CEC class test 1 questions

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					                          Chemistry Enhancement Course

Questions for the Class Test to be held at 11:00 on Wednesday 15 th February
are given below. The class test will consist of two questions selected from the
five. Periodic Tables will be provided.

Question 1

(a)   Calculate the numbers of protons, neutrons and electrons in each of the
      following atoms:

      (i) 16O       (b) 18O        (ii) 27Al          (iii) 40Ca   (iv) 243Am
                                                                            (3 marks each)

(b)   Give a definition of an isotope
                                                                                  (3 marks)

(c)   Calculate the average atomic mass of sulphur from the masses and
      abundances of its isotopes given below:

         Isotope mass (amu)               Abundance
                 31.972                             95%

                 32.972                         0.8%

                 33.969                         4.2%


                                                                                  (7 marks)

Question 2

(a)   Which nuclei are formed in the following radioactive decay processes?

      (i) -decay of 226Ra         (ii) --decay of 24Na           (iii) -decay of 60Co


      (iv) +-decay (positron decay) of   27
                                               Si
                                                                            (3 marks each)

(b)   Complete the following equations using a Periodic Table to identify the
      elements X, Y, Z, and Q:

      (i) 24Na  X + -            (ii) 14N + n  14Y + 1Z         (iii) Si  27Q + +
                                                                             (3 marks each)

(c)   Define the half-life of a radioactive nucleus. If the half-life of 222Rn is 3.8 days,
      roughly what proportion of radioactive material will remain after a week?
                                                                              (4 marks)
Question 3

(a)   Calculate the number of moles of the substances specified:

      (i) 10g MgCl2        (ii) 2 kg CaPO4      (iii) 4 mg C6H4 (NHCOCH3) (OH)
                                                              (Paracetamol)

                                                                        (3 marks each)

(b)   The compound -pinene is a natural antiseptic found in the resin of the piňon
      tree. A 7.50g sample was found to contain 6.61g carbon and 0.89g hydrogen.
      Determine the mass percentages of carbon and hydrogen, and the empirical
      formula of -pinene.
                                                                        (12 marks)

(c)   The empirical formula of glucose is determined to be CH2O. If the molar mass
      of glucose is 180, determine its molecular formula.
                                                                         (4 marks)

Question 4

(a)   What is the molarity of the following solutions?

      (i) 1.345g KNO3 in 25 cm3 (ii) 10g C12H22O11 (sucrose) in 200 cm3

(b)   What mass of the following substances is required to produce solutions of the
      volume and molarity specified?

      (i) Oxalic acid (C2H2O4 (aq)), 50 cm3, 0.125M      (ii) AgBr, 100 cm3, 0.5M

(c)   A solution of barium hydroxide (Ba (OH) 2) was prepared by adding 2.577g to
      a 250 cm3 volumetric flask and adding water to the mark

      (i) What is the molarity of the solution prepared?

      (ii) What volume of the solution should be used to make a new solution
      containing 10 cm3 of 10-3 M Ba (OH) 2?




                                                            Question 5 on next page 
Question 5

(a)   Using electron in orbit diagrams, explain the bonding in the following
      molecules, and identify whether it is ionic or covalent:

      (i) NaF       (ii) F2       (iii) HCl
                                                                        (3 marks each)
(b)   Draw Lewis Structures for the following molecules:

      (i) HF        (ii) CH4      (iii) O2      (iv) N2
                                                                             (8 marks)

(c)   Give the electron configuration in orbital notation for the following atoms:

      (i) Be        (ii) N        (ii) F        (iv) Ar
                                                                             (8 marks)

				
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