JAMB UTME - Chemistry - 1999

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The given chemical equation represents a reaction between RS and HF to form RF and HS. The value of ΔH (-65.7 kJ/mol) indicates the heat change associated with the reaction. A negative value of ΔH indicates that the reaction is exothermic, meaning that the heat content of the products is lower than the heat content of the reactants. Therefore, the correct answer is "the heat content of the reactants is higher than that of the products." "the heat content of the reactants is lower than that of the products," is incorrect as it contradicts the given value of ΔH. "the reaction is slow," and "a large amount of heat is absorbed," are irrelevant and not supported by the given information.

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Water molecules are the most disorderly arranged in the gaseous state, i.e., as steam at 100°C. In the gaseous state, water molecules have the highest amount of kinetic energy, and they move randomly in all directions at high speeds, colliding with each other and other molecules in the surroundings. This random motion results in a highly disordered arrangement of water molecules. In contrast, at lower temperatures and higher pressures, water molecules tend to have less kinetic energy and move less randomly, resulting in more orderly arrangements, such as in ice at 0°C or even -10°C.

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Hydrogen bonding is a type of intermolecular force that occurs between a hydrogen atom bonded to a highly electronegative atom (such as nitrogen, oxygen or fluorine) and another highly electronegative atom in a separate molecule. The strength of a hydrogen bond depends on the electronegativity of the atoms involved and the distance between them. In the given compounds, HF has the strongest hydrogen bond because it has the highest electronegativity difference between the hydrogen and fluorine atoms. Fluorine is the most electronegative element in the periodic table, so the bond between hydrogen and fluorine is highly polarized. This results in a strong partial positive charge on the hydrogen atom, which attracts the highly electronegative fluorine atom of another molecule, forming a strong hydrogen bond. In contrast, NH3 and CH4 have weaker hydrogen bonds because nitrogen and carbon are less electronegative than fluorine. HCl has the weakest hydrogen bond because hydrogen and chlorine have a smaller electronegativity difference than hydrogen and fluorine.

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Hydrogen is used in oxy-hydrogen flames for melting metals because it evolves a lot of heat when burnt. When hydrogen gas is burned in the presence of oxygen, it undergoes a highly exothermic reaction to form water vapor. The heat released during this reaction is intense and can be used to melt metals, such as gold, silver, and copper. This process is known as oxy-hydrogen welding, and it is commonly used in jewelry making, metal sculpture, and other metalworking applications. While hydrogen can be explosive when mixed with air or oxygen in certain conditions, oxy-hydrogen welding relies on the controlled burning of hydrogen in the presence of oxygen to generate heat for melting metals. Hydrogen is also a very light gas, but this property is not relevant to its use in oxy-hydrogen flames for melting metals. Additionally, while hydrogen can be used as a rocket fuel, this is not related to its use in oxy-hydrogen welding.

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The metal that can be extracted from cassiterite is tin. Cassiterite is a mineral containing tin oxide (SnO2) which is the main source of tin. The process of extracting tin from cassiterite involves several stages including concentration, smelting, and refining. Tin is used in many applications including the manufacturing of tinplate, which is used for packaging food and drinks, and in the production of various alloys such as bronze and pewter.

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The gas that will form a white precipitate with acidified silver trioxonitrate (v) is hydrogen chloride (HCl). When HCl is reacted with silver trioxonitrate (v) in the presence of water, it produces a white precipitate of silver chloride (AgCl), which is insoluble in water and forms a white solid. The other options, NH3, SO2, and CO2, do not react with silver trioxonitrate (v) to form a white precipitate.

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The given equation shows a reaction between magnesium and hydrochloric acid which produces magnesium chloride and hydrogen gas. The question asks for the mass of magnesium required to react with a given amount of hydrochloric acid. To solve this problem, we need to use the following formula: moles = concentration x volume / 1000 where moles is the number of moles of hydrochloric acid, concentration is the molarity of hydrochloric acid, and volume is the volume of hydrochloric acid in liters. First, we need to calculate the number of moles of hydrochloric acid in 250 cm³ of 0.5 M HCl: moles HCl = 0.5 x 250 / 1000 = 0.125 moles From the balanced chemical equation, we know that 1 mole of magnesium reacts with 2 moles of hydrochloric acid to produce 1 mole of hydrogen gas. Therefore, the number of moles of magnesium required is half the number of moles of hydrochloric acid: moles Mg = 0.125 / 2 = 0.0625 moles Finally, we can calculate the mass of magnesium required using its molar mass: mass = moles x molar mass = 0.0625 x 24 = 1.5 g Therefore, the answer is option B: 1.5g.

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The electronic configuration given in the question represents an atom with 26 electrons. To determine the identity of the element, we can count the number of electrons in each energy level and sub-level. The highest energy level, 4, has 2 electrons in the s sub-level and 0 electrons in the d sub-level, which means that it is a Group 2 element. The 3d sub-level has 7 electrons, which confirms that the element is a transition element. Therefore, the correct answer is "transition element."

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The gas that will diffuse fastest is the gas with the lowest molecular mass which in this case is methane, CH4.

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4 Faradays of electricity is required to liberate one mole of oxygen gas
∴ quantity of electricity required
= 0.125 * 4 * 96500 = 48250 coulombs

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The electrochemical series is a list of metals and non-metals in order of their relative reactivity towards other substances in electrochemical reactions. The statement that is true of the electrochemical series is that electropositivity of metals decreases down the series. This means that the most electropositive metals (such as potassium and sodium) are found at the top of the series, while the least electropositive metals (such as gold and platinum) are found at the bottom. As you go down the series, the metals become less likely to lose electrons and form positive ions, which means that they become less reactive.

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The entropy and enthalpy of a system are both thermodynamic properties used to describe the state of a system. Entropy is a measure of the degree of disorderliness or randomness of a system, while enthalpy is a measure of the heat content of a system at constant pressure. In other words, entropy tells us how much energy in a system is unavailable to do work, while enthalpy tells us how much energy is stored in the chemical bonds of the system. Therefore, the correct option is: - degree of disorderlinesss and heat content respectively

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From the reactivity series in the table, the least reactive element is Z. This is because Z is placed at the bottom of the series and is the only element that does not react with any of the other elements. Elements higher up the series are more reactive because they can displace the ions of elements below them in the series. Therefore, since Z is placed at the bottom of the reactivity series and does not react with any of the other elements, it is the least reactive element in the table.

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The oxidation state or number is a measure of the degree of oxidation of an atom in a compound, which is determined by counting the number of electrons transferred from or to the element when it forms a compound. In this question, we are given three transition metal compounds, K2Cr2O7, V2O5, and KMnO4, and we are asked to arrange them in order of increasing oxidation number of the metal ion. The oxidation number of the metal ion in each compound can be determined by assigning electrons to the metal and oxygen atoms based on their electronegativity values and the overall charge of the compound. Oxygen is generally assigned an oxidation number of -2, and the sum of the oxidation numbers of all the atoms in the compound should equal the overall charge of the compound. For K2Cr2O7, we can assign an oxidation state of +6 to the chromium ion, since each oxygen atom contributes -2 to the total charge, and the two potassium ions each contribute +1. For V2O5, we can assign an oxidation state of +5 to the vanadium ion, since each oxygen atom contributes -2 to the total charge. For KMnO4, we can assign an oxidation state of +7 to the manganese ion, since each oxygen atom contributes -2 to the total charge, and the potassium ion contributes +1. Therefore, the correct order of increasing oxidation number of the metal ions in these compounds is: V2O5 < K2Cr2O7 < KMnO4.

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Hard water contains high levels of dissolved minerals like calcium and magnesium, which can cause problems like soap scum, scale buildup, and decreased efficiency of water heaters and pipes. Soft water, on the other hand, contains very low levels of these minerals and is more desirable for household use. One effective method of converting hard water to soft water is the use of an ion-exchange resin. This resin contains sodium ions that can exchange with the calcium and magnesium ions in the water, effectively removing them and replacing them with sodium ions. This process is called ion exchange, and it can be done using a device called a water softener. Chlorination, passage over activated charcoal, and aeration are not effective methods of converting hard water to soft water.

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56.00cm3 of a gas at S.T.P weighed 0.11g
Molar volume of the gas = 22.4dm3 = 22400cm3
molar mass = (22400 x 0.11)/56
molar mass = 2464/56 = 44
Vapour density = Molar mass/2 = 44/2 = 22

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The diagram shows two solids, P and Q, mixed together. The question is asking how these two solids can be separated from each other. Crystallization involves dissolving a solid in a solvent to create a solution, then allowing the solvent to evaporate slowly to produce crystals of the dissolved solid. This method can be used when one of the solids is soluble in a particular solvent and the other is not. However, from the diagram, it is not clear whether either of the solids is soluble in a particular solvent, so we can eliminate options C and D. Distillation is a process used to separate liquids based on differences in their boiling points. This method would not be effective for separating solids, so we can eliminate option A. Fractional distillation is similar to distillation, but is used to separate a mixture of liquids with similar boiling points. This method also would not be effective for separating solids, so we can eliminate option B. Therefore, the correct answer is option C, crystallization.

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When excess ethanol is heated to 145°C in the presence of concentrated H2SO4, the product formed is diethyl ether. The reaction is known as the Williamson ether synthesis. In this reaction, ethanol acts as a nucleophile and attacks the protonated form of ethanol to form an intermediate compound. The intermediate compound loses a molecule of water to form diethyl ether. The other products mentioned in the options are not formed during this reaction. Ethyne is formed by the dehydration of ethanol in the presence of sulfuric acid, but the reaction conditions mentioned in the question are not suitable for the formation of ethyne. Diethyl sulphate is formed when ethanol is heated with excess concentrated H2SO4 at higher temperatures, while acetone is not formed by this reaction.

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The balanced chemical equation for the reaction between lead (II) trioxonitrate (V) and hydrochloric acid is: Pb(NO3)2(aq) + 2HCl(aq) → PbCl2(s) + 2HNO3(aq) From the equation, we can see that 1 mole of lead (II) trioxonitrate (V) reacts with 2 moles of hydrochloric acid to produce 1 mole of lead (II) chloride. Therefore, we need to first calculate the number of moles of lead (II) trioxonitrate (V) and hydrochloric acid present in the solution: Number of moles of Pb(NO3)2 = concentration × volume = 0.1 × (200/1000) (convert cm³ to dm³) = 0.02 moles Number of moles of HCl = concentration × volume = 0.1 × (200/1000) = 0.02 moles From the equation, we can see that 1 mole of Pb(NO3)2 produces 1 mole of PbCl2. Therefore, the number of moles of PbCl2 that will be formed is also 0.02 moles. Now, we can calculate the mass of PbCl2 formed: Mass of PbCl2 = number of moles × molar mass = 0.02 × (207 + 2(35.5)) = 0.02 × 278 = 5.56 g Therefore, the mass of lead (II) chloride that will be precipitated is 5.56g. The correct option is: 5.56g.

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The energy required to remove an electron from an atom is called ionization energy. In this case, the question specifically states that the energy required to remove one electron from a 3S orbital of gaseous sodium atom is 496 kJ/mol. Therefore, the correct answer is ionization energy. Ionization energy is a measure of how strongly an atom holds onto its electrons. The higher the ionization energy, the more difficult it is to remove an electron from the atom. The ionization energy is often used to describe the reactivity of an element and its ability to form chemical bonds.

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Polyvinyl chloride (PVC) is a synthetic plastic material that is widely used in various applications due to its versatility, durability, and affordability. One of the most common uses of PVC is in the production of pipes. PVC pipes are used in various industries, including construction, agriculture, and plumbing, because they are strong, lightweight, and easy to install. PVC is not used in the production of bread, pencils or ink. Bread is made from flour, water, yeast, and other ingredients, while pencils are made from graphite and wood or plastic. Ink is typically made from a mixture of pigments or dyes, a solvent, and a binder. PVC is not a common component in any of these products.

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When materials are heated in air, they can undergo a variety of chemical reactions such as combustion, oxidation, or decomposition. These reactions can result in a change in the mass of the material. Out of the options provided, the material that is most likely to have its mass increased when heated in air is "Magnesium". This is because magnesium is a reactive metal that undergoes combustion in air, which means it reacts with oxygen in the air to form magnesium oxide. The magnesium oxide has a greater mass than the original magnesium metal, so the overall mass of the system increases. Helium is a noble gas and is chemically inert, which means it does not react with other substances under normal conditions, including when heated in air. Therefore, its mass remains the same. Copper pyrites is a mineral composed of various compounds, including copper and sulfur. When heated in air, it can undergo various chemical reactions, but none of these reactions result in an overall increase in mass. Glass is a non-crystalline solid that is formed by heating a mixture of silica, soda, and lime. When heated further in air, it may undergo some minor chemical reactions, but these do not result in a significant increase in mass. Therefore, out of the options provided, magnesium is the material that is most likely to have its mass increased when heated in air.

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Chlorine, bromine, and iodine resemble one another in that they displace one another from solutions of their salts. This is due to the fact that they are all halogens and have similar chemical properties. Halogens are highly reactive non-metals that have seven electrons in their outermost energy level. Because they all have a similar electronic configuration, they react similarly with other elements and compounds. In the case of displacing one another from solutions of their salts, this is because they are all capable of oxidizing and reducing one another. As a result, if a more reactive halogen is added to a solution containing a less reactive halogen, the more reactive halogen will displace the less reactive halogen from its salt. This displacement reaction is a common property of halogens and is used in various chemical applications.

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The given percentage of M in the gaseous metallic chloride MCl_x is 20.22%. We need to determine the formula of the chloride. First, we can assume that we have 100g of the compound. This would mean that there are 20.22g of M and 100 - 20.22 = 79.78g of Cl in the compound. Next, we need to determine the ratio of M to Cl in the compound. We can do this by dividing the mass of each element by its atomic weight and then dividing by the smaller result to get the simplest ratio. For M, (20.22 / 27) gives a result of 0.748 and for Cl, (79.78 / 35.5) gives a result of 2.25. Dividing both by 0.748 gives a ratio of approximately 1:3. This means that the formula for the compound is MCl3, which is option (C).

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Duralumin is an alloy made from aluminum, copper, and magnesium. The properties of duralumin that make it more useful than its constituent metals are its strength and lightness. Duralumin is much stronger than pure aluminum, which makes it suitable for use in applications where high strength-to-weight ratios are important, such as in aircraft construction. Additionally, duralumin is resistant to corrosion and has a high level of ductility, which means it can be easily shaped without breaking. Therefore, duralumin has a combination of properties that make it an excellent material for many industrial applications, including aircraft construction, automotive parts, and structural components.

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We can solve this problem using the combined gas law, which relates the pressure, volume, and temperature of a gas: (P1 V1) / T1 = (P2 V2) / T2 where P1 and T1 are the initial pressure and temperature, P2 and T2 are the final pressure and temperature, and V1 and V2 are the initial and final volumes (which are held constant in this problem). We can plug in the values we know and solve for the unknown temperature: (9 atm)(V1) / 273 K = (3 atm)(V1) / T2 Cross-multiplying and simplifying gives: T2 = (3 atm / 9 atm) * 273 K = 91 K Therefore, the temperature of the gas is 91K. Answer is correct.

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M1 V1 = M2 V2
∴ Mn Vn represent volume and molar concentration of HCL also MyVy represent volume and molar concentration of Na2CO3
MnVn = MyVy
0.25 * 15 = 12.50 * My
My = (0.25 * 15)/12.50
My = 0.3m/dm3

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An organic compound that does not undergo a reaction with both hydrogen cyanide and hydroxylamine can be an alkane. Hydrogen cyanide (HCN) and hydroxylamine (NH2OH) are chemical reagents that are commonly used to test for the presence of a carbonyl group (-C=O) in organic compounds. When these reagents are added to a carbonyl-containing compound, a chemical reaction occurs, and a new product is formed. However, alkanes do not contain a carbonyl group and are therefore unreactive towards both HCN and NH2OH. Hence, an organic compound that does not undergo a reaction with both HCN and NH2OH can be an alkane. Alkenes contain a carbon-carbon double bond (-C=C-) and are generally more reactive than alkanes. Alkanals, alkanones, and alkanoc acids all contain a carbonyl group and are therefore reactive towards HCN and NH2OH.

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From M = zit
Where M = to the mass of the metal liberated
z = Is the electrochemical equivalent
∴ X g = 1 * 1 * 40 * 60
X g = 2400 I
Let Y represent the new mass
Y = 1*2I * 10 * 60
Y = 1200 I
Y/(X g) = 1200 I/2400 I
Y = X/2 g

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The compound that would react to take up two molecules of bromine during bromination is l only. This is because l has a double bond between carbon and carbon, which allows it to undergo addition reactions, such as bromination. The double bond is broken, and a bromine atom is added to each carbon atom, resulting in the product with two bromine atoms attached to it. On the other hand, lll has no double bonds and cannot undergo addition reactions like bromination. Therefore, l and ll only have double bonds and can react to take up two molecules of bromine during bromination.

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