Vapor Pressure of a Solution of a Non-Volatile Solute

Vapor Pressure of a Solution of a Non-Volatile Solute.?

A solution is made by dissolving 32.5g of urea (H2NCONH2, a non-volatile non-electrolyte) in 284g of water.
Calculate the vapour pressure of this solution at 50°C. (note the vapour pressure of pure water at 50°C is 92.5 torr.)


Chemistry
Best Answer - Chosen by Asker

Number of moles of urea = 32.5 / 60 = 0.542 mol
Number of moles of water = 284/18 = 15.778 mol

Mole fraction of water = 15.778 / ( 15.778 + 0.542) = 0.967

Using Raoult's Law,
Vapour pressure = 0.967 x 92.5 = 89.45 torr.

Electrophilic Substitution

Resolved Question

Electrophilic substitution?
Which of the following are all meta directing and activating substituents in aromatic electrophilic substitution reactions?

a. methoxy group, chloride group, nitro group
b. none known
c. bromide group, methyl group, phenyl group
d. aldehyde group, nitro group, carboxylic acid group, ketone group
e. hydroxyl group, amino group, phenyl group

by joeyeehu...

d.

Activating substituents means it activates the substitution reaction. It makes the reaction to proceed faster. A substituent that is an electron donating group will activate the benzene ring.

It increases the electron charge density of the benzene ring and it becomes more susceptible for the attack of an electrophile.

Solvent Extraction

Resolved Question

1. what are the advantages or disadvantage of using ether as an extraction solvent?

2. in extracting an organic compound from an aquous solution, what practical advantage ensues
if the organic solvent used is more dense than water?

3. why must the stopper be removed from a separatory funnel before the liquid can be
withdrawn from it?

by joeyeehu...



Best Answer - Chosen by Voters

Advantages:

1. it is a great solvent. It can dissolve most of the organic compounds.
2. it has low boiling point. It can be distilled over easily
3. it is chemically inert.

Disadvantage:

1. highly flammable
2. toxic

Q2: It will form two separate distinct layers. So it can be separated easily.

Q3: The stopper must be removed so that the air pressure will help push the liquid out of the
funnel. If not, the flow of liquid is obstructed.

Polar Molecule

Resolved Question
Which of the following molecules may be polar: S03, XeF4, S F4 1 day ago

by joeyeehu...

Contributing In:
Chemistry

Best Answer - Chosen by Asker
First, calculate the number of electrons around the central atom. You can use the Group number in the Periodic Table to help you.

Next, determine the number of electron pair around the central atom and state the geometrical arrangement of electron pairs.

2 pairs - linear
3 pairs - trigonal planar
4 pairs - tetrahedral
5 pairs - trigonal bipyramidal
6 pairs - octahedral

Determine the number of bond pairs and lone pairs.
Determine the shape of the molecule.

1) SO3

S--> 6
O---> 3(2) = 6
total 12 electrons = 6 electron pairs

sulphur forms three double bonds with three oxygen.
The shape is trigonal planar. (non polar)

2) XeF4

Xe - 8e
4F - 4e
Total = 12 e = 6 pairs
Basic electron pair arrangement is octahedral
4 bond pair and 2 lone pair
The shape is square planar (non polar)

3) SF4

S = 6e
F = 4e
Total =10e = 5 electron pairs
Basic electron pair arrangement = trigonal bipyramidal
4 bond pair and 1 lone pair
The shape is irregular or see-saw shaped (polar)

Standard Reduction Potential

Resolved Question
Standard reduction potential for Pt2+/Pt?

An electrochemical cell of notation Pt/Pt2+ Ni2+/Ni has Eo = -1.45 V.
If we know that the standard reduction potential of Ni2+/Ni is Eo = -0.25 V,
what is the standard reduction potential for Pt2+/Pt?

Chemistry
Best Answer - Chosen by Asker

From the cell diagram given,
E(Pt2+/Pt) = aode (oxidation) and
E(Ni2+/Ni) = cathode (reduction)

Eo cell = E (reduction) - E ( oxidation)
.......... = E (Ni2+/Ni) - E (Pt2+/Pt)
-1.45 = -0.25 - E(Pt2+/Pt)E(Pt2+/Pt)
= 1.45 - 0.25
= 1.20 V

Asker's Comment:
Thank you

Hybridised Orbital

Resolved Question

Which of the following compounds contain an sp2 hybridised carbon atom?

a) n-butane
b) propanal
c) propanol
d) 2,3-dimethylheptane

by joeyeehu...


Chemistry

In sp2 hybridised carbon atom, it must be bonded to 3 groups or atoms. Normally, the carbon atom must form a double bond in order to be bonded to three groups/atoms instead of four.
Only propanal contains an sp2 hybridesed orbitals.

In CH3CH2CHO, the first carbon is sp3 hybridesed ( it is bonded to four groups/atoms, ie, three hydrogen and CH2CHO).

The second carbon is also sp3 hybridised. ( one CH3, two H and one CHO)The third carbon is sp2.( one CH3CH2, one H and one O)

This rule only applies to carbon atom.

Strongest acid ?

Resolved Question

Acids... which is stronger?

Which one of the following is the strongest acid?
(a) ICH2CO2H
(b) BrCH2CO2H
(c) ClCH2CO2H
(d) FCH2CO2H
(e) ICH2CH2CO2H

by joeyeehu...
Chemistry

The answer is (d).

A strong acid is the one that can donate a proton(H+) easily.The presence of halogen will increase the ability of the acid to donate proton. This is so because halogen being more electronegative will attract the electrons toward itself. This will reduce the electron charge density of the OH bond (COOH). It weakens the OH bond and hence it becomes easier for the H+ to be donated.

Since F is the most electronegative among the halogen, it has the strongest effect ( negative inductive effect ). It weakens the OH bond the most and it will cause the molecule to donate H+ readily.