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Predictions for Chemistry 2014 HSC? (2 Viewers)

zhertec

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Solutions containing nickel (II) ions were analysed by AAS. A standard solution of

5 ppm nickel had an absorbance of 0.200. A second solution of unknown

concentration was found to have an absorbance of 0.500.

100 mL of this second solution was reacted with excess sodium carbonate solution.

The precipitate formed was weighed and dried.

What mass of precipitate formed?

(A) 2.5 x 10^-3

(B) 1.3 x 10^-3

(C) 1.7 g

(D) 2.5 g
For this one I'm a bit iffy on it and did it this way:

0.200 absorbance/5 ppm = absorbance of 1 ppm of nickel
0.500/absorbance of 1 ppm of nickel = number of ppm of nickel in the second solution so I got 12.5 ppm

12.5/1000000 x 100mL = amount of nickel ions in 100 mL
when reacted with Na2CO3 :
Ni2+ + Na2CO3 --> NiCO3 + 2 Na+
Since Ni2+ and NiCO3 is a 1:1
the resultant is 1.25x10^-3 particles of NiCO3
So then I did 1.25=10^-3 x mm of NiCO3 which was like 118.7023g and got 0.148g of precipitate.
So what concept did I get wrong?
 

seventhroot

gg no re
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The conversion of sulfur dioxide to sulfur trioxide is an equilibrium reaction, involving a fine delicate balance between a set of compromise conditions which maximise the yield at the smallest cost possible. 2SO2(g) + O2(g) (equilibrium) 2SO3(g) + heat. (catalyst = vanadium oxide). Increasing the temperature or the pressure of the reaction vessel increases the rate of reaction as it provides more kinetic energy for successful collisions between particles to occur. However, increasing temperature, causes equilibrium to shift to the left, favouring the reverse reaction, producing more of the reactants and thus a lower sulfur trioxide yield. Hence why compromise conditions of 450 degrees celsius are enforced. Increasing the pressure not only increases the rate of reaction, but also the yield because of the 3 to 2 mol ratio of gases, with equilibrium shifting to the right hand side as it contains the lesser number of moles of gas. But, due to economical reasons, cost savings and for safety, only pressures of 1-2 atmospheres are enforced in this reaction vessel. The yield of sulfur trioxide could be also increased through the removal of the product, causing equilibrium to shift to the right and produce more sulfur trioxide. One factor that industrial chemists have manipulated and enforced, to acquire maximum yield is through decreasing the temperature while subsequently passing it over catalytic beds of vanadium oxide. Chemists, pass it over a first catalytic bed at 450 degrees celsius and have a 70% conversion rate of sulfur dioxide to sulfur trioxide. Lowering temperatures increases yield however decreases the rate, but passing it over a second catalytic bed counteracts that dilemma, converting sulfur dioxide into 97% sulfur trioxide, and finally a third conversion results in 99.7% sulfur trioxide formation. These steps are necessary as it allows for maximum yield to be produced in a cheap and economically viable manner, thus leading to increased gains and profits.
dayum; I don't put that much effort into anything

I give it 4/4

with the commercial papers yes, and like 2 selective schools, but i am limited in the number of papers i have.
srs? then you're all set for the HSC
 

SuchSmallHands

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Identify the systematic names for:
- Vinyl Chloride
- Styrene
(2 marks)
 

zhertec

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Vinyl Chloride - Chloroethene
Styrene - Ethenyl Benzene
 

QZP

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@faisalabdul16, "These steps are necessary as it allows for maximum yield to be produced in a cheap and economically viable manner, thus leading to increased gains and profits."

You missed an important environmental consideration o:
 

zhertec

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Seventhroot, is it possible for you to obtain marking guidelines or comments or answers for the papers? Thanks!
 
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For this one I'm a bit iffy on it and did it this way:

0.200 absorbance/5 ppm = absorbance of 1 ppm of nickel
0.500/absorbance of 1 ppm of nickel = number of ppm of nickel in the second solution so I got 12.5 ppm

12.5/1000000 x 100mL = amount of nickel ions in 100 mL
when reacted with Na2CO3 :
Ni2+ + Na2CO3 --> NiCO3 + 2 Na+
Since Ni2+ and NiCO3 is a 1:1
the resultant is 1.25x10^-3 particles of NiCO3
So then I did 1.25=10^-3 x mm of NiCO3 which was like 118.7023g and got 0.148g of precipitate.
So what concept did I get wrong?
It's hard to explain
 
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2010/2011 James Ruse Chemistry Trial Papers:
Thanks :D
@faisalabdul16, "These steps are necessary as it allows for maximum yield to be produced in a cheap and economically viable manner, thus leading to increased gains and profits."

You missed an important environmental consideration o:
Wot? I'm supposed to talk about environmental problems?
 

SuchSmallHands

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Assess the uses of polystyrene and a named biopolymer in terms of their properties with reference to environmental issues (5 marks)
 
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Since the 2011 Ruse paper does not have solutions, could someone be bothered to do the multiple choice so i can compare my answers against theirs? lol :D
 

SuchSmallHands

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2011 won't open on my computer for some reason, want to do 2010 together instead?
 

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