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Comparative Study Of S And P Block Elements Question Paper
Comparative Study Of S And P Block Elements
Course:Bachelor Of Science In Biochemistry
Institution: Egerton University question papers
Exam Year:2005
UNIVERSITY EXAMINATIONS
FIRST SEMESTER 2004/2005
SECOND YEAR EXAMINATION FOR THE DEGREE OF BACHELOR OF SCIENCE AND BACHELOR OF EDUCATION(SCIENCE)
CHEM 201-COMPARATIVE STUDY OF S AND P BLOCK ELEMENTS
TIME:2 HRS
INSTRUCTIONS:
ANSWER ALL QUESTIONS.
1.(a) (i) Lithium ion in solution should conduct electricity better than other ions of this group but this is not the case.Comment on this statement.(3 marks)
(ii) What is electronegativity and how does it vary across period 2?.(2 marks)
(iii) State fajan's rules.(2 marks)
(iv) Give the trend,with explanation,of the first ionization energies of these elements.H,Li and Na.(2 marks)
(b) (i) Explain the term "diagonal relationship".(2 marks)
(ii) Show using equations how the diagonal relationship is observed in the oxides of Be and Al in the formation of their salts with acids and water.(4 marks)
(iii) Comment on the solubility of fluorides and carbonates down the group compared to the solubility of other s-block compounds.(2 marks)
2.(a) Comment on the following statements
(i) The first ionization energy of lithium is lower than that of boron but higher than that of sodium.(3 marks)
(ii) Aqueous Na2 CO3 is alkaline while aqueous NH4CL is acidic.
Give reasons for your explanation.(3 marks)
(b) Element X,on complete removal of electrons from its energy levels shows the trend given below.
I.E Value (Kjmol-1)
1st 200
2nd 600
3rd 7,000
4th 10,000
5th 13,000
6th 16,500
7th 20,500
8th 30,700
9th 45,000
10th 60,000
11th 455,000
12th 700,000
Answer the following questions:
(i) Why is the 3rd ionization energy much higher than the 2nd?(1 mark)
(ii) Explain the general trend in ionization energies from 3rd to 10th.(2 marks)
(iii) Why are the values of 11th and 12th I.E higher than the rest?(2 marks)
(c) (i) Describe briefly the behavior of alkali metals in ammonia.(2 marks)
(ii) Explain why water solutions of most beryllium salts are acidic.(2 marks)
3.(a) Explain briefly the following observations:
(i) The atomic radius of Aluminium is 1.43 while that of Gallium is 1.41.(2 marks)
(ii) The usual co-ordination number of Be2+ is four whereas for Mg2+ is six.(2 marks)
(iii) Most beryllium and lithium salts are soluble in organic solvents.(2 marks)
(iv) Aluminium bromide is a poor conductor of electricity even in fused state,but is good conductor in aqueous solution.(2 marks)
(b) (i) Show by equations the reactions that take place when Aluminium powder is warmed with slight excess of sodium hydroxide solution,the mixture cooled,filtered and excess dilute sulphuric acid added to the filtrate.(6 marks)
(ii) HCL (g) can be prepared from NaCL(s) and conc.H2SO4,but HBr(g) cannot be prepared by the reaction of NaBr(s) and conc.H2SO4.Explain.(2 marks)
4.(a) (i) Define an orgo-metallic compound and show whether sodium acetate is an organo-metallic compound or not.(3 marks)
(ii) Give equations for the preparation of the following compounds.
CH3-Mg-Br; Al (CH3)3.(4 marks)
(iii) Why are boron compounds used as fuels for rockets and missiles?(1 mark)
(iv) Boron hydride fuels must be kept free from water.Explain using equation this phenomenone.(2 marks)
(b) Draw the structures of the following
(i) Pyro phosphorus acid (2 marks)
(ii) Red phosphorus(2 marks)
(iii) Diborane(1 mark)
(c) Briefly explain how Al can be obtained from Al2O3.Illustrate your answer with suitable chemical equations including the reactions at the electrodes.(5 marks)
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