Chemistry: Post your doubts here!

[The Sarcastic Retard]

26 Use of the Data Booklet is relevant to this question. 2.40g of propan-2-ol were mixed with excess acidified potassium dichromate(VI). The reaction mixture was then boiled under reflux for twenty minutes. The organic product was then collected by distillation. The yield of product was 75.0%. What mass of product was collected? A 1.74g B 1.80g C 2.22g D 2.32g

propan-2-ol will be oxidised to propanone.
Mr of propan-2-ol = 60
Mr of propanone = 58
moles of propan-2-ol = 0.04mol
1:1 ratio
moles of propaone = 0.0.4mol
mass of propaone = 2.32g
75% of mass was the product = 75% of 2.32g = 1.74g

 

[The Sarcastic Retard]

View attachment 57471
question 6 plz

4H20 + Al4C3 + 4NaOH ----------> 4NaAlO2 + 3CH4

 

[The Sarcastic Retard]

it will shift backwards so the "yield" of products on LHS increases.
increasing temperature increases "rates" whether the reaction is exo or endo. And the effect is on both sides.

Same goes for pressure right? Increasing pressure increases both forward and backward rate?

 

[awesomaholic101]

4H20 + Al4C3 + 4NaOH ----------> 4NaAlO2 + 3CH4

its an equation we should know? or did u get by balancing?

 

[The Sarcastic Retard]

its an equation we should know? or did u get by balancing?

Balancing.

 

[awesomaholic101]

Balancing.

ohkay so u tried each of the options?

 

[The Sarcastic Retard]

ohkay so u tried each of the options?

No, I first balanced Al and Na. Then I balanced O, then I saw there are 3 atoms of carbon present, so I knew that option A or C can come I saw option C, H molecules were not balancing so I tried with A.

 

[forest822]

For 2, why C is not the answer? Usually PV=constant right?

 

[The Sarcastic Retard]

View attachment 57472For 2, why C is not the answer? Usually PV=constant right?View attachment 57473

2) At constant temprature, Pv is proportional to n.
15) Answer is B?

 

[donewithtime80]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_12.pdf

q 1: change in ox.no for Cr in option C is from 12 to 3 which has a difference of 9 ...then y is option B the right answer?

 

[donewithtime80]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w12_qp_12.pdf

q:3 how is a borohydride ion a tetrahydral?

how to go about the 4th question? i got my anwer close to the right answer...is it sth to just assume and write w/o a definite answer?

q:10 and 11 15 16 17 23 24 please...

q 19: why is the answer A and not D?

q:30 what's the difference between molecules in B and C except that they are reverse order of each other?

TIA

 

[forest822]

2) At constant temprature, Pv is proportional to n.
15) Answer is B?

Yes Answer is B

 

[awesomaholic101]

No, I first balanced Al and Na. Then I balanced O, then I saw there are 3 atoms of carbon present, so I knew that option A or C can come I saw option C, H molecules were not balancing so I tried with A.

ok thanx

 

[Metanoia]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w12_qp_12.pdf

q 1: change in ox.no for Cr in option C is from 12 to 3 which has a difference of 9 ...then y is option B the right answer?

Oxidation state of Cr in Cr2O7 2- is +6 (not +12), we look at individual Cr, not the total of all Cr.

The "VI" in the name dichromate (VI) should already give us the idea that its oxidation state is +6.

 

[awesomaholic101]

can someone plz explain the 8th one

 

[awesomaholic101]

20th one ... how nucleophilic addition?

 

[Metanoia]

View attachment 57478
can someone plz explain the 8th one

Density of the gases is related to the Mr of the gases in the mixture and their % composition.

For example, for option A = 0.898 x 2 + 0.102 x 4 = 2.204
Repeat for the other options and choose the highest value among the 4 options.

 

[The Sarcastic Retard]

2) At constant temprature, Pv is proportional to n.
15) Answer is B?

No reaction between Mgcl2 and H2o

 

[awesomaholic101]

Density of the gases is related to the Mr of the gases in the mixture and their % composition.

For example, for option A = 0.898 x 2 + 0.102 x 4 = 2.204
Repeat for the other options and choose the highest value among the 4 options.

yes i had done that ... but i got a wrong answer ... the highest value is that of B, but answer is D

 

[The Sarcastic Retard]

yes i had done that ... but i got a wrong answer ... the highest value is that of B, but answer is D

Highest is for D. Check it.