Chemistry: Post your doubts here!

[smartangel]

in ester formation, OH is from the acid and H from the alcohol combine to form water or is it the opposite?

 

[saudha]

Chlorofluoroalkanes, commonly known as CFCs, undergo homolytic fission by ultraviolet
irradiation in the stratosphere.
Which radical could result from this irradiation of CHFClCF2Cl?
A) CHFClC·FCl
B) C·HClCF2Cl
C) C·HFCF2Cl
D) C·FClCF2Cl
how do u get this ?

 

[smzimran]

Chlorofluoroalkanes, commonly known as CFCs, undergo homolytic fission by ultraviolet
irradiation in the stratosphere.
Which radical could result from this irradiation of CHFClCF2Cl?
A) CHFClC·FCl
B) C·HClCF2Cl
C) C·HFCF2Cl
D) C·FClCF2Cl
how do u get this ?

AoA,
Go a little back, in this thread i have answered the question before!

 

[smzimran]

in ester formation, OH is from the acid and H from the alcohol combine to form water or is it the opposite?

AoA,
Its the opposite
R---COO---H
R---CH2---OH
The red coloured bonds break in each case
So, H from acid and OH from alcohol form water

 

[saudha]

What is the number of molecules in 500 cm3
of oxygen under room conditions?
A 1.25 x 10^22
B 1.34 x 10^22
C 3.0 x 10^22
D 3.0 x 10^26

how do u get A?

 

[smzimran]

Please explain how is the answer A??

This question needs you to use the values of 1st and 2nd ionisation energies
Check which elements sum of 1st two I.Es equals that of Al

 

[smzimran]

What is the number of molecules in 500 cm3
of oxygen under room conditions?
A 1.25 x 10^22
B 1.34 x 10^22
C 3.0 x 10^22
D 3.0 x 10^26

how do u get A?

500 cm3 of O2 means (500/1000) dm3 = 0.5 dm3

In 24 dm3 (one mole), there are (6.02 * 10^23) molecules
In 1 dm3, there are {(6.02 * 10^23) / 24} molecules

So in 0.5 dm3, there will be
= 0.5 * {(6.02 * 10^23) / 24}
= 1.25 * 10^22 molecules

So, the correct answer is A

 

[saudha]

Which of the following solids has a simple molecular lattice?
A magnesium oxide
B sodium
C silicon(IV) oxide
D sulphur

why D? why not B?

 

[saudha]

How many structural and cis-trans isomers are there for dichloropropene, C3H4Cl2?
A 3 B 5 C 6 D 7
is there any other way other than drawing all of them?

 

[smzimran]

Given the following enthalpy changes,​

I2(g) + 3Cl2(g) → 2ICl3(s) ∆H = –214kJmol​

I2(s) → I2(g) ∆H = +38kJmol​

What is the standard enthalpy change of formation of iodine trichloride, ICl3(s)?​

A +176kJmol​

B –88kJmol​

C –176kJmol​

D –214kJmol​

whats the answer?...........................

its B

See the image

 

[smzimran]

Which of the following solids has a simple molecular lattice?
A magnesium oxide
B sodium
C silicon(IV) oxide
D sulphur

why D? why not B?

Sodium has metallic bonding,
positive ions bonded by sea of electrons, thats why not B

 

[smzimran]

How many structural and cis-trans isomers are there for dichloropropene, C3H4Cl2?
A 3 B 5 C 6 D 7
is there any other way other than drawing all of them?

Unfortunately, there isn't
I have solved this before as well!

 

[smzimran]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_1.pdf
Q27..why is the answer sulfuric acid..can someone plz tell me the rxn these compounds undergo with H2SO4?

Elimination reaction
The elimination of water to form double bond (alkene)
Check some text book for detail

 

[smzimran]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf Q20..im sorry the answer is B. my question is that whats the other isomer besides cis trans?

The other (third) isomer is:
(Cl2)C = C(H2)

 

[smzimran]

More doubts x_x . The correct answers are circled.View attachment 8831

AoA,
First of all, we know CS2 is the limiting reactant
So 10 cm3 CS2 needs 30 cm3 O2 (See molar ratio)
That means 50 - 30 = 20 cm3 O2 is left after the reaction
Further,
10 cm3 CO2 and 20 cm3 SO2 are produced (See molar ratio)
So total volume of gases left after burning = 20 cm3 O2 + 10 cm3 CO2 + 20 cm3 SO2 = 50 cm3

The answer must be either C or D

Adding NaOH will neutralise (or remove) acidic gases
It will remove 10 cm3 CO2 and 20 cm3 SO2 = 30 cm3 acidic gases
Gas left after NaOH is added = 50 - 30 = 20 cm3

So, C is correct!

 

[Anoushay]

u r wecome, it is correctly balanced equation and they ask u 4 which you put in front of (as far as i remember the question) I2 and H2O, u understand now?

umm...no. can you please elaborate.?

 

[saudha]

Which of these samples of gas contains the same number of atoms as 1g of hydrogen
(Mr
: H2, 2)?
A 22g of carbon dioxide (Mr
: CO2, 44)
B 8 g of methane (Mr
: CH4, 16)
C 20 g of neon (Mr
: Ne, 20)
D 8g of ozone (Mr
: O3, 48)

 

[saudha]

hieeee...

if there are diagrams in the Q... then just post Q no an d the ppr ur solving.. ok

 

[étudiante]

Which of these samples of gas contains the same number of atoms as 1g of hydrogen
(Mr
: H2, 2)?
A 22g of carbon dioxide (Mr
: CO2, 44)
B 8 g of methane (Mr
: CH4, 16)
C 20 g of neon (Mr
: Ne, 20)
D 8g of ozone (Mr
: O3, 48)

C since they are talking abt atoms....
1 g of H2 gas will have 6.02 x 10^22 ATOMS as it is diatomic... Neon will also have the same no of atoms in 20 g as it is monatomic

 

[saudha]

C since they are talking abt atoms....
1 g of H2 gas will have 6.02 x 10^22 ATOMS as it is diatomic... Neon will also have the same no of atoms in 20 g as it is monatomic

thxx a lot