JAMB UTME - Chemistry - 2019

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Question 2 Report

Which of the following alkaline metals react more quickly spontaneously with water?

Calcium

Beryllium

Magnesium

Strontium

Answer Details

The alkaline earth metals (Be, Mg, Ca, Sr, Ba, and Ra) are the second most reactive metals in the periodic table, and, like the Group 1 metals, have increasing reactivity in the higher periods. Beryllium (Be) is the only alkaline earth metal that does not react with water or steam, even if metal is heated to red heat. Additionally, beryllium has a resistant outer oxide layer that lowers its reactivity at lower temperatures.

Magnesium shows insignificant reaction with water, but burns vigorously with steam or water vapor to produce white magnesium oxide and hydrogen gas:

Mg(s) + 2 H2O(l) ⟶ Mg(OH)2(s) + H2(g)

A metal reacting with cold water will produce metal hydroxide. However, if a metal reacts with steam, like magnesium, metal oxide is produced as a result of metal hydroxides splitting upon heating.

The hydroxides of calcium, strontium and barium are only slightly water-soluble but produce sufficient hydroxide ions to make the environment basic, giving a general equation of:

M(s) + 2 H2O(l) ⟶ M(OH)2(aq) + H2(g)

Order of reactivity	Metal	Reactions with water or steam
most reactive	potassium (K)	very vigorous reaction with cold water
↑	sodium (Na)	vigorous reaction with cold water
↓	calcium (Ca)	less vigorous reaction with cold water
least reactive	magnesium (Mg)	slow reaction with cold water, vigorous with steam

If metals react with cold water, hydroxides are produced.
Metals that react with steam form oxides.
Hydrogen is always produced when a metal reacts with cold water or steam.

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Read lesson note on Organic Compounds (JAMB)

Metals And Their Compounds

Organic Compounds

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Question 3 Report

What mass of magnesium would be obtained by passing a current of 2 amperes for 2 hours, through molten magnesium chloride?
[1 faraday = 96500C, Mg = 24]

1.12g

4.48g

1.80g

2.00g

Answer Details

Current (I) = 2A; Time (t) = 2 hours = 7200 secs
Q = It
= 2 x 7200 = 14400C
1 F = 96500C
x = 14400C
x =

\frac{14400}{96500}

= 0.15F
Mg

^{2 +}

+ 2e

^{-}

\to

Mg
2F

\to

24g
0.15F

\to

x
2x = 24 x 0.15
x =

\frac{24 \times 0.15}{2}

= 1.8g

Read lesson note on Chemical Kinetics And Equilibrium Systems (Ghana Only) (WAEC)

Read lesson note on Electrolysis (JAMB)

Chemical Kinetics And Equilibrium Systems (Ghana Only)

Electrolysis

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Question 4 Report

2-methylprop-1-ene is an isomer of

3-methyl but-1-ene

2-methyl but-1-ene

but-2-ene

pent-2-ene

Answer Details

2-methylprop-1-ene is an isomer of 3-methyl but-1-ene and 2-methyl but-1-ene. An isomer is a molecule that has the same molecular formula as another molecule, but a different arrangement of atoms. In this case, 2-methylprop-1-ene has the molecular formula C4H8, and so do 3-methyl but-1-ene and 2-methyl but-1-ene. The difference between these three molecules is in the arrangement of the carbon and hydrogen atoms. 2-methylprop-1-ene has a branched structure with a double bond between the first and second carbon atoms. 3-methyl but-1-ene is also a branched molecule, but the double bond is between the second and third carbon atoms. Similarly, 2-methyl but-1-ene has a double bond between the first and second carbon atoms, but it has a different branching pattern. On the other hand, pent-2-ene has five carbon atoms, so it has a different molecular formula than 2-methylprop-1-ene. Therefore, 2-methylprop-1-ene is an isomer of 3-methyl but-1-ene and 2-methyl but-1-ene, but not of pent-2-ene, because it has the same molecular formula and a different arrangement of atoms compared to the other two isomers.

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

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Question 5 Report

What technique is suitable for separating a binary solution of potassium chloride and potassium trioxochlorate (V)?

Fractional crystallization

Fractional distillation

Filtration

Evaporation

Answer Details

Fractional crystallization is the most suitable technique for separating a binary solution of potassium chloride and potassium trioxochlorate (V). This is because fractional crystallization is a process that separates a mixture of substances based on their solubility in a solvent at a particular temperature. In this case, potassium chloride and potassium trioxochlorate (V) have different solubilities in a solvent such as water at different temperatures. By carefully controlling the temperature, the solubility of each compound can be selectively increased or decreased, allowing them to be separated by crystallization. The less soluble compound will form crystals first and can be separated from the more soluble compound, which remains in the solution. Therefore, fractional crystallization can be used to separate potassium chloride and potassium trioxochlorate (V) in a binary solution.

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 6 Report

Elements in the periodic table are arranged in the order of their

atomic numbers

metallic character

mass number

relative atomic mass

Answer Details

Elements in the periodic table are arranged in the order of their atomic numbers. The atomic number of an element is the number of protons in the nucleus of an atom of that element. The elements are arranged in order of increasing atomic number from left to right and from top to bottom in the periodic table. The elements in each row, also known as a period, have the same number of electron shells, while the elements in each column, also known as a group or family, have the same number of valence electrons. This arrangement makes it possible to predict the chemical and physical properties of an element based on its position in the periodic table. Therefore, the correct answer is: - atomic numbers

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Question 7 Report

How many electrons will be found in the nucleus of an atom with mass number 23 and 17 neutrons?

none

6

7

8

Answer Details

Electrons are not found in the nucleus of an atom. The nucleus of an atom only contains protons and neutrons, while electrons are located outside the nucleus in the electron cloud. The mass number of an atom is equal to the sum of the number of protons and the number of neutrons in the nucleus. Therefore, if an atom has a mass number of 23 and 17 neutrons, then the number of protons in the nucleus can be calculated as: Protons = Mass number - Neutrons Protons = 23 - 17 Protons = 6 This means that the nucleus of the atom contains 6 protons. The number of electrons in a neutral atom is equal to the number of protons, so the atom also contains 6 electrons in the electron cloud surrounding the nucleus. In summary, the answer is that there are 6 protons and 6 electrons in the atom.

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Question 8 Report

Which of the following statements about catalyst is false?

biological catalysts are called enzymes

catalyst do not appear in the balanced equation

catalyst reduce the activation energy for a reaction

catalysts do not alter the mechanism of the reaction and never appear in the rate low

Answer Details

The false statement about catalysts is: "catalysts do not alter the mechanism of the reaction and never appear in the rate law." Catalysts are substances that speed up chemical reactions without being consumed in the process. They achieve this by reducing the activation energy needed for the reaction to occur. Enzymes are a type of biological catalysts. In a chemical reaction, a catalyst is not consumed and does not appear in the overall balanced equation. However, catalysts can alter the mechanism of a reaction by providing an alternative pathway with a lower activation energy. This alternative pathway can have a different rate-determining step, which means that the presence of the catalyst can change the rate law of the reaction. Therefore, the statement that catalysts do not alter the mechanism of the reaction and never appear in the rate law is false.

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

Chemical Kinetics And Equilibrium System (Nigeria Only)

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Question 9 Report

The emission of two successive beta particles from the nucleus $ {}^{32}_{15}\mathrm{P} $ will produce

_{14}^{30}

Si

_{13}^{32}

Al

_{17}^{32}

Cl

_{16}^{32}

S

Answer Details

Explanation:

_{15}^{32}

P

\to

2

_{- 1}^{0}

e +

_{b}^{a}

X
32 = 2(0) + a
a = 32
15 = 2(-1) + b
b = 15 + 2
b = 17

∴

_{b}^{a}

X =

_{17}^{32}

Cl

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Structure Of The Atom

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Question 10 Report

A secondary alkanol can be oxidized to give an

alkanone

alkyne

alkanoic acid

alkanal

Answer Details

A secondary alkanol is an alcohol with two carbon atoms attached to the carbon bearing the hydroxyl group (-OH). Secondary alkanols can be oxidized by a strong oxidizing agent, such as potassium dichromate (K2Cr2O7), to give an alkanone. During the oxidation process, the oxygen atom from the oxidizing agent replaces the hydroxyl group of the secondary alkanol to form a carbonyl group (C=O) in the alkanone. Since alkanones contain a carbonyl group, they are also known as ketones. Therefore, the answer to the question is alkanone, as secondary alkanols can be oxidized to form ketones.

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

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Question 11 Report

Which of the following represents the kind of bonding present in ammonium chloride?

ionic only

covalent only

ionic and dative covalent

dative covalent

Answer Details

Ammonium chloride contains both ionic and covalent bonds. In ammonium chloride, the ammonium ion (NH4+) is positively charged and the chloride ion (Cl-) is negatively charged. These ions are held together by ionic bonds, which are formed between positively and negatively charged ions. However, the bond between the hydrogen atom in the ammonium ion and the nitrogen atom in the ammonium ion is also a covalent bond. This type of covalent bond is known as a dative covalent bond, or a coordinate covalent bond, because the electron pair being shared is supplied by one atom only (the nitrogen atom in this case). So, the kind of bonding present in ammonium chloride is both ionic and dative covalent. In simple terms, ammonium chloride contains both ionic bonds between its positive and negative ions, and a dative covalent bond between the hydrogen atom and nitrogen atom within the ammonium ion.

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Question 12 Report

Which of the following pollutants will lead to the depletion of ozone layer?

chlorofluorocarbon

carbon (ii) oxide

hydrogen sulphide

sulphur (iv) oxide

Answer Details

The pollutant that leads to the depletion of the ozone layer is chlorofluorocarbon (CFCs). CFCs are man-made chemicals that were widely used in the past as refrigerants, solvents, and propellants. When CFCs are released into the atmosphere, they rise into the stratosphere, where they come into contact with ozone molecules. The chlorine atoms in CFCs react with ozone, breaking apart the ozone molecules and causing a reduction in the overall amount of ozone in the stratosphere. This process continues until all of the ozone-depleting chlorine atoms have been depleted. The resulting decrease in ozone in the stratosphere leads to an increase in the amount of harmful ultraviolet radiation that reaches the Earth's surface, which can have negative impacts on human health and the environment.

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Environmental Pollution

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Question 13 Report

If acidified Potassium Dichromate(VI) ($\mathrm{K_2Cr_2O_7}$) acts as oxidizing agent, color changes from

yellow to green

orange to green

yellow to red

orange to red

Answer Details

Potassium Dichromate (VI), when it is acidified, acts as an oxidizing agent. When this happens, the color changes from orange to green. This is because the orange color of the potassium dichromate is due to the presence of Cr(VI) ions, which are oxidized to Cr(III) ions. The green color that is produced is due to the formation of chromium(III) ions. In this reaction, the dichromate ions are being oxidized, which means that they are losing electrons, and the chromium ions are being reduced, which means that they are gaining electrons. The transfer of electrons causes the color change from orange to green.

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Oxidation And Reduction

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Question 14 Report

If the cost of electricity required to discharge 10g of an ion $X^{3+}$ is N20.00, how much would it cost to discharge 6g of ion $Y^{2+}$?

[1 faraday = 96,500C, atomic masses are X = 27, Y = 24]

N10.00

N6.00

N20.00

N9.00

Answer Details

X

^{3 +}

+ 3e

^{-}

\to

X
3F = 27g
xF = 10g

\frac{x}{3} = \frac{10}{27} ⟹ x = \frac{10}{9} F

\frac{10}{9}

F

\equiv

N20.00
1F is equivalent to x

\frac{1}{\frac{10}{9}} = \frac{x}{20}

\frac{9}{10} = \frac{x}{20} ⟹ x = N 18.00

1F is equivalent to N18.00.
Y

^{2 +}

+ 2e

^{-}

\to

Y
2F = 24g
xF = 6g
x =

\frac{6 \times 2}{24} = \frac{1}{2} F

1F = N18.00

\frac{1}{2}

F =

\frac{1}{2} \times N 18.00

= N9.00

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Question 15 Report

The hybridization in the compound $ \mathrm{CH_3-CH_2-C\equiv H} $ is

sp

^{3}

and sp

sp

^{2}

sp

^{3}

and sp

^{2}

Answer Details

The hybridization in a and b is sp

^{3}

hybridization while in c and d is sp hybridization.

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Question 16 Report

The IUPAC name for $ \mathrm{CH_3CH_2COOCH_2CH_3} $ is

methylpropanoate

ethylethanoate

ethylpropanoate

methylethanoate

Answer Details

The IUPAC name for the given molecule is ethyl propanoate. To arrive at the IUPAC name, we first identify the longest continuous chain of carbon atoms, which in this case is a 4-carbon chain (propane). We then identify and name the substituent groups attached to this chain, which are a methyl group (CH3) attached to the second carbon atom and an ethoxy group (OC2H5) attached to the third carbon atom. The ethoxy group is named as an ethyl group, and the entire molecule is named as ethyl propanoate, following the standard IUPAC naming conventions for esters.

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

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Question 17 Report

The oxidation state(s) of nitrogen in ammonium nitrite is/are

-3, +3

+5

-3, +5

-3

Answer Details

Ammonium nitrite = NH

_{4}

NO

_{2}

NH

_{4}^{+}

: Let the oxidation number of Nitrogen = x
x + 4 = 1

⟹

x = 1 - 4
x = -3
NO

_{2}^{-}

: x - 4 = -1
x = -1 + 4

⟹

x = +3.
The oxidation numbers for Nitrogen in Ammonium Nitrite = -3, +3.

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Oxidation And Reduction

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Question 18 Report

Methane is prepared in the laboratory by heating a mixture of sodium ethanoate with soda lime. The chemical constituent(s) of soda lime is/are

Ca(OH)

_{2}

and NaOH

Na

_{2}

CO

_{3}

NaCl

NaOH

Answer Details

The chemical constituent of soda lime used to prepare methane in the laboratory is Ca(OH)2 (calcium hydroxide) and NaOH (sodium hydroxide). Soda lime is a mixture of these two compounds. When sodium ethanoate (NaC2H3O2) is heated with soda lime, it undergoes a reaction known as the Kolbe's reaction, which produces methane gas (CH4) as one of the products. The reaction can be represented as follows: 2NaC2H3O2 + 2Ca(OH)2 → 2CH4 + 2NaOH + 2CaCO3 In this reaction, the sodium ethanoate reacts with the calcium hydroxide to form calcium acetate (Ca(C2H3O2)2) and sodium hydroxide. The calcium acetate then decomposes to produce methane gas and calcium carbonate (CaCO3), which is a solid precipitate. Therefore, the chemical constituents of soda lime used to prepare methane in the laboratory are calcium hydroxide (Ca(OH)2) and sodium hydroxide (NaOH).

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Chemical Combination

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Question 19 Report

The following are isoelectronic ions except

Na

^{+}

Mg

^{2 +}

Si

^{2 +}

O

^{2 +}

Answer Details

Two or more ions are said to be isoelectronic if they have the same electronic structure and the same number of valence electrons.
Na

^{+}

= 10 electrons = 2, 8
Mg

^{2 +}

= 10 electrons = 2,8
O

^{2 -}

= 10 electrons = 2,8
Si

^{2 +}

= 12 electrons = 2,8,2

⟹

Si

^{2 +}

is not isoelectronic with the rest.

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

Read lesson note on Atomic Structure And Bonding (JAMB)

Acids, Bases And Salts (Nigeria Only)

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Question 20 Report

Which of the following is the best starting material for the preparation of oxygen? Heating of trioxonitrate (v) with

Pb

Zn

Ca

Na

Chemical Combination

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Question 21 Report

A cell shorthand notation can be written as $A / A^{+} // B^{2+} / B$. The double slash in the notation represents the

electrolyte

electrodes

salt bridge

solid - liquid interface

Answer Details

The double slash in the cell shorthand notation represents the salt bridge. A salt bridge is a component of an electrochemical cell that connects the two half-cells and allows the flow of ions between them. It consists of an inert electrolyte solution (usually a salt) that is placed between the two half-cells. The purpose of the salt bridge is to maintain electrical neutrality in each half-cell by allowing the flow of ions to balance the charge buildup in the half-cells. In the cell shorthand notation, the double slash "//" represents the salt bridge that connects the two half-cells of the electrochemical cell. The first half-cell is represented on the left-hand side of the slash and the second half-cell is represented on the right-hand side of the slash. The anode (where oxidation occurs) is represented on the left side, and the cathode (where reduction occurs) is represented on the right side. Therefore, the correct answer is option number 3: salt bridge.

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Electrolysis

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Question 22 Report

For the general equation of the nature

XP + yQ ⇌ mR + nS, the expression for the equilibrium constant is

k[P]

^{x}

[Q]

^{y}

\frac{m [R] [S]}{x [P] y [Q]}

\frac{[P]^{x} [Q]^{y}}{[R]^{m} [S]^{n}}

\frac{[R]^{m} [S]^{n}}{[P]^{x} [Q]^{y}}

Answer Details

The expression for the equilibrium constant for the general equation XP + yQ ⇌ mR + nS is: Kc = [R]m[S]n / [P]x[Q]y where Kc is the equilibrium constant, [R] and [S] are the concentrations of the products, and [P] and [Q] are the concentrations of the reactants, all raised to the stoichiometric coefficients (m, n, x, y) in the balanced equation. This equation is known as the equilibrium constant expression and it represents the ratio of the concentrations of the products and reactants at equilibrium for a particular chemical reaction. The equilibrium constant is a measure of how far a reaction proceeds towards completion, with a larger value indicating a greater extent of reaction. The equilibrium constant expression is derived from the law of mass action, which states that the rate of a chemical reaction is proportional to the product of the concentrations of the reactants raised to their stoichiometric coefficients. At equilibrium, the rates of the forward and reverse reactions are equal, and the equilibrium constant expression represents the ratio of the rate constants for these two reactions. Therefore, the correct expression for the equilibrium constant for the general equation XP + yQ ⇌ mR + nS is Kc = [R]m[S]n / [P]x[Q]y.

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Read lesson note on Chemical Equilibria (JAMB)

Chemical Kinetics And Equilibrium Systems (Ghana Only)

Chemical Equilibria

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Question 23 Report

Which of the following is a physical change?

Exposing white phosphorus to air

Burning kerosene

Dissolving calcium in water

Freezing ice cream

Answer Details

A physical change refers to a change in a substance that does not result in a change in its chemical composition. Out of the options provided, freezing ice cream is a physical change. This is because when ice cream is frozen, it changes from a liquid state to a solid state without any chemical reaction occurring. Exposing white phosphorus to air is a chemical change, as it reacts with oxygen in the air to form a new substance, phosphorus oxide. Burning kerosene is also a chemical change, as it undergoes combustion to form new substances, such as carbon dioxide and water vapor. Dissolving calcium in water is a physical change, as it simply involves the physical mixing of two substances without any chemical reaction occurring. Therefore, the only option that is a physical change is freezing ice cream.

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

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Question 24 Report

Which of the following gases contains the least number of atoms at s.t.p?

1 mole of butane

4 moles of chlorine

3 moles of ozone

7 moles of argon

Answer Details

At standard temperature and pressure (s.t.p), all gases have the same number of atoms or molecules. What changes between them is the volume they occupy, and this is dependent on their molecular mass and the number of moles. Comparing the number of moles between the gases listed above, 7 moles of argon will contain the most number of atoms, followed by 4 moles of chlorine, then 3 moles of ozone, and finally 1 mole of butane would contain the least number of atoms. In summary, the number of atoms in a gas sample depends on the number of moles, but at s.t.p, the volume occupied by each gas depends on its molecular mass and the number of moles.

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

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Question 25 Report

Which of the following does not support the fact that air is a mixture?

the constituents of air are in a fixed proportion by mass

it cannot be represented with a chemical formula

the constituents of air can be separated by physical by physical means

none of the above

Answer Details

The option that does not support the fact that air is a mixture is "the constituents of air are in a fixed proportion by mass". Air is a mixture of different gases, primarily nitrogen (78%) and oxygen (21%), with small amounts of other gases such as carbon dioxide, argon, and neon. The proportion of each gas in air is not fixed and can vary depending on the location and other factors. For example, the amount of carbon dioxide in air can increase in areas with high levels of pollution, while the proportion of oxygen can decrease at high altitudes. Therefore, the composition of air is not in a fixed proportion by mass. On the other hand, the fact that air cannot be represented with a chemical formula and its constituents can be separated by physical means support the fact that air is a mixture. A chemical formula represents a pure substance, and since air is a mixture of gases, it cannot be represented by a single formula. Air can be separated into its individual components through physical means such as distillation or filtration, which is a characteristic of mixtures.

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Air

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Question 26 Report

Consider the reaction

$ \mathrm{A(s) + 2B(g) \rightarrow 2C(aq) + D(g)} $

What will be the effect of a decrease in pressure on the reaction?

the equilibrium will shift

rate of forward reaction will increase

rate of backward reaction will increase

rates of forward and backward reaction are not affected

Answer Details

Given: The equation below

A $_{(s)}$ + 2B $_{(g)}$ → 2C $_{(a q)}$ + D $_{(g)}$

Since we have a higher number of moles of gaseous species on the LHS, i.e 2, a decrease in pressure will favor the forward reaction.

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

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

Chemical Kinetics And Equilibrium Systems (Ghana Only)

Periodic Chemistry (Ghana Only)

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Question 27 Report

In the reaction between sodium hydroxide and tetraoxosulphate (VI) solutions, what volume of 0.5 molar sodium hydroxide would exactly neutralize 10cm$^{3}$ of 1.25 molar tetraoxosulphate (vi) acid?

25cm

^{3}

10cm

^{3}

20cm

^{3}

50cm

^{3}

Answer Details

Equation of reaction : 2NaOH + H

_{2}

SO

_{4}

→ Na

_{2}

SO

_{4}

+ 2H

_{2}

O

Concentration of a base, CB = 0.5M

Volume of acid, V $_{A}$ = 10cm $^{3}$

Concentration of an acid, C $_{A}$ = 1.25M

Volume of base, V $_{B}$ = ?

Recall:
$\frac{C_{A} V_{A}}{C_{B} V_{B}} = \frac{n_{A}}{n_{B}}$ ... (1)
N.B: From the equation,
$\frac{n_{A}}{n_{B}} = \frac{1}{2}$

From (1)
$\frac{1.25 \times 10}{0.5 \times V_{B}} = \frac{1}{2}$
$\frac{12.5}{0.5 V_{B}} = \frac{1}{2}$
25 = 0.5V $_{B}$

VB = 50.0 cm $^{3}$

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Stoichiometry And Chemical Reactions

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Question 28 Report

By what amount must the temperature of 200cm$^{3}$ of Nitrogen at 27°C be increased to double the pressure if the final volume is 150cm$^{3}$ (Assume ideality)

150°C

177°C

75°C

120°C

Answer Details

Using the ideal gas law and equation:

\frac{P_{1} V_{1}}{T_{1}} = \frac{P_{2} V_{2}}{T_{2}}

\frac{P_{1} \times 200 {cm}^{3}}{300 K} = \frac{2 P \times 150 {cm}^{3}}{T_{2}}

Cross multiply:

T_{2} = \frac{300 \times 150 \times 2 P}{200 \times P}

= 450 K

or

177^{\circ} C

Don't forget to convert to

^{\circ} C

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

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Question 29 Report

Which important nitrogen-containing compound is produced in Haber's process?

NH

_{3}

NO

_{2}

NO

HNO

_{3}

Answer Details

The important nitrogen-containing compound that is produced in Haber's process is NH3, which is also known as ammonia. Haber's process is a chemical process used to produce ammonia by reacting nitrogen gas (N2) and hydrogen gas (H2) under high pressure and temperature in the presence of an iron catalyst. The reaction between nitrogen and hydrogen produces ammonia as the main product, along with some nitrogen and hydrogen gases that do not react. NH3 is an important compound that is widely used in industry for the production of fertilizers, plastics, and other chemical products. It is also used as a cleaning agent, a refrigerant, and a fuel for engines. In addition, NH3 is an essential compound for life, as it is a key component of amino acids, which are the building blocks of proteins.

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Question 30 Report

The molecular shape and bond angle of water are respectively

linear, 180°

bent, 109.5°

tetrahedral, 109.5°

bent, 105°

Answer Details

The shape of water molecule = Bent/ V- shaped
The bond angle of water = 104.5°/ 105°

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Question 31 Report

Which two gases can be used for the demonstration of the fountain experiment?

SO

_{3}

and NH

_{3}

SO

_{2}

and NH

_{3}

HCl and NH

_{3}

SO

_{2}

and HCl

Answer Details

Two gases that can be used in the study of fountain experiment is ammonia gas and hydrogen chloride gas. The experiment introduces concepts like solubility and the gas laws at the entry level.

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

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Question 32 Report

Which of the following will give a precipitate with an aqueous solution of copper (I) chloride?

But-2-ene

But-1-ene

But-2-yne

But-1-yne

Rates Of Chemical Reaction

Chemical Bonds (Ghana Only)

Redox Reactions

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Question 33 Report

Which of the following sets of operation will completely separate a mixture of sodium chloride, sand and iodine?

addition of water, filtration, evaporation to dryness and sublimation

filtration, evaporation to dryness, addition of water and sublimation

sublimation, filtration, evaporation and addition of water

sublimation, addition of water, filtration and evaporation to dryness

Answer Details

The set of operations that will completely separate a mixture of sodium chloride, sand, and iodine is: - filtration, to separate the sand and iodine from the sodium chloride - evaporation to dryness, to concentrate the sodium chloride solution and remove any remaining water - sublimation, to separate the iodine as a solid from the remaining sodium chloride By using these operations, you can separate each component of the mixture into separate, pure forms. The order of the operations is important because each step must be done in a way that effectively separates the components and does not interfere with subsequent steps.

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 34 Report

At 27°C, 58.5g of sodium chloride is present in 250cm$^3$ of a solution. The solubility of sodium chloride at this temperature is?

(molar mass of sodium chloride = 111.0gmol$^{-1}$)

2.0 moldm

^{- 3}

0.25 moldm

^{- 3}

1.0 moldm

^{- 3}

0.5 moldm

^{- 3}

Answer Details

Given the Mass of the salt = 58.5g
Volume = 250 cm

^{3}

= 0.25 dm

^{3}

Mass concentration =

\frac{M a s s}{V o l u m e}

=

\frac{58.5}{0.25}

= 234 gdm

^{- 3}

Solubility (in moldm

^{- 3}

=

\frac{234}{111}

= 2.11 moldm

^{- 3}

≊

2.0 moldm

^{- 3}

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Solubility Of Substances (Ghana Only)

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Question 35 Report

What volume of 0.100M sodium trioxonitrate (V) solution contains 5g of solute.

[Na = 23, N = 14, O = 16]

1.7 litres

0.420 litres

0.588 litres

2.35 litres

Answer Details

To calculate the volume of a solution, we need to use the formula: moles of solute = concentration x volume First, let's find the number of moles of sodium trioxonitrate (V) in 5g of the solute. The molar mass of NaNO3 is: Na = 23 N = 14 3 x O = 3 x 16 = 48 Molar mass = 23 + 14 + 48 = 85 g/mol The number of moles of NaNO3 in 5g is: moles = mass / molar mass = 5 / 85 = 0.0588 moles Now, we can use the formula above to find the volume of the solution: moles of solute = concentration x volume volume = moles of solute / concentration volume = 0.0588 moles / 0.100 M volume = 0.588 litres Therefore, the correct answer is 0.588 litres of 0.100M sodium trioxonitrate (V) solution contains 5g of solute.

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Stoichiometry And Chemical Reactions

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Question 36 Report

Which of the following could not be alkane?

C

_{4}

H

_{10}

C

_{5}

H

_{12}

C

_{7}

H

_{14}

C

_{8}

H

_{18}

Answer Details

An alkane is a type of hydrocarbon with only single bonds between the carbon atoms. It follows the general formula CnH2n+2, where "n" is the number of carbon atoms in the molecule. To determine whether a molecule is an alkane or not, we can calculate its molecular formula and check if it fits the general formula of alkane. Out of the given options, the third one (C7H14) cannot be an alkane. To see why, let's use the general formula of alkane, which is CnH2n+2. For C7H14 to be an alkane, it should have 2n+2 = 2(7) + 2 = 16 hydrogen atoms. However, C7H14 has only 14 hydrogen atoms, which means it does not follow the general formula of alkane. Therefore, C7H14 cannot be an alkane. The other options are as follows: - C4H10: This is butane, which is an alkane with four carbon atoms. - C5H12: This is pentane, which is an alkane with five carbon atoms. - C8H18: This is octane, which is an alkane with eight carbon atoms. In summary, the molecule C7H14 cannot be an alkane because it does not follow the general formula of alkane, while the other options are all examples of alkanes.

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Question 37 Report

Elements X and Y have electronic configurations $1s^2 2s^2 2p^4$ and $1s^2 2s^2 2p^6 3s^2 3p^1$ respectively. When they combine, the formula of the compound formed is

XY

X

_{2}

Y

_{2}

X

_{3}

X

_{2}

Y

_{3}

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Question 38 Report

The heat of formation of ethene, $ \mathrm{C_2H_4} $ is 50 $ \mathrm{kJmol^{-1}} $, and that of ethane, $ \mathrm{C_2H_6} $ is -82$ \mathrm{kJmol^{-1}} $. Calculate the heat evolved in the process:

\[ \mathrm{C_2H_4 + H_2 \rightarrow C_2H_6} \]

-122kJ

-132kJ

-88kJ

-60kJ

Answer Details

The heat evolved in a chemical reaction can be calculated by subtracting the heat of formation of the reactants from the heat of formation of the products. In this case, the reactants are ethene (C2H4) and hydrogen (H2), and the product is ethane (C2H6). The heat of formation of ethene is 50 kJ/mol and that of hydrogen is 0 kJ/mol (because hydrogen is a reference element). The heat of formation of ethane is -82 kJ/mol. So, the heat evolved in the reaction is given by: Heat evolved = (Heat of formation of products) - (Heat of formation of reactants) = (-82 kJ/mol) - (50 kJ/mol + 0 kJ/mol) = -82 kJ/mol - 50 kJ/mol = -132 kJ/mol. Therefore, the heat evolved in the process is -132 kJ.

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Energy Changes

Stoichiometry And Chemical Reactions

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Question 39 Report

Which quantum divides shells into orbitals?

Spin

Principal

Azimuthal

Magnetic

Answer Details

The quantum that divides shells into orbitals is the "Azimuthal" quantum number, also known as the "angular momentum" quantum number. The azimuthal quantum number determines the shape of an electron's orbital, which is a region in space where there is a high probability of finding an electron. It describes the angular momentum of an electron in an atom and the number of subshells within a given shell. Each subshell is associated with a specific shape, and can hold a certain number of electrons. The azimuthal quantum number is represented by the letter "l" and can have integer values ranging from 0 to (n-1), where "n" is the principal quantum number. Each value of "l" corresponds to a different subshell shape: - l = 0 corresponds to an "s" subshell, which is spherical in shape. - l = 1 corresponds to a "p" subshell, which has a dumbbell shape with two lobes. - l = 2 corresponds to a "d" subshell, which has a more complex shape with four lobes and a doughnut-like ring. - l = 3 corresponds to an "f" subshell, which has an even more complex shape with eight lobes. The number of orbitals within a subshell is equal to 2l+1. For example, a "p" subshell (l = 1) has three orbitals (2l+1 = 3), which are labeled as "px", "py", and "pz". In summary, the azimuthal quantum number determines the shape of the electron's orbital and the number of subshells within a given shell, and it is represented by the letter "l".

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