### Chemistry Past Questions

4016

D is 2.00M ethanoic acid.  E is 2.00M potassium hydroxide solution.

(a) Using a 50cm$$^3$$ measuring cylinder, measure 50cm$$^3$$ of D and transfer the solution into plastic cup.Record the temperature T$$_1$$ of the solution. Rinse the cylinder distilled water and allow to dry.

(b) Using the dry measuring cylinder from (a) above, measure 50cm of E. Record the temperature, T$$_2$$ of the solution.

(c) Find the average temperature T$$_3$$ of the two solutions and record the value.

(d) Pour the measured quantity of solution E quickly from the measuring cylinder into the plastic cup containing solution D. Stir the mixture with the thermometer. Record the highest temperature T$$_4$$ attained.

(e)(i) Find the rise in temperature (T$$_4$$ - T$$_3$$ ad record the value

(ii) Calculate the mass of the reaction mixture, given that during the reaction 1cm$$^3$$ of the mixture weighs 1g

(f) From your results in (a) to (e) above, calculate the;

(i) Heat evolved during the reaction, giving that the specific heat capacity of water is 4.2Jg$$^{-1}$$C $$^{-1}$$ and using the formula; heat evolved = mass x specific heat capacity x rise in temperature

(ii) Heat of neutralization of one mole of ethanoic acid by potassium hydroxide

(g) List two sources of error in the method used for determining the heat of neutrailzation and suggest how their effect can be minimized.

WAEC 1989
4017

Credit will be given for strict adherence to instructions, for observations precisely recorded, and for accurate inferences. All tests, observations, and inferences must be clearly entered in your answer book, in ink, at the time they are made.

Carry out the following exercises on sample F. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test.

(a) Put all of F into a beaker and add about 10cm$$^3) of water. Stir the mixture and filter. Keep both the residue and the filtrate. (b)(i) Test the filtrate with litmus paper. (ii) Add a few drops of the fehling's solution provided to about 2cm\(^3$$ of the filtrate in a test tube. Boil the mixture.

(c) Put the residue from (a) above into a test tube and add about 5cm$$3$$ of hydrochloric acid. Identify the gas evolved.

(d) To about 2cm$$^3$$ of the clear solution from (c) above add dilute sodium into hydroxide solution dropwise and then in excess.

(e) From your results deduce what F is and its constituent

WAEC 1989
4018

(a) A mixture consist of sodium chloride, ammonium chloride and lead (II) tetraoxosulphate (VI). Describe how you would obtain each component in a pure state.

(b) You are required to determine the concentration of a solution of tetraoxosulphate (VI) acid by titrating it against sodium trioxocarbonate (IV) solution of known concentration.

(i) Name the indicator you would use

(ii) List two precautions you would take to ensure accurate readins

(iii) State the colour of the sodium trioxocarbonate (IV) solution after adding the named indicator and then at the end point.

WAEC 1989
4019

A solution of a mineral acid containing 0.10 mol of the acid per dm of solution. B IS a solution Containing 1.325g of anhydrous sodium trioxocarbonate (IV) per dm of solution.

(a) Put A into the burette and titrate with 20cm$$^3$$ or 25cm$$^3$$ portions of B using methyl orange as an indicator. Record the volume of your pipette

(b) From your results and the information is given, calculate;

(i) The number of mole of acid in the average titre

(ii) The number of mole of sodium trioxocarbonate (IV) in the volume of B pipette,

(iii) The mole ratio of acid to base in the reaction [H = 1, C = 12, O = 16, Na 23]

(c) Suggest what the acid in (a) Could be giving reasons for your answer. Hence, write the equation for the reaction.

WAEC 1988
4020

Carry out the following exercises on sample C. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test.

(a) Put about half of sample C into a conical flask and add about 5cm$$^3$$ of tetrachloroethane followed by 15cm$$^3$$ of water. Shake vigorously for about one minute. Put the resulting mixture into a burette and allow to stand until two layers separate. Run the two layers into two separate conical flasks and label them accordingly.

(b) Using the following reagents only, bench sodium hydroxide solution, aqueous ammonia solution, aqueous lead (II) trioxonite (V) solution, silver trioxonitrate (V) solution. bench trioxonitrate (V) acid. Identify the ions present in the upper layer solution

(c) Add 2 - 3 drops of the lower layer solution to about 2cm$$^3$$ of starch solution from your result, name the substances which dissolved in the upper and lower layers.

WAEC 1988