Answers To Difficult Questions (5 Viewers)

[jbai]

Q15 Multi Choice
Yes, Cl radical IS A CATALYST :wave:

http://en.wikipedia.org/wiki/Catalyst

"Examples of homogeneous catalysts are H+(aq) which acts as a catalyst in esterification, and chlorine free radicals in the break down of ozone."

-----------------------------------------

Chemical Reason for lower Heat of Combustion: Incomplete Combustion (took me some time to figure out lol)

----------------------------------------

Anyone have anything on why you can't flame test? Edit : Lead poisoning apparently

Edit: For industrial chem ppl: Hope nobody put down Solid Sulfur in their Equilibrium K constant ;P

 

[Pyros89]

One of the samples had lead in it, cant burn lead cause its bad for you

 

[ssglain]

Well I do hope it is a catalyst, because other sources are convincing me that it is an initiator. I think Q15 might have been one of those questions with 2 right answers, one of which a bit more right than the other.

About flame test - HCl contains no metal ions so flame test can't identify it. Also, do Pb and Na show colour in flame test...? I thought only transitional metals did. The one containing Ba would be the only identifiable solution, and the other three solutions will still remain indistinguishable. I might be wrong but that's what I wrote in the exam.

 

[Pyros89]

Lead gives off a blue white colour, sodium gives off a bright orange colour. By logical deduction you could figure out that hydrogen was the odd one out.

Thats why I thought we shouldn't be burning lead.... but hey, I could be wrong

 

[Martyno1]

Yes, Cl is a catalyst in the reaction as it is regenerated.

 

[jbai]

Can't burn lead sounds logical, but if you do it in a fume cupboard or what not you still can. Sodium actually produces the most distinct flame colour (which is why you need to rinse with HCl before you use a platinum wire, in case of Sodium contamination). And yes, by logical deduction you should be able to figure all of them...right..?

http://chemistry.about.com/library/weekly/aa110401a.htm

Lead = Blue flame
Yellow = Sodium

 

[mat2154]

Lead gives off a blue white colour, sodium gives off a bright orange colour. By logical deduction you could figure out that hydrogen was the odd one out.

Thats why I thought we shouldn't be burning lead.... but hey, I could be wrong

you shouldn't burn it cause if you inhale the fumes it stuffs up your health

 

[Forbidden.]

I love you all here, all of your answers are consistent with mine.

My justification for Q15 being a catalyst is that Chlorine catalyses the destruction of ozone.
Furthermore, I stated that a flame test would be inappropriate as one of the solutions contained lead compounds which is toxic and is much more dangerous when vapourised.

Well here's how I calculated the answer to the 50ppm sulfur dioxide question.

50 ppm = 50 x 10^-6
60 kg = 60,000 g

m = 60,000 g x 50 x 10^-6 = 3
n = m / M = 3 / 96.06
n
Volume of SO₂ released = ( 3 / 96.06 ) x 24.79
= 0.7742036227 ... L

.: The volume of SO₂ is 774.2 mL

As for the Chlorine one, I don't get why I have 146,000ppm as my answer, that's even saltier than sea water !

3.65g of Chlorine precipitate in 50mL

x ppm = x mg L^-1

Convert g to mg and mL to L

3650 mg / 0.05 L

Cancel out the 0.05 by multiplying it by 20

146,000 mg L^-1 = 146,000 ppm

 

[champo14]

Yes, Cl is a catalyst in the reaction as it is regenerated.

But the definitipn of a catalyst (at least from BOS) is one that doesn't affect the position of the reaction, just lowers the activation energy required.

The free radical is an initiator, just like in addition polymerisation.

Also, what did you guys get for the ppm of Cl in water? I had like 29000 ppm

 

[champo14]

But the definitipn of a catalyst (at least from BOS) is one that doesn't affect the position of the reaction, just lowers the activation energy required.

The free radical is an initiator, just like in addition polymerisation.

Also, what did you guys get for the ppm of Cl in water? I had like 29000 ppm

I think its because the precipitate was Silver Chloride, so you had to convert the 3.65g to moles, and then find out how many grams of Cl, etc. But I still had a really high answer.

EditAh crap, I just realised I wrote Silver Chloride as AgCl2, instead of AgCl, Noooo!

 

[Martyno1]

But the definitipn of a catalyst (at least from BOS) is one that doesn't affect the position of the reaction, just lowers the activation energy required.

The free radical is an initiator, just like in addition polymerisation.

Also, what did you guys get for the ppm of Cl in water? I had like 29000 ppm

The notes my teacher put up on the board for us say that Cl acts as a catalyst in breaking down ozone so that's why I put that basically.. heh

Well I got a completely different number to you but it had 5 digits and I'm expecting to get 0 for that question. I never understood ppm.

 

[jbai]

I love you all here, all of your answers are consistent with mine.

My justification for Q15 being a catalyst is that Chlorine catalyses the destruction of ozone.
Furthermore, I stated that a flame test would be inappropriate as one of the solutions contained lead compounds which is toxic and is much more dangerous when vapourised.

Well here's how I calculated the answer to the 50ppm sulfur dioxide question.

50 ppm = 50 x 10^-6
60 kg = 60,000 g

m = 60,000 g x 50 x 10^-6 = 3
n = m / M = 3 / 96.06
n
Volume of SO₂ released = ( 3 / 96.06 ) x 24.79
= 0.7742036227 ... L

.: The volume of SO₂ is 774.2 mL

As for the Chlorine one, I don't get why I have 146,000ppm as my answer, that's even saltier than sea water !

3.65g of Chlorine precipitate in 50mL

x ppm = x mg L^-1

Convert g to mg and mL to L

3650 mg / 0.05 L

Cancel out the 0.05 by multiplying it by 20

146,000 mg L^-1 = 146,000 ppm

Why did you divide 3g sulfur by 90.xx? Moles = m / M = 3 / 32.07 (sulfur only, not oxide)

For chlorine, its 3.65 g of AgCl , not Cl itself
You've got to calculate Cl as a percentage of AgCl, multi by 3.65, then divide by 35.45 (Cl fw.)

Edit: Bloody hell, as if burning lead is dangerous. Half-life told me scientists like gordon freeman are invulnerable to everything. There goes a mark...

 

[nooj]

I love you all here, all of your answers are consistent with mine.

My justification for Q15 being a catalyst is that Chlorine catalyses the destruction of ozone.
Furthermore, I stated that a flame test would be inappropriate as one of the solutions contained lead compounds which is toxic and is much more dangerous when vapourised.

Well here's how I calculated the answer to the 50ppm sulfur dioxide question.

50 ppm = 50 x 10^-6
60 kg = 60,000 g

m = 60,000 g x 50 x 10^-6 = 3
n = m / M = 3 / 96.06
n
Volume of SO₂ released = ( 3 / 96.06 ) x 24.79
= 0.7742036227 ... L

.: The volume of SO₂ is 774.2 mL

As for the Chlorine one, I don't get why I have 146,000ppm as my answer, that's even saltier than sea water !

3.65g of Chlorine precipitate in 50mL

x ppm = x mg L^-1

Convert g to mg and mL to L

3650 mg / 0.05 L

Cancel out the 0.05 by multiplying it by 20

146,000 mg L^-1 = 146,000 ppm

for the sulfur question it said 50 ppm of SULFUR not sulfur dioxide

and for the chlorine question u had find the no. grams of chlorine then work it out as 3.65 includes Ag as well

 

[nadz001]

But the definitipn of a catalyst (at least from BOS) is one that doesn't affect the position of the reaction, just lowers the activation energy required.

The free radical is an initiator, just like in addition polymerisation.

Also, what did you guys get for the ppm of Cl in water? I had like 29000 ppm

i totally agree with yiou the clorine is seen as an iniatiare for it breaks the ozone bond. a catayst lower rate of reaction it does play an actual role

 

[nooj]

lol jbai too quick for me

 

[Martyno1]

I think its because the precipitate was Silver Chloride, so you had to convert the 3.65g to moles, and then find out how many grams of Cl, etc. But I still had a really high answer.

EditAh crap, I just realised I wrote Silver Chloride as AgCl2, instead of AgCl, Noooo!

I got 18050 or something

 

[nooj]

I got 18050 or something

yep that sounds like wat i got

 

[Martyno1]

And I think for the sulfur dioxide question I got 1.16L or 2.26L I can't remember

 

[aanka]

i got the same - 18 168 ppm

 

[Pyros89]

I got similar(ish) - 16500 and something....