JAMB UTME - Chemistry - 2006

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The oxidation number of an element is a number that represents the number of electrons that an atom has gained or lost. In the case of sulfur, it can have different oxidation numbers depending on the compound it is present in. When the oxidation number of sulfur is -2, it means that sulfur has gained two electrons. So, we need to identify the compound in which sulfur has an oxidation number of -2. Out of the given options, only the second option - H2S - contains sulfur with an oxidation number of -2. In H2S, hydrogen has an oxidation number of +1 and sulfur has an oxidation number of -2, which makes the overall charge of the compound neutral. In the other options: - S8 is a form of elemental sulfur and has an oxidation number of 0 since it is uncombined. - SO2 contains sulfur with an oxidation number of +4. - SO32- contains sulfur with an oxidation number of +4. Therefore, the correct answer is the second option - H2S.

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When a copper salt moistened with concentrated hydrochloric acid is placed on a platinum wire and introduced into a flame, it produces a characteristic green color. This is due to the emission of photons by excited copper atoms as they return to their ground state. The photons emitted have a wavelength of about 510 nm, which corresponds to the green part of the visible spectrum. Therefore, the correct answer is green.

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To separate a mixture of sand, ammonium chloride, and sodium chloride, we need to use methods that take advantage of their distinct physical properties: ammonium chloride can sublime, sodium chloride is soluble in water, and sand is neither soluble in water nor sublimes.

The correct order of separation steps should be:

1. Sublimation: Heat the mixture to sublime the ammonium chloride. Ammonium chloride will transition from solid to gas without passing through the liquid phase, leaving behind sand and sodium chloride.
2. Dissolution: Dissolve the remaining mixture of sand and sodium chloride in water. Sodium chloride is soluble in water, while sand is not.
3. Filtration: Filter the mixture to separate the insoluble sand from the sodium chloride solution.
4. Evaporation: Evaporate the water from the sodium chloride solution to obtain solid sodium chloride.

Given these steps, the correct order is:

C. sublimation → dissolution → filtration → evaporation

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The molar mass of a substance is the mass of one mole of the substance. We are given that 0.4 mole of the substance has a mass of 25.0 g. To find the molar mass, we can use the formula: Molar mass = Mass / Number of moles Plugging in the given values, we get: Molar mass = 25.0 g / 0.4 mol Simplifying this expression, we get: Molar mass = 62.5 g/mol Therefore, the molar mass of the substance is 62.5 g/mol. Answer: 62.5 g

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The electron configuration provided in the question indicates that the element has two electrons in its 1s orbital, two electrons in its 2s orbital, two electrons in its 2p orbital, and three electrons in its 3p orbital. Based on this electron configuration, the element is "nitrogen."

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Dynamic equilibrium describes a situation where both forward and reverse reactions proceed at the same rate, resulting in no net change in the concentration of reactants and products over time. This means that even though the reaction is still ongoing, the concentrations of both reactants and products remain constant. It is important to note that the reactants and products are still being converted into each other, but at the same rate. This state of balance can only be reached under certain conditions, such as constant temperature and pressure.

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The question is asking why the group IA metals are not found free in nature. The correct answer is "are very reactive and unstable." This means that the group IA metals, such as sodium and potassium, react very easily with other elements in the environment and are not stable enough to exist on their own. They are typically found in combination with other elements, such as sodium chloride (table salt), rather than in their pure, free form. The other options are not correct because they do not explain why the group IA metals are not found free in nature.

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When a candle is burned, the heat of the flame melts the wax near the wick. This liquid wax then moves up the wick, where the heat of the flame vaporizes the liquid wax molecules. These vaporized molecules react with oxygen from the air to form new compounds, releasing heat and light in the process. The main products of the combustion of candle wax are carbon dioxide (CO2) and water (H2O). Therefore, the correct answer is "carbon (IV) oxide and water."

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The presence of certain gases and particles in the air can contribute to the formation of acid rain. Acid rain occurs when rainwater mixes with these gases and particles, forming acidic solutions that fall to the ground. Out of the given options, the oxides of sulfur are known to be the main contributor to acid rain. When sulfur dioxide (SO2) and nitrogen oxides (NOx) are released into the atmosphere, they react with water, oxygen, and other chemicals to form sulfuric acid and nitric acid, respectively. These acids then fall to the ground in the form of acid rain, damaging forests, lakes, and other ecosystems. Therefore, the correct answer is "Oxides of sulphur."

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Zinc and carbon rods are used as anode and cathode respectively in a type of battery called a "Leclanche cell".

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AgNO3 → 2Ag + O2 + 2NO2

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The compound shown in the question is 2-butanone, also known as methyl ethyl ketone. The oxidation of 2-butanone produces 2-butanal, also known as butyraldehyde. The carbonyl group (C=O) in the 2-butanone is converted to an aldehyde group (-CHO) during the oxidation reaction. Therefore, the correct answer is 2-butanal.

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The structure of 2-methylbut-2-ene can be determined by identifying the location of the double bond and the position of the methyl group. The name indicates that there are four carbon atoms in the main chain, with a methyl group attached to the second carbon and the double bond between the second and third carbon. Looking at the options, it can be seen that option A and B have the double bond between the first and second carbon, which is incorrect. Option C has the correct position of the double bond, but the methyl group is attached to the first carbon instead of the second carbon. Therefore, the correct structure for 2-methylbut-2-ene is option D, where the double bond is between the second and third carbon and the methyl group is attached to the second carbon.

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The main difference between chemical and physical change is that in a chemical change a new substance is formed. In other words, the chemical composition of the original substance changes, resulting in the formation of a new substance with different chemical and physical properties. Physical changes, on the other hand, do not involve a change in the chemical composition of the substance. In physical changes, only the physical properties of the substance such as its shape, size, color, or state of matter may change, but the chemical identity of the substance remains the same.

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The question is asking for the volume of 2.5 moles of oxygen at standard temperature and pressure (s.t.p), given that the molar volume of a gas at s.t.p is 22.4 dm^3. To solve this problem, we can use the following formula: Volume = (number of moles) x (molar volume at s.t.p) Substituting the given values, we get: Volume = 2.5 mol x 22.4 dm^3/mol Volume = 56.0 dm^3 Therefore, the volume of 2.5 moles of oxygen at s.t.p is 56.0 dm^3. So, the answer is the last option: 56.0 dm^3.

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In the industrial production of hydrogen gas from natural gas, carbon dioxide is produced as a byproduct. To remove the carbon dioxide from the hydrogen gas, the mixture is washed under pressure. Therefore, the correct option is "washing under pressure."

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The gas obtained as a product of anaerobic action on organic matter buried in the earth is methane. Anaerobic decomposition of organic matter such as dead plants and animals, in the absence of oxygen, leads to the formation of methane gas, which is a major component of natural gas. Methane is also a greenhouse gas that contributes to climate change.

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The reaction given is a chemical equation. It represents a chemical change where reactants combine to form products. The equation shows the reactants on the left-hand side and the products on the right-hand side. In this particular equation, the reactants are 5SO2(g), 2KMnO4(aq), and 2H2O(l). The products are K2SO4, 2MnSO4(aq), and 2H2SO4(aq). Now, to answer the question, the equation does not involve any purple solution or purple precipitate, so we can eliminate the first two options. The products of the reaction are K2SO4, 2MnSO4(aq), and 2H2SO4(aq). None of these products is a colourless precipitate, so we can eliminate the third option as well. Therefore, the correct answer is that the products give a colourless solution.

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2VD = Rmm VD = Vapour density; Rmm - Relative
2 * 20 = 40 Molecular mass
Mole of carbon = 36/12 = 3
Mole of H2 = 40 - 36 = 4
The compound contains 3 mole of carbon and 4 hydrogen

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Carbon exists naturally in the combined state as all of the options provided: graphite, coal, diamond, and wood. Graphite is a form of carbon that is used in pencils, while coal is a fossil fuel that is formed from the remains of ancient plants and animals. Diamond is a precious gemstone made entirely of carbon atoms arranged in a crystal lattice structure, while wood is a natural composite material made up of cellulose, hemicellulose, and lignin, all of which contain carbon. Therefore, the correct answer is that carbon exists naturally in the combined state as graphite, coal, diamond, and wood.

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The observation that a crystal added to a clear solution of its salt does not dissolve and the solution remains unchanged indicates that the solution is already holding as much of the salt as it can at that particular temperature. This means that the solution is saturated with the salt. Therefore, the correct option is "saturated".

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Nuclear fission is a process in which the nucleus of a heavy atom is split into two nuclei of smaller atoms. In this process, a large amount of energy is released, which can be harnessed for various applications. When the nucleus is split, the two resulting nuclei are not of nearly equal masses, but rather of unequal masses. Additionally, the process results in the release of energy and radiation. Therefore, the correct option is "unequal masses with a release of energy and radiation."

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An aliphatic unsaturated hydrocarbon is a hydrocarbon that does not contain any aromatic rings and has at least one double or triple bond between its carbon atoms. Pentane is an example of an aliphatic hydrocarbon, but it is not unsaturated, meaning it contains only single bonds between its carbon atoms. Butanol is also aliphatic, but it contains an -OH group and does not have any double or triple bonds. Propene, on the other hand, is an aliphatic unsaturated hydrocarbon because it has one double bond between its two carbon atoms. Finally, benzene is not aliphatic, but rather it is an aromatic hydrocarbon, which contains at least one aromatic ring with alternating double bonds. Therefore, the correct answer is "propene."

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$\frac{C_A{V}_A}{C_B{V}_B}=\frac{a}{b}$

$\frac{0.05\times 10}{C_B\times 25}=\frac{2}{1}$

50CB = 0.5

CB = $\frac{0.5}{50}=\frac{5}{100}$

= 0.01

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The particle described in the question has 11 protons, which makes it an atom of the element sodium (Na) since the atomic number of sodium is 11. The particle also has 12 neutrons, which means it has a mass number of 23 (11 protons + 12 neutrons = 23). However, the particle has 10 electrons, which is not the same as the number of protons. Therefore, the particle has a charge of +1 since it has one less electron than protons. This means that the particle is a metallic ion. So, the correct option is "metallic ion".

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Nigerian crude oil is described as light crude because of its low sulfur content. "Light crude" refers to the oil's density and refers to crude oil that has low viscosity and low specific gravity. Low sulfur content is also a characteristic of light crude oil, which makes it less polluting when burned.

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The question is asking for the solubility of sugar at 40°C given the mass of dry solid obtained after evaporating a known volume of a saturated solution of sugar. To solve this problem, we need to use the formula: Solubility = (mass of solute ÷ molar mass of solute) ÷ (volume of solvent in dm³) Using the given data, we can find the mass of sugar dissolved in 50cm³ of the saturated solution: mass of sugar = 34.2g Next, we need to calculate the number of moles of sugar dissolved: number of moles = mass of sugar ÷ molar mass of sugar = 34.2g ÷ 342g/mol = 0.1mol Finally, we can use the formula to calculate the solubility: solubility = (0.1mol ÷ 0.05dm³) = 2.0 mol dm⁻³ Therefore, the solubility of sugar at 40°C is 2.0 mol dm⁻³. The main labels for this question would be: Chemistry, Solubility, Sugar, Saturated solution, Evaporation, Molar mass, Volume, Mass.

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Water has a unique molecular structure which makes it a universal solvent. A water molecule consists of two hydrogen atoms and one oxygen atom. The oxygen atom has a slightly negative charge, while the hydrogen atoms have a slightly positive charge. This uneven distribution of charge creates a polarity in the molecule, with one end being more positively charged and the other end being more negatively charged. Therefore, the correct answer is: "one positive end and one negative end".