Chemistry Paper 5 question

[TJ-56]

Can someone please help me with q2 (f) May June 2008?
My x and y values are 5.70 and 4.00 respectively, but what should I do next??
Please reply asap, exam is tomorrow
thanx in advance

[Sue T]

x and y are what - depends wat u plotted on the x and y axis (if u've plotted gases released then i really cant be of any help - lots of ppl asked about ths - u never really get wat th markin scheme says but- i myt be able 2 help a bit if u tell me wats wat...)
hurry!

[TJ-56]

x and y are what - depends wat u plotted on the x and y axis (if u've plotted gases released then i really cant be of any help - lots of ppl asked about ths - u never really get wat th markin scheme says but- i myt be able 2 help a bit if u tell me wats wat...)
hurry!

Ok sorry for not being clearer and thanx for helping out.
So, my y-axis is the mass of CuO (referring to the headings of the table on the opposite page of the graph: C - A ) and the x-axis is the mass of the basic carbonate ( B - A ). So the 2 required values as I stated are 4 (y axis) and 5.70 (x axis), what do you suggest I do next?
And thanx again, I really appreciate your help.

[leebux101]

ok for this question , here is what i did >>
get the gradient of the line using any values on the graph.
gradient = 0.693 for me
gradient is mass of copper oxide deposited / mass of basic carbonate (this is what i plotted on the y and x axis respectively)
so 0.693 = mass of copper oxide deposited / mass of basic carbonate
now mass = number of moles * Mr
so 0.693 = 2*Mr of Cuo / 1*Mr of carbonate  <<<< i got the moles from the mole ratio in the equation.
u will get 0.693 = 159/(221+18x)
now solve for x , ur x value should be around 0.5
if u dont get it please tell me ok?

[leebux101]

did u get the value of x?

[TJ-56]

did u get the value of x?

Well my gradient is almost the same as yours (~0.7). And I did exactly what you said! Thanks for helping.
I did the calculation using your gradient and the x value was 0.31, so how is that 'rounded' to 0.50?
Because I did that with my value and the x-value again was 0.31, so I thought it was wrong.

[leebux101]

when i did it with my value, i got x as 0.46,
i would suggest change ur line a bit, make it more fitting
the points i used for my gradient are
x axis >> 7.5 to 0
y axis > 5.2 to 0
 try again and tell me then.. =D

[TJ-56]

when i did it with my value, i got x as 0.46,
i would suggest change ur line a bit, make it more fitting
the points i used for my gradient are
x axis >> 7.5 to 0
y axis > 5.2 to 0
 try again and tell me then.. =D

As long as its a problem of accuracy, then thats a relief, I thought I was doing it all wrong. I will repeat the graph and hopefully I'll get the value right.
THanx for the help.
+rep

[TJ-56]

I have another question, in may june 2010, q1 (c), the drawing. What do we draw so that "over-heating of the solution is prevented" ?
A water bath?

[Ria.khan]

hey!
I was wondering if there is anything specific we need to know for p5 prep apart from practicing the past papers that is!

[TJ-56]

hey!
I was wondering if there is anything specific we need to know for p5 prep apart from practicing the past papers that is!

Actually I just went through the past papers (solved them twice) and I don't think there is anything else to do, just practice and concentrate full on those papers.

[leebux101]

well what i did is that for preventing overheating, i would stop the fire once temperature reaches a constant value, becuase at the boiling point, temperature remains constant, you should just write this on the side, i suppose
secondly the marking scheme says that u cant use a water bath but an oil bath and heating mantle are ok << i dont know what those are so i am gonna stick with a good old bunsen burner
and position the thermometer such that half the bulb is in the water and half is above the water, this is because it is an equlibrium, use a beaker on a tripod to contain the water , label the beaker as 250 cm^3 and use a thermometer from range -10C to 110C
do not cover the beaker with a lid ok?
i hope that answers ur question.
thankyou for the +rep! =D

[leebux101]

pastpapers is the best thing for paper 5s, just do all and revise ur mistakes. =D

[TJ-56]

well what i did is that for preventing overheating, i would stop the fire once temperature reaches a constant value, becuase at the boiling point, temperature remains constant, you should just write this on the side, i suppose
secondly the marking scheme says that u cant use a water bath but an oil bath and heating mantle are ok << i dont know what those are so i am gonna stick with a good old bunsen burner
and position the thermometer such that half the bulb is in the water and half is above the water, this is because it is an equlibrium, use a beaker on a tripod to contain the water , label the beaker as 250 cm^3 and use a thermometer from range -10C to 110C
do not cover the beaker with a lid ok?
i hope that answers ur question.
thankyou for the +rep! =D

Your first 2 sentences answered my question thank you . And for the rest, I have them exactly correct, its good to make sure of that.

No problem, its the least I can do

[TJ-56]

And I repeated the graph and I got a gradient of 0.69, and it did the trick.
I cant believe 0.69 gives us an x-value of 0.52 but 0.70 gives us a 0.34 :S I hope something like that won't come tomorrow.