JAMB UTME - Chemistry - 2005

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The value of ΔG (change in Gibbs free energy) for a chemical reaction indicates whether the reaction is spontaneous or non-spontaneous. If ΔG is negative, the reaction is spontaneous, meaning it can occur without an external energy source. If ΔG is positive, the reaction is non-spontaneous, meaning it requires an external energy source to occur. If ΔG is zero, the reaction is at equilibrium. When iron rusts, it undergoes a chemical reaction with oxygen and water to form iron oxide (rust). This reaction is spontaneous, and as a result, the value of ΔG for the reaction is negative. Therefore, the correct answer to the question is "negative."

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When equal moles of ethyne and hydrogen iodide react, they undergo an addition reaction, where the double bond of ethyne is broken and a new bond is formed between the carbon atoms and iodine atoms. The product formed is called vinyl iodide, which has the chemical formula CH2=CHI. Therefore, the correct answer is: CH2=CHI.

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When water boilers are used for a long period of time, the solid substances left behind as scale are mostly composed of magnesium trioxosilicate (IV) and calcium tetraoxosulphate (VI). These substances are formed as a result of the reaction between the dissolved calcium and magnesium ions in the hard water and the anions in the soap used for washing. When water is heated, these substances tend to precipitate out of the water and form a hard layer of scale on the inner surface of the boilers. This scale can reduce the efficiency of the boilers and increase energy consumption, which is why it is important to periodically descale the boilers to remove the buildup.

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Cycloalkanes are a type of hydrocarbon where the carbon atoms form a closed ring. Open-chain alkanes, on the other hand, are hydrocarbons with linear carbon chains. In a single ring cycloalkane, each carbon atom is bonded to two other carbon atoms and two hydrogen atoms. However, in an open-chain alkane with the same number of carbon atoms, each carbon atom is bonded to three other carbon atoms and two hydrogen atoms. Therefore, in a single ring cycloalkane, each carbon atom has one less hydrogen atom than in the corresponding open-chain alkane. Since each carbon atom in the ring has one less hydrogen atom, the whole molecule will have two fewer hydrogen atoms than the corresponding open-chain alkane. Therefore, the answer is: Two.

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A solid's definite shape is due to its strong intermolecular attraction. In solids, the molecules are tightly packed together and have strong forces of attraction between them. These forces keep the molecules in a fixed position and prevent them from moving around freely. As a result, solids have a definite shape that is maintained even when the solid is subjected to external forces. In contrast, liquids and gases do not have a definite shape because their molecules have weak intermolecular forces and can move around more freely.

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The substance that is used as a ripening agent for fruits is ethene. Ethene, also known as ethylene, is a naturally occurring plant hormone that stimulates the ripening of fruits. It is used commercially to ripen fruits such as bananas, mangoes, and tomatoes, among others. When applied to fruits, ethene gas causes the fruits to soften, sweeten, and change color, indicating that they are ripe and ready to eat.

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Flotation is a process used to separate minerals from their ores. In this process, the ores are treated with a chemical reagent and air, which causes the minerals to be selectively attached to bubbles that float to the surface of the mixture. The minerals that are commonly concentrated by flotation are those that contain sulfide ores, such as copper, lead, and zinc ores. Therefore, the correct option from the given choices is "sulfide ores."

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In the purification of impure samples of ethyl ethanoate synthesized by esterification, concentrated sodium trioxocarbonate (IV) solution is used to remove acidic impurities. Sodium trioxocarbonate (IV) reacts with the acidic impurities present in the impure ethyl ethanoate to form carbon dioxide, water, and a salt. The salt is soluble in the ethyl ethanoate, while carbon dioxide and water are not. So, carbon dioxide and water can be easily separated from the ethyl ethanoate, leaving behind the purified ethyl ethanoate. Therefore, option C, which states "acidic impurities," is the correct answer.

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The volume of the mixture of noble gases is 25 cm³. This means that after the removal of other constituents, the remaining volume is 25 cm³. Since the noble gases were obtained from air, it means that the original volume of air was larger than 25 cm³. Therefore, the correct answer is either 2,500 cm³ or 1,250 cm³ since they are 100 or 50 times larger than the remaining volume of 25 cm³. It is impossible for the original volume to be 125 cm³ or 80 cm³ as they are smaller than the remaining volume of noble gases.

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Phenolphthalein is an indicator used to determine the endpoint of a chemical reaction. In acidic solution, phenolphthalein is colorless, meaning that the solution remains the same color as the acidic solution without the indicator. Therefore, the correct answer is "colourless."

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The decolourization of the purple colour of tetraoxomanganate (VII) ion is a test for alkenes. Alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond. In this test, the purple colour of tetraoxomanganate (VII) ion is due to the presence of this ion in a solution, which is added to the unknown compound. If the unknown compound is an alkene, it will react with the tetraoxomanganate (VII) ion and the purple colour will disappear. This is because alkenes can reduce tetraoxomanganate (VII) ion to manganese(II) ions, which are responsible for the colourless solution. Therefore, the decolourization of purple colour of tetraoxomanganate (VII) ion is a test for the presence of alkenes in a compound.

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The enzyme responsible for converting sucrose into two simple isomeric sugars is invertase. When sucrose is hydrolyzed by invertase, it breaks down into its component sugars, glucose and fructose. Maltase is responsible for breaking down maltose into two glucose molecules, amylase breaks down starch into maltose and glucose, and lactase breaks down lactose into glucose and galactose.

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Sugar is separated from its impurities by the process of crystallization. Crystallization involves dissolving a solid, in this case, sugar, in a solvent, usually water, to create a saturated solution. The solution is then cooled or allowed to evaporate, causing the sugar to come out of the solution and form crystals. The impurities remain dissolved in the solution or get trapped in the crystal lattice of the sugar, making it possible to separate the pure sugar crystals from the impurities. Precipitation, distillation, and evaporation are other methods of separating substances but are not typically used for separating sugar from its impurities.

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In the given chemical reaction, NH4Cl(s) ↔ NH3(g) + HCl(g), the reaction can only attain equilibrium if it is in a closed system. This means that the reaction vessel must be closed so that the products and reactants cannot escape. In a closed system, the concentrations of the reactants and products reach a state of balance, which is known as equilibrium. Adding a gaseous reactant or removing one of the products will disturb the equilibrium and shift the reaction in the direction that minimizes the disturbance. Therefore, the only option that is necessary for the reaction to attain equilibrium is that it is in a closed system.

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The hydrocarbon compound CH4 is composed of one carbon atom and four hydrogen atoms. The shape of the molecule is determined by the arrangement of its atoms and electron pairs. In CH4, the carbon atom is at the center of the molecule, and the four hydrogen atoms are arranged tetrahedrally around it, pointing towards the corners of an imaginary tetrahedron. Therefore, the shape of the hydrocarbon compound CH4 is tetrahedral.

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The given equation is a chemical equation for the combustion of hydrogen gas with oxygen gas to produce water. The negative sign in the value of ΔH = -571 kJ indicates that this reaction is exothermic, which means that heat is being released in the reaction. This means that for every mole of hydrogen gas burnt, 571 kJ of heat is released. To calculate the amount of heat released when 12.0g of hydrogen is burnt, we first need to calculate the number of moles of hydrogen present. The molar mass of hydrogen is approximately 2 g/mol. Therefore, 12.0 g of hydrogen is equivalent to 12.0/2 = 6.0 moles of hydrogen. From the chemical equation, we know that for every mole of hydrogen gas burnt, 571 kJ of heat is released. Therefore, for 6.0 moles of hydrogen gas burnt, the amount of heat released would be: 6.0 moles H2 x (-571 kJ/mole) = -3426 kJ The negative sign indicates that heat is being released in the reaction. Therefore, the answer is -3426 kJ, which is closest to the last option of -1713 kJ. So, the correct option is: -1713 kJ.

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The question is asking which of the combinations refers to the uses of radioactive isotopes. Radioactive isotopes are used in various fields such as medicine, geology, and chemistry. Among the given options, the combination of "I" and "IV" are not related to the uses of radioactive isotopes. Treatment of cancer involves chemotherapy, radiation therapy, and surgery. Preparation of drugs can involve the use of various techniques such as chromatography, filtration, and extraction. The combination of "II" and "III" is also not related to the uses of radioactive isotopes. Detection of leakages in water mains and detection of the ages of ancient tools are typically done using non-radioactive techniques such as acoustic leak detection and carbon dating, respectively. Therefore, the correct answer is the combination of "I, II, and III", as these fields make use of radioactive isotopes.

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A lightning conductor, also known as a lightning rod, is a metal rod that is attached to the top of a building and extends to the ground. It is designed to protect the building and its occupants from lightning strikes by providing a path for the lightning to follow into the ground, where it can be harmlessly dissipated. The most suitable metal that can be used as a lightning conductor should have good electrical conductivity and be resistant to corrosion. Out of the options given, the most suitable metal for a lightning conductor is copper. Copper has excellent electrical conductivity and is highly resistant to corrosion, making it an ideal material for lightning rods. Silver is also an excellent conductor, but it is too expensive to be used as a lightning conductor. Iron and aluminium are not as good conductors as copper and are more prone to corrosion.

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An element with 2, 8, and 1 electron configuration will readily form an electrovalent compound. This is because this electron configuration is characteristic of alkali metals, which have only one electron in their outermost shell. In order to achieve a stable electron configuration, they lose that one electron to form a positively charged ion. This ion can then combine with negatively charged ions to form an electrovalent compound. Therefore, the correct answer is "2, 8, 1."

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The gas law that applies to this question is Boyle's Law which states that the pressure and volume of a gas are inversely proportional to each other when the temperature is constant. This means that as the pressure of the oxygen is reduced from 750mmHg to 100mmHg, the volume of the gas will increase by a factor of 750/100 = 7.5. Therefore, the volume of the gas at the new pressure will be 100 cm^3 x 7.5 = 750 cm^3. Thus, the correct answer is 750 cm^3.

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When pure aluminum metal is heated to red hot in the presence of nitrogen gas, the compound formed is AlN. The reaction can be represented as: 2Al(s) + N2(g) → 2AlN(s) This is a synthesis reaction, where two or more reactants combine to form a single product. The product formed in this reaction is a binary compound composed of aluminum and nitrogen.

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The property used in the industrial preparation of nitrogen and oxygen from air is the boiling point. This is because nitrogen and oxygen have different boiling points from the other constituents of air, such as carbon dioxide and water vapor. Nitrogen has a boiling point of -196°C and oxygen has a boiling point of -183°C, while carbon dioxide and water vapor have much higher boiling points. Therefore, the air is cooled and compressed to separate the nitrogen and oxygen from the other gases, based on the differences in their boiling points.

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Smelting industries involve high-temperature processes that extract metals from their ores. The main labels that can be associated with the question are: identifying the pollutants likely to be present in the air around smelting industries. mentions the presence of H2S, CO, and NO2, which are all common air pollutants produced by industrial activities. Therefore, could be a possible answer. mentions the presence of CO2, SO3, and H2. While CO2 is a common air pollutant, SO3 is a highly reactive and unstable compound that quickly reacts with water to form sulfuric acid, which is a strong acid that can cause respiratory problems. Therefore, is also a possible answer. mentions the presence of H2, SO2, and CO2. While H2 and CO2 are common air pollutants, SO2 is a highly reactive gas that can cause respiratory problems and acid rain, which can damage buildings and harm plants and aquatic life. Therefore, is also a possible answer. mentions the presence of SO2, NO2, and CO2, which are all common air pollutants produced by industrial activities. Therefore, could also be a possible answer. In summary, the main pollutants that are likely to be present in the air around smelting industries include sulfur dioxide (SO2), carbon monoxide (CO), nitrogen dioxide (NO2), hydrogen sulfide (H2S), and carbon dioxide (CO2).

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To obtain pure carbon (II) oxide from its mixture with carbon (IV) oxide, the mixture should be passed over heated copper (II) oxide. This is because copper (II) oxide is a good oxidizing agent that reacts with carbon (II) oxide (CO) to form carbon dioxide (CO2) leaving behind pure carbon (II) oxide. The reaction is as follows:
2CO + CuO ? 2CO2 + Cu
is therefore the correct answer.
Bubbling the mixture through water () or sodium hydroxide () would not separate the two gases, as both CO and CO2 are soluble in water and sodium hydroxide. Bubbling the mixture through concentrated tetroxosulphate (VI) acid () could also not separate the two gases because carbon (II) oxide is reducing and would react with the acid to form carbon dioxide gas.

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Iron is an important component of steel, which is an alloy of iron and carbon. Therefore, any option that includes steel as one of its alloys will contain iron. The only option that includes steel as one of its alloys is "Steel and permalloy." Therefore, the answer is "Steel and permalloy."

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When ammonia gas (NH3) reacts with hydrochloric acid (HCl), a dense white fume is formed, which is actually ammonium chloride (NH4Cl). This is because the ammonia reacts with the hydrogen chloride in the air to form ammonium chloride, which is a white solid that sublimes at room temperature, meaning it turns directly from a solid to a gas. Therefore, the correct answer would be "HCl".

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A heterogeneous mixture is a type of mixture where the components are not evenly distributed throughout the mixture. This means that the composition of the mixture is not uniform, and it can be visually distinguished as having different parts or phases. This is in contrast to a homogeneous mixture, where the components are evenly distributed and the composition is uniform throughout. Therefore, the correct option is: "whose composition is not uniform".

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The most abundant element on the Earth's crust is oxygen. Oxygen makes up about 46% of the Earth's crust by weight. The Earth's crust is the outermost layer of the planet and consists mostly of silicate rocks and minerals. Oxygen is an essential element for life, forming a major component of the Earth's atmosphere and being a key element in the process of respiration.

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The component of an atom that contributes least to its mass is the electron. The electron is a negatively charged subatomic particle that orbits the nucleus of an atom. It has a much smaller mass compared to the proton and neutron, which are found in the nucleus. Therefore, even though electrons are present in large numbers in an atom, their individual mass is so small that they contribute the least to the overall mass of the atom.

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In a flame test for calcium, the flame appears brick-red when viewed through a blue-glass. When an element is heated, it absorbs energy and its electrons become excited and jump to higher energy levels. When these electrons come back to their original energy level, they emit the absorbed energy in the form of light. This emitted light produces a characteristic flame color for each element. In the case of calcium, when it is heated, it emits a brick-red color flame, which can be viewed through a blue-glass to reduce the interference of other colors in the flame.

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To determine the number of moles of limestone needed to produce 5.6g of CaO, we need to use stoichiometry and the molar mass of CaO and limestone. The balanced chemical equation for the thermal decomposition of limestone is: CaCO3 (s) → CaO (s) + CO2 (g) From the equation, we can see that 1 mole of CaCO3 produces 1 mole of CaO. The molar mass of CaO is 56.077 g/mol, while the molar mass of CaCO3 is 100.0869 g/mol. To find the number of moles of CaO produced from 5.6g of CaO, we divide the mass by the molar mass: moles of CaO = mass of CaO / molar mass of CaO moles of CaO = 5.6 g / 56.077 g/mol moles of CaO = 0.1 mol Since 1 mole of CaCO3 produces 1 mole of CaO, we need 0.1 mol of CaCO3 to produce 0.1 mol of CaO. Therefore, the answer is 0.10 mol. Hence, the correct option is: - 0.10 mol

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Arrhenius' law relates the temperature dependence of the rate constant of a chemical reaction. The equation states that the rate constant (k) increases exponentially with increasing temperature. The curve that best illustrates this relationship is curve X. As the temperature increases, the solubility of the solute increases, resulting in a higher concentration of the solute in the solvent, which is in line with Arrhenius' law. Therefore, the correct answer is X.

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The molecular mass of the gas can be determined using the ideal gas equation, which relates the density, molecular mass, pressure, and temperature of a gas. At standard temperature and pressure (STP), the pressure is 1 atm and the temperature is 273 K. The ideal gas equation can be written as: PV = nRT where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature. At STP, the volume of one mole of gas is 22.4 L. Therefore, the number of moles of the gas can be calculated as: n = V/22.4 where V is the volume of the gas. The density of the gas is given as 1.98 g/dm^3. Converting this to g/L, we get: 1.98 g/dm^3 x (1 dm/10 cm)^3 = 1.98 g/L Substituting the values into the ideal gas equation, we get: (1 atm) (V) = (n) (0.0821 L atm/mol K) (273 K) Solving for n, we get: n = (1 atm) (V) / (0.0821 L atm/mol K) (273 K) Substituting n = V/22.4, we get: V/22.4 = (1 atm) (V) / (0.0821 L atm/mol K) (273 K) Solving for V, we get: V = (22.4 L) (0.0821 L atm/mol K) (273 K) / (1 atm) = 22.4 L Therefore, the number of moles of the gas is: n = V/22.4 = 22.4 L / 22.4 L/mol = 1 mol The molecular mass of the gas can be calculated using the formula: molecular mass = mass / number of moles The mass of the gas is the density multiplied by the volume occupied by one mole of the gas, which is 22.4 L at STP. Therefore, the mass of the gas is: mass = density x volume = 1.98 g/L x 22.4 L/mol = 44.35 g/mol Thus, the molecular mass of the gas is approximately 44.0 g/mol, which is the first option.

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Kerosene is commonly used to remove the red colour stain of palm oil from clothes because it helps to dilute the oil and reduce its color. Kerosene is a solvent that dissolves the palm oil stain, making it easier to remove. It also helps to spread the oil over a larger surface area, making it easier to clean. Additionally, kerosene evaporates easily, which can help to remove the oil by dissolving it and allowing it to evaporate away.

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In the given equation, the forward reaction is exothermic (ΔH = -90 kJ), which means that the yield of ammonia will be favored at lower temperatures. Therefore, increasing the temperature will decrease the yield of ammonia. Additionally, removing ammonia from the reaction mixture as it is formed will drive the equilibrium towards the product side, increasing the yield of ammonia. On the other hand, increasing the pressure or adding a catalyst will not affect the yield of ammonia. Therefore, the correct answer is "increasing the temperature."

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Natural water collected from rivers and ponds contains oxygen, carbon (IV) oxide and "oxide" is not a valid option, as it is not a specific substance. Among the given options, neither hydrogen, chlorine, nor sulphur are commonly found in natural water in significant amounts. Therefore, the correct answer is "nitrogen". Nitrogen gas dissolves in water to some extent, and it is a common component of the Earth's atmosphere, making up about 78% of it.

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