chemistry Past Questions And Answers

Chemistry Past Questions And Answers

2141

(a)(i) Give three characteristics of homologous series.

(ii) Name two groups of compounds which form such a series.

(b) A saturated organic compound A containing two carbon atoms reacted with ethanoic acid in the presence of a mineral acid to form a compound B with a sweet smell. (i) Name the functional group present in A.

(ii) Draw the structure of A.

(iii) Write a chemical equation to show the formation of B.

(iv) Name the compound B.

(c)(i) Write a balanced equation for the reaction between ethyne and excess bromine.

(ii) Give IUPAC name of the product of the reaction in (c)(i)

(iii) State two conditions under which cracking takes place

(d)(i) Outline the preparation of ethanol from starch.

(ii) Give two properties of starch.

(iii) Give a reason why starch does not reduce Fehlings solution

(iv) Describe briefly a chemical test to confirm the presence of starch.

Explanation

(a)(i) Characteristics of homologous series: –All members can be represented by a general molecular formular. –Each member of the series differs from the next by a constant/Fixed number of atom-CH\(_2\)/Successive member differs by CH–All members of the group have similar chemical proterties. –All members have same functional group. –All members of the; roup are prepared using similar/same general methods. All members of the series show a gradual change in physical properties (e.g. density, solubility, etc).

(ii) Groups of compounds which form such a series: –Alkanes –Alkenes –Alkynes –Alkanols –Alkanoic acid –Alkanoates.

(b) A saturated organic compound A containing two carbon atoms reacted with ethanoic acid in the presence of a mineral acid to form a compound B with a sweet smell: The functional group present in A. Hydroxy/Hydroxyl.

(ii) Structure of A.

(iii) Chemical equation to show the formation of B:

CH\(_3\)COOH + CH\(_3\)CH\(_2\)OH \(\rightleftharpoons\) CH\(_3\)COOH\(_2\)CH\(_3\) + H\(_2\)O.

(iv) Name of compound B: Ethyl ethanoate

(c)(i) Balance equation for reaction between Ethyne and Excess bromine:

C\(_2\)H\(_2\) + 2Br\(_2\) --> C\(_2\)H\(_2\) Br\(_4\)

H— C \(\equiv\) C— H H 2Br\(_2\) —> H-CBr\(_2\)-CBr\(_2\)-H

(ii) IUPAC name of the product of the reaction in (c)(i) 1,1, 2, 2–tetrabromoethane.

(iii) Conditions under which cracking takes place: –High pressure –High temperature –Presence of a suitable catalyst.

(d)(i) Preparation of ethanol from starch: Treat starch with malt, diatase, convet starch to maltose.

2(C\(_6\) H\(_{(10)}\)O\(_5\) )n + nH\(_2\) O --> nC\(_{(12)}\) H\(_{(22)}\)O\(_{(11)}\). Add yeast. Ezyme maltase convert maltose to glucose.

C\(_{(12)}\)H\(_{(22)}\) + H\(_2\)O —> 2C\(_6\)H\(_{(12)}\)O\(_6\). Ezyme zymase convert glucose to maltase to ethanol and CO\(_2\)

C\(_6\)H\(_{(12)}\)O\(_6\) —> 2C\(_2\)H\(_5\)OH + 2CO\(_2\).

(ii) Properties of starch: –Can be hydrolysed. –Has no taste. –When suspension of starch is warmed, it forms colliodal solution. –It is insoluble in water. –It has no smell.

(iii) Reason why starch does not reduce Fehlings solution: It does not contain any free carbonyl group/No alkanol group/No hydrogen attached to the carbonyl group.

(iv) Chemical test to confirm the presence of starch: Add a few drops of iodine to a boiled starch. A dark-blue colouration appears.

View Discussion (0)WAEC 2015 THEORY

2142

Which of the following is a disaccharide?

A. fructose
B. starch
C. cellulose
D. sucrose

View Discussion (0)WAEC 1996 OBJ

2143

The entropy and enthalpy of a system are a measure of

A. degree of disorderlinesss and heat content respectively
B. heat content and degree of disorderliness respectively
C. heat content of a system only
D. degree of disorderliness only

View Discussion (0)JAMB 1999

2144

the elements that belong to the third period of the periodic table are

A) Li, Be, Al and P
B) Na, P, O and Cl
C) B, C, N and O
D) Nz, Mg, S and Ar

View Discussion (0)JAMB 2015

2145

What happens to the conductivity of an electrolyte as its concentration reduces?

A) increases
B) decreases
C) is unaffected
D) becomes resistivity

View Discussion (0)POST UTME OAU

2146

Which of the following electron configurations represents that of an atom in its ground state?

A.1s₂2s₁2p₁
B. 1s₂2s₂2p₆3s₁3p₁
1s₂2s₂2p₃
D. 1s₂2s₂2p₆3s₀

View Discussion (0)WAEC 2012 OBJ

2147

A gas that is not associated with global warming is

A. CO2
B. SO3
C. CH4
D. H2

View Discussion (0)JAMB 2000

2148

The scum formed when soap is mixed with hard water could be

A. calcium trioxocarbonate (IV)
B. propane- 1, 2, 3 - triol
C. calcium hydrogentrioxocarbonate (IV)
D. magnesium tetraoxosulphate (IV)

View Discussion (0)WAEC 1992 OBJ

2149

Trioxosulphate (lV) acid is not stored for a long period because it

A. is a weak dibasic acid
B. has bleaching properties
C. is unstable and eaily decomposed
D. smells strongly of sulphur (lV) oxide

View Discussion (0)WAEC 1993 OBJ

2150

Consider the following reaction equation H₃O⁺(aq) + OH(aq) â†’ 2H₂O(1) The reaction represents

A. Esterification
B. Hydrolysis
C. Neutralization
D. Redox

View Discussion (0)WAEC 2016 OBJ