HSC Chemistry Question Thread

[Furrrball]

Actually I'm still a bit confused (because I don't have resources with me right now). Is this what they mean by 'chain stiffening' because I genuinely don't recall this term being coined

Plus it doesn't seem as though some 'stiffening' is going on

My bad, that was for Q2

[Albertenouttaten]

Hello smartest people in Sydney, few questions to ask:

1) Is ammonia explosive
2) is NaHCO3 acid or base?
3) Do we have to know the method of how to create our biopolymer e.g. the polymersiation process or do we just have to know bacteria regarding polymerisation process?
4) Do we need to know the equations on how to make our chosen industrial and medical radioisotope e.g. equation on how to make Tc-99m and Co-60?

Good luck to everyone tommorow.

[Furrrball]

Hey guys, is the answer to this C? I can't find the answers to this paper online it's too old. Thanks

10.   C   
Molar mass of P2O5 = 2 x 31.0 + 5x 16.0  =  142.0 g/mol
Number of moles of P2O5 used  =  1.42/142  =  0.010
Moles of H3PO4 formed  =  0.020
Moles of NaOH needed  =  3 x 0.020  =  0.060 mol
Volume of NaOH needed  = 0.060/0.30  =  0.20 L

So yes, you're right! 

http://www.cci.net.au/conqchem/ExamComments06Frameset.htm

[RuiAce]

Hello smartest people in Sydney, few questions to ask:

1) Is ammonia explosive
2) is NaHCO3 acid or base?
3) Do we have to know the method of how to create our biopolymer e.g. the polymersiation process or do we just have to know bacteria regarding polymerisation process?
4) Do we need to know the equations on how to make our chosen industrial and medical radioisotope e.g. equation on how to make Tc-99m and Co-60?

Good luck to everyone tommorow.

1. Ammonia itself isn't explosive. It's just used in the manufacturing of OTHER explosives.
2. It's both. It's amphiprotic. You should well know what this means.
(However, it might be worth mentioning that in water it is basic)
3. Don't remember, ask Jake
4. You don't but I memorised them anyway just in case, because it demonstrates skill. It can also be used as your equations for the production of a commercial radioisotope dot point.

[RuiAce]

Ok so I'm just a little bit confused about the effect of errors on overall concentration or percentage in a tablet

* rinsing all glassware with water: dilutes--> Decreases conc in burette. so does that mean that more ___is added to burette? and then overall conc. will increase? percentage mass decrease?

*not drying Na2CO3= More water-->Dilutes conc.--> more __ added into the burette-->? more concentrated overall (final calc)??

* wrong indicator: will mean colour change doesn't match equivalence point and so more___ added in burette? Increasing concentration?

Thanks!

If you rinse all glassware with water and then don't do the required procedures afterwards, then you've decreased the concentration in both the burette AND the pipette. Which means you no longer wtf your calculated values even are anymore; they're not guaranteed to be too high or too low, we just don't know

Using hydrous Na₂CO₃ and not anhydrous means that your calculations will be wrong at the start. You can't find the concentration of your primary solution because you don't even know what the mass is anymore.

Wrong endpoint is all you need for wrong indicator. You can work out using logic what might come afterwards.
Note: Endpoint. Not equivalence point. (You could potentially that the endpoint and equivalence points don't match up at all.)

[massive]

Whats the difference between titre and titrant??

[nibblez16]

Can I have a solution with formulas used plz. One thing I sometimes get confused with is where to start the calculation... any tip on tht? Thanks

[RuiAce]

Can I have a solution with formulas used plz. One thing I sometimes get confused with is where to start the calculation... any tip on tht? Thanks

Question was addressed in post #993 including the starting point.

The wording should be enough for you to figure out what formulas got used.

[onepunchboy]

Hey does anyone know an equation to describe the reaction of saponifcation that is easy to memorise? all the ones ive come across are really big and look really hard to memorise...

THANKS

[Furrrball]

Whats the difference between titre and titrant??

Titrant (solution of known conc.) and titrate (solution of unknown conc.)

[g98]

What units is the turbidity measured in? and how to TOMS work for measuring ozone?
Thanks

[tennis1]

If you rinse all glassware with water and then don't do the required procedures afterwards, then you've decreased the concentration in both the burette AND the pipette. Which means you no longer wtf your calculated values even are anymore; they're not guaranteed to be too high or too low, we just don't know

Using hydrous Na₂CO₃ and not anhydrous means that your calculations will be wrong at the start. You can't find the concentration of your primary solution because you don't even know what the mass is anymore.

Wrong endpoint is all you need for wrong indicator. You can work out using logic what might come afterwards.
Note: Endpoint. Not equivalence point. (You could potentially that the endpoint and equivalence points don't match up at all.)

oh ok thanks. But if we dilute the burette with water, instead of washing with solution,  does that mean that as the concentration decreases so lower pH, means that more of the [     ] in the burette is added. Would this then increase the overall concentration and increase the percentage mass in tablet?
And why won't you know what mass is if it's hydrous? because there's extra water?

[RuiAce]

oh ok thanks. But if we dilute the burette with water, instead of washing with solution,  does that mean that as the concentration decreases so lower pH, means that more of the [     ] in the burette is added. Would this then increase the overall concentration and increase the percentage mass in tablet?
And why won't you know what mass is if it's hydrous? because there's extra water?

When the water molecules dissolve into the water you end up messing up the volume of the water as well. Plus you don't know the chemical formula for hydrous sodium carbonate to properly calculate the moles


With the burette it honestly depends on if you put acid or base in the burette, so you need to figure it out for your own scenario.

[RuiAce]

Hey does anyone know an equation to describe the reaction of saponifcation that is easy to memorise? all the ones ive come across are really big and look really hard to memorise...

THANKS

All you need to remember is
Fat/Oil + 3NaOH -> 3Soap + Glycerol

[RuiAce]

What units is the turbidity measured in? and how to TOMS work for measuring ozone?
Thanks

"Nephelometric Turbidity Units", but you don't even need to know that.