres agreeing within 0.1 mL) are obtained.

THANK YOU

Hi!
Not 100% sure if it's correct, attached is my working:

Hope this helps!

[winstondarmawan]

Hello! Can someone try part b) and tell me what they got? My answer was 6.12g/100mL and not sure if correct.
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20707856_1295797373879116_1462211558_n.jpg?oh=31a935ef9d78e511705d0f372d8e9beb&oe=598DE853
TIA!

[MisterNeo]

Hello! Can someone try part b) and tell me what they got? My answer was 6.12g/100mL and not sure if correct.
https://scontent-syd2-1.xx.fbcdn.net/v/t34.0-12/20707856_1295797373879116_1462211558_n.jpg?oh=31a935ef9d78e511705d0f372d8e9beb&oe=598DE853
TIA!

I also got 6.12g/100mL...
Was it marked wrong or something? 

[winstondarmawan]

I also got 6.12g/100mL...
Was it marked wrong or something? 

Nope! Just redoing the exam.

[anotherworld2b]

I tried to do these two questions but I got them wrong and I'm not sure why

[Natasha.97]

I tried to do these two questions but I got them wrong and I'm not sure why

Hi

Correct me if I'm wrong, but I don't think that the Core contains any naming of ketones, only for alkenes, alkanes, alkanols, alkanoic acids, and esters (Unless this part is in one of the Options)

Edit:
With that being said, the first one should be correct (It's apparently called Pinacolone).

[anotherworld2b]

thank you for your help

Hi

Correct me if I'm wrong, but I don't think that the Core contains any naming of ketones, only for alkenes, alkanes, alkanols, alkanoic acids, and esters (Unless this part is in one of the Options)

Edit:
With that being said, the first one should be correct (It's apparently called Pinacolone).

[anotherworld2b]

I was also wondering I have a prac on Wednesday that involves identifying three unknown substances.
I was wondering what would be some key observable differences between alkanes, alkenes, alkynes and alcohols?

[Natasha.97]

I was also wondering I have a prac on Wednesday that involves identifying three unknown substances.
I was wondering what would be some key observable differences between alkanes, alkenes, alkynes and alcohols?

Hi!

The only one I know of is the difference between Alkanes and Alkenes
Bromine water test:
-Alkanes = Solution still remains orange (requires time and UV light to undergo substitution reactions)
Alkenes = Solution becomes clear (Addition reaction)

Hope this helps

[anotherworld2b]

thank you for your help

Hi!

The only one I know of is the difference between Alkanes and Alkenes
Bromine water test:
-Alkanes = Solution still remains orange (requires time and UV light to undergo substitution reactions)
Alkenes = Solution becomes clear (Addition reaction)

Hope this helps

[anotherworld2b]

I was wondering if anyone had tips on how to tell which organic substance has a higher melting/boiling point than the other. I heard that intermolecular forces and the length of the carbon chain plays a part in the melting/boiling point of a organic?

[VanillaRice]

I was wondering if anyone had tips on how to tell which organic substance has a higher melting/boiling point than the other. I heard that intermolecular forces and the length of the carbon chain plays a part in the melting/boiling point of a organic?

Melting and boiling points are indeed influenced by a molecule's 1) shape and 2) the types of intermolecular bonding.

A molecule's shape will influence its ability to 'pack' close together, which will provide less opportunity to form intermolecular bonds. For example, butane would have a higher boiling point than 2-methylpropane, since the branched methyl group will prevent closer packing (unlike the straight chain of butane).

The stronger and greater (in number) the intermolecular bonding, the higher the boiling/melting point (since it will take more energy to break these intermolecular bonds). In particular, you should take note of any hydrogen bonding (esp. OH and NH-containing groups) and dipole-dipole interactions (e.g. C-Cl, C=O). You've also mentioned the length of the carbon chain - the longer the chain, the more opportunity there is for molecules to interact via dispersion forces (i.e. more intermolecular bonding).

Hope this helps

[anotherworld2b]

Thank you for your help

Melting and boiling points are indeed influenced by a molecule's 1) shape and 2) the types of intermolecular bonding.

A molecule's shape will influence its ability to 'pack' close together, which will provide less opportunity to form intermolecular bonds. For example, butane would have a higher boiling point than 2-methylpropane, since the branched methyl group will prevent closer packing (unlike the straight chain of butane).

The stronger and greater (in number) the intermolecular bonding, the higher the boiling/melting point (since it will take more energy to break these intermolecular bonds). In particular, you should take note of any hydrogen bonding (esp. OH and NH-containing groups) and dipole-dipole interactions (e.g. C-Cl, C=O). You've also mentioned the length of the carbon chain - the longer the chain, the more opportunity there is for molecules to interact via dispersion forces (i.e. more intermolecular bonding).

Hope this helps

[anotherworld2b]

I have a question about additition reactions. How do you know what state the resulting hydrocarbon is?

[Mathew587]

Can you give an example?