Chemistry: Post your doubts here!

[Faaiz Haque]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s07_qp_2.pdf

Q 2 D
How are we suppose to know these

 

[sidbloom1995]

I had a question in my head about the chemistry practical of titration. The problem is that i performed the experiment and there is huge fluctuation i.e 19 cm3 and 25 cm3. The teacher told me that it should be correct to 0.1 cm3. The problem is that why there is great difference b/w my result. I think i used only two drops of methy orange or i do not mixed throughly mixed the HCl with distill water.

there could be a lot of reasons!
1. like when you do when finish one tit-ration, you dont rinse the flask thoroughly or you dont dry it and add the next contents in it just like that
2. maybe you observe the color change for some as dark and for some as light!
3. maybe you pour the starting contents very quickly, that too can change your value, pour it slowly and shake it continuesly
4. you should keep the mixture on a light background so that you can observe the change quickly
5. you have to make sure that you tip all of the contents in the flask to the last drop!, because even a single drop can cause a change!
make sure that you dont do any of these sorts of mistakes! if you still dont get the answer right then i dont know of anything else!

 

[sidbloom1995]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s07_qp_2.pdf

Q 2 D
How are we suppose to know these

well about how should we know this, they are all general equations and you sort of have to remember them!
with phosphorus and iodine, there will be replacement of OH by I
with conc. H2SO4, there will be elimination of water, for that we will take the -OH group from one carbon and the -H from the carbon right next to it, and it will form an alkene
with hot K2Cr2O7, the double bond will dissolve (if any) and the -OH will be oxidised to -COOH, but not in tertiary alcohols!, they wont react!

 

[sidbloom1995]

https://www.xtremepapers.com/community/threads/as-physics-p1-mcqs-yearly-only.17330/
I saw this on the physics doubts thread! Anyone has a similar link for chemistry p1 ??? Would be really thankful if you people hellp me!

i like the idea, we can do something like that here by announcing the date and doing all of it one at time!

 

[roxylara]

0.2 mol of aluminium is burned in oxygen and the product reacted with 2.00 mol/dm-3 HCL. What is the minimum volume of acid required for a complete reaction?

A. 15 cm3
B. 20 cm3
C. 30 cm3
D. 60 cm3

Can someone please explain this to me? :/

 

[Thought blocker]

0.2 mol of aluminium is burned in oxygen and the product reacted with 2.00 mol/dm-3 HCL. What is the minimum volume of acid required for a complete reaction?

A. 15 cm3
B. 20 cm3
C. 30 cm3
D. 60 cm3

Can someone please explain this to me? :/

♣♠ Magnanimous ♣♠

 

[TheStallion-Reborn]

Can someone please explain the ideal gas equation? It is making no sense to me.

 

[sitooon]

Whats a smooth curve ?

 

[Thought blocker]

Whats a smooth curve ?

It means draw curve at once, no sharp edges at curve, no repetition

 

[sitooon]

It means draw curve at once, no sharp edges at curve, no repetition

What you mean by no repetition ?
do we join points by scale ?

 

[Thought blocker]

I mean no repeats on line (No scribbling on one line) No, it should be free hand drawing...

What you mean by no repetition ?
do we join points by scale ?

 

[sitooon]

In on2006 paper 4
can some one tell me why they chose ph to be the pka ?

 

[Thought blocker]

In on2006 paper 4
can some one tell me why they chose ph to be the pka ?

Still As level kid here.

 

[sitooon]

Still As level kid here.

But i didnt ask u

 

[Thought blocker]

But i didnt ask u

someone, includes me

 

[Faaiz Haque]

well about how should we know this, they are all general equations and you sort of have to remember them!
with phosphorus and iodine, there will be replacement of OH by I
with conc. H2SO4, there will be elimination of water, for that we will take the -OH group from one carbon and the -H from the carbon right next to it, and it will form an alkene
with hot K2Cr2O7, the double bond will dissolve (if any) and the -OH will be oxidised to -COOH, but not in tertiary alcohols!, they wont react!

For the phosphorus iodine, does iodine always replace OH in a reaction, or just for that alcohol the one that they gave?
And for h2SO4, does it always eliminate water?

Ty for help man, its hard to memorize when I dont understand

 

[Abdel Moniem]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_22.pdf
Question 1 Ciii , iv) and d)

 

[Haris Bin Zahid]

Which pair of reactions could have the same common intermediate?

W CH3CH2CH3 → intermediate → (CH3)2CHCN
X CH3CH(OH)CH3 → intermediate → (CH3)2C(OH)CN
Y CH3CH=CH2 → intermediate → CH3CH(OH)CH3
Z CH3CO2CH2CH2CH3 → intermediate → CH3CH2CH2Br

A W and X
B W and Y
C X and Z
D Y and Z

The answer is B. Explanation?

 

[ZaqZainab]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_22.pdf
Question 1 Ciii , iv) and d)

c(iii) th gas in (ii) is CO2 and if you see total of gas formed is 40 but only 30 remains when the tottal gas is shaken with KOH(aq) se where did the 10 go it reacted with Koh(aq) and the gas is CO2 so 10cm^3
iv) they gave 50 O2 whcih gave us total of 40 cm^3 of gases of which 10 is CO2 so we have 30 left This 30 is O2 which is left from 50 so 50-30=20cm^3 got it?
d) the ms explains it quite well though but here we will use the volume ratio from balancing in b the ration between A used is 10 and CO2 produced is 10 so 1 cm^3 of A give 1 cm^3 of Co2 x=1
and 10 cm^3 of A reacts with 20 cm^3 of O2 so 1cm^3 of A reacts 2 cm^3 of O2
x=1
2=x+(y/4)
2=1+(y/4)
y=4
CxHy will be CH4

 

[Snowysangel]

To convert an alcohol into oliec acid (an acid with a double bond), why do you add dilute hcl?