Chemistry MCQ thread...

[ideggkr]

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
?????????????????????

I think it's D..?

 

[xHazeMx]

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
?????????????????????

D

 

[aliya_zad]

pls help...

 

[xHazeMx]

pls help...

C

 

[xHazeMx]

Red lead oxide, Pb3O4, is used in metal priming paints. It can be made by heating PbO in air.
6PbO(s) + O2(g) → 2Pb3O4(s)
Which two values are needed to calculate the enthalpy change for this reaction?
A enthalpy change of combustion of lead and enthalpy change of formation of Pb3O4
B enthalpy change of combustion of PbO and enthalpy change of formation of Pb3O4
C enthalpy change of formation of PbO and enthalpy change of atomisation of O2
D enthalpy change of formation of PbO and enthalpy change of formation of Pb3O4
HOW TO SOLVE THIS KIND OF PROBLEMS ??????????

its D, enthalpy changes considered from the initial and final states of a reaction.

 

[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

is it D plz confirm

Yes, it is! how did you do it?

 

[xHazeMx]

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

Yes, it is! how did you do it?

sulphur in SO2 has oxidation number +4. after oxidation it forms SO3, sulphur has oxidation number +6 in SO3. so the change in oxidation number is from +4 to +6

 

[histephenson007]

 

[histephenson007]

 

[sweetiepie]

14.B H2SO4+NACL----->NASO4+H2+CL2
BECAUSE H2SO4 PREVENTS OXIDATION OF FOOD THAT S WHY IT IS A REDUCING AGENT....


I HOPE IT CLEAR...

 

[meoooow]

39 Textiles for use in aircraft are treated with a finish containing a halogenoalkane.
What is the reason for this?
1 The textile burns less easily, improving safety.
2 The fabric forms hydrogen bonds to water more readily, making the fabric easier to wash.
3 The halogenoalkane undergoes addition polymerisation, stiffening the fabric.

 

[histephenson007]

@sweetpie : Answer for 14 is A...

 

[xHazeMx]

14.B H2SO4+NACL----->NASO4+H2+CL2
BECAUSE H2SO4 PREVENTS OXIDATION OF FOOD THAT S WHY IT IS A REDUCING AGENT....


I HOPE IT CLEAR...

the equation is NaCl + H2SO4 --------> NaHSO4 + HCl .. it is a neutralisation reaction ( acid/base reaction )

 

[abdullah181994]

http://www.xtremepapers.me/CIE/Internat ... 5_qp_1.pdf
please visit above link and explian Q11 and Q12

 

[ShootingStar]

Question!
Please explain

 

[kshumaila52]

pls help...

Consider initial mole of N2O4 =2, intial mole of NO2=0
after 50% dissociation, mole of N2O4=1, mole of NO2=2 (according to equation)
total no. of mole=3, find partial pressure of each (N2O4=1/3atm and NO2=2/3atm)
put values in formula and get ans.
Best wishes for tomorrow

 

[xHazeMx]

39 Textiles for use in aircraft are treated with a finish containing a halogenoalkane.
What is the reason for this?
1 The textile burns less easily, improving safety.
2 The fabric forms hydrogen bonds to water more readily, making the fabric easier to wash.
3 The halogenoalkane undergoes addition polymerisation, stiffening the fabric.

B ?

 

[meoooow]

39 Textiles for use in aircraft are treated with a finish containing a halogenoalkane.
What is the reason for this?
1 The textile burns less easily, improving safety.
2 The fabric forms hydrogen bonds to water more readily, making the fabric easier to wash.
3 The halogenoalkane undergoes addition polymerisation, stiffening the fabric.

B ?

nope, its D

 

[sweetiepie]

@ histephenson007 bt u hav marked it as B okay
@ xHazeMx thanks 4 corecting mee......

 

[meoooow]

24 Tartaric acid is present in some wines. It may be synthesised in the laboratory in two steps.
OHCCHO intermediate HO2CCH(OH)CH(OH)CO2H
step 1 step 2
tartaric acid
Which reagents could be used for this synthesis?
step 1 step 2
A HCl (aq) HCN(g)
B HCN, NaCN(aq/alcoholic) H2SO4(aq)
C H2SO4(aq) K2Cr2O7 / H2SO4(aq)
D KCN(aq/alcoholic) K2Cr2O7 / H2SO4(aq

I know its B, but i want to know why its not D!
can someone pleease explain?