HSC Chemistry Question Thread

[bluecookie]

Any tips for remembering solubility rules and colour charts? I'm currently trying to remember the solubility and colours of certain substances and nothing is sticking help >.<

[jakesilove]

Hi quick question ( Daniell cell ),

If I were to mix Cu(NO₃)₂ solution in a single beaker with ZnSO₄ solution with a copper and zinc electrode in the single beaker, what are two predictions why the cell won't work? ( wire and load is still present )

I didn't do this cell, so to be honest I'm genuinely unsure! Potentially the total voltage is negative (check the table of standard reduction potentials), or the mixture will create some sort of chemical reaction that results in a solid being precipitated, before any current can be produced.

[jakesilove]

Any tips for remembering solubility rules and colour charts? I'm currently trying to remember the solubility and colours of certain substances and nothing is sticking help >.<

Hey! I can definitely help you out a little bit

The below device is what I used to learn my solubility rules.



It essentially says that EVERYTHING is soluble, except for certain exceptions (which you can find on the right). Let me know if you're struggling to understand what it means.

For the flame test colours, I found it helpful to come up with my own way of remembering them. Here are mine:



Jake

[Nicko912]

I didn't do this cell, so to be honest I'm genuinely unsure! Potentially the total voltage is negative (check the table of standard reduction potentials), or the mixture will create some sort of chemical reaction that results in a solid being precipitated, before any current can be produced.

Thanks for the response Jake, appreciate it.

[jakesilove]

Thanks for the response Jake, appreciate it.

Sorry I couldn't be of more help Maybe shoot your teacher a message?

[Nicko912]

Sorry I couldn't be of more help Maybe shoot your teacher a message?

No problem. I'll find out soon enough from my teacher

[bluecookie]

Thank you! (:

[bananna]

Hi I have a q in chemical monitoring ...
why is ammonia liquidated during the haber process?

Thanks!!! 😀

[RuiAce]

Hi I have a q in chemical monitoring ...
why is ammonia liquidated during the haber process?

Thanks!!! 😀

It's not liquidated until we need to extract it.

And well, the reason why we liquidate it to collect it is kinda obvious. If we didn't liquidate it and left it as a gas, it's too easy for us to accidentally capture some N2 and H2 as well. We are exploiting the fact that NH3 has a higher boiling/condensation point than N2 and H2.

[bsdfjnlkasn]

Hiiiiii,

Just a few questions that I can't seem to find an answer to in my textbook, any guidance would be appreciated!

a)   In the context of AAS, explain what is meant by the phrase: “a fingerprint of a cation.”

b)   Explain what is meant by 9.5 ppm and then convert it to a concentration of mol/L.
(I don't really understand ppm, all I know is what it stands for)


Thanks again 

[RuiAce]

Hiiiiii,

Just a few questions that I can't seem to find an answer to in my textbook, any guidance would be appreciated!

a)   In the context of AAS, explain what is meant by the phrase: “a fingerprint of a cation.”

b)   Explain what is meant by 9.5 ppm and then convert it to a concentration of mol/L.
(I don't really understand ppm, all I know is what it stands for)


Thanks again 

Personally never heard of that first one before.

Ppm is similar to %. 1% is basically 1 in 100, so 1 ppm is 1 in 1,000,000.


Note that this implies that we need to know the substance. If we don't know the substance, we're stuck at 9.5 ppm, because we don't have a molar mass.

[bsdfjnlkasn]

Personally never heard of that first one before.

Ppm is similar to %. 1% is basically 1 in 100, so 1 ppm is 1 in 1,000,000.


Note that this implies that we need to know the substance. If we don't know the substance, we're stuck at 9.5 ppm, because we don't have a molar mass.

Hey thanks for the reply!
Sorry, the ppm question was being specific to lead, so would we just divide by the formula mass?

[RuiAce]

Hey thanks for the reply!
Sorry, the ppm question was being specific to lead, so would we just divide by the formula mass?

Yep

[anotherworld2b]

Hi I was wondering if someone could check my answers to these questions please. I am having a bit of trouble in particular or Q4 and Q5
mass weighed = 2.65g

Spoiler

Q2. What does it mean when a substance is anhydrous?
Anhydrous literally means 'no water'. Substances without water are anhydrous. The term is most often applied to crystalline substances when the water of crystallization is removed.

Q3. Why was the anhydrous sodium carbonate placed in the oven? In brief:
The primary standard, Na2CO3 (s) is made anhydrous by heating it in an oven at 260-270 degrees celcius. To prevent the anhydrous Na2CO3 (s) from reabsorbing water vapour from the air, it is kept in a desiccator. Silica gel crystals inside the dessicator keep the air dry by absorbing water vapour.

Q4. Calculate the precise concentration in mol.L-1

N = c x v
N = 0.05 x 0.5 = 0.025 mol
m = n x M
m = 0.025 x { (23 x 2) + 12 + (16 x 3) }
m = 0.025 x 106 = 2.65g

Q5. List any factors (systematic or random errors) that may have contributed to minor inaccuracies.

Instrument Error: error caused by an inaccurate instrument

[jakesilove]

Hi I was wondering if someone could check my answers to these questions please. I am having a bit of trouble in particular or Q4 and Q5
mass weighed = 2.65g

Spoiler

Q2. What does it mean when a substance is anhydrous?
Anhydrous literally means 'no water'. Substances without water are anhydrous. The term is most often applied to crystalline substances when the water of crystallization is removed.

Q3. Why was the anhydrous sodium carbonate placed in the oven? In brief:
The primary standard, Na2CO3 (s) is made anhydrous by heating it in an oven at 260-270 degrees celcius. To prevent the anhydrous Na2CO3 (s) from reabsorbing water vapour from the air, it is kept in a desiccator. Silica gel crystals inside the dessicator keep the air dry by absorbing water vapour.

Q4. Calculate the precise concentration in mol.L-1

N = c x v
N = 0.05 x 0.5 = 0.025 mol
m = n x M
m = 0.025 x { (23 x 2) + 12 + (16 x 3) }
m = 0.025 x 106 = 2.65g

Q5. List any factors (systematic or random errors) that may have contributed to minor inaccuracies.

Instrument Error: error caused by an inaccurate instrument

All looks great! Other errors include human error (not quite reading to the calibration point when filling up the 500mL of distilled water), purity error (maybe the 2.65g was not purely the substance you were looking for), splashing of the water (potentially losing some of the substance) etc.