chem mcq...

[xHazeMx]

thats correct ! .. actually i thought it was B but she said why it is D so i just ignored my answer .. didnt look to the mark scheme though .. so what would be the explanation for B ?

 

[xHazeMx]

sorry the answer is B nothing would increase the volume of O2 except adding more H2O2 as the rate of forward reaction increases according to le charle's principle

 

[Xthegreat]

for o/n 2007, why is ques 9 answer B?

 

[xHazeMx]

the metallic salt reacts with sodium sulphate ( Na2SO4 ) forming metal sulphate, sulphate ion has oxidation number -2. Total oxidation number should be zero. Hence ( X - 2 = 0 ) giving +2

 

[alisha]

the metallic salt reacts with sodium sulphate ( Na2SO4 ) forming metal sulphate, sulphate ion has oxidation number -2. Total oxidation number should be zero. Hence ( X - 2 = 0 ) giving +2

thanx! but why have they given sooo much of information then? like conc, volume and the equation and all? i dint knw the answer was so simple!

 

[xHazeMx]

you welcome
another part i didnt mention is
the metal could be from group 1 or group 2, having either oxidation number +1 or +2. so if u look to the values given
v= 0.05 dm^3
c= 0.10 mol dm^-3

then, n= c x v , 0.10 x 0.05 = 0.005 moles
also,
v= 0.025 dm^3
c= 0.10 mol dm^-3

then, n= c x v , 0.025 x 0.10 = 0.0025 moles

so to know whether this metal is from group 1 or 2
divide the number of moles u got

0.005/0.0025 = 2 .... This shows that the metal is from group 2

 

[xHazeMx]

this is why they have given u all these values

 

[Hateexams93]

Chlorofluorocarbons (CFCs) have been widely used in aerosol sprays, refrigerators and in making
foamed plastics, but are now known to destroy ozone in the upper atmosphere.
Which of the following will not destroy ozone, and therefore can be used safely as a replacement
for CFCs?
A CHBr3 B CCl3CBr3 C CHClFCClF2 D CH3CH2CH2CH3
WHY ITS NOT A ???BUT D

 

[hassam]

OZONE IS DESTROYED BY halogen free radicals....primarily chlorine free radical.....so u shud go to the most obvious anser D...where only hazard is of flammability and adding CO2 to atmosphere

 

[xHazeMx]

Chlorofluorocarbons (CFCs) have been widely used in aerosol sprays, refrigerators and in making
foamed plastics, but are now known to destroy ozone in the upper atmosphere.
Which of the following will not destroy ozone, and therefore can be used safely as a replacement
for CFCs?
A CHBr3 B CCl3CBr3 C CHClFCClF2 D CH3CH2CH2CH3
WHY ITS NOT A ???BUT D

Br acts as free radical too so its usage is strictly forbidden as it would deplete the ozone layer, the first 3 choices contains either Br or Cl. Hence, the only possible answer is D

 

[xHazeMx]

is polyethene
flammable?
releases toxic gases when burnt?
odourless ( doesnt have a smell ) ?
reactive ?
biodegradable?
and what are its uses ?

 

[xHazeMx]

A compound X has all of the following properties:

it is a liquid at room temperature and atmospheric pressure;
it does not mix completely with water;
it does not decolorise acidified potassium manganate(VII).

What could X be?

A ethane

B ethanoic acid

C ethanol

D ethyl ethanoate
why B is not possible?

 

[Hateexams93]

A sample of chlorine containing isotopes of mass numbers 35 and 37 was analysed in a
mass-spectrometer.
How many peaks corresponding to +2Cl were recorded?
A 2 B 3 C 4 D 5
WHY ITS B ?

 

[ideggkr]

Which statement about bromine is correct?

A Bromine is insoluble in non-polar solvents.
B Bromine vapour is more dense than air.
C Bromine will not vapourise significantly under normal conditions.
D Gaseous bromine is purple.

The MS says it's D.. but it doesn't make sense. I think it's a typo. Shouldn't the answer be B ??

 

[Zishi]

Which statement about bromine is correct?

A Bromine is insoluble in non-polar solvents.
B Bromine vapour is more dense than air.
C Bromine will not vapourise significantly under normal conditions.
D Gaseous bromine is purple.

The MS says it's D.. but it doesn't make sense. I think it's a typo. Shouldn't the answer be B ??

Yep. IT IS a typo. The answer IS B.

 

[ideggkr]

@Zishi
Thanks a lot. This typo made me confused a lot.

 

[alisha]

A 5g sample of an anhydrous Group 2 metal nitrate loses 3.29g in mass on strong heating. Which metal is present?

A Magnesium
B Calcium
C Strontium
D Barium

The answer is B, but how do u get it?

 

[rocker]

after heating metal nitrate changes to metal oxide (xo)which must be 5-3.2 because air escape out now equate the mole of metal nitrate and metal oxide and find ar of metal tally it with the element in databooklet!

 

[intel1993]

hey can any one plzz expalin the mcq no 33 in M J 2003......................

 

[alisha]

after heating metal nitrate changes to metal oxide (xo)which must be 5-3.2 because air escape out now equate the mole of metal nitrate and metal oxide and find ar of metal tally it with the element in databooklet!

Can you do the working? im still not getting the answer