WAEC SSCE - Chemistry - 1996

Which of the following is a disaccharide?

Détails de la réponse

Sucrose is a disaccharide. A disaccharide is a type of carbohydrate made up of two monosaccharides linked together by a glycosidic bond. Sucrose, also known as table sugar, is composed of glucose and fructose joined together by a glycosidic bond. The other options listed are not disaccharides; fructose is a monosaccharide, starch, cellulose, and glycogen are polysaccharides.

When an atom gains an electron, it becomes properties

Détails de la réponse

When an atom gains an electron, it becomes negatively charged because it now has more electrons than protons. This negatively charged atom is called an anion. The extra electron is held by the nucleus through the electromagnetic force and affects the chemical properties of the atom. The anion has a greater affinity for positively charged ions or cations and can undergo chemical reactions, forming compounds with other atoms or ions. Therefore, the correct option is "negatively charged."

Amphoteric oxides are oxides which

Détails de la réponse

The rate of production of hydrogen gas from the reaction between zinc granules and hydrochloric acid can be increased by

Détails de la réponse

The rate of production of hydrogen gas from the reaction between zinc granules and hydrochloric acid can be increased by using zinc powder instead of zinc granules. The rate of reaction between zinc and hydrochloric acid is determined by the surface area of the zinc that is exposed to the acid. Zinc powder has a higher surface area than zinc granules, which increases the rate of reaction between the zinc and the acid. Cooling the reaction mixture would slow down the reaction rate because the reaction is exothermic and releasing energy as heat, and lowering the temperature would reduce the kinetic energy of the reacting particles. Using a zinc rod instead of zinc granules would not increase the surface area, but would decrease it, slowing down the reaction rate. Carrying out the reaction at a higher pressure or in a closed vessel would not increase the surface area of the zinc and would not affect the rate of reaction.

The cleansing action of soap in hard water is not satisfactory because soap

Détails de la réponse

Soap is made up of sodium or potassium salts of long-chain fatty acids. The cleaning action of soap is due to its ability to dissolve in water and attach to oil and dirt particles, enabling them to be washed away. However, in hard water, which contains dissolved calcium and magnesium ions, soap forms insoluble salts with these ions. These salts, called scum, are insoluble in water and stick to surfaces, reducing the effectiveness of the soap. As a result, the cleansing action of soap in hard water is not satisfactory.

What amount of hydrogen will be required for complete hydrogenation of one mole of pent-3-yne?

Détails de la réponse

What amount of copper is deposited when 13.0g of zinc reacts with excess copper (ll) tetraoxosulphate (IV) solution according to the following equation? Zn _(s) + CuSO_4(aq) → ZnSO_4(aq) + Cu _(s) [Cu =63,5, Zn = 65]

Détails de la réponse

Ammonia gas is suitable for performing the 'Fountain' experiment because the gas is

Détails de la réponse

Ammonia gas is suitable for performing the 'Fountain' experiment because it is very soluble in water. In the experiment, ammonia gas is passed through water, where it dissolves to form an alkaline solution. The gas bubbles produced rise to the top of the solution, and as more gas bubbles are produced, the solution becomes saturated with the gas. Eventually, the pressure of the gas forces the solution to rise up and out of the container, creating a fountain-like effect. Ammonia gas is preferred for this experiment because of its high solubility in water, which allows for a sufficient amount of gas to dissolve in the solution and produce the necessary pressure for the fountain effect.

Use this following information to answer this question. Compound X was boiled with concentrated hydrochloric acid for a long time. One of the products was found to be a sugar. What type of reaction was involved between compound X and concentrated hydrochloric acid?

Détails de la réponse

The reaction between compound X and concentrated hydrochloric acid involves hydrolysis. Hydrolysis is a type of chemical reaction in which a compound is broken down into two or more simpler compounds through the addition of water. In this case, the concentrated hydrochloric acid acts as a catalyst, promoting the breakdown of compound X into simpler compounds, one of which is a sugar. Therefore, the reaction between compound X and concentrated hydrochloric acid is a hydrolysis reaction.

Which of the following metals will be the most suitable for use where lightness and resistance to corrosion are of importance?

Détails de la réponse

The most suitable metal for use where lightness and resistance to corrosion are of importance is Aluminium. This is because Aluminium is a lightweight metal that has a low density and is resistant to corrosion. Aluminium forms a protective layer of oxide on its surface that prevents further oxidation, making it highly resistant to corrosion. In addition, Aluminium is a good conductor of heat and electricity and can be easily shaped into different forms, making it useful for a wide range of applications, such as in the aerospace and automotive industries, where weight reduction and corrosion resistance are critical factors. Therefore, the correct answer is Aluminium.

The products formed when sodium hydrogen trioxocarbonate (IV) is heated strongly are

Détails de la réponse

What does X represent in the following equation? H _2(g) + 1/2O_2(g) → H₂O _(l); ∆H = xKJ.

Détails de la réponse

In the given chemical equation, X represents the Enthalpy of Formation. Enthalpy of formation (∆H_f) is defined as the amount of heat energy released or absorbed when one mole of a compound is formed from its constituent elements in their standard states under standard conditions. In the given equation, the reactants are hydrogen gas and oxygen gas in their standard states, and the product is liquid water. The value of ∆H represents the amount of heat energy that is either released or absorbed when one mole of water is formed from its constituent elements. If the value of ∆H is negative, it means that the reaction is exothermic, i.e., heat energy is released during the reaction, while a positive value of ∆H represents an endothermic reaction, i.e., heat energy is absorbed during the reaction.

Which of the following exhibits resonance?

Détails de la réponse

Benzene exhibits resonance. Resonance is a phenomenon in which electrons move between different possible locations within a molecule, resulting in the stabilization of the molecule. In benzene, the carbon atoms are arranged in a ring with alternating double bonds and single bonds. The electrons in the double bonds are delocalized and move freely around the ring, resulting in a more stable molecule. This is an example of resonance. The other molecules listed do not have a similar arrangement and therefore do not exhibit resonance.

What is the role of MnO₂ in the reaction represented by the following equation?MnO₂ + 4HCI₂ + CI₂ + 2H₂O

Détails de la réponse

Nitrogen is prepared on a large scale by the

Détails de la réponse

Nitrogen is prepared on a large scale by the fractional distillation of liquefied air. Air is composed of about 78% nitrogen and 21% oxygen, along with other gases. To obtain nitrogen, the air is liquefied by compressing and cooling it to a very low temperature. This liquefied air is then separated into its components by fractional distillation, a process in which the different gases are separated based on their boiling points. Since nitrogen has a lower boiling point than oxygen, it boils off first and can be collected. This process is used to obtain large amounts of nitrogen for industrial and commercial purposes.

Use this following information to answer this question. Compound X was boiled with concentrated hydrochloric acid for a long time. One of the products was found to be a sugar. Compound X was probably

Détails de la réponse

The fact that a sugar was produced by boiling Compound X with concentrated hydrochloric acid suggests that Compound X was likely a carbohydrate, specifically a type of polysaccharide such as cellulose. When polysaccharides undergo hydrolysis (a reaction with water), they are broken down into their constituent monosaccharides (simple sugars) by the addition of water molecules. Therefore, the production of a sugar as a product of the reaction between Compound X and hydrochloric acid suggests that the reaction involved hydrolysis of the polysaccharide. The other compounds listed (rubber, polyethylene, nylon, and ethanol) are not polysaccharides and would not be expected to produce a sugar upon hydrolysis.

''Equal volumes of all gases at the same temperature and pressure contain the same number of molecules'' is an expression of

Détails de la réponse

The statement ''Equal volumes of all gases at the same temperature and pressure contain the same number of molecules'' is an expression of Avogadro's Law. This law is named after the Italian scientist Amedeo Avogadro, who discovered that the volume of a gas is directly proportional to the number of molecules or atoms present, provided that the temperature and pressure remain constant. This law can be used to determine the molar volume of gases and is important in many fields of science, such as chemistry and physics. In simple terms, this law states that two gases at the same temperature and pressure will have the same number of molecules in a given volume, regardless of their chemical identity or atomic/molecular weight.

When acidified KMnO₄ solution is decolorised by ethene, the gas acts as

Détails de la réponse

When acidified KMnO₄ solution is decolorised by ethene, it means that ethene is oxidised to a colorless compound and KMnO₄ is reduced. Therefore, ethene is acting as a reducing agent. So, the correct option is (c) a reducing agent.

In which of the following compounds is the oxidation number of nitrogen equal to + 3?

Détails de la réponse

The oxidation number of an element is the hypothetical charge it would have if all its bonds were purely ionic. In other words, it is a measure of the degree of oxidation of an atom in a molecule. To determine the oxidation number of nitrogen in each compound, we need to know the electronegativity of the other elements involved in the bond. In NO₂, the electronegativity of oxygen is higher than nitrogen, so nitrogen is assigned an oxidation number of +4. In N₂O, the oxidation number of nitrogen is +1. In NO, nitrogen is assigned an oxidation number of +2. In HNO₂, nitrogen is assigned an oxidation number of +3. In HNO₃, nitrogen is assigned an oxidation number of +5. Therefore, the only compound in which the oxidation number of nitrogen is equal to +3 is HNO₂.

What volume of carbon (lV) oxide is produced at s.t.p. when 2.5g of CaCO₃ reacts with excess acid according to the following equation? CaCO₃ + 2HCI → CaCI2 +H₂O + CO₂ [CaCO₃ = 100; molar volume of a gas at s.t.p = 22.4dm³]

Détails de la réponse

The balanced equation for the reaction between CaCO₃ and 2HCI is: CaCO₃ + 2HCI → CaCI₂ + H₂O + CO₂ The molar mass of CaCO₃ is 100 g/mol, which means that 100 g of CaCO₃ will produce 1 mole of CO₂. Therefore, 2.5 g of CaCO₃ will produce: 1 mole CO₂ = 22.4 dm³ at s.t.p. x moles CO₂ = (2.5 g / 100 g/mol) = 0.025 moles x = 0.56 dm³ (rounded to two decimal places) Therefore, the volume of CO₂ produced at s.t.p is 0.56 dm³. Hence, the answer is (d) 0.56 dm³.

Which of the following statements is not correct about electrolysis?

Détails de la réponse

The statement that is not correct about electrolysis is "Reduction occurs at the anode". During electrolysis, reduction occurs at the cathode and oxidation occurs at the anode. At the anode, positively charged ions (cations) lose electrons to become neutral atoms or molecules. At the cathode, negatively charged ions (anions) gain electrons to become neutral atoms or molecules. Anions migrate to the anode, while positive ions migrate to the cathode. The concentration of the electrolyte affects the rate of the reaction and the discharge of ions. Electrolytes conduct electric current because they contain ions that are free to move and carry charge.

The existance of two or more forms of the same element in the same physical state is known as

Détails de la réponse

The existence of two or more forms of the same element in the same physical state is known as allotropy. Allotropy is the property of some elements to exist in two or more different forms, called allotropes. These allotropes have different physical and chemical properties due to the different arrangements of atoms in their crystal lattice structures. For example, carbon has three common allotropes: diamond, graphite, and fullerene. Each of these allotropes has different physical and chemical properties despite being made up of the same element.

The following are properties of transition metals except

Détails de la réponse

The incorrect statement about transition metals is "low melting points". Transition metals are characterized by a high melting and boiling point due to their strong metallic bonding, which involves the delocalization of electrons over a large number of atoms. Other properties of transition metals include variable oxidation states, tendency to form complex ions, formation of coloured ions, and ability to act as catalysts.

When excess carbon (lV) oxide is passed into lime water, the turbidity produced initially disappears due to the formation of

Détails de la réponse

What is the likely formula of compound formed between element M in group two and element X in group seven?

Détails de la réponse

When elements in group two (alkaline earth metals) react with elements in group seven (halogens), they form ionic compounds with a general formula of MX₂. Therefore, the likely formula of the compound formed between element M in group two and element X in group seven is MX₂.

The alkali metals exhibit similar chemical properties because

Détails de la réponse

The alkali metals are a group of elements in the periodic table that include lithium, sodium, potassium, rubidium, cesium, and francium. They exhibit similar chemical properties because they all have one valence electron in their outermost shell, which they readily give up to form positive ions. This makes them highly reactive and they are easily oxidized in air or water. The similarity in their electronic configuration results in similar chemical behavior, such as the ability to form ionic compounds with non-metals and the tendency to react vigorously with water to produce hydrogen gas and an alkali metal hydroxide.

The following acids are monobasic except

Détails de la réponse

The component of air that can be removed by alkaline pyrogallol solution is

Détails de la réponse

Alkaline pyrogallol solution is commonly used to remove oxygen from a gas mixture. This is because pyrogallol can easily react with oxygen in the air to form a brown precipitate. Therefore, the component of air that can be removed by alkaline pyrogallol solution is oxygen.

A solution of pH 7 is

Détails de la réponse

A solution of pH 7 is neutral. The pH scale ranges from 0 to 14, with pH 7 being the midpoint of the scale. A pH of 7 indicates a balance of hydrogen ions (H+) and hydroxide ions (OH-) in the solution, with equal concentrations of both ions. In other words, a neutral solution is neither acidic nor basic.

On exposing palm wine to air for some days, it becomes sour owing to the conversion of

Détails de la réponse

Palm wine is a fermented beverage that is produced from the sap of certain palm trees. The fermentation process is mainly carried out by yeast, which converts glucose to ethanol. When palm wine is exposed to air, the ethanol undergoes oxidation, which results in the formation of ethanoic acid. This is what causes the sour taste of the palm wine. Therefore, the correct answer is "ethanol to ethanoic acid."

An arrangement of two different metals in aqueous solutions of their salts to produce an electronic current is known as

Détails de la réponse

An arrangement of two different metals in aqueous solutions of their salts to produce an electronic current is known as an electrochemical cell. This is because the cell involves a chemical reaction that converts chemical energy into electrical energy. One of the metals acts as a negative electrode and the other as a positive electrode, and the movement of electrons between them through the salt bridge or porous membrane generates an electric current. This process is used in batteries and other electronic devices to produce electrical energy.

Which of the following is not correct about a catalyst? It

Détails de la réponse

The statement that is not correct about a catalyst is: "can start a chemical reaction which will normally not take place." A catalyst cannot start a chemical reaction that will normally not take place because a catalyst only speeds up the rate of an existing reaction. It works by lowering the activation energy required for a reaction to occur, thus making it easier for the reaction to take place. Once the reaction is completed, the catalyst remains unchanged and can be used again. Therefore, options a, b, d, and e are all correct statements about a catalyst, while the statement in option c is not correct.

If the third member of a homologous series is C₃H₈, the fifth member will be

Détails de la réponse

A homologous series is a series of organic compounds having the same functional group and similar chemical properties in which the successive members differ by a CH₂ unit. So, the general formula of the homologous series would be C_nH_2n+2. If the third member of a homologous series is C₃H₈, it means that the general formula of the series is C_nH_2n+2, where n = 3. C₃H₈ belongs to the alkane series, so the fifth member of the series would also belong to the alkane series and have the general formula C_nH_2n+2, where n = 5. Substituting n = 5 in the general formula, we get C₅H₂₍₅₎₊₂ = C₅H₁₂. Therefore, the fifth member of the homologous series would be C₅H₁₂.

The following salts will produce a gas on reacting with hydrochloric acid except

Détails de la réponse

Which of the following equations represents a neutralization reaction?

Détails de la réponse

The equation that represents a neutralization reaction is: H₂SO₄ + KOH → KHSO₄ + H₂ O. In this reaction, an acid (H₂SO₄) reacts with a base (KOH) to form a salt (KHSO₄) and water (H₂O). Neutralization reactions involve the combination of an acid and a base to form a salt and water, with the acid and base neutralizing each other's acidic and basic properties. The other options either do not involve an acid and a base or do not form a salt and water, and thus do not represent neutralization reactions.

During water treatment for town supply, water is passed through layers of send beds in order to

Détails de la réponse

During water treatment for town supply, water is passed through layers of sand beds in order to filter the water. The sand beds act as a physical barrier that separates large particles, sediments, and debris from the water. As the water flows through the sand bed, the sand traps the suspended particles, and clean water passes through. This process is called filtration and is an essential step in water treatment, as it removes impurities and improves the quality of the water. The filtered water can then be treated further to remove any remaining impurities or disinfect it to kill any harmful bacteria and viruses.

 Use the following energy profile diagram to answer Questions (a) to (c) below.

(a) From the diagram, determine the value of the; (i) enthalpy of the reaction (ii) activation energy of the reaction.

(b) State whether the profile diagram is for an endothermic reaction or an exothermic reaction.

(c) What name is given to substances which can provide an alternative pathway for the reaction?

Détails de la réponse

None

(a) List two gases which are monatomic

(b) Mention one gas which forms:

(i) dense white fumes with ammonia vapour

(ii) yellow precipitate with ammoniacal silver trioxonitrate (V) solution.

Détails de la réponse

None

(a) Determine the oxidation number of manganese in MnO\(_4\)

(b)(i) List two metals that are extracted from their ores by electrolysis

(ii) Give one difference between a conductor and an electrolyte.

Détails de la réponse

None

(a)(i) Explain what is meant by an effective collision

(ii) What does each term represent in the following expression? \(\Delta G\) = \(\Delta H\) — T\(\Delta\)S

(iii) What deduction can be made about a system given that the value of its \(\Delta\)G is zero?

(b)(i) State Le Chatelier's principle.

(ii) Suggest three conditions necessary for maximum yield of A\(_2\)B in the reaction represented by the following equation 2A\(_{2(g)}\) + B\(_{2(g)}\) \(\rightleftharpoons\) 2A\(_2\)B\(_{(g)}\) \(\Delta\)H = xkj.

(iii) Write an expression for the equilibrium constant of the reaction in (b)(ii) above.

(c)(i) Give the reason why a log of wood of a given mass does not burn out as quickly as sawdust of the same mass, under the same conditions.

(iii) List two examples of chemical reactions that are catalyzed by light

Détails de la réponse

None

(a) (i)Name the class of oxides to which copper (II) oxide belongs.

(ii) Give the reason why copper (II) oxide increases in mass on exposure to the atmosphere

(iii) Write an equation to show the action of dilute hydrochloric acid on copper (II) oxide.

(b) List two methods of removing total hardness from water.

Détails de la réponse

None

(a)(i) Give one major use of alkenes.

(ii) Name the simplest alkane that exhibits structural isomerism

(iii) Determine the molar mass of an alkane that is represented as C\(_x\)F\(_{22}\). [H = 1, C = 12]

(iv) List two types of chemical reactions which the alkenes and alkynes undergo.

(b)(i) State the type of reaction involved in the conversion of palm oil to margarine.

(ii) Give the reason why the palm oil for manufacturing margarine is first treated activated charcoal

(iii) What is commonly used to catalyse the conversion of vegetable oils to margarine?

(c)(i) Name the class of organic compounds to which oils belong.

(ii) Describe briefly procedure for the manufacture of soap from vegetable oils

(iii) Explain why the presence of calcium ions in domestic water supply wastes soap.

Détails de la réponse

None

(a)(i) List three factors which affect the discharge of ions during electrolysis

(ii) Describe in outline, the purification of copper by electrolysis.

(b) the following data were collected in an experiment on electrolysis:

(i) Copy and complete the table above calculating the quantity of electricity passed in each case

(ii) Plot a graph of the mass of M deposited against the quantity of electricity passed.

(iii) From the graph, determine the mass of M that was deposited by the same current passing for 20 minutes.

(iv) From the shape of the graph, which of the laws of electrolysis does the experiment verify?

Détails de la réponse

None

(a) What is the anhydride of each of the following acids?:

(i) H\(_2\)SO\(_4\)

(ii) HNO\(_3\)

(b) Classify each of the: following as normal salt/acid salt/basic salt/double salt

(i) Sodium hydrogentrioxocarbonate (IV)

(ii) Iron (III) chloride

(iii) Sodium ethanoate.

Détails de la réponse

None

(a)(i) What is an acid?

(ii) List three chemical properties of tetraoxosulphate (VI) acid

(iii) Give two uses of tetraoxosulphate (VI) acid.

(b)(i) Describe a suitable laboratory procedure for preparing a sample of zinc tetraoxosulphate (VI) crystals, starting from zinc oxide.

(ii) Write two equations to show why zinc oxide is classified as an amphoteric oxide.

(c) Zinc reacts with copper (II) tetraoxosulphate (VI) according to the following equation: Zn + CuSO\(_4\) -> ZnSO\(_4\) + Cu

(i) State the type of reaction involved

(ii) Determine the mass of zinc that would react completely with 8.0g of copper (II) tetraoxosulphate (VI). [CuSO\(_4\) = 160; Zn = 65]

Détails de la réponse

None

(a) The elements listed below to the same group in the Periodic Table \(_9F\)  \(_{17}CI\) \(_{35}Br\) \(_{53}I\).

(i) Write the electronic structure of the first member

(ii) What is the family name of the elements.

(iii) Which of the elements has the strongest oxidizing ability?

(b) Use the information provided in the following table to answer Questions (i) to (ii) below

(b)(i) Which of the chlorides would exist as discrete molecules?

(ii) What type of bonding holds atoms of A and chlorine together in ACI?

(iii) Which of the chlorides would be a good conductor of electricity?

Détails de la réponse

None

(a) State the monomer units of (i) polyethene; (ii) cellulose

(b) Name the two fuels obtained when steam and air are passed over red-hot coke.

Détails de la réponse

None

(a)(i) State two physical properties of hydrogen sulphide

(ii) Name the laboratory equipment used for intermittent production of hydrogen sulphide

(b) What property of hydrogen sulphide is illustrated in the reaction represented by the following equation?

H\(_2\)S\(_{(g)}\) + 2NaOH\(_{(aq)}\) \(\to\) Na\(_2\)S\(_{(aq)}\) + H\(_2\)O\(_{(l)}\)

Détails de la réponse

None

(a) State three postulates of the kinetic theory

(b) Name the process involved in the;

(i) spread of the smell of a perfume across a room

(ii) decrease in the yellow of a liquid after exposure in an open vessel.

Détails de la réponse

None

(a) Give the name of the:

(i) process for obtaining ethanol from sugars;

(ii) compound produced when ethanol undergoes bacterial oxidation.

(iii) enzyme in yeast which catalyses the conversion of maltose to glucose.

(b)(i) Write the structural formula of ethanol

(ii) Name the organic product formed when propanoic acid reacts with ethanol.

Détails de la réponse

None