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PHYSICAL CHEMISTRY PRACTICE QUESTIONS

The branch of chemistry concerned with the application of the techniques and theories of physics to the study of chemical systems.

                              PHYSICAL CHEMISTRY

1). Methanoic acid and ethanoic acid are weak monobasic acids.

  • (i) What is meant by the term mono basic acid
    • Write o an equation for the ionization of methanoic acid.
    • Write an expression for the ionization constant Ka for methanoic acid.
  • 25cm3 of 0.1M ethanoic acid solution was reacted with 50cm3 of 0.05M sodium hydroxide solution
    • Write the equation for the reaction that took place
    • Calculate the pH of the resultant solution (Ka for methanoic acid is 1.77 x 10-4 moldm-3) (iii) Explain why the pH of the resultant solution is not equal to seven.

(c ) Name a reagent that could be used to distinguish between methanoic acid and ethanoic acid and state is observed in each case when the  each of the mistreated with the named reagent. (d) To 200cm3 of 0.075M ethanoic acid was added with 123g of sodium ethanoate to make a solution.

  • Calculate the pH of the resultant solution.
  • 10cm3 of 0.1M hydrochloric acid was added to the resultant solution in (d) above. Calculate the change in pH of the resultant solution (Ka = 1.8 x 10-5 moldm-3)

 

  1. 2. (a)(i) State Raoult’s law and mention its limitations.

(ii) Explain what is meant by the term ideal solution

(b) Water (1000C) and nitric acid (860C) when mixed forms a miscible liquid mixture that deviate negatively from Ideal solution.

  • Explain why the mixture deviates negatively from ideality.
  • Draw a well labeled temperature –composition diagram for the mixture (Azeotropic mixture composition and boiling point are 68% nitric acid and 120.5OC)

(c)(i) Describe the shape of the diagram

(ii) Explain what happens when 80% of the solution containing nitric acid is fractionally distilled.

 

 

(d) (i) Calculate the morality of nitric acid in the  Azeotropic mixture.

  • Given one method that could be used to increase the percentage of nitric acid in the azeotropic mixture

 

3). (a) (i) Define the term lattice energy

  • State two factors that affect lattice energy

(b) The Thermodynamic data for aluminum, fluorine and aluminum fluoride are given below.

-The standard enthalpy of formation of aluminum fluoride is -130KJmol-1

-The standard enthalpy of atomization of aluminum is +314 kJmo1-1

-The standard enthalpy of bond dissociation of fluorine is +158 kJmo1-1

-First ionization energy of aluminum is +577 kJmo1-1

-Second ionization energy of aluminum is +1820 kJmo1-1

-Third ionization energy of aluminum is +2740 kJmo1-1

-First electron affinity of fluorine is -348 kJmo1-1

  • Draw an energy level diagram for formation of aluminum fluoride.
  • Use the diagram you have drawn to determine the lattice energy of aluminum fluoride
  • Given that the hydration energies of aluminum ions and fluoride ions are -4690 and -364kjmo1-1 Calculate the enthalpy of solution of aluminum fluoride and comment on the solubility of aluminum fluoride in water.

4). (a) State;

  • Partition law
  • Three limitations of the law

(b) Describe an experiment to determine the partition co-efficient of butane -1, 4-dioic acid between ethoxyethane and water.

(ii) State two advantages and disadvantage of using ethoxyethane as a solvent in this experiment. (c) An aqueous solution containing 10g of butane 1, 4-dioic acid per litre. When 100cm3 of this solution is shaken with 20cm3  of ethoxyethane, the ethoxyethane layer extracts 0.8g of butane 1, 4-dioic acid calculate mass of butane -1, 4-dioic acid extracted when 500cm3 of the aqueous layer was shaken with.

  • 50cm3 of ethoxyethane
  • Two successive 25cm3 portion of the ethoxyethane.
  • Comment of on your results in (c) above.
  • State two applications of partition coefficient.

 

5). (a) Define each of the following terms

  • Enthalpy of neutralization
  • Enthalpy is a reaction
  • Bond energy

(b) Use of the following thermo chemical data to calculate the enthalpy of reaction in the equation below

2𝐶2𝐻6(𝑔) + 702(𝑔)                             4𝐶𝑂2(𝑔) + 6𝐻2𝑂(𝑖)

Enthalpy of formation of carbon dioxide is -394 kJmo1-1

Enthalpy of formation of water is -286 kJmo1-1

(c )Explain each of the following observation

  • The enthalpy of neutralization of a weak acid with a strong base is less than that between a strong acid with a strong base.
  • The bond energies of the halogens are 158, 242, 192 and 151 kJmo1-1 for Flourine, Chlorine, Bromine and Iodine respectively.

 

(d) During the experiment to determine the enthalpy of neutralization between hydrochloric acid and sodium hydroxide, 25cm3 of 1.0M hydrochloric acid was pipetted into a plastic beaker and titrated with 1.0M sodium hydroxide from the burette. The temperature of the solution was recorded after every addition of the sodium hydroxide solution in the table below.

Value of NaOH added (cm3) 0 10 20 25 30 35 40 45
Temperature of soln (OC) 22 24.7 27.4 28.2 28.2 28.3 280 27.3
Temperature change (OC) 0 2.7 5.4 6.2 6.5 6.3 6.0 5.8

 

(i).Plot a graph of temperature change against volume of sodium hydroxide solution added.

  • Determine the maximum temperature change from the graph.
  • Determine the volume of the sodium hydroxide solution at the end point.

(i) . Using 4.18kjmoi-1 C-1 kg-1 as the Specific heat capacity of the solution, calculate the enthalpy of neutralization of the reaction.

 

6). (a) Define the terms

  • Conductivity
  • Molar conductivity

(b) The table below shows the molar conductivities of an aqueous solution of sodium hydroxide

Concentration (moldn-3 0.01 0.04 0.09 0.16 0.25 0.36
Molar conductivity (n-1cm2ma1 238 230 224 217 210 202
  • Plot a graph of molar conductivity against of sodium hydroxide a t infinite dilution.
  • Explain the shape of the graph

(c). (i) Draw a sketch graph to show the change in the conductivity with volume of ammonia solution when 25cm3 of  0.1M methanoic a acid is filtrated with 0.1M ammonia solution.

(ii) Explain the shape of the graph.

(c)The conductivity of a saturated solution of silver phosphate at 25 oC is 2.661 x 10-6 Scm-1 and that a of pure water is 1.519 x 10-6 Scm-1. If the molar ionic conductivities of silver ion and phosphate ions at infinite dilution at 250C are 61.9 and 2405cm2moi-1 respectively, calculate the

  • Solubility of silver phosphate in moldm-3 at 250C
  • Solubility product of silver phosphate at 250C and state its unit

           

  1. 7. Explain what is meant by
  • Emission spectrum
  • Absorption spectrum of hydrogen
  • The atomic spectrum of hydrogen is given by the following relationship;

 

  • What does λH represent?
  • What do the terms n1 and n2 represent
  • The spectrum of hydrogen comprises of a number of lines which may be divided into a number of series.
    • Why does the spectrum consist of line?
    • Why is there a small number of series in the spectrum?
    • Explain why each series converges and in what direction it converges.
  • What do you under by the term first ionization energy?
  • State the factors that affect ionization energy

      

  1. 8. Define the following terms
  • Eclectic point
  • Eutectic mixture

(b) The table below shows the melting points and compositions of various mixtures of bismuth and cadmium.

Percentage 20 35 50 65 80 95
Melting point (OC) 226 190 156 154 242 300

Draw a well labeled phase diagram for cadmium-bismuth system. Use your graph to;       (i) Determine the melting points of pure cadmium and pure bismuth.

  • Determine the composition and melting point of the eclectic mixture.
  • Describe what happen when a liquid mixture containing 10% of cadmium at 3500C is gradually cooled.

(iv). Determine the mass of bismuth that crystallized when 200g of the mixture containing

25% cadmium was cooled from 3000C to 1680C

(c)(i). State two similarities between a eutectic mixture and a pure metals.      (ii) State two uses of eutectic mixtures

            

9).(a)  Methyl orange can be used as an acid base indicator.

  • What is meant by the term acid base indicator?
  • Describe briefly how methyl orange works as an acid base indicator.
  • The indicator constant Kin, for methyl orange is 2.0 x 10-4 moldm-3. Determine the approximate pH working range for methyl orange.

(b) 50cm3 of 0.02M ethanoic acid was pipetted into a clean conical flask and 2-3 drops of phenolphthalein indicator added and the mixture titrated with an equal volume 0.02M sodium hydroxide solution until the equivalence point had reached.

  • What is meant by the term equivalence point?
  • State the colour change at equivalence point
  • Calculate the pH of the mixture at equivalence point (Ka of ethanoic acid = 1.75 x 10-5 moldm-3 and Kw for water = 1.0 x 10-14 mol2dm6)

(c) Sodium hydroxide was added to 25cm3 of 0.1M ethanoic acid and the pH of the solution was measured at intervals. The results are given in the table below

vol of NaOH(cm3) 0 4 8 12 16 20 22 22.5 23 24 28
pH of mixture 2.8 3.5 4 4.5 5.1 5.8 7 9 10.5 11.4 12.3
  • Plot a graph of pH against volume of sodium hydroxide
  • Explain the shape of the curve
  • Determine the pH at the end point
  • Calculate the molarity of sodium hydroxide solution

          

 

 10)(a).  Explain what is meant by the term order of a reaction.

  • Describe an experiment that can be carried out to show that the decomposition of hydrogen peroxide solution follows first order kinetics.
  • The iodination of propanone in acidic solution takes place according to the equation.

CH3COCH3(aq)   + I2(aq)                       CH3COCH3(aq)  +   HI(aq)

The rate of the reaction as followed by withdrawing 10cm3 samples from the reaction mixture quenching and filtrating against standard sodium thiosulphate solution. The following results were obtained.

Time (min) 0 10 20 30 40
Vol of Na2S2O3(cm3) 8.0 6.5 5.0 3.5 2.0
  • Plot a graph of volume of sodium thiosulphate against time.
  • What is the order reaction with respect to iodine. Explain your answer.
    • Write an expression for the rate of the reaction if the reaction is first order over all.
    • What would be the effect on the gradient of your graph of doubling the initial concentration of iodine. Give a reason for your answer.

 

11). (a).Explain what is meant by;

  • Osmosis
  • Osmotic pressure

 

  • (i) With the aid of a well labeled diagram, describe an experiment you would perform under typical laboratory conditions to determine the relative formula mass of a solute using  osmotic pressure method.
    • State the weaknesses of the osmotic pressure method.
    • Suggest why osmotic pressure measurements are more suitable for determining high value relative formula masses such as polymers than any other colligative property

(iv). State one practical applicable of reverse osmosis

  • The osmotic pressures at various concentrations of a solute in a certain solvent G at 250C were shown below.

 

 

Concentration 1.2 2.5 3.6 4.8 6.0 7.2
Osmotic pressure (Nm-2) 25 39 55 77 94 112

 

(i) Plot a graph of osmotic pressure against concentration in gl-1 (ii) Workout the relative formula mass (R=8.3138).

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