Chemistry MCQ thread...

[diwash]

3. Use of the Data Booklet is relevant to this question.
Most modern cars are fitted with airbags. These work by decomposing sodium azide to liberate
nitrogen gas, which inflates the bag.
2NaN3 ---> 3N2 + 2Na
A typical driver’s airbag contains 50 g of sodium azide.
Calculate the volume of nitrogen this will produce at room temperature.
A 9.2 dm3 B 13.9 dm3 C 27.7 dm3 D 72.0 dm3

9 Which substance, in 1 mol dm–3 aqueous solution, would have the same hydrogen ion
concentration as 1 mol dm
3 of hydrochloric acid?
A ethanoic acid
B nitric acid
C sodium hydroxide
D sulphuric acid

For the first Q...
Firstly calculate the no of moles of NaN3....n= m/Mr
..n= 50/(23+14*3)
= 0.769
and from the eqn...
2mol Nan3...gives...3 mol N2
1 mol Nan3 ..gives 3/2 mol N2
0.769 mol NaN3 gives....1.1535 mol N2

and in Room temp and pressure...
1 mol gas occupies 24 dm3 volume ..so 1.1535 mol gas occupies 24* 1.1535 = 27.7 dm3...So ans is C

..........................................
for 2nd Q

HCl is a strong monobasic acid and from the list select a strong monobasic acid
though ethanoic acid is a mono bacis acid it is not strong reject it...
Naoh is a base not an acid...reject it...
H2so4 is a strong acid but dibasic...
Hno3 is correct because it is strong and monobacis...So answer is B

 

[diwash]

How many different substution products are possible,in prnciple, when a mixture of ethene and bromine are allowed to react? (0/N 04)
A. 3
B. 5
C. 7
D. 9

Can anyone explain how is the answer D.

Some one please Help me with this.

you actually typed the question wrongly, it's suppose to be ethane.
well talk about ethane before we go to ethene.
so ethane + bromine = free- radical substituition.
its actually very very long to type and the answer is 9.
* u should check your book under free-radical substituition, I M 100% SURE they have the exact mechanism there.
i'll show you a few,
C2H6 + Br' -> C2H5' + HBr ( that is 1 )
C2H5' + Br2 -> C2H5Br + Br'
C2H5Br + Br' -> C2H4Br' + HBr
* the substitution goes on and on, see the pattern?

and if you are using ethene, then it depends whether you are using AQUEOUS bromine or Br in CCl4.
if in aqueous bromine then there are 2 types.

.........................................................................................................................................................................

Sory and thankyou very much...
I intended to write ethane ...i think its a typing error...
i Know the mechanism of Free redical substution very well..just that ..I am just unclear about the termination step...thanks for making me clear...
if u use Br in CCl4 then there is only 1 product.

 

[diwash]

pls explain. Im a little confused over here. Should we consider the no of moles produced or consider the bonds...

Some one please answer this Q as well..

 

[ninjas4life]

 

[hassam]

are poly(alkenes) flammable

 

[ninjas4life]

yup highly flammable

 

[hassam]

but ms sau=id nOOO

 

[hassam]

Which equation represents the reaction for which the enthalpy change is the standard
enthalpy change of formation, ∆Hf
○
, of sodium nitrate, NaNO3?
A 2Na(s) + N2(g) + 3O2(g) → 2NaNO3(s)
B Na(s) + ½N2(g) + 1½O2(g) → NaNO3(s)
C Na(s) + N(g) + 3O(g) → NaNO3(s)
D Na(g) + ½N2(g) + 1½O2(g) → NaNO3(g)

 

[diwash]

firstly think what Can be a compound that has a single O atom and is unreactive towards mild oxidising agent( eg..Cr2o7^ 2- and Mno4^-1 ) is either a Tertiary alcohol group or a ketone group.
Now look at the another information given in the Q...its says Compound is formed by dehydration..which means that...the compound Has a alcohol group(tertiary alcohol) as ketone cannot be dehydrated.
A. when rehydrating the Coumpound ...we canno get tertiary alcohol group so reject it
B and c . this also doesnot gives a tertiary alcohol group
d. It gives Tertiary alcphol group( the Oh---group attached to the C atom nearest to the benzene ring would produce a teritary alcohlo on rehydratin..
So the ans is D

 

[diwash]

Which equation represents the reaction for which the enthalpy change is the standard
enthalpy change of formation, ∆Hf
○
, of sodium nitrate, NaNO3?
A 2Na(s) + N2(g) + 3O2(g) → 2NaNO3(s)
B Na(s) + ½N2(g) + 1½O2(g) → NaNO3(s)
C Na(s) + N(g) + 3O(g) → NaNO3(s)
D Na(g) + ½N2(g) + 1½O2(g) → NaNO3(g)

Its B...am i right?

 

[Zishi]

Which equation represents the reaction for which the enthalpy change is the standard
enthalpy change of formation, ∆Hf
○
, of sodium nitrate, NaNO3?
A 2Na(s) + N2(g) + 3O2(g) → 2NaNO3(s)
B Na(s) + ½N2(g) + 1½O2(g) → NaNO3(s)
C Na(s) + N(g) + 3O(g) → NaNO3(s)
D Na(g) + ½N2(g) + 1½O2(g) → NaNO3(g)

B

 

[Zishi]

D, because if we put a -OH on double bonded carbon atoms with a benzene ring and methyl group, it will be counted as a tertiary alcohol, and of course, they can't be oxidised.

 

[aliya_zad]

Which equation represents the reaction for which the enthalpy change is the standard
enthalpy change of formation, ∆Hf
○
, of sodium nitrate, NaNO3?
A 2Na(s) + N2(g) + 3O2(g) → 2NaNO3(s)
B Na(s) + ½N2(g) + 1½O2(g) → NaNO3(s)
C Na(s) + N(g) + 3O(g) → NaNO3(s)
D Na(g) + ½N2(g) + 1½O2(g) → NaNO3(g)

B

Isn't it C? I mean shouldnt they be in pure elemental states for formation. ie, even N2 bonds have to be broken down to 2N and then the reaction proceeds..Im nt sure if this is rite bt im confused...with the ans as B..

 

[aliya_zad]

shuldn't we balance and find the no of moles????
nov 2004 q20.

 

[workinghard]

da ans is D rite?!
u balance da equation i mol of (NH4)2SO4 ll produce one mol of sulphuric acid 2 mol of HNO3 n 2 mol oF H2O
so da overall moles of O2 required is 4

 

[aliya_zad]

yea it's rite... i counted the no of o2 atoms in s04 as well.

 

[hassam]

36 Element X is a solid. It occurs as a contaminant of carbonaceous fuels.
Its oxide Y is formed in car engines.
Further oxidation of Y to Z can occur in the atmosphere.
Which statements about Y and Z are correct?
1 Molecule Y has lone pairs of electrons.
2 The atmospheric oxidation of Y to Z is a catalysed reaction.
3 Y is a colourless gas.

 

[Anonymousx3]

Which equation represents the reaction for which the enthalpy change is the standard
enthalpy change of formation, ∆Hf
○
, of sodium nitrate, NaNO3?
A 2Na(s) + N2(g) + 3O2(g) → 2NaNO3(s)
B Na(s) + ½N2(g) + 1½O2(g) → NaNO3(s)
C Na(s) + N(g) + 3O(g) → NaNO3(s)
D Na(g) + ½N2(g) + 1½O2(g) → NaNO3(g)

B

Isn't it C? I mean shouldnt they be in pure elemental states for formation. ie, even N2 bonds have to be broken down to 2N and then the reaction proceeds..Im nt sure if this is rite bt im confused...with the ans as B..

The standard enthalpy change of formation is the energy required to form one mole of a compound from its elements in their STANDARD STATES and under standard conditions. The standard state of nitrogen is N2 and that of oxygen is O2.

 

[Anonymousx3]

36 Element X is a solid. It occurs as a contaminant of carbonaceous fuels.
Its oxide Y is formed in car engines.
Further oxidation of Y to Z can occur in the atmosphere.
Which statements about Y and Z are correct?
1 Molecule Y has lone pairs of electrons.
2 The atmospheric oxidation of Y to Z is a catalysed reaction.
3 Y is a colourless gas.

A?

 

[hassam]

YA A