Study resources on Kenyaplex

Get ready-made curriculum aligned revision materials

Exam papers, notes, holiday assignments and topical questions – all aligned to the Kenyan curriculum.

Or go directly to:

Class notes Holiday assignments Topical questions Other resources

Using a solid naphthalene as an example,describe how impurities affects the melting point of a substance.

Answers

(i) Put a very small amount of naphthalene in a capillary tube sealed at one end. You can pull
out the capillary tube from heated glass tubing. Use a rubber band to attach the capillary
tube, sealed end down, to a thermometer. Heat a thermometer and capillary tube in a
beaker of water on a tripod. Use the thermometer to stir the water but do not let water
enter the capillary tube. Slowly raise the temperature of the water. Note the temperature
of the naphthalene when it melts. Let it cool and note the temperature when the
naphthalene solidifies Calculate the average of these two values.
(ii) Use a clean test-tube and thermometer to repeat the experiment using stearic acid, mp
69^o, or use any other substance, mp < 100^oC.
Mix stearic acid with the naphthalene, thus making the naphthalene impure. Look for
changes in the melting point.You notice that Impurities lower the melting point.

sharon kalunda answered the question on April 12, 2019 at 06:45

Answer Attachments

Next: What is Debtors’ circularization and what are it's purposes?

Previous: Describe the advantage of over-sowing

View more Chemistry Questions and Answers | Return to Questions Index

Exams With Marking Schemes

Related Questions

Explain how a burette is used. (Solved)

Explain how a burette is used.

Date posted: April 12, 2019 . Answers (1)
Draw and name the apparatus used in the laboratory. (Solved)

Draw and name the apparatus used in the laboratory.

Date posted: April 12, 2019 . Answers (1)
Describe an experiment to demonstrate the purity of water using boiling point. (Solved)

Describe an experiment to demonstrate the purity of water using boiling point.

Date posted: April 11, 2019 . Answers (1)
State three examples of allotropes of carbon (Solved)

State three examples of allotropes of carbon.

Date posted: April 9, 2019 . Answers (1)
Define the following terms as used in chemistry: atom,molecule, element and compound (Solved)

Define the following terms as used in chemistry: atom,molecule, element and compound

Date posted: April 9, 2019 . Answers (1)
Describe how the mixture of sugar, iodine and lead (II) carbonate can be separated (Solved)

Describe how the mixture of sugar, iodine and lead (II) carbonate can be separated.

Date posted: April 9, 2019 . Answers (1)
The diagram below shows an investigation on a property of ammonia gas. (Solved)

The diagram below shows an investigation on a property of ammonia gas.

(a) The platinum wire is observed to glow. Explain the cause of that observation.
(b) State the observations made when the rubber bang is removed.

Date posted: April 1, 2019 . Answers (1)
The molar masses of gases W and X are 16.0 and 44.0 respectively. If the rate of diffusion of W through porous material is 12cm³s^-1.... (Solved)

The molar masses of gases W and X are 16.0 and 44.0 respectively. If the rate of diffusion of W through porous material is 12cm³s^-1. Calculate the rate of diffusion of X through the same material.

Date posted: April 1, 2019 . Answers (1)
The lattice energy of sodium bromide and hydration energies of sodium and bromide ions are:- 733, 406 and 335kJ/mol respectively. (Solved)

The lattice energy of sodium bromide and hydration energies of sodium and bromide ions are:- 733, 406 and 335kJ/mol respectively.
(i) Complete the energy cycle diagram below by inserting the values of changeH1, changeH2 and changeH3.

(ii) Determine the molar heat of solution of solid sodium bromide.

Date posted: April 1, 2019 . Answers (1)
Using dots (.) and crosses (x), show bonding in:-Sodium oxide (Na = 11; O = 8 ) (Solved)

Using dots (.) and crosses (x), show bonding in:-Sodium oxide (Na = 11; O = 8 )

Date posted: April 1, 2019 . Answers (1)
Using dots (.) and crosses (x), show bonding in:The compound formed when nitrogen reacts with fluorine. (F = 9, N = 7) (Solved)

Using dots (.) and crosses (x), show bonding in:The compound formed when nitrogen reacts with fluorine. (F = 9, N = 7)

Date posted: April 1, 2019 . Answers (1)
20.0cm³ of a solution containing 4gm per litre of sodium hydroxide was neutralized by 8.0cm³ of dilute sulphuric acid. Calculate the concentration of sulphuric acid in... (Solved)

20.0cm³ of a solution containing 4gm per litre of sodium hydroxide was neutralized by
8.0cm³ of dilute sulphuric acid. Calculate the concentration of sulphuric acid in moles per litre.( Na = 23.0; O = 16.0; H = 1.0 )

Date posted: April 1, 2019 . Answers (1)
The diagram below represents a paper chromatogram for three brands of juices suspected to contain banned food colourings by the Kenya Bureau of Standards. (Solved)

The diagram below represents a paper chromatogram for three brands of juices suspected to contain banned food colourings by the Kenya Bureau of Standards.

The results showed the presence of banned food colourings in L and M only. On the same diagram
(a) Circle the spots which show the banned food colourings.
(b) Show the solvent front.
(c ) Name one possible solvent that can be used in this experiment / research.

Date posted: April 1, 2019 . Answers (1)
The diagram below represents the extraction of sulphur by frasch process in Louisiana U.S.A. (Solved)

The diagram below represents the extraction of sulphur by frasch process in Louisiana U.S.A.

(a) Name the substance that passes through tube:-
I
II
(b) What is the purpose of hot compressed air in this process ?

Date posted: April 1, 2019 . Answers (1)
Give the differences between esterification and neutralisation. (Solved)

Give the differences between esterification and neutralisation.

Date posted: April 1, 2019 . Answers (1)
The table below gives elements represented by letters U V W X Y Z and their atomic numbers. (Solved)

The table below gives elements represented by letters U V W X Y Z and their atomic numbers.

Use the information to answer the questions below.
(a) In which period do these elements belong ? Give a reason.
(b) How does the atomic radius of W and Y compare ? Explain.
(c ) Give the formula of the compound that could be formed between V and X.
(d) What type of bonding will be present in a compound formed between V and Z. Explain.
(e) Arrange the species U, U^- and U⁺ in increasing order of size.
(f) Which of the ions Y²⁺ and Y^2- is the most stable ? Explain.
(g) Give the formula of
(i) An acidic oxide formed when one of the elements in the table is heated in air.
(ii) A basic oxide formed when one of the elements in the table is heated in air.

Date posted: April 1, 2019 . Answers (1)
57.2g of hydrated sodium carbonate (Na₂CO₃.XH₂O) were dissolved in water and the solution made to one litre. 20cm₃ of 0.5M HCl recated with 25cm₃ of... (Solved)

57.2g of hydrated sodium carbonate (Na₂CO₃.XH₂O) were dissolved in water and the solution made to one litre. 20cm₃ of 0.5M HCl recated with 25cm₃ of the hydrated sodium carbonate solution. Determine the value of X. (Na = 23, C = 12, O = 16)

Date posted: April 1, 2019 . Answers (1)
The table below shows the formulae of the chlorides of P, Q, R and S ( not the actual symbols ) (Solved)

The table below shows the formulae of the chlorides of P, Q, R and S ( not the actual symbols )

(i) State the group to which the elements belong.
P
Q
R
S
(ii) Which of the chlorides would conduct electricity when dissolved in water . Explain.

Date posted: April 1, 2019 . Answers (1)
The equilibrium reaction of phenolphthalein indicator in water may be represented as follows. (Solved)

The equilibrium reaction of phenolphthalein indicator in water may be represented as follows.

State and explain the observations made when an acid is added to the equilibrium
mixture.

Date posted: April 1, 2019 . Answers (1)
The diagram below shows the appearance of two pieces of paper placed in different parts of a non-luminous flame of a Bunsen burner and removed... (Solved)

The diagram below shows the appearance of two pieces of paper placed in different parts of a non-luminous flame of a Bunsen burner and removed quickly before they caught fire.

(a) What do the experiments show about the outer region of the flame?
(b) From the above experiment, which part of the flame is better to use for heating? Give a reason

Date posted: March 29, 2019 . Answers (1)