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O level Chemistry Questions and Answers(6)

Question 1

(a) The diagram below shows how an organic compound, Q,is produced
from ethene.
Ethanol from ethene

(i) Name reagent x and compound P.
(ii) Draw the displayed structural formula of Q.
(iii) Give any two uses of P.
(iv) Describe any one chemical test that is used to distinguish ethene from P.

(b) The diagram below shows the structure of a protein molecule.
Protein polymer

(i) Name the smaller units (monomers) that make up the
protein molecule.
(ii) Describe how the protein molecule can be broken down
into the smaller units.

Solution 1

(a)(i) Water (steam).
Ethene and steam combine at 300 degrees Celsius, 70 atm pressure and with phosphoric acid as a catalyst to form ethanol.

(ii)Ethanoic acid

(iii) P is ethanol.
the uses of P are:

  • in alcoholic beverages
  • as a fuel
  • as a disinfectant
  • as a solvent for organic substances

(iv) Add each substance to a solution of bromine in trichloromethane, ethene will decolourise bromine solution.
this test is called "unsaturation test" because all unsaturated hydrocarbons will decolourise bromine solution.

(b)(i) amino acids

(ii) By the action of an enzyme pepsin in the stomach during digestion.

Question 2

The diagram below shows a set up of apparatus that was used to identify a blue pen that was used to write a bad message by a student. The ink that was used to write the message is marked M. Sample inks 1,2 and 3 were taken from pens suspected to have been used.

Chromatography

(a)(i) State the number of dyes in ink M.
(ii) Describe one difference and one similarity between inks in samples 1 and 3.
(iii) Identify with reasons the sample ink that could have been used to write the bad message.

(b)(i) Name one property that determines the distance travelled by a dye in chromatography.
(ii) The solvent travelled 8.0 cm and the dye in ink 3 travelled 3.0 cm. Calculate the Rf value of the dye into 3.
(iii) State the importance of Rf values.
(c) Explain why the container was covered.

Solution 2

(a)(i) 3
because the ink produced 3 different dots, representing 3 different dyes.

(ii) similarity – they have a common dye.
difference – ink sample 1 is made up of 2 dyes and ink sample 3 is made up of 1 dye.

(iii) ink sample 2 could have been used to write the message because it contains the same dye components as ink M.

(b)(i) solubility of the dyes

(ii) The retention factor, or Rf, is defined as the distance traveled by the compound divided by the distance traveled by the solvent.
Rf = 3/8
= 0.375

(iii) Rf values are used to predict where a component of an ink will be when seperating the ink by chromatography.

(c) to prevent the loss of solvent by evaporation.

Question 3

(a) Define the term ionic bonding.
(b) The table shows some physical properties of three compounds.

compound electricalconductivity melting point
naphthalenedoes not conductlow
copper (II) chloridegood conduction when in solutionhigh
ethanedoes not conductlow

(i) Explain why

  1. copper (II) chloride has a higher melting point than ethane.
  2. naphthalene does not conduct electricity.

(ii) Describe and explain what happens when

  1. solid naphthalene is added to water.
  2. an electric current is passed through a concentrated solution of copper (II) chloride.

(c) Element X has 9 protons and 10 neutrons.
(i) Draw a diagram showing the full electronic structure of X,
(ii) State two physical properties of the compound formed when X reacts with sodium

Solution 3

(a) Ionic bonding is the combination of atoms that involves the transfer of electrons from one atom to another.

(b)(i)

  1. The particles in copper (II) chloride are held together by strong electrostatic forces of attraction in a strong lattice that is difficult to break. The ethane particles are held together by weak intermolecular force that are easily broken when melting.
  2. naphthalene is a covalent substance which doesnt contain the ions or free electrons needed to conduct electricity.

(ii)

  1. Naphthalene doesn’t dissolve in water because it is a non-polar substance.
  2. The positively charged copper ions are attracted by the cathode where they gain electrons to produce copper atoms. The negatively charged chlorine ions are attracted to the anode where they lose electrons to become chlorine gas. Therefore the copper (II) chloride is broken down by the movement of electric current to form copper at the cathode and chlorine at the anode.

(c)(i)Fluorine

(ii) High melting point, soluble in water, good electrolyte.

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