chemistry Past Questions And Answers

Chemistry Past Questions And Answers

881

The uncovered raw food that is sold along major roads is likely to contain some amounts of

A. Pb
B. Cu
C. Ag
D. Na

View Discussion (0)JAMB 2008

882

An aqueous solution of a metal salt, M. gives a white precipitate with NaOH which dissolves in excess NaOH. With aqueous ammonia, the solution of M also gives a white precipitate which dissolves in excess ammonia Therefore the cation in M is

A) Zn
B) Ca
C) Al
D) Po

View Discussion (0)JAMB 2018

883

Which of the following statements about enthalpy of neutralization is correct? It

A. is constant for a strong acid and a strong base
B. cannot be determined using calorimeter
C. has a positive value
D. is higher for strong acid and a weak base

View Discussion (0)WAEC 2011 OBJ

884

The solubility, in moles per dm3 of 20.2 g of potassium trioxonitrate (V) dissolve in 100 g of the resulting mixture is? (K = 39, O = 16, N =14).

A. 0.10
B. 0.20
C. 1.00
D. 2.00

View Discussion (0)JAMB 1994

885

Which of the following formula is that of a dicarboxylic acid?

A. (CH₃CH₂)₂CHCOOH
B. CH₂(OH)₂
C. CH₃CH(OH)COOH
D. CH₂(COOH)₂

View Discussion (0)WAEC 1991 OBJ

886

(a)(i) Draw the structure of the sixth member of the alkenes.

(ii) Calculate the relative molecular mass of the sixth member of the alkene.

(iii) State one difference between cracking and reforming in the petroleum industry. [H = 1, C = 12]

(b)(i) Define the term enthalpy of neutralization.

(ii) Describe briefly how the enthalpy of neutralization of the reaction of dilute hydrochloric acid and aqueous potassium hydroxide could be determined.

(i) State which of the electrodes will be the: 1. anode; II. cathode.

(ii) Give the reason for your answer in 3(c)(i).

(iii) State the type of reaction occurring at each electrode.

(iv) Write a balanced equation for the overall cell reaction.

(d)(i) Name the compound formed when iron is exposed to moist air for a long time.

(ii) Write a balanced chemical equation for the reaction in 3(d)(i).

(iii) Name one ore of iron.

Explanation

(a)(i) Structure of the sixth member of the alkenes: C\(_n\)H\(_{2n}\); n = 7, C\(_7\)H\(_{2 \times 7}\) = C\(_7\)H\(_14\)

(Double can be positioned within any of the carbon chain)

(ii) Relative molecular mass of the sixth member of alkene

(C\(_7\)H\(_14\) \(\begin {bmatrix} C & = 12 \\ H & = 1 \end{bmatrix}\)

(C\(_7\)H\(_14\) = (12 x 7) + (1 x 14)

= (12 x 7) + (1 x 14)

= 84 + 14

= 98 (no units)

(iii) One differences between cracking and reforming in the petroleum indutry:

CRACKING	REFORMING
Involves breaking large molecules of petroleumfractions into smaller molecules	Involves re-arrangement of atoms in molecules of petroleum fractio'n to obtain branched and cyclic hydrocarbons
Usect to improve the quantity of petrol.	Usect to improve the quality of petrol.
Can be achieved thermally or catalytically	Occurs in presence of a catalyst

(b)(i) Enthalpy of neuttalization is the beat evolved when an acid reacts with a base to form one mole of water or when one mole of OH\(^{+}\) from an acid reacts with one mole of OH\(^{-}\) from a base to form one mole of water.

(ii) Determination of enthalpy of neutralization of the reaction of dilute hydrochloric acid and aqueous potassium hydroxide

HCI\(_{(aq)}\)+ KOH\(_{(aq)}\) -> KC1 + H\(_{2}\)O

Equimolar solutions of hydrochloric acid and potassium hydroxide are prepared sepa'rately. A known volume of the acid is placed in a calorimeter/polystyrene beaker and the temperature recorded.

The same volume of the potassium hydroxide solution at the same temperature is poured into the calorimeter and the mixture stirred gently. The maximum temperature of the mixture is recorded.

Heat lost in the reaction = heat gained by the solution formed

OR \(\bigtriangleup\) H neutralization = mass of solution x specific heat capacity of water x change in temperature.

(ii) Cathode : silver electrode reasons in 3(c)(i)

(iii) Silver has a more positive Standard electrode potential than copper. Copper is more electropositive than silver or copper is higher in the electrochemical series

(iv) Type of reaction occuring at each electrode.

Anode : oxidation (occurs at the copper electrode).

Cathode : reduction (occurs at the siliver electrode).

(v) Balanced chemical equation for the overall cell reaction.

Cu\(_s\) + 2Ag\(^+\) \(\to\) CU\(^{2+}_{(aq)}\) + 2Ag\(_(s)\)

(d) Compound formed when iron is exposed to moist air for a long time; (i) Hydrated Iron(III) oxide. (ii) Balanced chemical equation for the reaction in 3(d)(i).

4Fe\(_s\) + 3O\(_{2(g)}\) + 2 x H\(_2\)O\(_l\) \(\to\) 2Fe\(_2\)O\(_3\).XH\(_2\)O

where X is 1

4Fe\(_s\) + 3O\(_{2(g)}\) + 2H\(_2\)O\(_l\) \(\to\) 2Fe\(_2\)O\(_3\).H\(_2\)O

(iii) One ore of iron: haematite, magnetite, siderite/spathic iron ore, limonite, iron pyrites

View Discussion (0)WAEC 2018 THEORY

887

How many protons does²⁰₄₀Ca contain?

A. 20
A. 20
C. 40
D. 60

View Discussion (0)WAEC 2009 OBJ

888

If the relative molecular mass of an element is not a whole number, it can be deduced that the element is

A. naturally radioactive
B. abundant in nature
C. a transition metal
D. an isotopic mixture

View Discussion (0)WAEC 2002 OBJ

889

When palm wine is left exposed to air for a few days, it goes sour. The bacteria in the air oxidises ________ in palm wine to _________

A) ethanol, ethanoic acid
B) ethanoic acid, ethanol
C) ester, ethanoic acid
D) ether, ethanol

View Discussion (0)POST UTME UI

890

A major factor coonsidered in selecting a suitable method for preparing a simple salt is its

A. crystalline form
B. melting point
C. reactivity with dilute acids
D. solubility in water

View Discussion (0)WAEC 2001 OBJ