WAEC SSCE - Chemistry - 2015
Question 2 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 4 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.
Question 5 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 6 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 7 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 8 Report
A change in the temperature of a saturated solution disturbs the equilibrium between the
Question 9 Report
Which of the following products of biotechnology can be used as a fuel in place of petrol?
Answer Details
Question 10 Report
The correct balanced equation for the reaction between aluminium metal and hot concentrated tetraoxosulphate(VI)acid is ?
Answer Details
Question 11 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 12 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 14 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 15 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 17 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 18 Report
To which group and period respectively does an element with 15 electrons belong?
Answer Details
Question 19 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 20 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 21 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 22 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 23 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 24 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 25 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 26 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 28 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 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
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 31 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 32 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 33 Report
Which of the following trioxonitrate(V) salts would decompose on heating to form a metal?
Answer Details
Question 34 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 35 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 36 Report
When a reaction is endothermic,
Question 37 Report
The vapour pressure of a liquid depends on:
I. Temperature II. rate of condensation III. Cohesive forces holding the particles together.
Question 38 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 39 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 40 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 41 Report
A metallic ion Z2+ with an inert gas structure contains 18 electrons. How many protons are contained in this ion?
Answer Details
Question 43 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 45 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 46 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 47 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 48 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 49 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 50 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 51 Report
(a) Consider the following table; (i) Which of the elements:
| Element | Atomic Number | Mass Number |
| J | 9 | 19 |
| Q | 13 | 27 |
| R | 16 | 32 |
| X | 19 | 39 |
| Y | 24 | 52 |
I. is a halogen?
II. is most likely to be attracted by a magnet?
III. belongs to group I?
IV. would readily form an ion with a double negative charge?
(ii) What type of bond would exist between J and X when they combine?
(iii) How many neutrons are there in Q?
(iv) Write the formula of the compound formed when R combines with X.
(v) State the element which exists as diatomic molecule..
(vi) Select the element which belong to the d-block of the periodic table.
(b)(i) Explain briefly the term atomic orbital
(ii) I. State three prostulates of Dalton's atomic theory.
II. List two limitations of this theory in the study of the atom
(iii) Describe briefly the structure of sodium chloride in its solid state.
(c) A sample of carbon is burnt at a rate of 0.50g per second for 30 minutes to generate heat.
(i) Write a balanced equation for the reaction
(ii) Determine the:
I. volume of carbon (IV) oxide produced at s.t.p.
II. moles of oxygen used up in the process at s.t.p. [C = 12.0, O = 16.0, Molar volume \(V_m\) = 22.4 dm\(^3\)].
Identify each element from its atomic number and mass number.
| Element | Atomic number | Mass number | Identity |
|---|---|---|---|
| J | 9 | 19 | Fluorine, F |
| Q | 13 | 27 | Aluminium, Al |
| R | 16 | 32 | Sulfur, S |
| X | 19 | 39 | Potassium, K |
| Y | 24 | 52 | Chromium, Cr |
(a)(i)
- I. Halogen: J (fluorine), a Group 7 element.
- II. Most likely attracted by a magnet: Y (chromium), a transition metal.
- III. Belongs to Group 1: X (potassium), configuration 2,8,8,1.
- IV. Readily forms an ion with a double negative charge: R (sulfur), which gains 2 electrons to form S2-.
(a)(ii) J is a Group 7 non-metal and X is a Group 1 metal, so they form an ionic (electrovalent) bond (potassium transfers one electron to fluorine, giving K+ and F-).
(a)(iii) Neutrons in Q:
\[\text{neutrons} = \text{mass number} - \text{atomic number} = 27 - 13 = \mathbf{14}\](a)(iv) R (S2-) combines with X (K+). Balancing charges gives K2S.
(a)(v) The element that exists as a diatomic molecule is J (fluorine, F2).
(a)(vi) The d-block element is Y (chromium).
(b)(i) An atomic orbital is a region in space around the nucleus of an atom where the probability of finding an electron is highest.
(b)(ii) I. Three postulates of Dalton's atomic theory:
- All matter is made up of tiny, indivisible particles called atoms.
- Atoms of the same element are identical in mass and chemical properties, while atoms of different elements differ.
- Atoms combine in simple whole-number ratios to form compounds, and atoms are neither created nor destroyed in a chemical reaction.
II. Two limitations of the theory:
- The atom is not indivisible; it is made up of smaller particles (protons, neutrons and electrons).
- Atoms of the same element are not always identical in mass, because of the existence of isotopes.
(b)(iii) In the solid state, sodium chloride has a giant ionic lattice. Na+ and Cl- ions are arranged alternately in a face-centred cubic structure, each Na+ surrounded by 6 Cl- ions and each Cl- surrounded by 6 Na+ ions (6:6 coordination), held together by strong electrostatic forces of attraction.
(c) Carbon burnt at 0.50 g per second for 30 minutes.
Total mass of carbon burnt:
\[m = 0.50\ \text{g s}^{-1} \times (30 \times 60)\ \text{s} = 0.50 \times 1800 = 900\ \text{g}\]Moles of carbon:
\[n_C = \frac{900}{12.0} = 75\ \text{mol}\](i) Balanced equation:
\[\text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g)\](ii) I. From the equation, 1 mol C gives 1 mol CO2, so 75 mol C gives 75 mol CO2.
\[V_{CO_2} = 75\ \text{mol} \times 22.4\ \text{dm}^3\,\text{mol}^{-1} = \mathbf{1680\ dm^3}\]II. From the equation, 1 mol C uses 1 mol O2, so:
\[n_{O_2} = 75\ \text{mol} \times \frac{1}{1} = \mathbf{75\ mol}\]Answer Details
Identify each element from its atomic number and mass number.
| Element | Atomic number | Mass number | Identity |
|---|---|---|---|
| J | 9 | 19 | Fluorine, F |
| Q | 13 | 27 | Aluminium, Al |
| R | 16 | 32 | Sulfur, S |
| X | 19 | 39 | Potassium, K |
| Y | 24 | 52 | Chromium, Cr |
(a)(i)
- I. Halogen: J (fluorine), a Group 7 element.
- II. Most likely attracted by a magnet: Y (chromium), a transition metal.
- III. Belongs to Group 1: X (potassium), configuration 2,8,8,1.
- IV. Readily forms an ion with a double negative charge: R (sulfur), which gains 2 electrons to form S2-.
(a)(ii) J is a Group 7 non-metal and X is a Group 1 metal, so they form an ionic (electrovalent) bond (potassium transfers one electron to fluorine, giving K+ and F-).
(a)(iii) Neutrons in Q:
\[\text{neutrons} = \text{mass number} - \text{atomic number} = 27 - 13 = \mathbf{14}\](a)(iv) R (S2-) combines with X (K+). Balancing charges gives K2S.
(a)(v) The element that exists as a diatomic molecule is J (fluorine, F2).
(a)(vi) The d-block element is Y (chromium).
(b)(i) An atomic orbital is a region in space around the nucleus of an atom where the probability of finding an electron is highest.
(b)(ii) I. Three postulates of Dalton's atomic theory:
- All matter is made up of tiny, indivisible particles called atoms.
- Atoms of the same element are identical in mass and chemical properties, while atoms of different elements differ.
- Atoms combine in simple whole-number ratios to form compounds, and atoms are neither created nor destroyed in a chemical reaction.
II. Two limitations of the theory:
- The atom is not indivisible; it is made up of smaller particles (protons, neutrons and electrons).
- Atoms of the same element are not always identical in mass, because of the existence of isotopes.
(b)(iii) In the solid state, sodium chloride has a giant ionic lattice. Na+ and Cl- ions are arranged alternately in a face-centred cubic structure, each Na+ surrounded by 6 Cl- ions and each Cl- surrounded by 6 Na+ ions (6:6 coordination), held together by strong electrostatic forces of attraction.
(c) Carbon burnt at 0.50 g per second for 30 minutes.
Total mass of carbon burnt:
\[m = 0.50\ \text{g s}^{-1} \times (30 \times 60)\ \text{s} = 0.50 \times 1800 = 900\ \text{g}\]Moles of carbon:
\[n_C = \frac{900}{12.0} = 75\ \text{mol}\](i) Balanced equation:
\[\text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g)\](ii) I. From the equation, 1 mol C gives 1 mol CO2, so 75 mol C gives 75 mol CO2.
\[V_{CO_2} = 75\ \text{mol} \times 22.4\ \text{dm}^3\,\text{mol}^{-1} = \mathbf{1680\ dm^3}\]II. From the equation, 1 mol C uses 1 mol O2, so:
\[n_{O_2} = 75\ \text{mol} \times \frac{1}{1} = \mathbf{75\ mol}\]Question 52 Report
(a) Define esterification.
(b) State two properties of plastic.
(c) Name the components of duralumin.
(d) What is meant by each of the following terms?
(i) Raw material.
(ii) Primary product.
(e) State Charles' law.
(f) List four pieces of protective equipment in the laboratory.
(g) Give two uses of ammonia.
(h) Name the:
(i) process by which lighter hydrocarbons are obtained from heavier ones;
(ii) products formed from the reaction between ethanol and sodium metal.
(i) Determine the oxidation number of sulphur in H\(_2\)SO\(_4\).
(j) Write the IUPAC name for each of the following compounds: (i) NaClO\(_3\); (ii) CuSO\(_4\)5H\(_2\)O.
(a) Esterification is the reaction between a carboxylic (alkanoic) acid and an alcohol (alkanol), in the presence of a little concentrated H2SO4, to form an ester (alkanoate) and water.
(b) Two properties of plastic: it is light (low density) and a poor conductor of heat and electricity (also resistant to corrosion, mouldable, non-biodegradable).
(c) Duralumin contains aluminium, copper, magnesium and manganese.
(d)(i) A raw material is a naturally occurring substance from which useful products are manufactured.
(ii) A primary product is the product obtained directly (first) from processing a raw material.
(e) Charles' law: the volume of a fixed mass of gas is directly proportional to its absolute (Kelvin) temperature at constant pressure. \(\dfrac{V}{T} = \text{constant}\).
(f) Four protective items: safety goggles; laboratory coat (overall); hand gloves; nose/face mask (also fume cupboard, safety boots).
(g) Two uses of ammonia: manufacture of fertilizers; manufacture of trioxonitrate(V) acid (also as a refrigerant).
(h)(i) The process is cracking.
(ii) Ethanol + sodium gives sodium ethoxide and hydrogen gas. \(2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2\)
(i) Sulphur in H2SO4: \(2(+1) + S + 4(-2) = 0 \Rightarrow S = +6\).
(j)(i) NaClO3: sodium trioxochlorate(V).
(ii) CuSO4·5H2O: copper(II) tetraoxosulphate(VI) pentahydrate.
Answer Details
(a) Esterification is the reaction between a carboxylic (alkanoic) acid and an alcohol (alkanol), in the presence of a little concentrated H2SO4, to form an ester (alkanoate) and water.
(b) Two properties of plastic: it is light (low density) and a poor conductor of heat and electricity (also resistant to corrosion, mouldable, non-biodegradable).
(c) Duralumin contains aluminium, copper, magnesium and manganese.
(d)(i) A raw material is a naturally occurring substance from which useful products are manufactured.
(ii) A primary product is the product obtained directly (first) from processing a raw material.
(e) Charles' law: the volume of a fixed mass of gas is directly proportional to its absolute (Kelvin) temperature at constant pressure. \(\dfrac{V}{T} = \text{constant}\).
(f) Four protective items: safety goggles; laboratory coat (overall); hand gloves; nose/face mask (also fume cupboard, safety boots).
(g) Two uses of ammonia: manufacture of fertilizers; manufacture of trioxonitrate(V) acid (also as a refrigerant).
(h)(i) The process is cracking.
(ii) Ethanol + sodium gives sodium ethoxide and hydrogen gas. \(2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2\)
(i) Sulphur in H2SO4: \(2(+1) + S + 4(-2) = 0 \Rightarrow S = +6\).
(j)(i) NaClO3: sodium trioxochlorate(V).
(ii) CuSO4·5H2O: copper(II) tetraoxosulphate(VI) pentahydrate.
Question 53 Report
(a) Define electrochemical cell.
(b) Aluminium can be prepared commercially by the application of electrolysis. Name the: I. electrolyte used in the process; II. ore from which the electrolyte is obtained; III. electrodes used in the electrolysis.
(ii) Give two reasons why cryolite, NaAl F\(_6\) is added to the electrolyte?
(c)(i) List the two gaseous fuels produced from coke.
(ii) Which of the two gases listed in (c)(i) is a better fuel?
(iii) Give a reason for your answer in (c)(i)
(iv) Write a balanced equation for the production of each gaseous fuel.
(d)(i) For each of the following reactions, state what would be observed when: I. chlorine gas is bubbled through aqueous sodium iodide; II. chlorine gas is passed over heated iron in a hard glass tube; III. aqueous silver trioxonitrate (V) is added to aqueous sodium bromide.
(ii) Write a balanced chemical equation for each of the reactions in (d)(i).
Question 54 Report
(a)(i) Name two gases that could be used to perform the fountain experiment.
(ii) State the physical property which makes the gases suitable for the experiment in (a)(i)
(b)(i) Define each of the following terms: I. solubility; II. saturated solution.
(ii) State two factors that affect the solubility of a solid in a liquid.
(iii) A salt Z of mass 10.2 g was dissolved in 15.4 cm\(^3\) of distilled water at 40°C. Calculate the solubility of Z in moldm\(^3\) at 40°C. [Mr (Z) = 331].
(c)(i) Town water supplies that have passed through iron pipes contain P and Q ions. In the presence of air, P ions are slowly converted to Q ions.
I. Identify P and Q ions. II. Write a balanced equation for the reaction between P ions, hydrogen ions and oxygen to give Q ions and water.
(ii) Explain briefly a test to confirm the purity of water.
(iii) State the effect of:
I. boiling a temporally hard water. II. adding sodium trioxocarbonate (IV) crystals to permanent hard water;
(iv) Write a balanced equation for the process in (c)(iii)I.
(a)(i) Two gases for the fountain experiment: ammonia (NH3) and hydrogen chloride (HCl).
(ii) The property is their very high solubility in water.
(b)(i) I. Solubility is the maximum amount of a solute that dissolves in a given amount of solvent at a stated temperature to form a saturated solution.
II. A saturated solution is one that contains the maximum amount of solute it can dissolve at a given temperature, in contact with undissolved solute.
(ii) Two factors affecting solubility of a solid in a liquid: temperature; the nature of the solute and solvent.
(iii) Mass per dm3 \(= 10.2 \times \dfrac{1000}{15.4} = 662.3\ \text{g dm}^{-3}\).
Solubility \(= \dfrac{662.3}{331} = \mathbf{2.0\ mol\ dm^{-3}}\).
(c)(i) I. P = Fe2+ (iron(II)), Q = Fe3+ (iron(III)).
II. \(4Fe^{2+} + 4H^+ + O_2 \rightarrow 4Fe^{3+} + 2H_2O\)
(ii) Test for purity of water: pure water boils at exactly 100 °C (and freezes at 0 °C) at 1 atmosphere; impurities raise the boiling point.
(iii) I. Boiling temporary hard water removes the hardness (it decomposes the hydrogentrioxocarbonate(IV) to insoluble trioxocarbonate(IV), softening the water). II. Adding sodium trioxocarbonate(IV) crystals to permanent hard water softens it by precipitating the Ca2+/Mg2+ ions as insoluble trioxocarbonate(IV).
(iv) \(Ca(HCO_3)_2 \xrightarrow{heat} CaCO_3 + H_2O + CO_2\)
Answer Details
(a)(i) Two gases for the fountain experiment: ammonia (NH3) and hydrogen chloride (HCl).
(ii) The property is their very high solubility in water.
(b)(i) I. Solubility is the maximum amount of a solute that dissolves in a given amount of solvent at a stated temperature to form a saturated solution.
II. A saturated solution is one that contains the maximum amount of solute it can dissolve at a given temperature, in contact with undissolved solute.
(ii) Two factors affecting solubility of a solid in a liquid: temperature; the nature of the solute and solvent.
(iii) Mass per dm3 \(= 10.2 \times \dfrac{1000}{15.4} = 662.3\ \text{g dm}^{-3}\).
Solubility \(= \dfrac{662.3}{331} = \mathbf{2.0\ mol\ dm^{-3}}\).
(c)(i) I. P = Fe2+ (iron(II)), Q = Fe3+ (iron(III)).
II. \(4Fe^{2+} + 4H^+ + O_2 \rightarrow 4Fe^{3+} + 2H_2O\)
(ii) Test for purity of water: pure water boils at exactly 100 °C (and freezes at 0 °C) at 1 atmosphere; impurities raise the boiling point.
(iii) I. Boiling temporary hard water removes the hardness (it decomposes the hydrogentrioxocarbonate(IV) to insoluble trioxocarbonate(IV), softening the water). II. Adding sodium trioxocarbonate(IV) crystals to permanent hard water softens it by precipitating the Ca2+/Mg2+ ions as insoluble trioxocarbonate(IV).
(iv) \(Ca(HCO_3)_2 \xrightarrow{heat} CaCO_3 + H_2O + CO_2\)
Question 55 Report
(a)(i) Give three characteristics of homologous series.
(ii) Name two groups of compounds which form such a series.
(b) A saturated organic compound A containing two carbon atoms reacted with ethanoic acid in the presence of a mineral acid to form a compound B with a sweet smell. (i) Name the functional group present in A.
(ii) Draw the structure of A.
(iii) Write a chemical equation to show the formation of B.
(iv) Name the compound B.
(c)(i) Write a balanced equation for the reaction between ethyne and excess bromine.
(ii) Give IUPAC name of the product of the reaction in (c)(i)
(iii) State two conditions under which cracking takes place
(d)(i) Outline the preparation of ethanol from starch.
(ii) Give two properties of starch.
(iii) Give a reason why starch does not reduce Fehlings solution
(iv) Describe briefly a chemical test to confirm the presence of starch.
(a)(i) Characteristics of a homologous series
- Members have the same general formula.
- Successive members differ by a \(\ce{-CH2-}\) unit.
- They have the same functional group and therefore similar chemical properties.
- They show a gradual change in physical properties, such as boiling point and density, as molecular mass increases.
(ii) Examples are alkanes and alkanols (alcohols).
(b) Compound A is ethanol, because a two-carbon alcohol reacts with ethanoic acid to form a sweet-smelling ester.
(i) The functional group in A is the hydroxyl group, \(\ce{-OH}\).
(ii) Structure of A, ethanol
(iii)
\[\ce{CH3COOH + CH3CH2OH <=>[conc. H2SO4][heat] CH3COOCH2CH3 + H2O}\]
(iv) B is ethyl ethanoate.
(c)(i)
\[\ce{HC#CH + 2Br2 -> CHBr2CHBr2}\]
(ii) The IUPAC name of the product is 1,1,2,2-tetrabromoethane.
(iii) Conditions for cracking
- High temperature, usually about \(500\text{ to }700\,^\circ\mathrm{C}\).
- Use of a suitable catalyst, such as silica-alumina or zeolite.
(d)(i) Preparation of ethanol from starch
- Warm starch with malt containing the enzyme diastase. The starch is hydrolysed to maltose:
\[\ce{(C6H10O5)_{n} + \tfrac{n}{2}H2O ->[diastase] \tfrac{n}{2}C12H22O11}\] - Add maltase to convert maltose to glucose:
\[\ce{C12H22O11 + H2O ->[maltase] 2C6H12O6}\] - Add yeast and keep the mixture warm, about \(30\,^{\circ}\mathrm{C}\), under anaerobic conditions. Zymase in the yeast ferments glucose to ethanol and carbon(IV) oxide:
\[\ce{C6H12O6 ->[zymase] 2C2H5OH + 2CO2}\] - Distil the fermented liquid to obtain ethanol.
(ii) Two properties of starch
- It is a white, tasteless solid and is insoluble in cold water.
- When warmed with water, it forms a colloidal paste or solution.
(iii) Starch does not reduce Fehling's solution because it has no free reducing carbonyl group.
(iv) Add iodine solution to the sample. A blue-black colour confirms the presence of starch.
Answer Details
(a)(i) Characteristics of a homologous series
- Members have the same general formula.
- Successive members differ by a \(\ce{-CH2-}\) unit.
- They have the same functional group and therefore similar chemical properties.
- They show a gradual change in physical properties, such as boiling point and density, as molecular mass increases.
(ii) Examples are alkanes and alkanols (alcohols).
(b) Compound A is ethanol, because a two-carbon alcohol reacts with ethanoic acid to form a sweet-smelling ester.
(i) The functional group in A is the hydroxyl group, \(\ce{-OH}\).
(ii) Structure of A, ethanol
(iii)
\[\ce{CH3COOH + CH3CH2OH <=>[conc. H2SO4][heat] CH3COOCH2CH3 + H2O}\]
(iv) B is ethyl ethanoate.
(c)(i)
\[\ce{HC#CH + 2Br2 -> CHBr2CHBr2}\]
(ii) The IUPAC name of the product is 1,1,2,2-tetrabromoethane.
(iii) Conditions for cracking
- High temperature, usually about \(500\text{ to }700\,^\circ\mathrm{C}\).
- Use of a suitable catalyst, such as silica-alumina or zeolite.
(d)(i) Preparation of ethanol from starch
- Warm starch with malt containing the enzyme diastase. The starch is hydrolysed to maltose:
\[\ce{(C6H10O5)_{n} + \tfrac{n}{2}H2O ->[diastase] \tfrac{n}{2}C12H22O11}\] - Add maltase to convert maltose to glucose:
\[\ce{C12H22O11 + H2O ->[maltase] 2C6H12O6}\] - Add yeast and keep the mixture warm, about \(30\,^{\circ}\mathrm{C}\), under anaerobic conditions. Zymase in the yeast ferments glucose to ethanol and carbon(IV) oxide:
\[\ce{C6H12O6 ->[zymase] 2C2H5OH + 2CO2}\] - Distil the fermented liquid to obtain ethanol.
(ii) Two properties of starch
- It is a white, tasteless solid and is insoluble in cold water.
- When warmed with water, it forms a colloidal paste or solution.
(iii) Starch does not reduce Fehling's solution because it has no free reducing carbonyl group.
(iv) Add iodine solution to the sample. A blue-black colour confirms the presence of starch.
