HSC Chemistry Question Thread

[Bubbly_bluey]

hey guys! remember the experiment with the can soda opening to let thecarbon dioxide out and we have to measure how much is release? So why is it not possible for ALL the carbon dioxide to be released using this method? It is because of Le Chatelier's Principle?
Thanks

[MisterNeo]

hey guys! remember the experiment with the can soda opening to let thecarbon dioxide out and we have to measure how much is release? So why is it not possible for ALL the carbon dioxide to be released using this method? It is because of Le Chatelier's Principle?
Thanks

It depends on the method you use.
If you just leave the soda open in room temperature, it will establish an "equilibrium with the air" until concentration of CO2 is equal in both the soda and the air.
If you were to heat the soda with a Bunsen, it will release more gas because dissolving gas is exothermic, and the rapid movement of water molecules kick the gas molecules out.
So you can't release all of the gas unless you boil it.

[phoebegresham]

hey!! could you please explain the formation of cellulose from glucose?! is it condensation polymerisation? it seems to say that in the atar notes book however on the formula sheet on this forum it says that it does not give off a water molecule? also what is the deal with alpha and beta glucoses, do we need to know them? thank you so much !!!

[MisterNeo]

hey!! could you please explain the formation of cellulose from glucose?! is it condensation polymerisation? it seems to say that in the atar notes book however on the formula sheet on this forum it says that it does not give off a water molecule? also what is the deal with alpha and beta glucoses, do we need to know them? thank you so much !!!

Hey!
Cellulose is a condensation polymer as it gives off water when formed.
The difference between alpha and beta glucose is the polymer they form and which way the -OH points.
Alpha glucose polymerises to form starch, whereas beta glucose polymerises to form cellulose.
They are both isomers.

2013 CSSA Trial paper
Question: A water sample was found to have a calcium chloride concentration of 1.5 x 10^-3

What is the concentration of chloride ions in this sample expressed in ppm??

Not sure how to do the conversion to PPM

I assume that is 1.5 x 10^-3 mol/L?
If so, you can deduce that there are 3 x 10^-3 because of the 1:2 mole ratio of calcium and chloride.
Then multiply the moles of chloride by its molar mass to find the mass of chloride ions.
Convert the mass into milligrams.
And that is your parts per million because mg/L is equivalent to ppm.
Hope this helps

[Rainbowhippocampus]

Hey guys
Just wondering if you have some tips on trying to learn, make notes and self teach the whole course in a week?  I know it sounds stupid but we have only just started our option and have  skimmed over the dot points.  Any advice would be greatly appreciated for this.  I also have no notes as the workbook we are provided with only has worksheets with little to no theory for revision.  I have purchased your atar notes book and the excel book as well in an attempt to improve, but I am a visual learner more than anything.  These are helping but I struggle with the content and remembering it.  Please suggest anything that could help me out with this, other than my last resort of recording myself and listening to it.  Thank you for any help. 

[Rainbowhippocampus]

Hey the option I'm doing is forensic chemistry.  I would do something like that but I don't have enough time.  That's the main issue I'm having is I need to do a massive amount of study to learn it and it could impact on my other subjects because of it.  Thanks

[elizag]

2015 CSSA TRIAL QUESTION 14:
What is the final pH of a soluation obtained by mixing 25.0mL of 0.120mol/L HNO3 with 40mL of 0.056 mol/L KOH?
A) 2.2
B) 2.6
C) 3.0
D) 3.4
The correct answer is A.
I can't seem to recall the process of how to figure these questions out, any help would be appriciated!  

[supersmartkid]

Hey I was just struggling with this question.

SO2 and HCl are both gases at room temp and pressure and both are soluble in water. Aqueous solutions of SO2 and HCl were prepared and the pH of each solution was measured.

Solution of SO2
Volume of Gas at 25 degrees and 100 kPa (L) = 2.48
Volume of solution= 1.00
pH= 1.43

Solution of HCl
Volume of Gas at 25 degrees and 100 kPa (L) = 0.49
Volume of solution= 2.00
pH= 2.0

a) Calculate the concentration of HCl
b) Write an ionic equation to represent the ionisation of the acid formed when SO2 gas is formed in water.
c) Contrast the concentration and the acid strength of the solution

[winstondarmawan]

What is the purpose of a monochromator in AAS?
TIA
EDIT: For a question like:
Describe the principle of atomic absorption spectroscopy and its application in
 environmental monitoring. Include a diagram in your answer.
Would describe the principle be asking for the theory of absorption spectrum or the process itself? Or both? Thanks.

[Rainbowhippocampus]

Hey!
Which option are you doing?
I do Industrial and I manage to memorise most things by writing lines every day.
Drawing diagrams of processes in the dotpoints can help remember info visually.

Hey the option I'm doing is forensic chemistry.  I would do something like that but I don't have enough time.  That's the main issue I'm having is I need to do a massive amount of study to learn it and it could impact on my other subjects because of it.  Thanks

[bsdfjnlkasn]

Hey there!

Was just wondering how you would justify the different conditions in which esterification is carried out.    

[winstondarmawan]

Hey there!

Was just wondering how you would justify the different conditions in which esterification is carried out.    

Here you are looking at safety and maximising yield.
The condensing column (not sure if thats what its called lol) is used to prevent waste of gaseous reactants, by turning them back into liquids and hence they fall back into the reactant chamber.
Concentrated sulfuric acid is acts as a catalyst. (Also a dehydrating agent, which by LCP also increases production of esters.
Boiling chips to spread heat evenly, maximising collisions of particles.
Water bath/electronic heating plate to prevent combustion of volatile reactants.
Hope this helps. 

[blasonduo]

Hey the option I'm doing is forensic chemistry.  I would do something like that but I don't have enough time.  That's the main issue I'm having is I need to do a massive amount of study to learn it and it could impact on my other subjects because of it.  Thanks

Hey, I'm doing Forensics too!

My main question is how far are you into the topic?

If it isn't too far, the first 2 subtopics, are really just common sense when you look at it

"Why is contamination at a crime scene a bad thing" - Well it would skew the results and could wrongly convict someone!

it's not much off the core, as its then distinguishing alkanoic acids, hydrocarbons, alkanols. Or acidic basic or neutral salts.

It's not until subtopic 3, where it starts to get BIG!. So if you are past there, I would be happy to answer them for you!

[supdood101]

Hi can you please help me with this question?

A solution was made by mixing 75.00 mL of 0.120 mol/L hydrochloric acid with 25.00 mL of 0.200 mol/L sodium hydroxide. what is the pH of the solution?

thank you xx

[Natasha.97]

What is the purpose of a monochromator in AAS?
TIA
EDIT: For a question like:
Describe the principle of atomic absorption spectroscopy and its application in
 environmental monitoring. Include a diagram in your answer.
Would describe the principle be asking for the theory of absorption spectrum or the process itself? Or both? Thanks.

Hi!
1) The monochromator splits light to be able to differentiate different wavelengths
2) My interpretation is both the theory and the process

Hope this helps

Hi can you please help me with this question?

A solution was made by mixing 75.00 mL of 0.120 mol/L hydrochloric acid with 25.00 mL of 0.200 mol/L sodium hydroxide. what is the pH of the solution?

thank you xx

Here you go