JAMB UTME - Chemistry - 2007

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Question 5 Report

An element used in the production of matches is

nitrogen

aluminium

copper

sulphur Correct answer

Answer Details

The element used in the production of matches is sulfur. Sulfur is used in the match head, which ignites when struck against a rough surface. When sulfur is mixed with an oxidizing agent and a fuel, such as powdered glass and potassium chlorate, it forms a highly flammable mixture that is ignited by the friction of striking the match. The sulfur helps to ignite the match by lowering the temperature at which the mixture will ignite.

Read lesson note on Non-metals And Their Compounds (JAMB)

Non-metals And Their Compounds

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Question 6 Report

The salt formed from strong acid and a strong base is

complex

neutral Correct answer

basic

acidic

Answer Details

When a strong acid and a strong base react with each other, they form a salt and water. Since both the acid and base are strong, they will fully dissociate into their respective ions in solution. When they react, the H+ ion from the acid combines with the OH- ion from the base to form water, while the remaining ions combine to form a salt. Since the salt is formed from a combination of cations and anions, it is neutral in nature. Therefore, the answer is "neutral".

Read lesson note on Acids, Bases And Salts (JAMB)

Acids, Bases And Salts

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Question 7 Report

Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l)

Which of the following would introduce the greatest increase in the rate of the chemical reaction above?

An increase in temperature and decrease in the concentration of the reactant

A decrease in the volume and increase in the pressure of the reactant

A decrease in the temperature and an incease in the concentration of the reactant

An increase in temperature and an increase in the concentration of the reactant Correct answer

Answer Details

The reaction given is a neutralisation reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl) to form sodium chloride (NaCl) and water (H2O). The question is asking which of the given options would increase the rate of this reaction the most. suggests an increase in temperature, which generally increases the rate of reaction, but also a decrease in the concentration of the reactant, which would decrease the rate of reaction. Thus, the overall effect is uncertain. suggests a decrease in volume and an increase in pressure of the reactant, which would not have a significant effect on the reaction rate as it is a solution reaction. suggests a decrease in temperature, which would decrease the rate of reaction, and an increase in the concentration of the reactant, which would increase the rate of reaction. Thus, the overall effect is uncertain. suggests an increase in temperature and an increase in the concentration of the reactant, both of which would increase the rate of reaction. Therefore, this option would introduce the greatest increase in the rate of the chemical reaction above.

Read lesson note on Kinetic Theory Of Matter And Gas Laws (JAMB)

Read lesson note on Chemical Kinetics And Equilibrium System (Nigeria Only) (WAEC)

Chemical Kinetics And Equilibrium System (Nigeria Only)

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Question 8 Report

A mixture of petrol and water can be separated through

centrifugation

distillation

the use of separating funnel Correct answer

the use of filter paper

Answer Details

Petrol and water can be separated by using a separating funnel. A separating funnel is a piece of laboratory apparatus used to separate immiscible liquids that have different densities. The mixture is poured into the funnel, and the heavier liquid settles at the bottom, while the lighter one stays on top. The tap at the bottom of the funnel is then opened, allowing the denser liquid to flow out into a separate container.

Read lesson note on Separation Of Mixtures And Purification Of Chemical Substances (JAMB)

Separation Of Mixtures And Purification Of Chemical Substances

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Question 9 Report

Trioxonitrate (V) acid is not used for preparing hydrogen gas from metals because it

is strongly oxidizing Correct answer

is volatile

renders the metal passive

forms a layer of oxide on the metal

Answer Details

Trioxonitrate (V) acid, also known as nitric acid, is not used for preparing hydrogen gas from metals because it is strongly oxidizing. This means that it readily gives up oxygen to other substances, including metals. When nitric acid reacts with metals, it can produce metal nitrates instead of hydrogen gas. In addition, nitric acid can also react with the hydrogen gas produced, forming water and nitrogen oxides. Therefore, other acids, such as hydrochloric acid or sulfuric acid, are used for preparing hydrogen gas from metals as they do not have such strong oxidizing properties.

Read lesson note on Acids, Bases And Salts (JAMB)

Acids, Bases And Salts

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Question 10 Report

How many structural isomers of chlorobutane are possible?

4 Correct answer

Answer Details

Read lesson note on Chemistry Of Carbon Compounds (Nigeria Only) (WAEC)

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Question 11 Report

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

Li, Be, Al and P

Na, P, O and Cl

B, C, N and O

Nz, Mg, S and Ar Correct answer

Answer Details

Read lesson note on Periodic Chemistry (Nigeria Only) (WAEC)

Periodic Chemistry (Nigeria Only)

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Question 12 Report

The reddish-brown rust on iron roofing sheets consists of

Fe3+(H2O)6

FeO.H2O

Fe2O3.3H2O Correct answer

Fe3O4.2H2O

Answer Details

Read lesson note on Metals And Their Compounds (JAMB)

Metals And Their Compounds

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Question 13 Report

The hydrocarbon used in the production of styrene is

ethyne

propyne

ethane

ethene Correct answer

Answer Details

The hydrocarbon used in the production of styrene is "ethene." Styrene is produced by the catalytic dehydrogenation of ethylbenzene, which is obtained by the alkylation of benzene with ethene. Therefore, the correct answer is "ethene."

Read lesson note on Chemistry Of Carbon Compounds (Nigeria Only) (WAEC)

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Question 14 Report

Which of the following compounds is the best possible anti-knock agent for petrol?

(CH3)2CH - CH(CH3)CH2CH3 Correct answer

CH3CH2(CH3)CHCH2CH2CH3

CH3CH2(CH3)-CHCH2CH2CH3

(CH3)3C - CH2CH2CH3

Answer Details

Read lesson note on Periodic Chemistry (Ghana Only) (WAEC)

Periodic Chemistry (Ghana Only)

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Question 15 Report

Calculate the number of moles of HCl present in 20cm3 of a 0.75M solution of the acid

0.015 mole Correct answer

0.038 mole

3.800 moles

1.500 moles

Answer Details

To calculate the number of moles of HCl, we need to use the formula: moles = concentration x volume We are given the volume of the solution as 20 cm^3, and the concentration as 0.75 M. First, we need to convert the volume to liters: 20 cm^3 = 20/1000 L = 0.02 L Then we can plug in the values: moles = 0.75 M x 0.02 L = 0.015 moles Therefore, the number of moles of HCl present in the solution is 0.015 mole. So the correct option is 0.015 mole.

Read lesson note on Stoichiometry And Chemical Reactions (WAEC)

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Question 16 Report

The reaction that takes place in Daniell cell is

direct combination

redox Correct answer

double decomposition

neutralization

Answer Details

The reaction that takes place in a Daniell cell is a redox reaction. In a Daniell cell, zinc metal (Zn) is oxidized to Zn2+ ions at the anode, while copper (Cu2+) ions are reduced to copper metal (Cu) at the cathode. This is a classic example of a redox reaction, where oxidation and reduction occur simultaneously.

Read lesson note on Oxidation And Reduction (JAMB)

Oxidation And Reduction

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Question 17 Report

\(\mathrm{MnO_2(s)} + x\mathrm{HCl(aq)} \rightarrow \mathrm{MnCl_2(aq)} + y\mathrm{H_2O(l)} + z\mathrm{Cl_2(g)}\)

In theequation above, what are the values of x, y and z respectively

2, 1, 2

4, 1, 2

4, 2, 1 Correct answer

1, 2, 1

Answer Details

The equation represents a reaction between solid manganese dioxide (MnO2) and hydrochloric acid (HCl) to produce manganese(II) chloride (MnCl2), water (H2O), and chlorine gas (Cl2). The balanced chemical equation for the reaction is: MnO2(s) + 4HCl(aq) → MnCl2(aq) + 2H2O(l) + Cl2(g) Thus, the values of x, y, and z are 4, 2, and 1, respectively. This is because four moles of hydrochloric acid are needed to react with one mole of MnO2, producing two moles of water and one mole of chlorine gas.

Read lesson note on Stoichiometry And Chemical Reactions (WAEC)

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Question 18 Report

Copper and silver metals are commonly use as coin because they are

easily reduced

not easily reduced

easily oxidized

not easily oxidized Correct answer

Answer Details

Read lesson note on Oxidation And Reduction (JAMB)

Oxidation And Reduction

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Question 19 Report

A metal X forms two bromides with the formulae XBr2 and XBr3. What type of bonding exists between X and bromine in the bromide?

Ionic bonding Correct answer

Metallic bonding

Dative bonding

Covalent bonding

Answer Details

The metal X forms two bromides with the formulae XBr2 and XBr3. The type of bonding between X and bromine in the bromides is ionic bonding. Ionic bonding is a type of chemical bond that occurs when there is a transfer of electrons from one atom to another. In this case, X loses electrons to the bromine atoms to form positive ions, while bromine gains electrons to form negative ions. These positive and negative ions are then attracted to each other by electrostatic forces, forming an ionic bond. Therefore, X and bromine are held together by ionic bonding in the bromides XBr2 and XBr3.

Read lesson note on Oxidation And Reduction (JAMB)

Oxidation And Reduction

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Question 20 Report

The conversion of open chain alkanes into cycloalkanes and aromatic compounds is called

cracking

reforming Correct answer

isomerization

polymerization

Answer Details

The conversion of open chain alkanes into cycloalkanes and aromatic compounds is called "reforming". Reforming is a process used in the petroleum industry to convert low octane gasoline into high octane gasoline or liquid petroleum gas (LPG). The reforming process involves breaking the carbon-carbon bonds of the straight-chain hydrocarbons, then rearranging them into branched or cyclic compounds, which are higher in octane number. This process is carried out in the presence of a catalyst, typically a platinum or palladium catalyst, at high temperatures and pressures.

Read lesson note on Chemistry Of Carbon Compounds (Nigeria Only) (WAEC)

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Question 21 Report

C2H4(g) + H2(g) → C2H6(g) ΔH = -137kJ mol-1

The reaction represented above is

exothermic Correct answer

spontaneous

endothermic

in equilibrium

Answer Details

The reaction represented in the given equation involves the reactants carbon dioxide (CO2) and hydrogen gas (H2) to form the product, ethane (C2H6), with the release of energy (enthalpy change, ΔH) of -137 kJ/mol. As the reaction releases energy in the form of heat, it is exothermic. The negative value of ΔH indicates that the reaction is exothermic.

Read lesson note on Energy Changes (JAMB)

Energy Changes

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Question 22 Report

Which of the following represents an aromatic compound?

C6H5OH Correct answer

C6H12

C6H9OH

C6H8

Answer Details

Read lesson note on Chemistry Of Carbon Compounds (Nigeria Only) (WAEC)

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Question 23 Report

CH3CH2Cl + KCN → CH3CH2CN + KClIn the reaction above, the cyanide is

hydrophobic

hydrophilic

nucleophilic Correct answer

electrophilic

Answer Details

Read lesson note on Chemistry Of Carbon Compounds (Nigeria Only) (WAEC)

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Question 24 Report

The IUPAC nomenclature of compound CH3CH2COOCH2CH3 is

propyl ethanoate

ethyl butanoate

ethyl propanoate Correct answer

methyl butanoate

Answer Details

The compound CH3CH2COOCH2CH3 is named using the IUPAC nomenclature system, which follows a set of rules to name organic compounds. The first step is to identify the longest continuous carbon chain, which in this case is a five-carbon chain, so the parent name is pentanoate. The chain has two substituents, which are ethyl and methyl groups, located on the second and fourth carbon, respectively. The complete name of the compound is ethyl 4-methylpentanoate. Therefore, the correct option is "ethyl butanoate."

Read lesson note on Chemistry Of Carbon Compounds (Nigeria Only) (WAEC)

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Question 25 Report

Which of the following alkanes has the highest boiling point?

Pentane Correct answer

Ethane

Propane

Methane

Answer Details

The boiling point of a compound depends on the strength of the intermolecular forces between its molecules. The stronger the intermolecular forces, the higher the boiling point. In this case, all of the given alkanes are nonpolar molecules and have only weak London dispersion forces between their molecules. Therefore, the boiling point of these alkanes increases with increasing molecular weight (number of carbon atoms). Out of the given alkanes, pentane has the highest molecular weight and therefore, it has the highest boiling point. Hence, the answer is pentane.

Read lesson note on Chemistry Of Carbon Compounds (Ghana Only) (WAEC)

Chemistry Of Carbon Compounds (Ghana Only)

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Question 26 Report

When temporary hard water is boiled for sometime in a kettle, the inner surface of the kettle becomes coated with a deposit of

calcium tetraoxosulphate(VI)

calcium trioxocarbonate (IV) Correct answer

calcium hydrogentrioxocarbonate (IV)

aluminium trioxocarbonate (IV)

Answer Details

When temporary hard water is boiled for some time in a kettle, the inner surface of the kettle becomes coated with a deposit of calcium trioxocarbonate (IV). This is because temporary hard water contains soluble calcium hydrogen trioxocarbonate (IV) which decomposes upon heating to form insoluble calcium trioxocarbonate (IV) which deposits on the inner surface of the kettle. This deposit is commonly known as limescale and can be difficult to remove.

Read lesson note on Acids, Bases And Salts (Ghana Only) (WAEC)

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Question 27 Report

A good drying agent should be

deliquescent

effervescent

hygroscopic Correct answer

efflorescent

Answer Details

A good drying agent is a substance used to remove moisture or water from a solution or compound. A drying agent should be hygroscopic, which means that it should have the ability to absorb or adsorb water molecules from the surroundings. This makes it effective in removing water from a compound or solution. Deliquescent compounds are those that absorb water so vigorously from the atmosphere that they dissolve in their own water of crystallization. Effervescent compounds release gas upon contact with water, while efflorescent compounds lose water of crystallization upon exposure to air. Therefore, the correct option for a good drying agent is hygroscopic.

Read lesson note on Solubility (JAMB)

Read lesson note on Kinetic Theory Of Matter And Gas Laws (JAMB)

Solubility

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Question 28 Report

If the electron configuration of a element is p1s2 2s2 2P5, how many unpaired electron are there?

1 Correct answer

Answer Details

The electron configuration of an element provides information about the arrangement of electrons in its orbitals. In this case, the element has 1 electron in the 2p sublevel, which means it has one unpaired electron. The remaining 7 electrons are paired up in the other orbitals (2 electrons in the 2s sublevel and 4 electrons in the 2p sublevel). Therefore, the answer is (C) 1 unpaired electron.

Read lesson note on Atomic Structure And Bonding (JAMB)

Atomic Structure And Bonding

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Question 29 Report

How long would it take to deposit 0.08g of copper from CuCl2 solution by passing a current of 0.5A?

[Cu = 64, F = 96500 C mol-1]

6 mins

8 mins Correct answer

24 mins

48 mins

Answer Details

Cu2+ + 2e → Cu(s)
2 * 96500C deposit 64g of Cu
∴ x quantity of electricity wil deposit 0.08
x = (2 * 96500 * 0.08)/64 =241.25 coulomb.
Q = It
241.25 = 0.5t
t = 241.25/60 = 8 mins

Read lesson note on Electrolysis (JAMB)

Electrolysis

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Question 30 Report

Calculate the mass of chlorine gas which occupies a volume of 1.12dm3 at s.t.p

[Cl = 35.5, molar volume of gas at s.t.p = 22.4 dm3

15.50 g

7.10 g

3.55 g Correct answer

1.80 g

Answer Details

2 * 35.5g of chlorine has a volume of 22.4 dm3 at s.t.p
∴ xg of chlorine will have a volume of 1.12 dm3x = (1.12 * 35.5 * 2)/22.4 = 3.55g

Read lesson note on Kinetic Theory Of Matter And Gas Laws (JAMB)

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Question 31 Report

Smog usually occurs over cities which

burn a lot of fossil fuels
Correct answer

have very few plants

are surrounded by water

are overpopulated

Answer Details

Smog usually occurs over cities which burn a lot of fossil fuels. When fossil fuels such as coal, oil, and natural gas are burned, they release pollutants into the air. These pollutants include particulate matter, nitrogen oxides, sulfur dioxide, and volatile organic compounds. When these pollutants react with sunlight, they form a mixture of air pollutants known as smog. Cities with high levels of traffic and industrial activity tend to produce more smog than areas with fewer sources of pollution. Smog can cause a variety of health problems, such as respiratory issues, eye irritation, and cardiovascular problems, so it is important to monitor and manage smog levels in cities.

Read lesson note on Environmental Pollution (JAMB)

Environmental Pollution

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Question 32 Report

A supersaturated solution is said to contain

more solute than it can dissolve at that temperature in the presence of undissolved solute

as much solute as it can dissolve at that temperature in the presence of undissolved solute

as much solute as it can dissolve at that temperature

more solute than it can dissolve at that temperature Correct answer

Answer Details

A supersaturated solution is a solution that contains more than the maximum amount of solute that is capable of being dissolved at a given temperature. A saturated solution contains the maximum amount of solute that will dissolve at that temperature while a supersaturated solution contains more than the maximum amount of solute that can be dissolved at that temperature.

Read lesson note on Solubility Of Substances (Ghana Only) (WAEC)

Solubility Of Substances (Ghana Only)

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Question 33 Report

When calcium oxide is heated with carbon, the oxide will

be converted to carbide Correct answer

be converted to the trioxocarbonate (IV) salt

decompose to the metal

melt,producingg carbon (IV) oxide

Answer Details

When calcium oxide is heated with carbon, it will be converted to carbide. This is because calcium oxide and carbon undergo a redox reaction in which calcium oxide is reduced to calcium carbide, while carbon is oxidized to carbon monoxide. The balanced chemical equation for this reaction is: CaO + 3C → CaC2 + CO So, the correct option is "be converted to carbide".

Read lesson note on Chemical Combination (JAMB)

Chemical Combination

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Question 34 Report

If chlorine is bubbled into water and the resulting yellowish-green solution is exposed to bright sunlight for a while, the solution will decompose giving out

oxygen and leaving behind aqueous hydrochloric acid Correct answer

chlorine and oxygen

oxygen, hydrogen and chlorine

oxygen, thereby producing hypochlorous acid

Answer Details

When chlorine is bubbled into water, it reacts to form a yellowish-green solution of aqueous chlorine. This solution is unstable and will decompose on exposure to sunlight, forming oxygen gas and aqueous hydrochloric acid. The reaction can be represented as follows: 2Cl2 + 2H2O + sunlight -> 4HCl + O2 Therefore, the correct answer is "oxygen and leaving behind aqueous hydrochloric acid."

Read lesson note on Acids, Bases And Salts (Ghana Only) (WAEC)

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Question 35 Report

Which of the following decreases when a given mass of gas is compressed to half its initial volume?

Average intermolecular distance Correct answer

Frequency of collisions

Number of molecules present

Atomic radius of each particle

Answer Details

Read lesson note on Kinetic Theory Of Matter And Gas Laws (JAMB)

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Question 36 Report

What happens when zinc rod is immersed in copper (II) tetraoxosulphate (VI) solution

The blue colour of the solution disappears Correct answer

Electrons flow from copper to zinc

The zinc rod remain undissolved

The copper generate more copper ions

Answer Details

Read lesson note on Electrolysis (JAMB)

Read lesson note on Chemical Combination (JAMB)

Electrolysis

Chemical Combination

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Question 37 Report

What is the volume of oxygen required to bum completely 45cm\(^{3}\) of methane at s.t.p?

135.0cm

^{3}

180.0cm

^{3}

45.0cm

^{3}

190.0cm

^{3}

90.0cm

^{3}

Correct answer

Answer Details

When methane burns completely in oxygen, it produces carbon dioxide and water vapor. According to the balanced chemical equation for the combustion of methane: CH4 + 2O2 → CO2 + 2H2O From the equation, we see that 1 mole of methane (16g) reacts with 2 moles of oxygen (32g) to give 1 mole of carbon dioxide (44g) and 2 moles of water vapor (36g). At s.t.p, 1 mole of any gas occupies 22.4 liters or 22,400 cm3. Therefore, the volume of 45cm3 of methane is equal to 45/22,400 = 0.002 moles. Since methane reacts with oxygen in a 1:2 mole ratio, we need twice the number of moles of oxygen to react completely with the given amount of methane. Thus, we need 2 x 0.002 = 0.004 moles of oxygen. At s.t.p, 1 mole of oxygen occupies 22.4 liters or 22,400 cm3. Therefore, the volume of 0.004 moles of oxygen required is 0.004 x 22,400 = 89.6 cm3. Therefore, the correct option is 90.0cm3, which is closest to the calculated volume of oxygen required.

Read lesson note on Stoichiometry And Chemical Reactions (WAEC)

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Question 38 Report

What weight of NaCl is needed to make 2.0 dm3 of a 1.5M solution?

[Na = 23, Cl = 35.5]

116 g

175 g Correct answer

87 g

58 g

Answer Details

To find the weight of NaCl required, we need to use the formula: moles = concentration x volume First, we need to find the number of moles of NaCl required to make 2.0 dm^3 of a 1.5 M solution: moles = concentration x volume moles = 1.5 mol/dm^3 x 2.0 dm^3 moles = 3.0 mol Next, we can use the molar mass of NaCl (58.44 g/mol) to convert moles to grams: grams = moles x molar mass grams = 3.0 mol x 58.44 g/mol grams = 175.32 g Therefore, the weight of NaCl required to make 2.0 dm^3 of a 1.5 M solution is approximately 175 g. So, the correct answer is.

Read lesson note on Stoichiometry And Chemical Reactions (WAEC)

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Question 39 Report

The presence of nitrogen in air is to slow down

respiration and combustion

combustion and corrosion Correct answer

corrosion and respiration

respiration and transpiration

Answer Details

Read lesson note on Air (JAMB)

Read lesson note on Separation Of Mixtures And Purification Of Chemical Substances (JAMB)

Air

Separation Of Mixtures And Purification Of Chemical Substances

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Question 40 Report

Certain useful waxes are composed mainly of

amino acids

glycerols Correct answer

alkanols

alkanoates

Answer Details

Read lesson note on Organic Compounds (JAMB)

Organic Compounds

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Question 41 Report

The tincture of iodine means iodine dissolved in

ethanol Correct answer

bromine chloride

chlorine water

water

Answer Details

The tincture of iodine is a solution that contains iodine dissolved in a solvent. The question asks about the solvent used in the tincture of iodine. The correct answer is "ethanol." Therefore, the tincture of iodine means iodine dissolved in ethanol.

Read lesson note on Acids, Bases And Salts (Ghana Only) (WAEC)

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Question 42 Report

The oxidation state of oxygen in tetraoxosulphate(IV) acid is

-4

-2 Correct answer

Answer Details

The oxidation state (or number) of an element is a number that represents the total number of electrons that an atom can gain, lose, or share when forming a chemical compound. In tetraoxosulphate(IV) acid, the formula is H2SO4, which means that there are four oxygen atoms. To determine the oxidation state of oxygen, we can use the rule that hydrogen has an oxidation state of +1 and oxygen has an oxidation state of -2 in most compounds. Since there are two hydrogen atoms in H2SO4, their total oxidation state is +2. To balance this out, the four oxygen atoms must have a total oxidation state of -8. Therefore, the oxidation state of each oxygen atom is -2. Hence, the answer is -2.

Read lesson note on Acids, Bases And Salts (JAMB)

Acids, Bases And Salts

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Question 43 Report

Which experiment led to the measurement of the charge on an electron?

Mass spectrometric experiment

Oil-drop experiment Correct answer

Scattering α - particles

Discharge-tube experiment

Answer Details

The experiment that led to the measurement of the charge on an electron is the "Oil-drop experiment." In this experiment, Robert Millikan observed oil droplets falling between two charged plates and was able to determine the charge on an electron. He applied an electric field to the charged plates to slow down the motion of the droplets and then calculated the charge on each droplet by measuring the strength of the electric field required to keep the droplets suspended in mid-air. By using this information, he was able to determine the charge on an individual electron.

Read lesson note on Rates Of Chemical Reaction (JAMB)

Rates Of Chemical Reaction

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Question 44 Report

How many electrons are in the L shell of 3115P?

8 Correct answer

Answer Details

The atomic number of phosphorus (P) is 15, which means it has 15 electrons in total. To determine the number of electrons in the L shell, we need to know the electronic configuration of phosphorus. The electronic configuration of phosphorus is 1s2 2s2 2p6 3s2 3p3. To find out how many electrons are in the L shell, we need to add up the number of electrons in the 2s and 2p subshells. The 2s subshell contains 2 electrons, and the 2p subshell contains 6 electrons. Therefore, the total number of electrons in the L shell of phosphorus is 8. So the answer is 8.

Read lesson note on Atomic Structure And Bonding (JAMB)

Atomic Structure And Bonding

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Question 45 Report

The soft solder used for welding and plumbing is alloy of

lead and tin Correct answer

iron and tin

lead and zinc

iron and zinc

Answer Details

The soft solder used for welding and plumbing is an alloy of lead and tin. This alloy has a low melting point, which makes it ideal for welding two pieces of metal together. When the solder is heated, it melts and flows into the joint, bonding the two pieces of metal together. The lead provides the ability to flow easily and the tin provides the strength to hold the joint together.

Read lesson note on Non-metals And Their Compounds (JAMB)

Non-metals And Their Compounds

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Question 46 Report

H3PO4(aq) + H2O(l) ↔ H2PO4-(aq) + H3O+(aq)

ΔH = -13kJ at 298K

In the reaction above, an increase in temperature would

slow downthe reverse reaction

have no effect on the reaction

favour the reverse reaction Correct answer

favour the forward reaction

Answer Details

The given chemical equation is a reversible exothermic reaction, and the value of enthalpy change, ΔH, is negative. According to Le Chatelier's principle, an increase in temperature will favor the endothermic reaction to absorb heat and therefore, will shift the equilibrium towards the reactants' side. Thus, an increase in temperature would favor the reverse reaction. Hence, the correct option is: "favor the reverse reaction."

Read lesson note on Kinetic Theory Of Matter And Gas Laws (JAMB)

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Question 47 Report

Dissolving some pellets of NaOH in water would result in

a decrease in the free energy of the solution

a decrease in the entropy of the solution

a lowering of the temperature of te solution

an increase in the entropy of the solution

Correct answer

Answer Details

When pellets of NaOH are dissolved in water, they ionize into Na+ and OH- ions, which are surrounded by water molecules. This process increases the entropy of the solution, since the Na+ and OH- ions are now dispersed throughout the solution rather than being confined to the pellets. Therefore, the correct answer is: an increase in the entropy of the solution.

Read lesson note on Acids, Bases And Salts (Ghana Only) (WAEC)