Chemistry: Post your doubts here!

[hammadfbh]

Chemistry Paper 33 May June 2017, anybody knows what is coming?

 

[JamesV Gibbs]

Once you have this paste, stir in some orange zest. Apply the mask to your face and allow it to set for 15 minutes.

 

[Metanoia]

In China, the concentration of blood glucose, C6H12O6, is measured in mmol / l . In Pakistan, the concentration of blood glucose is measured in mg/ dl. The unit l is a litre (1dm3 ). The unit dl is a decilitre (0.1dm3 ). A blood glucose concentration of 18.5mmol/l indicates a health problem. What is 18.5mmol/l converted to mg/ dl?
A 33.3mg/ dl B 178mg/ dl C 333mg/ dl D 3330mg/ dl can someone solve this?

Converting mmol/l to mg/dl

First, focus on changing mmol to mg
mass (milligrams) = millimoles x Mr = 18.5 x 180 = 3330 mg

Next, change l to dl
1 l = 10 dl

Therefore 18.5mmol/l = 3330 mg/ 10 dl = 333 mg/dl

 

[anastasia grey113]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s11_ms_33.pdf

question 2 is abt heating a hydrated salt
i dont get point III in part a)

 

[Zaki ali asghar]

t

Converting mmol/l to mg/dl

First, focus on changing mmol to mg
mass (milligrams) = millimoles x Mr = 18.5 x 180 = 3330 mg

Next, change l to dl
1 l = 10 dl

Therefore 18.5mmol/l = 3330 mg/ 10 dl = 333 mg/dl

thank you

 

[Zaki ali asghar]

does any here has any idea whats coming in chemistry practical 33 which is on 23 may?

 

[SohaibButt]

Hi

 

[SohaibButt]

does any here has any idea whats coming in chemistry practical 33 which is on 23 may?

First question titration

 

[SohaibButt]

It's answer is B need explanation

 

[anastasia grey113]

It's answer is B need explanation

the equation for complete combustion is as follows
1C3H7OH + 4.5O2 -> 3CO2 +4H2O

so if we use 0.1 instead the equation will be like
0.1C3H7OH + 0.45O2 -> 0.3CO2 + 0.4H2O

so 0.3 moles of CO2 are produced which means 0.3 x 24 i.e. 7.2dm3 of CO2 is produced
however since only 0.45 moles of O2 reacted out of 0.5, 0.05 moles of O2 r still left
so adding its volume as well v have (0.05 x 24) + 7.2
this equals 8.4dm3

hoping this helps

 

[SohaibButt]

the equation for complete combustion is as follows
1C3H7OH + 4.5O2 -> 3CO2 +4H2O

so if we use 0.1 instead the equation will be like
0.1C3H7OH + 0.45O2 -> 0.3CO2 + 0.4H2O

so 0.3 moles of CO2 are produced which means 0.3 x 24 i.e. 7.2dm3 of CO2 is produced
however since only 0.45 moles of O2 reacted out of 0.5, 0.05 moles of O2 r still left
so adding its volume as well v have (0.05 x 24) + 7.2
this equals 8.4dm3

hoping this helps

Thanks a lot! ☺

 

[Alpharaptor]

paper 33 predictions ???

 

[Alpharaptor]

chemistry paper 33 predictions ???

 

[anastasia grey113]

chemistry paper 33 predictions ???

is this discussion allowed here?

 

[Thelastmoment]

Oh I messed up the timetables ,we have Chem 33 on 23rd May o:

 

[SohaibButt]

http://papers.gceguide.com/A Levels/Chemistry (9701)/9701_s11_ms_33.pdf

question 2 is abt heating a hydrated salt
i dont get point III in part a)

You have to measure mass of crucible plus FA4 added in it

 

[amina1300]

Cambridge International AS/A Level – May/June 2016 9701 35
QP:
ii) A student suggested that the accuracy of the experiment in (b)(i) would be improved by weighing FA 5 using a balance measuring to two decimal places. State and explain whether or not the student is correct.
MS:
(ii) The student is wrong because MgO is in excess or The student is wrong because H2SO4 is the limiting reagent

Can someone explain?

 

[anastasia grey113]

Cambridge International AS/A Level – May/June 2016 9701 35
QP:
ii) A student suggested that the accuracy of the experiment in (b)(i) would be improved by weighing FA 5 using a balance measuring to two decimal places. State and explain whether or not the student is correct.
MS:
(ii) The student is wrong because MgO is in excess or The student is wrong because H2SO4 is the limiting reagent

Can someone explain?

it will not be more accurate becuz here v have to find the enthalpy change using the mass of MgO that reacted with H2SO4
but not all of it reacted some of it remained
this shows it is in excess

so the mass of all the MgO doesnt help rather the mass of the MgO which reacted will help obtain an accurate result
hope this helps

 

[amina1300]

--> Place a small spatula measure of FB 5 in a boiling tube, add a 1cm depth of dilute hydrochloric acid and warm the contents of the tube gently.
Observation : FB 5 + HCl: effervescence/ fizzing/ bubbling gas pops with lighted splint

-->Place small spatula measures of FB 5 and FB 6 in a single boiling tube. Use a test-tube holder to hold the tube. Add a 2cm depth of aqueous sodium hydroxide. CARE
Observation: FB 5 + FB 6 + NaOH: vigorous / violent/ exothermic / great/ extreme/ lots of and effervescence/ fizzing/ bubbling gas/NH3 turns (damp) red litmus (paper) blue.

How do we identify FB 5 is???

Fb5 is Al or Zn (s)
Is there a logical way to deduce this???

--> "Al and Zn reduce NO3- to ammonia in basic solutions"?

I searched, found out that this reaction is called "a nitrate test using Devarda's alloy", but there is no specific description of the process in our syllabus so how do the examiners expect us to know this!!

 

[asad1212]

Q Do we get Organic Questions In our Practicals?? (Pakistan)

Yes, i guess its mostly dnph or tollens reagent to test for carbonyl group