chemistry Past Questions And Answers

Chemistry Past Questions And Answers

731

Which of the following is the correct order of decreasing activity of the metals Fe, Ca, Al and Na?

A. Fe> Ca> Al> Na
B. Na> Ca> Al> Fe
C. Al> Fe> Na> Ca
D. Ca> Na> Fe>, Al

View Discussion (0)JAMB 1994

732

When CuSO₄ solution is treated with ammonia solution drop by drop till it is added in excess, a precipitate is first formed which then dissolves in excess to give a deep blue solution. The deep blue solution is

A) Cu(OH)₂
B) (Cu(NH₃)₄)(OH)₂
C) CuSO₄
D)(Cu(NH₃)₂)SO₄

View Discussion (0)POST UTME OAU

733

A metal that is widely used in the manufacture of paints and overhead electric cables is

A. aluminium
B. copper
C. iron
D. lead

View Discussion (0)WAEC 2012 OBJ

734

CuSO₄ 5H₂O can be obtained from an aqueous solution of copper (ll) tetraoxosulphate (VI) by

A. evaporation to dryness
B. using chromatography
C. precipitation
D. crystallization

View Discussion (0)WAEC 2001 OBJ

735

(a)i. With the aid of an equation, explain briefly why aluminum metal is not affected by air.

(ii) In the extraction of aluminum from bauxite, state the:

- substance used for purifying the ore;

- composition of the mixture electrolyzed.

(b) ZnO is an amphoteric oxide. Write equations to illustrate this statement.

(c)i) List three uses of sodium trioxocarbonate(IV).

(ii) Explain briefly why a solution of trioxonitrate(V) acid turns yellowish on storage for some time.

(ii) Describe briefly how trioxonitrate(V) ions could be tested for in the laboratory.

(d) Write balanced chemical equations for the preparation of hydrogen chloride.

(i) using concentrated H\(_{2}\)SO\(_{4}\):

(ii) by direct combination of its constituent elements.

(iii) State one use of hydrogen chloride.

Explanation

(a) Aluminum first reacts With oxygen in the air to form a film of oxide/oxide layer on the Surface.

Al\(_{(s)}\) + 3O2\(_{(g)}\) \(\implies\) 2AlO3\({(s)}\). The film of oxide formed is not porous and insoluble in water (in the air) and hence protects the metal underneath from further attack.ORThe film of oxide coats the metal and prevents it from further attack.

(ii) The composition of the ore:- Cryolite / Na\(_{3}\)AlF\(_{6}\) -Aluminà / Al\(_{2}\)O\(_{3}\)

(b) ZnO is an amphoteric oxide. Write an equation to illustrate this statement.

ZnO\(_{(s)}\) + 2HCl\(_{(aq)}\) \(\implies\) ZnCl\(_{2(aq)}\) + H\(_{2}\)O\(_{(l)}\); ZnO\(_{(s)}\) + 2NaOH\(_{(aq)}\) + Na\(_{2}\)ZnO\(_{2(aq)}\) + H\(_{2}\)O\(_{l}\)

(c)i. List three uses of Sodium Trioxocarbonate(IV):

- Glass production.

- Water treatment/ softening hard water

- Preparation of baking powder.

- Removal of sulfur (IV) Oxide in power stations.

- As a standard alkali in acid-base titration.

- As an analytical reagent.

- Production of rayon polymer.

- As a household cleaning agent used in laundry.

- As food additive.

- Used in textile industry.

- In petroleum refining.

- Manufacturing of other sodium compounds.

- production of soaps and detergents

- paper production

- production/ preparation of NaHCO\(_{3}\)

(ii) Explain briefly why a solution of trioxonitrate( V) acid turns yellowish on storage for sometime:- The yellowish color is caused by dissolved nitrogen(IV) oxide which results from the slow decomposition of the acid.

(iii) Describe briefly how trioxonitrate (V) ions could be tested for in the laboratory:-

To the solution, add freshly prepared iron (ll) tetraoXoSulphate (Vl) solution and followed by Conc H\(_{2}\)SO\(_{4}\), a brown ring is observed or warm the solid with ( copper turnings and ) Conc. H\(_{2}\)SO\(_{4}\) in a test tube. Brown fumes are observed.

(d)i. H\(_{2}\)SO\(_{4(aq)}\) + 2NaCl\({s}\) \(\implies\) Na\(_{2}\)SO\(_{4(aq)}\) + 2HCl\(_{g}\).OR

H\(_{2}\)SO\(_{4}\) + 2KCl \(\implies\) K\(_{2}\)SO\(_{4(aq)}\) + 2HCI (ll) H\(_{2(g)}\) + Cl\(_{2(g)}\) \(\implies\) 2HCl\(_{(g)}\)

(ii) State one use of hydrogen chloride:

- Manufacturing of drug.

- Cleaning

- Pickling

- Electroplating metals

- Tanning leather

- Refining

-Production of CH\(_{3}\)Cl/PVC/plastics.

View Discussion (0)WAEC 2021 THEORY

736

.(a)(i) Name two gases that can be used to perform the fountain experiment. (ii) What is the aim of he fountain experiment? (iii) Describe briefly the fountain experiment.

(b)(i) Name two chemical industries. (ii) State three effects of a chemical industry on the community in which it is sited.

(c)(i) Name three products of the destructive distillation of coal. (ii) Give one use each of any two of the products named in 5(c)(1).

(d)(i) Name two substances responsible for hardness in water. (ii) State two methods for the removal of hardness in water. (iii) State two advantages of hard water.

Explanation

(a)(i) ammonia: - hydrogen chloride: - sulphur (iv) Oxide (ii) To demonstrate high/extreme solubility of gases HCl / NH\(_3\) / SO\(_2\) in water.

(iii) A flask. fitted with a glass jet is filled with dry ammonia or any soluble gas. Inject water through the inlet into the flask. this dissolves the ammonia soluble gas and causes a fountain through the jet.

-a round bottomed flask is filled with gas and fitted with two delivery tubes and closed by use of clips A and B; - Invert the flask into a beaker of water: - open a clip A to allow small volume of water to enter the flask. then close it - the gas dissolves in water causing sudden reduction of pressure in the flask: open clip B: reduced gas pressure causes water from the beaker through delivery tube into the flask forming fountain.

(b) (i)-Textiles: Tannery: - Brewery Bottling company: Soaps and detergents: - food industry: pharmaceuticals: - cosmetics: petrochemical Industry: - petroleum industry; dyes: paints; agrochemicals: fertilizers; - pesticides; plastic

(ii) Improvement in the standard of living of people: - employment opportunities: - development in the community: pollution (air. land. water. etc.)

(ii) Coke (solid) fuel production of water gas extraction of metals. Coal tar; synthesis of chemicals.perfumes dyes/paints / drugs / plastics explosives / tanning of roads. Coal gas; as fuel (in homes and industries). Ammoniacal liquor;- production of fertilizer

(d)i) calcium hydrogen trioxocarbonate (IV): -calcium tetraoxosulphate (Vi): - magnesium tetraoxosulphate (Vi)

- magnesium hydrogen trioxocarbonate (IV); - iron (III) chloride.

(ii)heating the water to boiling / distillation: addition of calculated amount of calcium hydroxide: - addition of washing soda crystals: - ion exchange resin permutit

(iii)- calcium ions in the water are good for method children's teeth and bones: it helps to reduce heart diseases; does not dissolve lead pipes: - tastes better than soft water:- provides calcium salts used in manufacturing of food in plants: production of exoskeleton of animals / shells Tannery:

View Discussion (0)WAEC 2020 THEORY

737

Which of these require crystallization most?

A) Drug making
B) Cement making
C) Paint making
D) Perfume making

View Discussion (0)JAMB 2015

738

A given volume of methane diffuses in 20s. How long will it take the same volume of sulphur (IV) oxide to diffuse under the same conditions? [C = 12, H = 1, S = 32, O = 16

A. 5s
B. 20s
C. 40s
D. 60s

View Discussion (0)JAMB 2004

739

An organic compound that does not undergo a reaction with both hydrogen cyanide and hydroxylamine can be

A. alkene
B. alkanal
C. alkanone
D. alkanoic acid

View Discussion (0)JAMB 1999

740

What would be observed when aqueous ammonia is added in drops and then in excess to a solution of copper(II) ions?

A. blue precipitate is formed which is soluble in excess ammonia
B. brick red precipitate is produced which is insoluble in excess ammonia
C. which precipitate is formed which is excess in ammonia
D. green precipitate is formed which is insoluble in excess ammonia

View Discussion (0)WAEC 2021 OBJ