Chemistry MCQ thread...

[Zishi]

I thought there is CO+ (1/2)O2 = CO2 so I chose A but the answer is C?

oxidation of CO to CO2 can't occur in atmosphere. If that was so, then why'd we have been worrying about its effects?

 

[Banglarbagh]

. Flask X contains 1 dm3 of helium at 2 kPa pressure and flask Y contains 2 dm3
Flask X contains 1 dm3 of helium at 2 kPa pressure and flask Y contains 2 dm3
of neon at 1 kPa.


If the flasks are connected at constant temperature, what is the final pressure?

A 1.33 kPa B 1.5 kPa C 1.67 kPa D 2 kPa


10. For which equilibrium does Kc have no units?

A. C(s) + H2O(g) = CO(g) + H2(g)

B. CH3OH(l) + CH3CO2H(l) = CH3CO2CH3(l) + H2O(l)

2+
C. Cu2+(aq) + 4NH3(aq) = Cu(NH3) (aq)
4
D. N2O4(g) = 2NO2(g)

12. Which species represented by the following formulae has the largest radius?
A P3–
B Cl–
C Ar
D K+

17. Which statement explains the observation that magnesium hydroxide dissolves in aqueous
ammonium chloride, but not in aqueous sodium chloride?
A The ionic radius of the NH4+ ion is similar to that of Mg2+ but not that of Na+
B NH4Cl dissociates less fully than NaCl.
C The ions Na+and Mg2+are isoelectronic (have the same number of electrons).
D The ion NH4+acts as an acid.

18 Sulphur dioxide is an important food preservative.
What property makes sulphur dioxide useful in this role?
A It is a gas.
B It is a reducing agent.
C It reacts with oxygen to form sulphur trioxide.
D It reacts with water to form an acidic solution.

21 What is the total number of different chloroethanes (formula C2H6-n Cln, where n can be any
integer from 1 to 6)?
A 6 B 8 C 9 D 10

25 Which compound on reaction with hydrogen cyanide produces a compound with a chiral centre?
A CH3CHO
B CH3CH2COCH2CH3
C CH3CO2CH3
D HCHO

31 Which pairs of compounds have the same empirical formula?
1 ethane and ethene
2 ethene and cyclohexane
3 cyclohexane and oct-1-ene

32 In which sequences are the molecules quoted in order of increasing bond angle within the
molecule?

1 H2O NH3 CH4
2 H2O SF6 BF3
3 CH4 CO2 SF6

40 Which alcohols on oxidation with acidified potassium dichromate(VI) give an organic product
which causes an effervescence when reacted with sodium carbonate?
1 butan-1-ol
2 2-methylpropan-1-ol
3 2-methylpropan-2-ol

 

[Serenity]

Hey anyone smart out there who can explain this question to me??
May june 2006 question 20

 

[ideggkr]

. Flask X contains 1 dm3 of helium at 2 kPa pressure and flask Y contains 2 dm3
Flask X contains 1 dm3 of helium at 2 kPa pressure and flask Y contains 2 dm3
of neon at 1 kPa.


If the flasks are connected at constant temperature, what is the final pressure?

A 1.33 kPa B 1.5 kPa C 1.67 kPa D 2 kPa


10. For which equilibrium does Kc have no units?

A. C(s) + H2O(g) = CO(g) + H2(g)

B. CH3OH(l) + CH3CO2H(l) = CH3CO2CH3(l) + H2O(l)

2+
C. Cu2+(aq) + 4NH3(aq) = Cu(NH3) (aq)
4
D. N2O4(g) = 2NO2(g)

12. Which species represented by the following formulae has the largest radius?
A P3–
B Cl–
C Ar
D K+

17. Which statement explains the observation that magnesium hydroxide dissolves in aqueous
ammonium chloride, but not in aqueous sodium chloride?
A The ionic radius of the NH4+ ion is similar to that of Mg2+ but not that of Na+
B NH4Cl dissociates less fully than NaCl.
C The ions Na+and Mg2+are isoelectronic (have the same number of electrons).
D The ion NH4+acts as an acid.

18 Sulphur dioxide is an important food preservative.
What property makes sulphur dioxide useful in this role?
A It is a gas.
B It is a reducing agent.
C It reacts with oxygen to form sulphur trioxide.
D It reacts with water to form an acidic solution.

21 What is the total number of different chloroethanes (formula C2H6-n Cln, where n can be any
integer from 1 to 6)?
A 6 B 8 C 9 D 10

25 Which compound on reaction with hydrogen cyanide produces a compound with a chiral centre?
A CH3CHO
B CH3CH2COCH2CH3
C CH3CO2CH3
D HCHO

31 Which pairs of compounds have the same empirical formula?
1 ethane and ethene
2 ethene and cyclohexane
3 cyclohexane and oct-1-ene

32 In which sequences are the molecules quoted in order of increasing bond angle within the
molecule?

1 H2O NH3 CH4
2 H2O SF6 BF3
3 CH4 CO2 SF6

40 Which alcohols on oxidation with acidified potassium dichromate(VI) give an organic product
which causes an effervescence when reacted with sodium carbonate?
1 butan-1-ol
2 2-methylpropan-1-ol
3 2-methylpropan-2-ol

lol i was trying to answer in ur thread n u deleted
Plz confrm first since i did them very roughly
6. A
10.B
12.A
17.D
18.B
21.B
25.A
31. 2 n 3
32. 1 Only
40. 1 n 2

 

[Banglarbagh]

12. (C) 21. (C) others r correct can u briefly xplain me ur correct answers pls.!

 

[ideggkr]

12. (C) 21. (C) others r correct can u briefly xplain me ur correct answers pls.!

12 has be to A..
n yea 21 is C.

I'll explain the rest wait

 

[Xthegreat]

Hey anyone smart out there who can explain this question to me??
May june 2006 question 20

what do you not understand?
A - cannot because there are no changes in the oxidation number
B - for AS level, electrophilic addition occurs only across C=C
D - from alcohol to aldehyde is oxidation

ans : C because reactions that occurs across C=O is nucleophilic reaction.

*the mechanism is not in our syllabus thou.

 

[Banglarbagh]

12. (C) 21. (C) others r correct can u briefly xplain me ur correct answers pls.!

12 has be to A..
n yea 21 is C.

I'll explain the rest wait

sry 12 is A ma bad.!

 

[Vanto1994]

Check this one out guys ..kindly explain please

 

[whimsical]

Greetings.
I need help on these questions. thanks in advance guys..

 

[Xthegreat]

1 and 2.

when propane form free radicals that DOES NOT contain any halogen group, there are only 2 types of free-radical.

either its CH3CH'CH3 or CH3CH2CH2'

and if you join them together, the one in 3 is not possible because no matter how you separate it into two, one of them is bound to have 4 C which is not possible.

ok?

 

[Xthegreat]

24. ans : A.
- the alcohol will be dehydrated to form an alkene.
- the double can be on the left or right, making it 2 types.
- if the double bond is on the left side, then the alkene have cis-trans isomers
in total : 3

34. only 1 rite?

 

[ideggkr]

. Flask X contains 1 dm3 of helium at 2 kPa pressure and flask Y contains 2 dm3
Flask X contains 1 dm3 of helium at 2 kPa pressure and flask Y contains 2 dm3
of neon at 1 kPa.


If the flasks are connected at constant temperature, what is the final pressure?

A 1.33 kPa B 1.5 kPa C 1.67 kPa D 2 kPa


10. For which equilibrium does Kc have no units?

A. C(s) + H2O(g) = CO(g) + H2(g)

B. CH3OH(l) + CH3CO2H(l) = CH3CO2CH3(l) + H2O(l)

2+
C. Cu2+(aq) + 4NH3(aq) = Cu(NH3) (aq)
4
D. N2O4(g) = 2NO2(g)

12. Which species represented by the following formulae has the largest radius?
A P3–
B Cl–
C Ar
D K+

17. Which statement explains the observation that magnesium hydroxide dissolves in aqueous
ammonium chloride, but not in aqueous sodium chloride?
A The ionic radius of the NH4+ ion is similar to that of Mg2+ but not that of Na+
B NH4Cl dissociates less fully than NaCl.
C The ions Na+and Mg2+are isoelectronic (have the same number of electrons).
D The ion NH4+acts as an acid.

18 Sulphur dioxide is an important food preservative.
What property makes sulphur dioxide useful in this role?
A It is a gas.
B It is a reducing agent.
C It reacts with oxygen to form sulphur trioxide.
D It reacts with water to form an acidic solution.

21 What is the total number of different chloroethanes (formula C2H6-n Cln, where n can be any
integer from 1 to 6)?
A 6 B 8 C 9 D 10

25 Which compound on reaction with hydrogen cyanide produces a compound with a chiral centre?
A CH3CHO
B CH3CH2COCH2CH3
C CH3CO2CH3
D HCHO

31 Which pairs of compounds have the same empirical formula?
1 ethane and ethene
2 ethene and cyclohexane
3 cyclohexane and oct-1-ene

32 In which sequences are the molecules quoted in order of increasing bond angle within the
molecule?

1 H2O NH3 CH4
2 H2O SF6 BF3
3 CH4 CO2 SF6

40 Which alcohols on oxidation with acidified potassium dichromate(VI) give an organic product
which causes an effervescence when reacted with sodium carbonate?
1 butan-1-ol
2 2-methylpropan-1-ol
3 2-methylpropan-2-ol

6. You may use p1v1 = p2v2
But I use ratio to solve this qu.. I think it may confuse u

10. It's B cuz there are 2 reagents and 2 products
So there will be same units on the bottom and the top when calculating Kc
It can't be A because C(s) is solid, and is ignored when calculating Kc

12. It should be P3-. Among these atom/ions, P3- has smallest no. of protons (15) while electrons would be same as others
So that means there will be weaker nuclear attration. Hence it will be quite large

17. urgh.. I think it's better to learn this. When X is any group 2 metal,
2NH4Cl + X(OH)2 --> XCl2 + 2NH3 + 2H2O
So basically ammonium sulphate + base --> water + ammonia + etc
When sth + base --> water , it has to be a acid-base reaction
Also, u can see that NH4+ donated a proton(H+) and has become NH3. We know proton donator is an acid

21. Draw these out
C2H5Cl --> only 1 isomer
C2H4Cl2 --> 2 isomers
C2H3Cl3 --> 2 isomers
C2H2Cl4 --> 2 isomers
C2HCl5 --> 1 isomer
C2HCl6 --> 1 isomer

25. A - CH3CHO would react wih HCN to form CH3CH(OH)CN
The bolden C is a chiral centre with 4 different groups attched to it

31. The empirical formula for cycloalkane = alkene = CnH2n
Wouldn't harm to learn it

32.
Best method is try to draw all of them
(bond angle)
1 H2O (104.5) NH3 (107) CH4 (109.5)
2 H2O (104.5) SF6 (90 and 120 i think.. it's octahedral) BF3 (120)
3 CH4 (109.5) CO2 (180) SF6 (see above)

40
from 'causes an effervescence when reacted with sodium carbonate'
we can deduce that it has to be a carboxylic acid.

Primary alcohol + oxidation with acidified potassium dichromate(VI) ---> aldehyde ---> carboxylic acid
Secondary alcohol + oxidation with acidified potassium dichromate(VI) --> ketone
tertiary alcohol + oxidation with acidified potassium dichromate(VI) --> no change

Again, draw these out and they turn out to be..

1 butan-1-ol -- primary
2 2-methylpropan-1-ol -- primary
3 2-methylpropan-2-ol -- tertiary

Plz ask again if u don't get them

 

[hassam]

welll y it shud nt be B but A???

 

[ideggkr]

welll y it shud nt be B but A???

I think you've discussed this enough with Zishi..

Well

delta H = bonds broken - bonds formed
bonds broken : c-c in graphite (let it be x)
bonds formed : c-c in diamond (let it be y)

x-y = +3
so x is greater than y

 

[ideggkr]

welll y it shud nt be B but A???

I think you've discussed this enough with Zishi..

Well

delta H = bonds broken - bonds formed
bonds broken : c-c in graphite (let it be x)
bonds formed : c-c in diamond (let it be y)

x-y = +3
so x is greater than y

Oh sorry! my bad!
I think it should be B too! does the ms say only 1 is correct?

 

[meoooow]

4 Sulfur dioxide, SO2, is added to wines to prevent oxidation of ethanol by air. To determine the
amount of SO2, a sample of wine is titrated with iodine, I2. In this reaction, one mole of SO2 is
oxidised by one mole of I2.
What is the change in oxidation number of sulfur in this reaction?

A +2 to +4 B +2 to +6 C +4 to +5 D +4 to +6

 

[ideggkr]

24. ans : A.
- the alcohol will be dehydrated to form an alkene.
- the double can be on the left or right, making it 2 types.
- if the double bond is on the left side, then the alkene have cis-trans isomers
in total : 3

34. only 1 rite?

He says 1 and 2 are right

HPO4 is formed when PO4 ion accept H+ from acid

PO4 ion is used up, so that means the position of first equilibrium will shift to RHS

 

[ideggkr]

4 Sulfur dioxide, SO2, is added to wines to prevent oxidation of ethanol by air. To determine the
amount of SO2, a sample of wine is titrated with iodine, I2. In this reaction, one mole of SO2 is
oxidised by one mole of I2.
What is the change in oxidation number of sulfur in this reaction?

A +2 to +4 B +2 to +6 C +4 to +5 D +4 to +6

is it D plz confirm

 

[Hateexams93]

Which hydrocarbon can form a monochloro-substitution derivative which shows both chirality
and cis-trans isomerism?
A CH3CH=CH2
B (CH3)2C=CH2
C CH3CH=C(CH3)2
D CH3CH=CHCH2CH3
?????????????????????