VCE Chemistry Question Thread

[knightrider]

6 g in 100 mL
So how many 100 mL portions do you need to get to 1000 mL, aka 1 L?

Thanks lzxnl 

10  100 mL portions
------> 6x10=60g/L right ?

[lzxnl]

Thanks lzxnl 

10  100 mL portions
------> 6x10=60g/L right ?

Yep

[klippo]

Ohhk I understand. Thanks EulerFan and lzxnl!!

[Apink!]

Hi guys!
I could really use some help! I really appreciate it

In volumetric analysis, the properties of the reactants, as well as the nature of the reaction between them, will determine if a back titration is to be used. Consider the following cases:
I. The substance being analysed is volatile
II The substance being analysed is insoluble in water but it is soluble in dilute acid
III The end point of the reaction is difficult to detect.
In which cases would a back titration be more suitable than a simple forward titration?
The answer is I, II, and III (all the above)
Could someone please explain to me WHY (for each I, II and III)? I don't get why it would be more suitable for back titration. Why wouldn't it not be feasible to do a forward titration?

Another question is:
Consider the following unbalanced ionic equation.

Hg(l) + Cr₂O₇^2- (aq) + H⁺ (aq) --> Hg²⁺(aq) + Cr³⁺(aq) +H₂O (l)

When this equation is completely balanced, the coefficient of Hg (l) will be:
A. 1
B. 2
C. 3
D. 4

I tried just balancing atoms (disregarding the charges) and I got A
So then I took the charges into account and then I got B
The correct answer is C
Could you please explain how it is C? (and not A or B)
Thanks so much!!

[Apink!]

bump ~

[@#035;3]

write two half equations then the overall balanced equation.
Hg(l) -> Hg2+(aq) + 2e- (balance charges)

Cr2O72-(aq) -> 2Cr3+(aq) (balance chromiums)
Cr2O72-(aq) -> 2Cr3+(aq) + 7H2O(l) (balance oxygens)
Cr2O72-(aq) + 14H+(aq) -> 2Cr3+(aq)+ +7H2O(l) (balance hydrogens)
Cr2O72-(aq) + 14H+(aq) + 6e- -> 2Cr3+(aq)+ +7H2O(l) (balance charges)

3Hg(l) -> 3Hg2+(aq) + 6e- (balance electrons)

whole equation: 3Hg(l) + Cr2O72-(aq) + 14H+(aq) -> 3Hg2+(aq) + 2Cr3(aq)+ +7H2O(l)

[avince]

Hi, I need help with this question..

If the volume of the water sample being tested is 50.0 ml and the mass of the dried precipitate obtained is 3.65 g, calculate the chloride ion concentration in the water sample in ppm.

and

Why is it important to determine the chloride ion concentration in water?

Thank You

[keltingmeith]

Hi, I need help with this question..

If the volume of the water sample being tested is 50.0 ml and the mass of the dried precipitate obtained is 3.65 g, calculate the chloride ion concentration in the water sample in ppm.

and

Why is it important to determine the chloride ion concentration in water?

Thank You

Is there more context to this question? It feels like you've just given us questions without their particular stem, which usually has useful information in it that we need.

[blacksanta62]

Hey everyone, hope the 2016 school year has been off to a great start. I just need some help with this question.
18) An impure sample of iron (III) sulfate, weighing 1.545 g was treated to produce a precipitate of Fe203 (s). If the mass of dried precipate was 0.315 g, calculate the percentage of iron in the sample. Do I need to find what it precipitates with (or assume?) before I can find the percentage of iron? I got this far before I started question my thinking process with this question:
Fe^3+(aq) + O^2-(aq) --------> Fe2O3(s), but where did the oxygen come from if the question doesn't specify 'it reacts with the atmosphere'? As you can read I'm in a bit of a delema, if anyone could help I would be grateful
Thank you

[HasibA]

Hey everyone, hope the 2016 school year has been off to a great start. I just need some help with this question.
18) An impure sample of iron (III) sulfate, weighing 1.545 g was treated to produce a precipitate of Fe203 (s). If the mass of dried precipate was 0.315 g, calculate the percentage of iron in the sample. Do I need to find what it precipitates with (or assume?) before I can find the percentage of iron? I got this far before I started question my thinking process with this question:
Fe^3+(aq) + O^2-(aq) --------> Fe2O3(s), but where did the oxygen come from if the question doesn't specify 'it reacts with the atmosphere'? As you can read I'm in a bit of a delema, if anyone could help I would be grateful
Thank you

calculate number of moles of fe203, and then use mole ratios to calc number of moles of iron (iii) sulfate. thats youre first step. if you still need help, http://imgur.com/RM8ovFx but the other reactant and other product is not needed.

[blacksanta62]

calculate number of moles of fe203, and then use mole ratios to calc number of moles of iron (iii) sulfate. thats youre first step. if you still need help, http://imgur.com/RM8ovFx but the other reactant and other product is not needed.

Cheers bro!

[Apink!]

Hello,
Could someone please help me with this question. I googled for like an hour, and then I gave up.

So, the Checkpoints for Chem says: " [in AAS] at the monochromator, the light from the flame is separated into its different frequenies and the frequency absorbed by the sample is passed to the detector"

Okay, so I get the general gist of what it's saying. Basically it's saying the monochromator isolates the absorption line from the background interference lines. But I don't understand the part that says: that the absorption line is  separated from the "flame". Isn't the purpose of the flame just to atomise the sample? Wouldn't the absorption line be separated from the light emitted from the  hollow cathode lamp or something? Could someone please tell me why it's separated from the flame?

Thanks

[lzxnl]

Hello,
Could someone please help me with this question. I googled for like an hour, and then I gave up.

So, the Checkpoints for Chem says: " [in AAS] at the monochromator, the light from the flame is separated into its different frequenies and the frequency absorbed by the sample is passed to the detector"

Okay, so I get the general gist of what it's saying. Basically it's saying the monochromator isolates the absorption line from the background interference lines. But I don't understand the part that says: that the absorption line is  separated from the "flame". Isn't the purpose of the flame just to atomise the sample? Wouldn't the absorption line be separated from the light emitted from the  hollow cathode lamp or something? Could someone please tell me why it's separated from the flame?

Thanks

You've misread it. The flame isn't separated from anything. Light, that is coming from the flame, contains many frequencies. These frequencies of light are themselves separated into their individual frequencies.

[Apink!]

Hey lzxnl,
Could you explain this further?

[Stephrockz23]

If i dilute 100ml of 1.00M HCl with 900ml or 0.0222M NaOH how do i calculate the concentration of only the HCl after the dilution?