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Chemistry MCQ thread...

A

Anonymousx3

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xHazeMx said:
How does ammonia behave when its aqueous solution is used to dissolve silver chloride, AgCl ?

A as a base
B as a ligand with the Ag+ ion
C as a ligand with the Cl– ion
D as a reducing agent

EXPLANATION ????
Click to expand...

Is it B?
 
Zishi

Zishi

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xHazeMx said:
An experiment is set up to measure the rate of hydrolysis of methyl ethanoate.

CH3CO2CH3 + H2O CH3CO2H + CH3OH
The hydrolysis is found to be slow in neutral aqueous solution but it proceeds at a measurable
rate when the solution is acidified with hydrochloric acid.
What is the function of the hydrochloric acid?

A to dissolve the methyl ethanoate
B to ensure that the reaction reaches equilibrium
C to increase the reaction rate by catalytic action
D to suppress ionisation of the ethanoic acid formed
Click to expand...
C
 
M

Mssamgirl15

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QUESTION 34 MAY/JUNE 2010 QP 12



When organic refuse decomposes in water carboxylic acids are formed. The water becomes acidic and aquatic life is destroyed.
Which additives are suitable to remove this acid pollution?
1 calcium carbonate
2 calcium hydroxide
3 potassium nitrate



Markscheme says its B. But what does Calcium Carbonate have to do with acidity?
 
D

diwash

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think about Caco3 and HCl reaction...it is possible...then why not...reaction with carboxylic acid?
 
MHHaider707

MHHaider707

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Ash1994 said:
http://www.xtremepapers.me/CIE/International%20A%20And%20AS%20Level/9701%20-%20Chemistry/9701_s10_qp_11.pdf

Q.4 Please?
And Explain as well!
Click to expand...


Bond breakin is endothermic and bond formation is exothermic......just learn it!!

Now in P. Br-Br bond is broken so enthalpy change is +193

In Q Cl-Cl bond is formed so enthalpy change is -244

in R C-Cl bond is formed so enthalpy change is -340

in S C-H bond is broken so enthalpy change is +410


So order will be R Q P S i-e C !!!
 
MHHaider707

MHHaider707

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kakarocks said:
Guys October November 2005 . Question 25 . Need help quick . Explain your answer please!
Click to expand...



Answer is D.....

It says that only one of them reacts with 2,4-DNPH so it means only one of them have carbonyl group...this eliminates B n C!!!

It also states that they all react with PCl3....

In A Y has two aldehyde groups which does not react with PCl3....
and in D Y has one carboxylic group and one carbonyl group so it will react with PCl3 so answer is D!!
 
A

Abdulrab

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Use of data booklet is relevant to this question

A garden fertilizer is said to have a phosphorus content at 30% P2O5 soluble in water.
What is the percentage of phosphorus by mass in the fertilizer ?

A. 6.55%
B. 13.1%
c. 26.2%
D. 30.0%

ANSWER WITH FULL EXPLANATION !!! THNX :)
 
H

hassam

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first find percentage of P in P2O5....AN THEN WAT PERCENT IT CONSTITUTES OF THAT NUMBER 30
 
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libra94

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Abdulrab said:
Use of data booklet is relevant to this question

A garden fertilizer is said to have a phosphorus content at 30% P2O5 soluble in water.
What is the percentage of phosphorus by mass in the fertilizer ?

A. 6.55%
B. 13.1%
c. 26.2%
D. 30.0%

ANSWER WITH FULL EXPLANATION !!! THNX :)
Click to expand...
Ar of P...31
Mr of P2O5....(31*2 + 16*5) = 142

so...(2*31)/ 142
0.4366*30% = 13.1%
 
K

kirashinagami

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hey guys, newbie here :DD
very n00b at chemistry hope i can get more knowledge here..hahaha
its nov 03..
and please include some explanations on the answers given :)

15 One mole of each of the following compounds is strongly heated and any gas produced is
collected at room temperature and pressure.
From which compound is 24dm3 of gas likely to be collected?
[One mole of any gas occupies 24dm3 at room temperature and pressure.]
A MgCl2 B MgCO3 C Mg(NO3)2 D Mg(OH)2

16 In black and white photographic film, light converts silver chloride into metallic silver. After the film
has been developed, the unexposed silver chloride is removed by reaction with sodium
thiosulphate to produce a ‘fixed’ negative.
AgCl + 2Na2S2O3 → 4Na+ + Cl – + [Ag(S2O3)2]3–
What is the function of thiosulphate?
A to make the silver ions soluble
B to oxidise the silver ions
C to oxidise the silver metal
D to reduce silver ions

26 Which alcohol gives only one oxidation product when warmed with dilute acidified potassium
dichromate(VI)?
A butan-1-ol
B butan-2-ol
C 2-methylpropan-1-ol
D 2-methylpropan-2-ol

27 What will react differently with the two isomeric pentanols, (CH3)3CCH2OH and
(CH3)2CHCH2CH2OH?
A acidified aqueous potassium manganate(VII)
B concentrated sulphuric acid
C phosphorus pentachloride
D sodium

28 How many hydrogen atoms in a molecule of glycerol, HOCH2CH(OH)CH2OH, may be substituted
by deuterium on dissolving it in an excess of D2O?
A 2 B 3 C 5 D 8

35 A farmer spreads lime on land which has already been treated with a nitrogenous fertiliser.
Which reactions will occur over a period of time?
1 Ca(OH)2 + CO2 → CaCO3 + H2O
2 Ca(OH)2 + 2H+(aq) → Ca2+(aq) + 2H2O
3 Ca(OH)2 + 2NH+
4(aq) → Ca2+(aq) + 2NH3 + 2H2O

and the last question is no 40, cant post it here because it contain picture.

ohh,and can anyone tell me about the concept of optical isomer? I understand that it is a carbon atom bonded to 4 different groups, but when we are given a ring or a long chain, i dunno how to choose the chiral carbon, can anyone give tips on this??

thanks very much..
 
MHHaider707

MHHaider707

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15- B
one mol of MgCO3 gives one mol of CO2 gas which is 24 dm^3...


16- A
the oxidation number of Ag remains same so no oxidation and no reduction of Ag and hence answer is A!!


26- B
Butan-2-ol oxidizes to ketones....A n C oxidizes to aldehydes and carboxylic acids...D is tertiary alcohol so it can not be oxidized!!
 
MHHaider707

MHHaider707

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27- B
first one can not be dehydrated!!


28- B
Duetrium will substitute H atom of (OH) group so three OH groups r present....


35- A
All reactions occur in soil when lime is added!!!
 
K

kirashinagami

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MHHaider707 said:
15- B
one mol of MgCO3 gives one mol of CO2 gas which is 24 dm^3...


16- A
the oxidation number of Ag remains same so no oxidation and no reduction of Ag and hence answer is A!!


26- B
Butan-2-ol oxidizes to ketones....A n C oxidizes to aldehydes and carboxylic acids...D is tertiary alcohol so it can not be oxidized!!
Click to expand...

wah thank you :D
for 15, CO2 is 12 + 16 + 16 = 44 right?? how come we can say it as 24??
for 16,haha ok, but how to determine whether a molecule is oxidised or reduced?? yeah from the definiton loss of electron gain of electron but in heree?
for 26, so A and C splits into two parts, why is that so???
 
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