WAEC SSCE - Chemistry - 2015 (Objective)
Question 1 Report
The number of unpaired electrons in an atom of an element 8Q is _______?
Answer Details
To determine the number of unpaired electrons in an atom of an element, we need to know its electron configuration. The electron configuration of an element describes how its electrons are distributed in energy levels or orbitals. The element Q has an atomic number of 8, which means it has 8 electrons in its neutral state. To determine its electron configuration, we can use the periodic table. Q is in the second period and the 6th group (also known as group 16 or the oxygen group), which means it has 6 valence electrons. The electron configuration for Q is: 1s2 2s2 2p4 To determine the number of unpaired electrons, we need to look at the electron configuration and identify how many electrons occupy each orbital. In the case of Q, there are two electrons in the 2s orbital and four electrons in the 2p orbitals. The 2p orbitals each have one electron with the same spin, which means they are unpaired. Therefore, Q has 2 unpaired electrons. The answer is (A) 2.
Question 2 Report
The vapour pressure of a liquid depends on:
I. Temperature II. rate of condensation III. Cohesive forces holding the particles together.
Question 5 Report
Consider the following reaction equation:
C2H4(g) + 3O2(g) \(\to\) 2CO2(g) + 2H2O(g)
The volume of CO2(g) produced at s.t.p when 0.05 moles of C2H4(g) was burnt in O2(g) is
[Molar Volume of gas = 22.4dm3
Answer Details
The balanced chemical equation is: C2H4(g) + 3O2(g) -> 2CO2(g) + 2H2O(g) From the equation, we can see that 1 mole of C2H4 produces 2 moles of CO2. Therefore, 0.05 moles of C2H4 will produce: 2 x 0.05 = 0.1 moles of CO2 Now we need to find the volume of 0.1 moles of CO2 at s.t.p. The molar volume of gas at s.t.p. is 22.4 dm3. So, the volume of 0.1 moles of CO2 at s.t.p. will be: 0.1 x 22.4 = 2.24 dm3 Therefore, the volume of CO2 produced at s.t.p when 0.05 moles of C2H4 was burnt in O2 is 2.24 dm3. Hence, the correct option is (b) 2.24 dm3.
Question 6 Report
The correct balanced equation for the reaction between aluminium metal and hot concentrated tetraoxosulphate(VI)acid is ?
Answer Details
Question 7 Report
The following transition metal ions would be coloured in aqueous solution except________?
Answer Details
The correct answer is Sc3+. Transition metal ions are often colored because their electrons can absorb light energy and jump to higher energy levels. When the electrons drop back down to their original energy levels, they release the energy as visible light, which we see as color. The color of the complex depends on the arrangement of the ligands around the metal ion. Scandium (Sc) has only one electron in its outermost shell, which it loses to form the Sc3+ ion. Since it has an empty d-orbital, it cannot absorb light in the visible region, and therefore it is colorless in aqueous solution. On the other hand, Cr3+, Fe3+, and Mn3+ ions have partially filled d-orbitals, which allow them to absorb light in the visible region and give them characteristic colors in aqueous solution. Cr3+ is violet, Fe3+ is yellow, and Mn3+ is pink.
Question 8 Report
When a reaction is endothermic,
Question 9 Report
Which of the following process does not take place in domestic water treatment?
Answer Details
The process that does not take place in domestic water treatment is neutralization. Domestic water treatment involves several processes to make water safe for human consumption. Chlorination is a process that involves adding chlorine to water to kill harmful microorganisms. Flocculation is the process of adding a chemical called a flocculant to water to help clump together small particles and impurities, making it easier to remove them through sedimentation. Sedimentation is a process in which the water is left to settle, allowing heavy particles and impurities to sink to the bottom. Neutralization, on the other hand, is a chemical process that involves the reaction of an acid with a base to form water and a salt. This process is not typically used in domestic water treatment, as the pH of the water is usually adjusted through other means such as adding lime or carbon dioxide.
Question 10 Report
Which of the following trioxonitrate(V) salts would decompose on heating to form a metal?
Answer Details
Question 11 Report
Which of the following pairs of compounds belongs to the same homologous series?
Answer Details
C2H6 and C4H10 belong to the same homologous series, which is the series of alkanes. The homologous series refers to a group of organic compounds that have similar structures and chemical properties, and the same functional group. They have a general formula, with the same difference in the number of carbon and hydrogen atoms between consecutive members. The alkanes are a homologous series of hydrocarbons with the general formula CnH2n+2. Therefore, C2H6 and C4H10 have different numbers of carbon atoms, but they both have only single bonds between the carbon atoms and hydrogen atoms.
Question 13 Report
Which of the following substances when boiled with aqueous solution of sodium hydroxide would be hydrolyzed?
i. Protein ii. Fat iii. Polythene
Answer Details
Protein and fat are both organic compounds that can undergo hydrolysis when boiled with an aqueous solution of sodium hydroxide. Polythene, on the other hand, is a synthetic polymer and is not susceptible to hydrolysis under such conditions. Therefore, the correct answer is (c) i and ii.
Question 14 Report
Which of the following gases is monoatomic?
Answer Details
Argon is the only monoatomic gas among the given options. Monoatomic gases are those that exist as individual atoms, not as molecules. Argon, with atomic number 18, exists as individual atoms and doesn't form molecules. Chlorine, nitrogen, and oxygen are all diatomic gases, meaning that they exist as molecules consisting of two atoms of the same element bonded together. Chlorine has the formula Cl2, nitrogen has the formula N2, and oxygen has the formula O2.
Question 16 Report
The shape of a graphite crystal is
Answer Details
The shape of a graphite crystal is hexagonal. Graphite is a form of carbon that consists of layers of carbon atoms arranged in a hexagonal lattice. The layers are held together by weak intermolecular forces called Van der Waals forces. Each carbon atom is bonded to three neighboring carbon atoms in a trigonal planar arrangement, resulting in a flat hexagonal structure. This gives graphite its characteristic layered structure, which makes it useful as a lubricant and as the "lead" in pencils.
Question 17 Report
The following diagram illustrates the rate curve that was obtained when Mg reacted with excess dilute HCl.
The diagram became horizontal at X because
Answer Details
Question 19 Report
How many orbits are contained in an atom with atomic number 13?
Answer Details
The atomic number of an element tells us the number of protons in its nucleus. For an electrically neutral atom, the number of electrons is equal to the number of protons. The electronic configuration of an atom with atomic number 13 is: 1s22s22p63s23p1. The electronic configuration tells us that there are three occupied energy levels or orbits, namely the first, second, and third energy levels. The first energy level has a maximum of 2 electrons, the second energy level has a maximum of 8 electrons, while the third energy level can hold a maximum of 18 electrons. Therefore, an atom with atomic number 13 has 3 energy levels, which are occupied by 13 electrons. So the answer is 3.
Question 20 Report
A substance responsible for the sour taste of unripe orange is
Answer Details
The substance responsible for the sour taste of unripe orange is an organic acid. Organic acids are a class of compounds that have at least one carboxyl group (-COOH) in their molecular structure. The most common organic acid found in oranges is citric acid. When an orange is unripe, it contains more citric acid, giving it a sour taste. As the fruit ripens, the citric acid content decreases, and the fruit becomes sweeter. Therefore, the correct option is alkanoic acid.
Question 21 Report
Which of the following compounds is a secondary alkanol?
Answer Details
A secondary alkanol is an alcohol where the carbon atom attached to the hydroxyl (-OH) group is bonded to two other carbon atoms. In other words, it has two alkyl groups attached to the carbon atom with the -OH group. Out of the options given, 2-methylbutan-2-ol and 3-methylpentan-2-ol have the required structure to be classified as secondary alkanols. Therefore, the correct answer is either 2-methylbutan-2-ol or 3-methylpentan-2-ol.
Question 22 Report
Consider the following reaction equation:
SO42-(aq) + 2H+(aq) + ye- \(\to\) SO42-(aq) + H2O(1).
The value of y in the equation is
Answer Details
The given reaction equation represents the reduction of sulfate ion (SO42-) to hydrogen sulfide (H2S) using two hydrogen ions (H+) and some number of electrons (e-). In order to balance the charges on both sides of the equation, the number of electrons must be equal to the positive charges on the left side. On the left side, there are 2 hydrogen ions (2H+) with a charge of +2 and one sulfate ion (SO42-) with a charge of -2. Thus, the total charge on the left side is 0. On the right side, there is one water molecule (H2O) with a charge of 0 and one sulfate ion (SO42-) with a charge of -2. Thus, the total charge on the right side is also -2. Since the charges on both sides must be equal, the number of electrons (y) involved in the reaction must be equal to the difference between the charges on both sides, which is 2. Therefore, the correct answer is y = 2.
Question 23 Report
Which of the following polymers in thermosetting?
Answer Details
Bakelite is a thermosetting polymer. Explanation: Thermosetting polymers are those that undergo a chemical reaction when heated and become irreversibly hard and rigid. Bakelite, which is also known as phenolic resin, is a thermosetting polymer that is synthesized by the reaction of phenol and formaldehyde. Once the reaction is complete, the resulting material is in a hard, infusible state that cannot be melted or reshaped by heating. On the other hand, nylon, polypropene, and polystyrene are thermoplastic polymers, which can be melted and reshaped upon heating.
Question 25 Report
A substance which dissolves readily in organic solvent would
Answer Details
A substance that dissolves readily in organic solvent would be a covalent compound. This is because organic solvents are usually nonpolar, which means that they dissolve substances that are also nonpolar or have weak polar characteristics. Covalent compounds are formed by the sharing of electrons between atoms and do not have strong electrostatic forces of attraction between their constituent atoms. This weak intermolecular attraction allows the organic solvent to penetrate and dissolve the covalent compound. In contrast, ionic compounds have strong electrostatic forces of attraction between their ions, which makes them insoluble in organic solvents. Covalent compounds typically have low melting points and do not conduct electricity in their solid or molten states because they do not have free-moving charged particles.
Question 26 Report
Solubility is practically applied in
Answer Details
Solubility is practically applied in solvent extraction. Solubility refers to the ability of a substance to dissolve in a given solvent. Solvent extraction is a process that uses solubility to separate a specific substance from a mixture. In this process, a substance is dissolved in a solvent that selectively dissolves the desired compound, leaving behind unwanted impurities. This technique is widely used in the chemical, pharmaceutical, and mining industries for the extraction and purification of various compounds.
Question 27 Report
Which of the following statements about intermolecular distances and cohesive forces between gas is correct? They are
Answer Details
The correct statement about intermolecular distances and cohesive forces between gases is "both negligible." The intermolecular distances between gas particles are very large compared to their size, so the cohesive forces between them are negligible. As a result, gases tend to expand to fill any available space and have no definite shape or volume. The kinetic energy of gas particles is much greater than the attractive forces between them, and as a result, they move freely and randomly in all directions.
Question 28 Report
Starch could be converted to glucose by the process of
Answer Details
Starch is a complex carbohydrate made up of many glucose units linked together. In order to convert it to glucose, the process of hydrolysis is required. Hydrolysis is a chemical reaction that involves breaking down a compound by adding water molecules. In the case of starch, enzymes can be used to break down the long chains of glucose molecules into individual glucose molecules by adding water. This process is used in the production of glucose syrup and other sweeteners, which are used in a variety of food products. The other options listed - condensation, dehydration, and fermentation - do not involve the breakdown of starch into glucose.
Question 29 Report
The general gas equation was deprived from______?
Answer Details
The general gas equation, also known as the ideal gas law, was derived from Boyle's and Charles' laws. Boyle's law states that the pressure of a gas is inversely proportional to its volume, while Charles' law states that the volume of a gas is directly proportional to its temperature. The general gas equation combines these two laws along with Avogadro's law, which states that equal volumes of gases under the same conditions of temperature and pressure contain the same number of molecules. The equation is PV = nRT, where P is pressure, V is volume, n is the number of moles, R is the gas constant, and T is temperature in Kelvin.
Question 30 Report
Which of the following statements about an electrochemical cell is correct? Oxidation occurs
Answer Details
The correct statement is "Oxidation occurs at the anode in an electrochemical cell." In an electrochemical cell, there are two half-cells: the anode and the cathode. At the anode, oxidation takes place, meaning that electrons are lost by the species being oxidized. These electrons travel through an external circuit to the cathode, where reduction takes place, and the electrons are gained by the species being reduced. This flow of electrons through the external circuit generates an electric current. The salt bridge is used to maintain electrical neutrality by allowing the flow of ions between the half-cells. The aqueous solution is where the species being oxidized and reduced are dissolved.
Question 31 Report
The number of oxygen molecules present in 16.0g of the gas is ______?
[Avogadro's number = 6.02 x 1023]
Answer Details
The molar mass of oxygen gas (O2) is 32 g/mol. Therefore, 16.0 g of oxygen gas will contain one-half the number of moles as its mass in grams. Number of moles = mass ÷ molar mass Number of moles of O2 in 16.0 g = 16.0 g ÷ 32 g/mol = 0.5 mol Since one mole of any substance contains Avogadro's number of particles (atoms or molecules), the number of oxygen molecules in 0.5 mol of O2 is: Number of molecules = Avogadro's number x Number of moles Number of molecules = 6.02 x 1023 x 0.5 = 3.01 x 1023 Therefore, the correct option is: 3.01 x 1023.
Question 32 Report
Which of the following gases will diffuse most rapidly?
[H = 1.00, C = 12.0, O = 16.0, S = 32.0, Cl = 35.5]
Answer Details
The rate of diffusion of gases is inversely proportional to their molar mass. Therefore, the gas with the lowest molar mass will diffuse the most rapidly. The molar mass of each gas is: - Cl2: 2 x 35.5 = 71.0 g/mol - SO2: 32.0 + 2 x 16.0 = 64.0 g/mol - CH4: 12.0 + 4 x 1.0 = 16.0 g/mol - C2H6: 2 x 12.0 + 6 x 1.0 = 30.0 g/mol Therefore, methane (CH4) has the lowest molar mass and will diffuse most rapidly among the given options.
Question 33 Report
The negatively charged particle in an atom is the
Answer Details
The negatively charged particle in an atom is the electron. Electrons are subatomic particles that orbit around the nucleus of an atom in shells or energy levels. They have a negative charge, which is equal in magnitude to the positive charge of a proton. Electrons are responsible for chemical bonding and the formation of ions in chemical reactions.
Question 34 Report
The Van der waals' forces are dominant intermolecular forces in_______?
Answer Details
The Van der Waals' forces are dominant intermolecular forces in Chlorine. Van der Waals' forces are weak intermolecular forces that exist between molecules due to temporary changes in electron density. These forces arise due to the attraction between the positively charged nucleus of one molecule and the negatively charged electrons of another molecule. Chlorine is a non-polar molecule, which means it has no net dipole moment. Van der Waals' forces are the strongest intermolecular forces acting between non-polar molecules, and as Chlorine is non-polar, it is the dominant intermolecular force acting between Chlorine molecules.
Question 35 Report
The bond formed when ammonia reacts with hydrogen ion to form ammonium ion is
Answer Details
The bond formed when ammonia reacts with hydrogen ion to form ammonium ion is a dative bond. In this reaction, the lone pair of electrons on the nitrogen atom of the ammonia molecule is donated to the hydrogen ion (H+) to form the ammonium ion (NH4+). This type of bond is also called a coordinate covalent bond, as both electrons in the bond come from the same atom (in this case, the nitrogen atom of the ammonia molecule).
Question 36 Report
The gas given off when ethanol reacts with sodium is
Answer Details
The gas given off when ethanol reacts with sodium is hydrogen. This is because sodium is a more reactive metal than hydrogen and it will displace the hydrogen in ethanol, forming sodium ethoxide and hydrogen gas. The reaction can be represented as follows: C2H5OH + Na → C2H5ONa + H2 So, during this reaction, hydrogen gas is evolved as a product.
Question 37 Report
A change in the temperature of a saturated solution disturbs the equilibrium between the
Question 38 Report
A compound has an empirical formular CH2O and molecular mass of 90.
[H = 1.00, C = 12.0, O = 16.0]
Answer Details
The empirical formula of the compound is CH2O, which indicates that for every carbon atom there are two hydrogen atoms and one oxygen atom. The molecular mass of the compound is 90, which is the sum of the atomic masses of all the atoms in the molecule. Let's calculate the molecular formula of the compound using this information. The empirical formula mass of CH2O is: (1 x 12.0) + (2 x 1.00) + (1 x 16.0) = 30.0 g/mol To calculate the molecular formula, we need to divide the molecular mass by the empirical formula mass: Molecular formula mass / Empirical formula mass = n 90.0 / 30.0 = 3 Therefore, the molecular formula of the compound is three times the empirical formula: C3H6O3 So, the correct option is C3H6O3.
Question 39 Report
The shape of a molecule of water is _______?
Answer Details
The shape of a molecule of water is non-linear. A water molecule consists of two hydrogen atoms and one oxygen atom. The oxygen atom is more electronegative than the hydrogen atoms, so it pulls the shared electrons towards itself, creating a partial negative charge on the oxygen and partial positive charges on the hydrogen atoms. This results in a bent or non-linear shape of the water molecule, where the oxygen atom is at the center, and the two hydrogen atoms are positioned at an angle of about 104.5 degrees with respect to each other.
Question 40 Report
Which of the following reactions would take place when concentrated sodium hydroxide solution is added to palm oil?
Answer Details
The correct answer is saponification. When concentrated sodium hydroxide is added to palm oil, the triglyceride esters present in palm oil react with the sodium hydroxide to form glycerol and sodium salts of fatty acids. This process is called saponification, and the resulting product is soap. Therefore, saponification is the correct answer.
Question 41 Report
The complete hydrogenation of benzene gives
Answer Details
The complete hydrogenation of benzene involves adding hydrogen gas (H2) to the benzene ring under the right conditions. This reaction is known as hydrogenation and it can be catalyzed by a metal catalyst, such as platinum or nickel. During the reaction, the double bonds in the benzene ring are broken and each carbon atom in the ring is bonded to two hydrogen atoms. The product of the reaction is cyclohexane, a six-membered ring hydrocarbon with single bonds between all the carbon atoms. Therefore, the correct answer is (b) Cyclohexane.
Question 42 Report
Which of the following products of biotechnology can be used as a fuel in place of petrol?
Answer Details
Question 43 Report
Consider the following equilibrium system:
2SO2(g) + O2(g) \(\rightleftharpoons\) 2SO3(g)
The addition of more O2(g) to the system will shift the equilibrium position to the
Answer Details
Question 44 Report
Which of the following compounds is the least soluble in water?
Answer Details
The solubility of a compound in water is determined by its ability to dissociate into ions in the water. Compounds that dissociate completely into ions are more soluble in water than those that do not dissociate as much. Looking at the given compounds, CaCl2 dissociates into three ions (Ca2+ and two Cl-) in water and NaCl dissociates into two ions (Na+ and Cl-). CaSO4 dissociates into two ions (Ca2+ and SO42-) but it is less soluble than CaCl2 because the SO42- ion is larger and more polar than the Cl- ion, so it has a stronger attraction to the Ca2+ ion, making it more difficult to dissociate. Na2SO4 dissociates into three ions (two Na+ and SO42-) but it is also less soluble than NaCl because of the larger, more polar SO42- ion. Therefore, CaSO4 is the least soluble compound in water because it has a weaker ability to dissociate into ions in water compared to the other given compounds.
Question 45 Report
The alkaline earth metals have similar chemical properties because________?
Answer Details
The correct option is: They have the same number of valence electrons. Alkaline earth metals are the elements in Group 2 of the periodic table. They have similar chemical properties because they have the same number of valence electrons, which is two. The valence electrons of an element are the electrons in the outermost shell of the atom, and they determine the chemical properties of the element. Because alkaline earth metals have two valence electrons, they have similar reactivity and form similar types of chemical bonds. For example, they react with nonmetals to form ionic compounds with a 2+ charge. So, their similar chemical properties are due to the fact that they all have two valence electrons.
Question 46 Report
To which group and period respectively does an element with 15 electrons belong?
Answer Details
Question 47 Report
A metallic ion Z2+ with an inert gas structure contains 18 electrons. How many protons are contained in this ion?
Answer Details
Question 48 Report
An example of an acid salt is
Answer Details
The correct answer is (c) NaHSO4. An acid salt is a salt that is derived from the partial neutralization of an acid, resulting in a substance that has both acidic and basic properties. NaHSO4 is an example of an acid salt because it is derived from the partial neutralization of sulfuric acid (H2SO4) with sodium hydroxide (NaOH). It has acidic properties because it can donate a hydrogen ion (H+) in water, and it has basic properties because it can accept a hydrogen ion (H+) in the presence of a strong acid. The other options are not acid salts. CH3COOONa is a salt of a weak acid (acetic acid) and a strong base (sodium hydroxide), and therefore it is a basic salt. Mg(OH)Cl is a salt of a strong base (magnesium hydroxide) and a strong acid (hydrochloric acid), and therefore it is a neutral salt. (NH4)2SO4 is a salt of a weak base (ammonia) and a strong acid (sulfuric acid), and therefore it is an acidic salt.
Question 50 Report
Consider the following reaction equation:
CuO(s) + H2(g) \(\to\) Cu(s) + H2O(1)
Which substance is oxidized?
Answer Details
In the given reaction equation, CuO reacts with H2 to form Cu and H2O. Here, CuO is reduced to Cu and H2 is oxidized to H2O. So, the substance that is oxidized in the reaction is H2.
