Geos

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Cheers,

- Rin (Sharrine Ishak)

Question No.5

Question:

The vapour pressure of benzene and methylbenzene are 1.0 x 105 Nm-2 and 4.5 x 104 Nm-2 at 85oC . Calculate the total pressure exerted by a mixture containing 101.4 g benzene and 73.6 g of methylbenzene at the same temperature.  (Molar mass ; benzene  = 78 mol-1 , methylbenzene  = 98 mol-1)

Answer:

mol of benzene:

101.4/78=1.3mol

mol of methylbenzene :

73.6/98=0.75mol

total pressure

(1.3mol x 1.0 x 105 Nm-2 )+(0.75mol x 4.5 x 104 Nm-2)=

1.6375 x 10^2 kNm-2

by: CCP

ps: I’m not sure is 1.0×105 or 1.0×10^5…

but I assume it as power by 5,

chemistry – question 7 (U6 Phy)

(a)Total pressure = Partial pressure of hexane + partial pressure of heptane

= 32.5k+12.3k

=44.8kPa

(b)mole fraction of hexane = 32.5/ (32.5+12.3)

= 0.73

-Hoi Hong Keen, U6phy

question 12 Bio class, by RofL

12

a) Volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance’s vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure. A volatile liquid has weak intermolecular forces.

The structure of intermolecular forces (Van der Waals forces) that bonds the three molecules are:

1. Ether, general structure R-O-R,  weak intermolecular forces (Van der Waals forces).

2. Water, structure O-H-O, strongest intermolecular forces .

3. Ethanol, structure CH3-CH2-OH,  strong intermolecular forces ( hydrogen bond).

Hence in conclusion, volatility of the three liquids are as follows: Ether>Ethanol>Water.

b) A substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.A more volatile liquid has a higher vapour pressure than less volatile liquid at the same temperature.The vapour pressure in ethanol is higher than water but lower than ether.Water has the lowest vapour pressure compared to ether and ethanol.

Hence in conclusion, the volatility of the the three subtances are as follows: Ether>Ethanol>Water.

c) The temperature of a subtance is measured by: (The more volatile the liquid,the lower its boiling point)

The boiling points of the three subtances are

1. Ether, boiling point is 34.6 °C, low boiling point.

2. Water, boiling point is 99.97°C, highest boiling point.

3. Ethanol, boiling point is 78.4 °C, high boiling point.

Hence in conclusion, the volatility of the the three subtances are as follows: Ether>Ethanol>Water.

Reference: www.chemfile.com , http://www.wikipedia.com

Krisnamogan ,U6 BIO

Question5 , U6Physic

5.  The vapour pressure of benzene and methylbenzene are 1.0 x 105 Nm-2 and 4.5 x 104 Nm-2 at 85oC . Calculate the total pressure exerted by a mixture containing 101.4 g benzene and 73.6 g of methylbenzene at the same temperature.  ( Molar mass; benzene  = 78 mol-1 , methylbenzene  = 98 mol-1 )

Number of moles of benzene,   101.4 / 78  = 1.3 mole

Number of moles of methylbenzene,    73.6 / 98  = 0.75 mole

Volume of benzene,    PV   =   nRT

                                                     V   =    (nRT) /P

                                                   V = (  1.3  )(  8.31  )(  85+273  )

                                                                (  1.0 x 10^⁵  )

                                                    V = 0.039 m³

Volume of methylbenzene,      PV = nRT

                                                                         V   =  (nRT) /P                                  

                                                            V = (  0.75  )(  8.31  )(  85+273  )

                                                                          (  4.5 x 10^⁴  )

                                                                V   =   0.05 m³

Total volume of mixture,   V_T   =   0.05 + 0.039

                                                            =   0.10 m³

 Partial pressure of benzene,   0.05/0.10  x    1.0 x 10^⁵   

                                                              =   50 kNm^-2                      

Partial pressure of methylbenzene,   0.039/0.10  x  4.5 x 10^⁴

                                                                      =   17.55 kNm^-2

Total pressure of the mixture,   17.55 + 50   =   67.55 kNm^-2

           

 By : FOO CHUN HOU  U 6 Physic

Chemistry-Question 2 (U6Phy)

One example of a mixture which forms nearly ideal solutions is hexane and heptane. These two ‘straight-chain’ hydrocarbons have similar molecular mass (they are six and seven carbon atoms in length respectively). They are both non-polar and therefore, can interact only using dispersion-type intermolecular forces.

by Pik Chi

Chemistry-Question 21 (U6 Phy)

Water and ethanol, for example, are miscible since they mix in all proportions. By contrast, substances are said to be immiscible if in some proportion, they do not form a solution. For example, benzene and water . This two solvents are not miscible since they are not soluble in all proportions. Water and Ethanol mix with each other due to H-bonding. Water and Benzene do not mix as H-bonds do not exist between them. Ethanol molecules are smaller than water molecules, so when the two liquids are mixed together the ethanol falls between the spaces left by the water which causes it to be a miscible liquids.

In organic compounds, the weight percent of hydrocarbon chain often determines the compound’s miscibility with water. For example, ethanol has two carbon atoms and is miscible with water. Benzene who has the longer carbon chains, cause them to almost always be immiscible with water. Benzene is non-polar. Water is polar. This makes them immiscible liquids and therefore it will form layers. The density of the two liquids will determine which layer is on the top and which layer is on the bottom.

by Zhao Yang

No 12

12)(a)           A volatile liquid has a weak intermolecular forces.As a results,the liquid particles have a higher tendency to escape from liquid surface.The intermolecular forces in ether is weakest compared to ethanol and water.Ether molecules are held together by weak intermolecular forces (Van der Waals forces) with the stuctures of R-O-R.Ethanol molecules are held together by  strong intermolecular forces ( hydrogen bond) with the structures of CH3-CH2-OH.Water molecules are held together by  strongest intermolecular forces compared to ether and ethanol with the stuctures of O-H-O.Hence,ether is more volatile than ethanol while ethanol is more volatile than water

(b)        At the same temperature,a more volatile liquid has a higher vapour pressure than less volatile liquid.Ether has a highest vapour pressure than ethanol and water because it is more volatile than ethanol and water.The vapour pressure in ethanol is higher than water but lower than ether.Water has a lowest vapour pressure compared to ether and ethanol.Hence,ether is more volatile than ethanol while ethanol is more volatile than water.
(c)        The more volatile the liquid,the lower its boiling point.Ether is most volatile liquid because it has the lowest boiling point compared to ethanol and water.Ethanol has a higher boiling point than ether but lower than water.Water has a highest boiling point compared to ether and ethanol.Liquids which evaporate quickly at low temperatures are called volatile liquids.Hence, ether is more volatile than ethanol while ethanol is more volatile than water.

By Leong Ming Choong

( U6 Physic)

no 3

3)     When A and B form an ideal solution,the partial vapour pressure of A in the vapour above the solution is lower than the vapour pressure of the vapour above pure A (likewise for B).This is because the number of molecules of A per unit volume in ideal solution of A and B is less than the number of molecules of A per unit volume in pure liquid A.The number of molecules of liquid A in the solution that escapes to form vapour is lower than that in pure A.Similarly the partial presure of Bin ideal solution is less than the vapour presure of pure B.

By Chow Siew Yee

( U6Physic)