multiple choice...WTF? (3 Viewers)

[mang]

Yeh but I thought water in lakes and rivers and stuff is slightly acidic due to the CO2 in the atmosphere and as its not really pure water. But yeh maybe I was looking for a trick in the question that wasn't actually there. And the limestone I thought made the water more basic, ie. higher pH, but I'm probably wrong about that too.

limestone methinks is calcium carbonate and creates basic conditions (thats why ya add lime to lower acidity of soils) ie.D......

 

[Rax]

For the naming one I put D, I coudnt remember what is more electronegative so I just when D. In retrospect it is prob C but awell

 

[Ultraviolent]

I got 14/15.

Deliberated over whether ethyl-pentanoate was a solvent or flavour. Went with solvent

For Q11: Answer is actually B Iodine
*snip* lol words

This does not necessarily make Iodine the best substance to be analysed. Metals are most suited to AAS.

 

[mybeachouse]

Hang on,

Wouldn't Q14 be C?
Thinkin we all know it's either C or D because of the basicity of the limestone. Wouldn't the river source have a whole lot of biological processes goin on? Hence there is a HIGH BOD (lots of aerobic critters need lots of oxygen) and due to such a high oxygen use, the oxygen concentration is low?

And for Q15 I think it's definitely B. 0.6 of thiosulfate means 0.3 of Iodine (mole ration 2:1)
Then transfer that 0.3 to Iodine in the 2nd equation. Therefore MnO(OH)2 has 0.3 moles. Times by two for top equation, i.e. MnO(OH)2 has 0.6 moles, therefore oxygen is 0.3 moles (ratio is 2:1).

Please tell me if I'm wrong thanks

 

[Captain Gh3y]

The one about the water was D, the one with the mole ratios was A.

 

[Ultraviolent]

Hang on,

Wouldn't Q14 be C?
Thinkin we all know it's either C or D because of the basicity of the limestone. Wouldn't the river source have a whole lot of biological processes goin on? Hence there is a HIGH BOD (lots of aerobic critters need lots of oxygen) and due to such a high oxygen use, the oxygen concentration is low?

And for Q15 I think it's definitely B. 0.6 of thiosulfate means 0.3 of Iodine (mole ration 2:1)
Then transfer that 0.3 to Iodine in the 2nd equation. Therefore MnO(OH)2 has 0.3 moles. Times by two for top equation, i.e. MnO(OH)2 has 0.6 moles, therefore oxygen is 0.3 moles (ratio is 2:1).

Please tell me if I'm wrong thanks

Both are incorrect.

Q 14) BOD (especially when it's so high) often indicates sewerage. It would make sense that sewerage run-off would occur in a town. Also, a higher BOD, and lower pH point mean that the water is more highly polluted. It follows that the river has become its most polluted as it hits a town. The answer is D.

Q 15) Your logic is incorrect. There are 0.3 mols of MnO, regardless of relative mole ratios. In the original quation, 2 relative moles = 0.3 moles worth. As such, 1 relative mole = 0.15 moles worth. The answer is A.

 

[Pokute-san]

I got 14/15.

Deliberated over whether ethyl-pentanoate was a solvent or flavour. Went with solvent



This does not necessarily make Iodine the best substance to be analysed. Metals are most suited to AAS.

Yes the solvent/flavour thing was mmmmeh as well. But Flavour was my answer.

So for Q11. If I was incorrect, then I should get it right for putting A.

Hmm

 

[Haku]

was 14. A?

is the discussion ended?

and 15 is A

 

[seadonkey]

me got
1.B
2.C
3.B
4.D
5.B
6.A
7.C
8.A (diprotic)
9.D (weak acid and conj. base)
10.C
11.A
12.B
13.C
14.A
15.A (follow the mole ratios)

i got all same as u cept 14 i got D

 

[Ultraviolent]

i got all same as u cept 14 i got D

You got full marks then

was 14. A?

is the discussion ended?

and 15 is A

Q14 was D. See my above post.

 

[Haku]

lol, for 14 i was actually thinking of the damn fish and crocodiles in the river...just now occured to me that they don't count

 

[Captain Gh3y]

Oh, but they do. More importantly in the 7 mark question in the core section about cleaning water before it reaches the town.

I can stand turbidity, maybe even a bit of algae, but i HATE it when I get crocodiles coming in through my tapwater.

 

[Haku]

Oh, but they do. More importantly in the 7 mark question in the core section about cleaning water before it reaches the town.

I can stand turbidity, maybe even a bit of algae, but i HATE it when I get crocodiles coming in through my tapwater.

i think the crocs wouldn't fit through the gravel filter, if they were not picked up in screening

lol, crocs through taps. oh craky

 

[SilveryNightsky]

I just hated how there was so much to effing read for every question!

 

[gogogadgetbrain]

unofficial Bored answers to the multiple choice

ive compiled this list from reading the post and my own study etc...

1) B: as any atom with an atomic number greater than 83 is radioactive (the better answer)

2) C: petrochemical industry relates to the pruduction of hydrocarbons and their derivatives

3) B:74.12g/mol :. 2676/74.12 kJ/g = 36.1kJ/g

4) D: condensation polymer :. molecule eliminated :. not B or C. the structure of monomer 1 in answer A is not consistent with the stimulus material

5) B: observations means you can see what is occuring :. not A or D, copper is being reduced :. copper ions will come out of solution ie blue fades and copper deposits

6) A: its the pinapple flavour

7) C: gas is less soluble at higher temp and lower pressure (straight from the text)

8) A: as it is diprotic 2 hydrogen ions will dissociate from 1 H2SO4 atom :. H+ concentration will be 0.2mol/L. pH = -logH+ = 0.69

9) D: the definition of a buffer: weak acid and conjugate base

10) C: the equivalence point is just above 7 :. cresolphthalein is the best (8.1-9.7)

11) A?- see below

12) B: experimental errors are minimalised

13) C: alphabetical order (chloro then flouro), keep the numbers lowest(112 not

14) D: the town would have pollution which would raise the BOD and make the
water acidic, it can also be assumed that the limestone would turn the water slightly alkaline

15) A: the iodine has half the amount of moles of thiosulfate, the MnO(OH)2 has the same amount of moles as iodine, the oxygen has half the amount of moles of MnO(OH)2. :. the oxygen has half of half the amount of thiosulfate ie 0.6/4 = 0.15

i believe there is a dicrepancy with Q11 as in the sucess one chemistry past paper book had a similar question where is said AAS is used to measure the concentration of metallic ions in solution. however conquering chemistry says AAS is used to detect trace element (which include iodine)


hope it helps - only physics to go which i should probs get back to revision on - see you all at SCHOOLIES

 

[Haku]

pretty sure its calcium!

cause most trace elements are metals anywayz

 

[gogogadgetbrain]

yeah the wording of the question was akward. It could have been asking which is AAS best at measuring or which is best measured by AAS...

i put A but looking back i guess it depends on how they wanted the question interpreted

nothing to do now except know i gave it a good shot and leave it till 16th Dec

 

[Haku]

well really hope that Q14 is A...hoping to get full marks.

 

[Ultraviolent]

well really hope that Q14 is A...hoping to get full marks.

It's D! You still havn't provided a reasoning for A...

Also gogogadgetbrain, for question 10, I think you mean "the equivalence point is just above 7" . A very nice list, by the way.

 

[Diiiiiana-_-]

Omg-0-

Yeah multiple choice was actually hard -0-~~
they had a lot of tricky questions,
so im expecting around 11/15 (corrected myself)
other than that,
it was a pretty easy exam ~