JAMB UTME - Chemistry - 2004

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When a solid substance disappears completely as a gas on heating, the substance is said to have undergone sublimation. Sublimation is the process by which a solid changes directly into a gas without passing through the liquid state. This is due to the fact that the substance's vapor pressure is high enough to overcome the atmospheric pressure at its melting point, causing it to transition directly from the solid to the gaseous state. Examples of substances that undergo sublimation include dry ice (solid carbon dioxide), mothballs (naphthalene), and camphor. Evaporation, on the other hand, is the process by which a liquid changes to a gas or vapor below its boiling point, while distillation and crystallization are methods of purifying substances.

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The question is asking for the general formula to represent an alkyl group. An alkyl group is a group of atoms that are formed by removing one hydrogen atom from an alkane molecule. Alkanes are hydrocarbons with the general formula CnH2n+2. The general formula for an alkyl group can be represented as CnH2n+1. This means that an alkyl group has one fewer hydrogen atom than the corresponding alkane. Therefore, the correct answer is option A: CnH2n+1.

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A carcinogenic substance is a substance that has the potential to cause cancer. Among the options given, asbestos dust is a known carcinogen, meaning it has been scientifically proven to cause cancer in humans. Sawdust is not generally considered a carcinogen, although it can cause respiratory problems. Nitrogen (II) oxide and carbon (II) oxide are not typically considered carcinogenic substances, although they can be harmful to human health in other ways. Therefore, the correct answer to this question is "asbestos dust."

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Alloys are a mixture of two or more metals, or a metal and a non-metal, that are combined to obtain specific desired properties. The best method for preparing alloys is by cooling a molten mixture of the metals. In this method, the metals are heated to their melting points, and then mixed thoroughly while in the molten state. The mixture is then allowed to cool, and the metals solidify to form an alloy. This process is called casting. The advantage of this method is that the metals mix together uniformly in the molten state, which leads to a homogeneous distribution of the constituent elements in the alloy. This ensures that the desired properties of the alloy, such as strength, durability, and resistance to corrosion, are consistent throughout the material. Other methods like reducing a mixture of their metallic oxide, electroplating, and arc-welding may be used to prepare alloys, but they are not as effective as cooling a molten mixture of the metals. Therefore, the correct answer is cooling a molten mixture of the metals.

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A chemical reaction is always associated with the formation of new substances. In a chemical reaction, the reactants undergo a chemical change resulting in the formation of new products with different properties from the reactants. The reactants and products have different chemical compositions and can have different physical properties such as color, odor, and state of matter. The formation of new substances is the defining characteristic of a chemical reaction. Therefore, the correct option is "the formation of new substances."

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Oxyacetylene flame is used for iron-welding because it evolves a lot of heat when burnt. The oxyacetylene flame is produced by mixing oxygen and acetylene gases. The flame produced has a temperature of around 3000°C, which makes it very hot and suitable for welding iron. The high temperature of the flame allows the metal to melt quickly, making it possible to fuse two pieces of metal together. The flame also produces a reducing atmosphere that protects the weld from oxidation and other impurities, ensuring a strong and clean weld.

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The method of downward delivery is used to collect gases that are denser than air. This is because such gases will sink and displace the air at the bottom of the container. Out of the given options, only chlorine is denser than air and can be collected by the method of downward delivery. Therefore, the correct answer is chlorine.

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Charles' law states that at a constant pressure, the volume of a gas is directly proportional to its temperature. As the temperature of the gas decreases, its volume also decreases. According to the law, the volume of a gas would theoretically become zero at a temperature of -273 oC (also known as absolute zero), at which point the gas would have no thermal energy left to contract or expand. Therefore, the correct option is: -273 oC.

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In the electrolysis of brine, the anode is typically made of either carbon or another material that is able to withstand the corrosive effects of the process. This is because the anode is the electrode where oxidation occurs, and in the case of brine electrolysis, chloride ions are oxidized to form chlorine gas. Platinum, copper, and zinc are not typically used as anodes in brine electrolysis because they would be rapidly corroded by the chloride ions and other reactive species present in the brine. Carbon, on the other hand, is an excellent choice for an anode because it is relatively inert and can withstand the harsh conditions of the electrolysis process.

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2NaOH + H2SO4 ? Na2SO4 + 2H2O
CaVa) ÷ (CbVb) = ratio of acid / ratio of base
0.5Va ÷ (0.1 × 20) = ½
Va = 2.0cm3

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In the given reaction, Zinc (Zn) has undergone a chemical change where it has combined with oxygen from carbon dioxide (CO2) to form Zinc oxide (ZnO). However, Zinc has not gained or lost electrons, and therefore its oxidation state has not changed. In other words, Zinc has not been oxidized or reduced, and it has not displaced any other element in the reaction, so it has not been a participant in a displacement reaction. Therefore, the correct answer is that Zinc has not been decomposed, displaced, oxidized or reduced in this reaction.

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CaCO3(s) + 2HCl(aq) → CaCl2 + H2O(l) + CO2
The relative molecular mass of CaCO3 = 40 + 12 + 16 * 3 = 52 +48 = 100 ; Relative molecular mass of CO2 = 12 + 10 * 2 = 44
From the above equation, 100g of CaCO3reacts with 44g of CO2 at s.t.p. i.e 22.4 dm3
2g of CaCO3 will react with (2*22.4)/100 of CO2 = 0.448 dm3
0.448 dm3 = 0.448 * 1000 = 448cm3

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An isomer of C₅H₁₂ means a molecule with the same chemical formula but different structural formula. The only option that has the same chemical formula as C₅H₁₂ isomer is "2-methylbutane". Therefore, "2-methylbutane" is the correct answer.

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The question is asking about the amount of silver deposited when an electric current is passed through a solution of a silver salt for a certain amount of time. The formula for calculating the amount of substance produced by electrolysis is given as: Amount of substance (in mol) = Current (in A) × Time (in s) / Faraday's constant (in C mol^-1) In this case, we are given the current (10 A), time (4830 s), and Faraday's constant (96500 C mol^-1), and we know that the substance being produced is silver (Ag), with a molar mass of 108 g mol^-1. Using these values and the formula, we can calculate the amount of silver produced in mol and then convert it to grams using its molar mass. Amount of substance (in mol) = 10 A × 4830 s / 96500 C mol^-1 = 0.5 mol Mass of silver (in g) = 0.5 mol × 108 g mol^-1 = 54.0 g Therefore, the mass of silver deposited when a current of 10 A is passed through a solution of silver salt for 4830 s is 54.0 g. The answer is.

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The reverse reaction given above is known as "Hydrolysis." Hydrolysis is a chemical reaction in which a water molecule is used to break a bond between two molecules. In the given reaction, the ester and water molecules react to form an alkanol and alkanoic molecule. When the reaction is reversed, the alkanol and alkanoic molecules react with each other in the presence of an acid catalyst to form an ester and water molecule. This is known as hydrolysis because a water molecule is used to break the bond between the alkanol and alkanoic molecules.

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A mixture of gases that is likely to burn in a flame must contain a flammable gas, which can react with oxygen to produce a flame. Among the given options, only the mixture of neon and hydrogen contains a flammable gas, which is hydrogen. Neon and helium are noble gases and do not react with oxygen to produce a flame. Similarly, neon and nitrogen do not contain a flammable gas. Therefore, the correct answer is "neon and hydrogen."

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Let the relative abundance of oxygen with mass 37 be x%
∴ The relative abundance of the isotope of mass 35 = (100 - x)%. Total mass of isotopes of mass 37 = 37x, while that of 35 = 35(100 - x)
∴ Total mass of the 100 atoms
= 37x + 35(100 - x) = 35.5
= 37x + 3500 - 35x = 35.5
∴ Mean mass of chlorine atom = (2x + 3500)/100 = 35.5
2x + 3500 = 3550; x = 50/2 = 25

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The given nuclear reaction represents the radioactive decay of 226Ra into an unknown nucleus (represented by the symbol 'x') and an alpha particle (α). An alpha particle is a positively charged particle that is identical to the nucleus of a helium atom. It consists of two protons and two neutrons. During the radioactive decay process, the nucleus of 226Ra loses an alpha particle, which means it loses two protons and two neutrons. This results in the formation of a new nucleus with a different atomic number and mass number. The atomic number of an element is equal to the number of protons in its nucleus. Therefore, the atomic number of the unknown nucleus 'x' can be calculated by subtracting the number of protons lost (i.e., two) from the atomic number of 226Ra, which is 88. 88 - 2 = 86 Hence, the atomic number of the unknown nucleus 'x' is 86. This corresponds to the element radon (Rn). Therefore, the value of x in the given nuclear reaction is 222, which is the atomic mass number of radon. So, the correct answer is (B) 222.

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The allotropy of carbon that is used in the decolourization of sugar is activated charcoal, which is also known as activated carbon. Activated charcoal is a highly porous form of carbon that has a large surface area available for adsorption. When sugar solution is passed through activated charcoal, impurities, such as colorants and other organic compounds, are adsorbed onto the surface of the activated charcoal, leaving behind a decolorized solution. Therefore, the answer to the question is charcoal.

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The balanced chemical equation for the reaction between tetraoxosulphate (VI) acid and copper (II) oxide is: H2SO4 + CuO → CuSO4 + H2O From the equation, we can see that one mole of CuO reacts with one mole of H2SO4. To find the amount of CuO that will react with 4.9g of H2SO4, we need to first find the number of moles of H2SO4 present: Molar mass of H2SO4 = 2(1) + 32 + 4(16) = 98g/mol Number of moles of H2SO4 = Mass of H2SO4/Molar mass of H2SO4 = 4.9g/98g/mol = 0.05mol Since one mole of CuO reacts with one mole of H2SO4, the number of moles of CuO needed will also be 0.05mol. The molar mass of CuO is: Molar mass of CuO = 64 + 16 = 80g/mol So, the mass of CuO needed to react with 0.05mol of H2SO4 is: Mass of CuO = Number of moles of CuO x Molar mass of CuO = 0.05mol x 80g/mol = 4g Therefore, 4g of CuO will react with 4.9g of H2SO4. The answer is 4.0g.

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The shape of s-orbitals is spherical. S-orbitals are the simplest type of orbitals, and they have a single spherical node at the nucleus. The probability of finding an electron in an s-orbital is highest at the nucleus and decreases as the distance from the nucleus increases. Spherical symmetry ensures that the probability of finding an electron in an s-orbital is the same in all directions around the nucleus.

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The property of chlorine that causes hydrogen chloride to be more ionic than the chlorine molecule is its electronegativity. Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond. Chlorine is more electronegative than hydrogen, so in a molecule of hydrogen chloride, chlorine pulls the shared pair of electrons in the bond closer to itself, creating a partial negative charge on the chlorine atom and a partial positive charge on the hydrogen atom. This unequal sharing of electrons in the bond creates an ionic character in the molecule, making hydrogen chloride more ionic than the chlorine molecule.

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The solubility of a substance is defined as the amount of that substance that can dissolve in a given amount of solvent at a specific temperature and pressure. In this case, we are given 40g of CuSO4 and 100g of water at 120°C, and we need to calculate the solubility of CuSO4 in mol dm-3. To solve this problem, we first need to calculate the molar mass of CuSO4. The molar mass of CuSO4 can be calculated by adding the molar masses of copper (Cu), sulfur (S), and four oxygen (O) atoms in CuSO4. The molar mass of CuSO4 = (64 g/mol for Cu) + (32 g/mol for S) + (4 × 16 g/mol for O) = 64 + 32 + 64 = 160 g/mol Next, we need to calculate the number of moles of CuSO4 that are present in 40g of the compound. This can be done by dividing the mass of CuSO4 by its molar mass. Number of moles of CuSO4 = 40g / 160 g/mol = 0.25 moles Finally, we need to calculate the solubility of CuSO4 in mol dm-3. The solubility is given by the number of moles of the solute (CuSO4) per unit volume of the solution (water). We are given 100g of water, but we need to convert this to dm3. Since the density of water is 1 g/cm3 or 1 g/mL, we can use the fact that 1 dm3 is equal to 1000 mL. Volume of water = 100g / 1 g/mL = 100 mL = 0.1 dm3 Therefore, the solubility of CuSO4 in mol dm-3 is given by: Solubility = Number of moles of CuSO4 / Volume of water in dm3 = 0.25 moles / 0.1 dm3 = 2.5 mol dm-3 So, the correct answer is 2.50 mol dm-3.

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A substance that can act as both a reducing agent and an oxidizing agent is known as an "oxidizing-reducing agent" or a "redox agent". In a redox reaction, one substance loses electrons (is oxidized) while another substance gains electrons (is reduced). Therefore, to determine which of the given options acts as both a reducing and an oxidizing agent, we need to find a substance that can both lose and gain electrons. Out of the given options, only sulfur dioxide (SO2) can act as both a reducing and an oxidizing agent. In the presence of a strong oxidizing agent, such as potassium permanganate (KMnO4), sulfur dioxide can be oxidized to form sulfuric acid (H2SO4), while the potassium permanganate is reduced. Conversely, in the presence of a strong reducing agent, such as zinc (Zn), sulfur dioxide can be reduced to form sulfurous acid (H2SO3), while the zinc is oxidized. Therefore, the answer is "SO2".

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The hardness of water is caused by the presence of ions of calcium and magnesium. These ions are typically found in the soil and rocks through which water flows, and they dissolve into the water as it passes through. When water is "hard," it means that it has a high concentration of these ions, which can cause issues with soap lathering, scaling in pipes and appliances, and other problems.

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Transition metals are elements that have partially filled d orbitals, which are orbitals that are located in the middle of the periodic table. These d orbitals have the capacity to hold different numbers of electrons, and this property allows transition metals to exhibit variable oxidation states. An oxidation state is a measure of the number of electrons that an atom has lost or gained in a chemical reaction. In the case of transition metals, their partially filled d orbitals can lose or gain electrons to form different oxidation states. This means that transition metals can lose or gain different numbers of electrons, depending on the specific reaction they are involved in, and can therefore exhibit different oxidation states. In summary, transition metals possess variable oxidation states because of the presence of electrons in their d orbitals, which have the capacity to hold different numbers of electrons and can lose or gain electrons to form different oxidation states.

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The alkane family is a group of hydrocarbons that consists of molecules containing only carbon-carbon single bonds and carbon-hydrogen bonds. One of the main characteristics of this family is their reactivity towards substitution reactions, where an atom or group of atoms is replaced by another atom or group of atoms. Therefore, the correct answer is "Substitution reaction".

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A normal salt is formed when all of the acidic hydrogen in an acid is replaced by a metal ion or ammonium ion. Among the given compounds, only Na2CO3 (sodium carbonate) is a normal salt because it is derived from a strong base (NaOH) and a weak acid (H2CO3), and all of the acidic hydrogens of H2CO3 have been replaced by Na+. NaHS (sodium hydrosulfide), NaHSO4 (sodium hydrogen sulfate), and NaHCO3 (sodium bicarbonate) are not normal salts. NaHS and NaHSO4 are acidic salts because they still have some acidic hydrogen atoms remaining. NaHCO3 is a basic salt because it still has some basic hydroxide ions.

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The question is asking to explain what is removed during vulcanization, and there are four options given. Vulcanization is a process in which rubber is treated with sulfur or other chemicals to improve its properties, such as durability and elasticity. During vulcanization, the rubber molecules form cross-links, or bridges, between them, which makes the rubber stronger and less prone to deformation. Among the given options, the correct answer is "The double bond". This is because natural rubber, which is made of long chains of hydrocarbons, has double bonds between some of the carbon atoms in the chain. These double bonds are responsible for the elasticity of rubber, but they are also vulnerable to attack by oxygen, ozone, and other chemicals, which can cause the rubber to break down and lose its properties over time. In vulcanization, sulfur or other chemicals are added to the rubber, and they react with the double bonds to form cross-links between the chains. This process removes the double bonds from the rubber, but it also creates a stronger and more stable material. Therefore, option "The double bond" is the correct answer.

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Sodium metal is always kept under oil because it reacts vigorously on exposure to air. Sodium is a highly reactive metal that reacts with moisture in the air, forming sodium hydroxide and releasing hydrogen gas. The reaction can be so vigorous that it can ignite the hydrogen gas produced, which can cause an explosion. To prevent this, sodium metal is kept under oil, which prevents contact with air and moisture.

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When steam is passed over red-hot carbon, a reaction called water gas shift reaction takes place. In this reaction, carbon reacts with water vapor (steam) to produce carbon monoxide (CO) and hydrogen gas (H2). Therefore, the correct option is "Hydrogen and carbon (II) oxide", which is another name for carbon monoxide.

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The given chemical equation represents the reaction of CH3COOH(g) which decomposes to produce H4(g) and CO2(g). The type of reaction is determined by the changes that take place during the reaction, and the given reaction is known as Decarboxylation. Decarboxylation is a type of chemical reaction that involves the removal of a carboxyl group (COOH) from a molecule, releasing CO2 as a byproduct.

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Aluminium hydroxide is used in the dyeing industry as a mordant. A mordant is a substance that is added to fabric or other materials to help the dye adhere to it better. Aluminium hydroxide works as a mordant because it forms a complex with the dye molecules, allowing them to bind more tightly to the fabric. This results in a more even and long-lasting color.

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The molecules are in constant, random motion and frequently collide with each other and with the walls of any container. The distances of separation between the molecules are so large that the forces of attraction or repulsion between them are negligible.

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Energy change (ΔH) = 2ΔHCO2 - (2ΔHCO + ΔHO)
= 7x - 393 - (7 * 110.4 + 0)
= -393 + 110.4 = -282.6 kJ

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Relative molecular mass of CH4 = 12 * 1 + 4 = 16
Relative molecular mass of SO2 = 32 + 10 *2 = 64
tSO2/tCH4 = √MSO2/MCH4
t/20 = √64/16 = √4
t/20 = 2
∴ t = 20 * 2 = 40sec

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When an electron is added to a halogen atom, it gains one electron to its outermost shell (valence shell) which is now fully occupied, and becomes a negatively charged ion known as a halide ion. Halogens have 7 valence electrons, therefore, the addition of one electron would result in a halide ion with 8 valence electrons, making it more stable. Thus, the correct answer is "8 valence electrons".