Chemistry MCQ thread...

[salman9k]

Why is the the third option not corect? Q 31. Please reply. Thanks

 

[Ahmed Aqdam]

Why is the the third option not corect? Q 31. Please reply. Thanks

Temperature is calculated in Kelvin which is degree C+273.
As its 298 K initially and then 323 K the volume is not doubled.

 

[salman9k]

Temperature is calculated in Kelvin which is degree C+273.
As its 298 K initially and then 323 K the volume is not doubled.

Thanks

 

[ashcull14]

 

[JAVERIA INAM DANISH]

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

 

[MaboroshI_I]

Could someone please help me with a few questions from this paper? http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
Qs 13, 19, 27, 29 and 34.

I'm sorry if these questions are being repeated. Thank you to anyone who can help me with these!

 

[Mustafa Malik]

Plz answer...

 

[Exo_luhan]

MJ 2008 Q15, Q21 Q27!!!some1 plz explain

 

[Abhi Mevawala]

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

n(NaN3)=50/(23+14*3)=0.77
n(N2)=n(NaN3)*3/2=1.15
Volume of (N2)=n(N2)*24=1.15*24=27.7dm^3

 

[SomeStudent]

M/J/01 2007
Q. 28, 39


Oct/Nov/01 2007
9, 20 (which type of isomerism changes the physical properties?)

 

[SomeStudent]

11 It is often said that the rate of a typical reaction is roughly doubled by raising the temperature by
10 °C.

What explains this observation?
A Raising the temperature by 10 °C doubles the average kinetic energy of each molecule.
B Raising the temperature by 10 °C doubles the average velocity of the molecules.
C Raising the temperature by 10 °C doubles the number of molecular collisions in a given time.
D Raising the temperature by 10 °C doubles the number of molecules having more than a
certain minimum energy.

why shouldn't e consider factors like speed? Isnot it doubled when we increase temp?

 

[SomeStudent]

37 Which mixtures, on heating, produce the gas ND3?
[D = H
2
1 , an isotope of hydrogen]
1 CaO(s) and ND4Cl(s)
2 CH3CN and NaOD in D2O
3 NDH3Cl and NaOD in D2O

Why is 2 correct too? isnot this reaction catalyzed by acid only?

 

[Love Islam]

View attachment 45027

Nitrogen per 100g of Fertilizer is 15g
So How much in 14g of Fertilizer? Ans: 2.1g (Cross-multiplication)
n=m/Mr ; 2.1/14= 0.15 moles of N (Ar of N:14)
What is the Conc. of N? c:n/v ; 0.15/5= 0.03 mol dm-3 (Ans:A)

 

[Love Islam]

37 Which mixtures, on heating, produce the gas ND3?
[D = H
2
1 , an isotope of hydrogen]
1 CaO(s) and ND4Cl(s)
2 CH3CN and NaOD in D2O
3 NDH3Cl and NaOD in D2O

Why is 2 correct too? isnot this reaction catalyzed by acid only?

CH3CN with NaOH is Basic Hydrolysis, that's why it is possible!

 

[Love Islam]

11 It is often said that the rate of a typical reaction is roughly doubled by raising the temperature by
10 °C.

What explains this observation?
A Raising the temperature by 10 °C doubles the average kinetic energy of each molecule.
B Raising the temperature by 10 °C doubles the average velocity of the molecules.
C Raising the temperature by 10 °C doubles the number of molecular collisions in a given time.
D Raising the temperature by 10 °C doubles the number of molecules having more than a
certain minimum energy.

why shouldn't e consider factors like speed? Is not it doubled when we increase temp?

Even If speed increases, The energy increases but it might not be sufficient to overcome Ea! but if the molecules posses enough energy to overcome Ea, then only the rate will double,
I hope you understand!

 

[ashcull14]

Nitrogen per 100g of Fertilizer is 15g
So How much in 14g of Fertilizer? Ans: 2.1g (Cross-multiplication)
n=m/Mr ; 2.1/14= 0.15 moles of N (Ar of N:14)
What is the Conc. of N? c:n/v ; 0.15/5= 0.03 mol dm-3 (Ans:A)

cn u ans other posts plx...thnks

 

[Love Islam]

M/J/01 2007
Q. 28, 39
View attachment 45100 View attachment 45101

Oct/Nov/01 2007
9, 20 (which type of isomerism changes the physical properties?)
View attachment 45102 View attachment 45103

Q28: Ans: C

It is an Aldehyde and it will get Oxidised by KMnO4 and it also reacts with 2,4 DNP to gve orange colour, Whereas in option A and D it will decolorize KMnO4 but will not react with 2,4 DNP. And Option B. is a Ketone, it doesn’t get oxidized, but it only reacts with 2,4 DNP!

Q39: Ans: C

Because it posses 3 Chiral centre so First is wrong, the 2 and 3 has to be correct!

Q9: Ans: B

The oxidation no. of S in SO3^-2 is +4 and on other side it is +6. So Oxidation No. increased by 2 so it means the metal in it, its oxidation will decrease by 2, but the mole of Metal: Sulphite (2:1) so total increase 2/2= +1, so before it was +3 but now it has changed by 1, so the Oxidation No. is 3-1 = +2

Q20: Ans: C

Because it is an Optical isomer it has same 3-D dimensional structure!

 

[Love Islam]

cn u ans other posts plx...thnks

Plz answer...View attachment 45054View attachment 45055 View attachment 45056

Q23: Answer is D,
Because KCN or NaCN is a reagent which can replace Halogen! Not HCN, it is only for Carbonyl groups ( Aldehydes or ketones)
There is a increase in carbon as you can notice: it is changing from bromoethane and to Sodium propanoate!
CH3CH2CN is formed basic hydrolysis is done to it by NaOH (aq)

Q24: Ans: A
beacause in these options first step is the curly arrow from a nucleophile (OH which is negative) to positively charged Carbon!
As Bond between C-Br breaks heterolytically, homolytic is only by sunlight between same atoms!
Q25: Ans D
It is dehydration, they has just turned it to right side!

Q40: Ans: D
As 1: CH3COO- + Ca+2 combines they form Ca(CH3COO)2 which is CaC4H6O4
2 & 3: Everything doubles!

 

[Love Islam]

MJ 2008 Q15, Q21 Q27!!!some1 plz explain

Q15: B

CaCO3 -----> CaO + CO2

Mass: 1200 x = 527

Mr: 100.1 44

Q21: A

C=C bonds break forming CHClBrCCl2Br (the first C if you notice is chiral)

Q27: D
As it is unreactive towards mild oxidising reagent it is Tertiary alcohol! If you see D, is a tertiary alcohol, others are not!

 

[Omar Haider]

Plz answer...View attachment 45054View attachment 45055 View attachment 45056

23. The answer for 23 is D (correct me if I'm wrong). You can see that we start off with a basic organic compound, which is ethane and the final product is basically propane (with a halogen group), so the reagent must add ANOTHER carbon group to get from 2 carbons (ethane) to 3 carbons (propane). So it can be either C or D now. The answer is D, because ONLY KCN reacts with a halogenoalkane, not HCN.

24. The answer is A because that's the only option which describes the Sn2 reaction, which occurs with primary halogenoalkanes. Note that they said 1-bromopropane which is a primary halogenoalkane and thus undergoes the SN2 reaction.

25. This one looks difficult, but it's extremely easy. Sulphuric acid is a dehydrating agent and thus takes away a certain number of moles of H20 away from a molecule. There is one -OH group, so it takes that and one H to form water and thus forming a double bond. The problem is that the double bond is supposed to be formed at the place where the OH group was, but there is no option like that. However, option D is a REFLECTION and so is an isomer of the dehydrated compound and is the answer.

Hope I helped