JAMB UTME - Chemistry - 1989

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The reason why the scale of a chemical balance is made of an iron plate and coated with copper electrolytically is that copper is less susceptible to corrosion than iron. When iron is exposed to air and moisture, it reacts with oxygen and forms iron oxide, which is commonly known as rust. Rust can weaken and damage the iron, which can ultimately affect the accuracy of the balance. Copper, on the other hand, is more resistant to corrosion and therefore is a better choice for coating the iron plate of the scale. This ensures that the scale remains accurate and can be used for a longer period of time.

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During the electrolysis of copper (II) tetraoxosulphate (VI) solution, copper ions (Cu2+) are discharged at the cathode. This is because copper ions have a positive charge and are attracted to the negative electrode (cathode) during electrolysis. Hydrogen ions (H+) are discharged at the cathode only if there are no other positively charged ions present in the solution. In this case, there are Cu2+ ions present which have a higher affinity for the cathode than H+ ions. Sulphate ions (SO42-) are not discharged at the cathode as they have a negative charge and are attracted to the positive electrode (anode) during electrolysis. Therefore, option A, "Cu2+ only," is the correct answer.

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When excess chlorine is mixed with ethene at room temperature, the product is 1,2-dichloroethane. The reaction between ethene and excess chlorine is an example of an addition reaction. In this reaction, the double bond in ethene is broken, and chlorine atoms add to the carbon atoms to form a new molecule. The product formed in this reaction depends on the conditions under which the reaction occurs. When excess chlorine is mixed with ethene at room temperature, the reaction proceeds in a stepwise manner to form 1,2-dichloroethane as the major product. The first chlorine atom adds to one of the carbon atoms in ethene, and the second chlorine atom adds to the adjacent carbon atom, forming a molecule with two chlorine atoms attached to adjacent carbon atoms, which is 1,2-dichloroethane. Therefore, the product formed when excess chlorine is mixed with ethene at room temperature is 1,2-dichloroethane.

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Detalhes da Resposta

The atomic number of an element represents the number of protons in the nucleus of an atom of that element. In this case, the atomic number of caesium is 55, which means that its nucleus contains 55 protons. The atomic mass of an element is the sum of the number of protons and neutrons in the nucleus of an atom of that element. The atomic mass of caesium is 133, which means that its nucleus contains 78 neutrons (133 - 55 = 78). Therefore, the correct option is "55 protons and 78 neutrons".

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The element represented by "31P15" is phosphorus (P), which has 15 electrons in total. To determine the number of valence electrons, which are the outermost electrons involved in chemical bonding, we look at the element's position on the periodic table. Phosphorus is in Group 15, so it has 5 valence electrons. This is because the number of valence electrons in elements in a particular group is equal to the group number. Therefore, phosphorus has 5 valence electrons.

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Calcium hydroxide is added to town water supply in order to facilitate coagulation of organic particles. Coagulation is the process of clumping together of small particles into larger particles, which can then be removed from the water through sedimentation. The addition of calcium hydroxide raises the pH of the water, which helps the coagulation process by making the particles more attracted to each other. This helps to remove impurities from the water, making it cleaner and safer to drink. It does not directly kill bacteria in the water or improve the taste of the water.

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The vapor pressure curves show the relationship between the boiling points and the vapor pressures of different liquids. The boiling point of a liquid is the temperature at which its vapor pressure is equal to atmospheric pressure. From the given vapor pressure curves, we can deduce that the liquid with the highest boiling point will have the lowest vapor pressure at a given temperature. Conversely, the liquid with the lowest boiling point will have the highest vapor pressure at a given temperature. Therefore, we can deduce that liquid I has the lowest boiling point since it has the highest vapor pressure at a given temperature. On the other hand, liquid III has the highest boiling point since it has the lowest vapor pressure at a given temperature. So, the correct answer is "liquid lll has the highest boiling point."

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The property that would support the conclusion that a solid sample is a mixture is the melting range. If the solid has a melting range, it means that it is composed of two or more substances with different melting points. A pure substance always has a specific melting point, so if the solid has a range of melting points, it must be a mixture of different substances. The other properties do not necessarily indicate that a solid is a mixture. For example, the fact that a solid can be ground to a fine powder only suggests that it is a physical property of the substance. The density of a solid also cannot be used to determine if it is a mixture or not. Likewise, the ability of a solid to absorb moisture from the atmosphere does not necessarily indicate that it is a mixture, as many pure substances are hygroscopic and can absorb moisture from the air. Therefore, the correct answer is the third option: the solid has a melting range of 300oC to 375oC, as this indicates that the solid is not a pure substance, but rather a mixture of substances with different melting points.

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The correct answer is "the number of the electron shells increases from Li to Na to K." This is because the atomic radius is determined by the number of electron shells an atom has. As you move down a group in the periodic table, the number of electron shells increases, resulting in a larger atomic radius. Since Li has the smallest atomic radius, it must have the fewest electron shells, while K has the largest atomic radius, meaning it has the most electron shells. Therefore, the correct explanation for the gradation in atomic radius from Li to Na to K is that the number of electron shells increases from Li to Na to K.

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The salt in the gunpowder mixture performs the function of an oxidant. An oxidant is a substance that accepts electrons from another substance, causing the oxidation of the other substance. In gunpowder, the potassium trioxonitrate (V) is the oxidant that reacts with the charcoal and sulfur to produce a large amount of heat and gas, which propels the bullet out of the gun. The potassium trioxonitrate (V) provides the necessary oxygen for the combustion reaction to occur, making it a crucial component of the gunpowder mixture.

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The liquids X and Y burning with sooty flames indicate that they contain carbon atoms, while Z not burning with sooty flames indicate that it does not contain carbon. Y being able to discharge the color of bromine water suggests that it contains a double bond, which means it is unsaturated. Therefore, only Y is unsaturated and contains a double bond, which makes it aromatic in nature. X and Z are both saturated and do not contain any double bonds, so they are not aromatic. Thus, the answer is Y.

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Detalhes da Resposta

The activation energy is the minimum energy required for a chemical reaction to occur. In the given diagram, the activation energy for the uncatalyzed reaction is the difference between the energy of the reactants and the maximum point on the curve representing the transition state. Similarly, the activation energy for the catalyzed reaction is the difference between the energy of the reactants and the maximum point on the curve representing the transition state in the presence of the catalyst. From the diagram, the activation energy for the uncatalysed reaction is 500 kJ (difference between the energy of the reactants and the maximum point on the curve representing the transition state for the uncatalysed reaction). The activation energy for the catalysed reaction is 300 kJ (difference between the energy of the reactants and the maximum point on the curve representing the transition state in the presence of the catalyst). Therefore, the activation energy for the uncatalysed reverse reaction (XY(g) → X(g) + Y(g)) would also be 500 kJ (same as the uncatalysed forward reaction). Similarly, the activation energy for the catalysed reverse reaction (XY(g) → X(g) + Y(g)) would also be 300 kJ (same as the catalysed forward reaction). So, the respective activation energies in kJ of the catalysed and uncatalysed reverse reactions are 300 and 500 kJ respectively.

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The process of extracting metals from their ores involves various methods, including reduction with carbon, reduction with other metals, reduction by electrolysis, and oxidation with oxidizing agents. We need to identify the option that is NOT involved in the extraction of metals from their ores. "oxidation with oxidizing agents" is NOT involved in the extraction of metals from their ores. This is because oxidation is the opposite of reduction, and the extraction of metals from their ores involves reducing the metal ions to the elemental form. In other words, during the extraction of metals, reducing agents are used to reduce the metal ions to their elemental form, whereas oxidizing agents are used to oxidize the metal ions to a higher oxidation state. Thus, the correct answer is "oxidation with oxidizing agents" is NOT involved in the extraction of metals from their ores. Note: The choice of extraction method depends on the reactivity of the metal and the cost of the extraction process.

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The gas responsible for most of the fatal explosions in coal mines is methane. Methane is a highly flammable gas that can be found in coal mines. Methane is produced during the geological formation of coal and is often found in pockets within coal seams. When methane gas mixes with air and reaches a certain concentration, it becomes highly explosive. This is why it is important to monitor methane levels in coal mines and take appropriate safety measures to prevent explosions.

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When a gas is collected over water, some of the water vapor in the air above the liquid will dissolve into the water, causing the total pressure above the liquid to be higher than the pressure of the gas alone. This additional pressure is called the vapor pressure or saturation pressure of the water and depends on the temperature. At standard atmospheric pressure and 25°C, the saturation vapor pressure of water is 23 mmHg. Therefore, if we collect hydrogen gas over water at this temperature and pressure, the total pressure will be the sum of the partial pressure of the hydrogen gas and the vapor pressure of water, which is 23 mmHg. To determine the partial pressure of the hydrogen gas alone, we can use Dalton's law of partial pressures, which states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual gases. In this case, we know that the total pressure is the standard atmospheric pressure, which is approximately 760 mmHg. So, the partial pressure of the hydrogen gas can be calculated as follows: Partial pressure of hydrogen gas = Total pressure - Vapor pressure of water Partial pressure of hydrogen gas = 760 mmHg - 23 mmHg Partial pressure of hydrogen gas = 737 mmHg Therefore, the correct answer is 737 mmHg.

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The catalyst used in the contact process for the manufacture of tetraoxosulphate (VI) acid is "vanadium (V) oxide." The contact process is the industrial method for the production of sulfuric acid. In this process, sulfur dioxide is converted to sulfur trioxide, which is then used to produce sulfuric acid. Vanadium (V) oxide acts as a catalyst in the conversion of sulfur dioxide to sulfur trioxide. It speeds up the reaction rate by providing an alternate pathway for the reaction that has a lower activation energy.

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$\frac{\text{Element X}}{1s^{2}2s^{2}1p^4}$

Valency of X is 2

$\frac{\text{Element Y}}{1s^{2}2s^{2}2p^{6}3s^{2}3P^1}$

valency of Y is 3

There is an exchange of valency when a compound is being formed. Hence, we have Y2X3

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ZnO is referred to as an amphoteric oxide. This means that it can react as both an acid and a base. ZnO dissolves in both sodium hydroxide solution (a strong base) and mineral acid solution (a strong acid) to give soluble products. When ZnO reacts with sodium hydroxide, it acts as an acid and forms a soluble salt. When it reacts with a mineral acid, it acts as a base and forms a soluble salt. Therefore, ZnO can react with both acids and bases, making it an amphoteric oxide.

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Vulcanization of rubber is a process by which sulphur is chemically combined in the rubber to make it more durable and less sticky. The process involves heating natural rubber with sulphur or other curatives, such as peroxides, under high pressure. The sulphur reacts with the rubber molecules to form cross-links, which improve the rubber's strength, elasticity, and resistance to heat, chemicals, and abrasion. This process was discovered by Charles Goodyear in the 19th century and revolutionized the rubber industry by making it possible to produce a wide range of rubber products for various applications.

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Detalhes da Resposta

From Faraday;s second law of electrolysis

$\frac{\text{Mass of silver deposited}}{\text{Mass of copper deposited}}$ = $\frac{\text{Equivalent mass of silver}}{\text{Equivalent mass of copper}}$

$\frac{\text{Mass of silver deposited}}{1.0g}$ = $\frac{108}{63.5}$

= 31.75g

Copper is devalent = Cu2+

Mass of silver deposited = $\frac{108g}{31.75g}$

= 3.30g

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The alkaline hydrolysis of fats and oils produces soap and propane - 1,2,3 - triol. When fats or oils are reacted with an alkali (such as sodium hydroxide), they undergo saponification, a process which breaks down the ester bonds in the fat or oil to produce soap and glycerol. Glycerol, also known as propane-1,2,3-triol, is a trihydroxy alcohol that has three hydroxyl (-OH) groups attached to a propane chain. Therefore, the correct answer is "propane - 1,2,3 - triol".

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A noble gas is an element with a complete outermost electron shell. The outermost shell of an atom can contain up to 8 electrons. The atomic number of P is 4, which means it has 4 electrons. The electron configuration of P is 1s2 2s2, which indicates that it has two electrons in the first shell and two electrons in the second shell. Since the outermost shell is not complete, P is not a noble gas. The atomic number of Q is 10, which means it has 10 electrons. The electron configuration of Q is 1s2 2s2 2p6, which indicates that it has two electrons in the first shell, two electrons in the second shell, and six electrons in the third shell. Since the outermost shell of Q is complete with 8 electrons, Q is a noble gas (specifically, it is neon). The atomic number of R is 12, which means it has 12 electrons. The electron configuration of R is 1s2 2s2 2p6 3s2 3p6, which indicates that it has two electrons in the first shell, two electrons in the second shell, six electrons in the third shell, and two electrons in the fourth shell. Since the outermost shell of R is not complete, R is not a noble gas. The atomic number of S is 14, which means it has 14 electrons. The electron configuration of S is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p2, which indicates that it has two electrons in the first shell, two electrons in the second shell, six electrons in the third shell, ten electrons in the fourth shell, and two electrons in the fifth shell. Since the outermost shell of S is not complete, S is not a noble gas. Therefore, the answer is (B) Q, which is neon and has a complete outermost electron shell.

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The reaction between ethanoic acid and sodium hydroxide is an example of neutralization. Neutralization is a chemical reaction between an acid and a base, producing a salt and water. In this reaction, ethanoic acid (an acid) reacts with sodium hydroxide (a base) to produce sodium ethanoate (a salt) and water. The reaction is as follows: CH3COOH (ethanoic acid) + NaOH (sodium hydroxide) → CH3COONa (sodium ethanoate) + H2O (water) The reaction is called neutralization because the acid and base neutralize each other's acidic and basic properties.

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