Chemistry Variant 32 Paper Discussion

[B333]

it was only out of two marks, right?

 

[Ashay]

Oh then you will get 1/2

 

[B333]

oh well, one mark already lost
um.. what did you write for the yeast question. Why was it used and why did its amount increase?

 

[Ashay]

It was used because it consumes glucose and the enzymes in yeast break the glucose into ethanol and carbon dioxide. The number of yeast cells increase because the energy released by this breakdown of glucose allows the yeast to reproduce

 

[Bassem]

No it was C5H10

r sure, can anybody remember the values all that were in the question so we can solve it again.
btw, can anyone get the unofficial mark scheme for this paper?PLEASE

 

[Ashay]

The question said that the moles of alkene were 0.01. Mass of oxygen was 2.4g and mass of co2 was 2.2g
Find the mole ratio and use it to find the alkene formula.

Moles of oxygen = mass/ molar mass = 2.4/32 = 0.075.
Moles of carbon dioxide = 2.2/44= 0.05.

When you simplify you get 1 : 7.5 : 5 which you multiply by 2 because ratio can't have decimal so the final ratio is

2: 15: 10.

The equation for the complete combustion is :

2C5H10 + 15O2 ---> 10CO2 + 10H2O

 

[Bassem]

The question said that the moles of alkene were 0.01. Mass of oxygen was 2.4g and mass of co2 was 2.2g
Find the mole ratio and use it to find the alkene formula.

Moles of oxygen = mass/ molar mass = 2.4/32 = 0.075.
Moles of carbon dioxide = 2.2/44= 0.05.

When you simplify you get 1 : 7.5 : 5 which you multiply by 2 because ratio can't have decimal so the final ratio is

2: 15: 10.

The equation for the complete combustion is :

2C5H10 + 15O2 ---> 10CO2 + 10H2O

thx, but u can exchange the 2C5H10 for C10H20?

 

[Ashay]

No because there is a particular ratio of moles in a hydrocarbon complete combustion equation.
The equation for the complete combustion of C10H20 would be different. There always has to be 2 molecules of the alkene hence it is 2C5H10

 

[Dandelion]

It was used because it consumes glucose and the enzymes in yeast break the glucose into ethanol and carbon dioxide. The number of yeast cells increase because the energy released by this breakdown of glucose allows the yeast to reproduce

dont they ask why the number decreases ? i put its bcs its killed by high conc of ethanol and the number increases because the yeast cells multiply and reproduce. is it correct ?:/

 

[mamoon123]

They asked "Why does the concentration of yeast increase"
The viable answer would have been "Yeast reproduce" although as explanation that they reproduce with the energy from respiration would highly credited.
Also, what was the catalyst that could produce ethanol from glucose, bar enzymes.

 

[Skyrior]

What are the two reasons for using cryolite...?

I wrote decrease temperature, so (1): decrease heating power cost, and (2) does not burn off the carbon electrode that quickly...

 

[JOEJOE]

decrease temp decrease cost (1) and increase conductivity of al2o3(1)

 

[Skyrior]

 

[Saank]

The properties are correct but in this case, light is the important . You have to mention low density which makes it light. Also, resistance to corrosion is very important. If you wrote that it is light and malleable, you will get 1/3 marks

the question was for two marks

 

[Saank]

The question said that the moles of alkene were 0.01. Mass of oxygen was 2.4g and mass of co2 was 2.2g
Find the mole ratio and use it to find the alkene formula.

Moles of oxygen = mass/ molar mass = 2.4/32 = 0.075.
Moles of carbon dioxide = 2.2/44= 0.05.

When you simplify you get 1 : 7.5 : 5 which you multiply by 2 because ratio can't have decimal so the final ratio is

2: 15: 10.

The equation for the complete combustion is :

2C5H10 + 15O2 ---> 10CO2 + 10H2O

what if you only wrote the number of moles but not the ratio?
do you lose all three marks?

 

[Skyrior]

What is another catalyst, other than yeast for the starch --> simple sugar thing?
Is it H2SO4..?

 

[Saank]

What is another catalyst, other than yeast for the starch --> simple sugar thing?
Is it H2SO4..?

it was HCl

 

[Skyrior]

oh lord, i wrote NaOH, completely wrong...
i guess i lost 3 marks in total....

 

[Ashay]

N

What is another catalyst, other than yeast for the starch --> simple sugar thing?
Is it H2SO4..?

The other catalyst is HCl

 

[Ashay]

what if you only wrote the number of moles but not the ratio?
do you lose all three marks?

No you will lose 1 mark, not all 3 as long as the calculation is correct.