JAMB UTME - Chemistry - 2010

Détails de la réponse

Détails de la réponse

The acid that is used to remove rust is hydrochloric acid. Rust is the common name for a very common compound, iron oxide. Hydrochloric acid reacts with rust and dissolves it, leaving the surface clean. The other options listed, boric acid, trioxonitrate (V), and tetraoxosulphate (VI), are not commonly used for rust removal.

Détails de la réponse

The haloalkanes used in dry-cleaning industries are trichloroethene and tetrachloroethene. These compounds are used because they have good solvent properties and can dissolve greasy stains.

Détails de la réponse

Carbon (II) oxide, also known as carbon monoxide (CO), is considered dangerous if inhaled because it competes with oxygen in the blood. Hemoglobin, which is responsible for carrying oxygen throughout the body, has a much greater affinity for CO than it does for oxygen. This means that when CO is inhaled, it binds to hemoglobin instead of oxygen, reducing the amount of oxygen that can be carried in the blood. This can lead to hypoxia, a condition in which the body is deprived of adequate oxygen, and can result in symptoms such as headache, dizziness, weakness, and even death.

Détails de la réponse

Elements in the same period in the periodic table have the same number of shells. A period is a row in the periodic table, and the number of shells an element has is determined by its position in the row. As you move from left to right in a period, the atomic number of elements increases, meaning that the number of protons in the nucleus also increases. This results in an increase in the number of electrons in the outermost shell, but the number of shells remains the same. Therefore, elements in the same period have the same number of shells, but different chemical and physical properties due to variations in their electron configurations.

Détails de la réponse

The gas produced in the diagram above is NO (nitric oxide). This can be determined by the chemical equation for the reaction shown in the diagram: 2NO2(g) + 4H2(g) → 2NH3(g) + 4H2O(g) + 2NO(g) Since there is no NH3 (ammonia) or N2O4 (dinitrogen tetroxide) in the options, the only gas produced in the reaction that is listed is NO (nitric oxide).

Détails de la réponse

The compound used as an anaesthetic is one of the four options given. To answer this question, we need to identify which of the options is commonly used as an anaesthetic. The correct answer is which is chloroform (CHCl3). Chloroform was used as an anaesthetic in the past but is now largely replaced by safer and more effective anaesthetics. Therefore, the compound used as an anaesthetic is chloroform (CHCl3).

Détails de la réponse

Détails de la réponse

The quantity of aluminium deposited can be calculated using the formula: Quantity of metal deposited = (I x t x m) / (n x F) where I is the current in amperes, t is the time in seconds, m is the molar mass of the metal, n is the number of electrons required to reduce one mole of the metal ions, and F is the Faraday constant. In this case, I = 10A, t = 1930s, m = 27g/mol, n = 3 (since aluminium ions have a 3+ charge and require three electrons to be reduced to metallic aluminium), and F = 96500 C/mol. Plugging these values into the formula, we get: Quantity of metal deposited = (10 x 1930 x 27) / (3 x 96500) = 1.8 g Therefore, the answer is option B: 1.8 g.

Détails de la réponse

Stainless steel is a type of steel that contains chromium, which makes it resistant to corrosion and staining. Due to its corrosion-resistant properties, stainless steel is commonly used for making products that require hygiene and durability, such as kitchen appliances, cutlery, surgical instruments, and industrial equipment. Therefore, the answer is "tools".

Détails de la réponse

Methyl orange is an acid-base indicator that is commonly used in the laboratory to determine the acidity or alkalinity of a solution. It changes color depending on the pH of the solution. In an acidic medium, it appears red, while in an alkaline medium, it appears yellow. Therefore, the correct answer is yellow.

Détails de la réponse

The organic compound that is very soluble in water is CH3COOH (option A), which is also known as acetic acid. This is because acetic acid is a polar molecule, which means that it has a positive and negative end. The positive end of acetic acid is attracted to the negative end of water molecules, while the negative end of acetic acid is attracted to the positive end of water molecules. This makes acetic acid very soluble in water. In contrast, the other compounds listed are either nonpolar or have very weak polar bonds, which means they are not very soluble in water.

Détails de la réponse

Détails de la réponse

When benzene reacts with hydrogen in the presence of nickel catalyst at 180°C, it undergoes a process known as hydrogenation. During this process, the double bonds between the carbon atoms in the benzene ring are broken and replaced with single bonds to form a cyclohexane ring. Therefore, the correct answer is "cyclohexane."

Détails de la réponse

The nitrogen atom has a total of 7 electrons arranged in different energy levels or sub-levels. To determine the number of unpaired electrons in the nitrogen sub-levels, we first need to know the electron configuration of nitrogen, which is 1s2 2s2 2p3. In the 2p sub-level, there are three orbitals available: 2px, 2py, and 2pz. Each of these orbitals can accommodate a maximum of 2 electrons. Nitrogen has three unpaired electrons in its 2p sub-level, one in each of the 2px, 2py, and 2pz orbitals. Therefore, the answer is 3.

Détails de la réponse

Détails de la réponse

If a reaction is exothermic, it means that heat is released during the reaction. When there is a great disorder, it means that the reactants have high entropy, or in other words, they are disordered. In general, exothermic reactions tend to favor products that are in a lower energy state than the reactants, while high entropy favors products that are in a more disordered state. Therefore, if a reaction is exothermic and there is a great disorder, it means that the reactants have high entropy, but the products have lower energy than the reactants. As a result, the reaction will proceed spontaneously towards the products, releasing heat in the process. Therefore, the correct option is: "There will be a large decrease in free energy."

Détails de la réponse

The reaction between methane and chlorine in the presence of ultraviolet light leads to a series of substitution reactions. The reaction can be represented by the equation: CH4 + Cl2 → CH3Cl + HCl CH3Cl + Cl2 → CH2Cl2 + HCl CH2Cl2 + Cl2 → CHCl3 + HCl CHCl3 + Cl2 → CCl4 + HCl Therefore, the final product of the reaction is tetrachloromethane (CCl4) and hydrogen chloride (HCl). So, the correct option is "tetrachloromethane".

Détails de la réponse

When iron is exposed to moist air, it gradually rusts due to the formation of hydrated iron (III) oxide. This happens when iron reacts with oxygen and water in the air, producing hydrated iron (III) oxide, which is a reddish-brown compound commonly known as rust. The reaction of iron with oxygen is called oxidation, and the presence of water is necessary for the reaction to occur. Rusting of iron is a common example of corrosion, which can weaken structures and cause them to fail over time. Therefore, it is important to take measures to prevent rusting, such as using protective coatings or keeping the iron dry.

Détails de la réponse

Alkanes are a type of hydrocarbon that consists of only single bonds between carbon atoms. One of the major uses of alkane is as domestic and industrial fuel. Alkanes are a type of hydrocarbon that burn in the presence of oxygen to produce heat and light, making them a good source of energy. They are commonly used as fuels for heating homes, powering vehicles, and generating electricity.

Détails de la réponse

The IUPAC nomenclature of the compound LiAlH4 is "lithium tetrahydridoaluminate (III)". In this name, "lithium" is listed first since it is more electropositive than aluminum. The prefix "tetra" indicates that there are four hydrogen atoms in the compound, and "hydrido" is used to specify that each hydrogen atom is acting as a hydride ion, which has a -1 charge. The Roman numeral "(III)" indicates the oxidation state of aluminum, which is +3 in this case.

Détails de la réponse

The reducing agent in a chemical reaction is the substance that causes another substance to be reduced, or to undergo a decrease in oxidation state. In the given chemical reaction, we can see that silver ions (Ag+) are being reduced to elemental silver (Ag), indicating that some other substance is causing the reduction to occur. Looking at the reaction, we can see that the substance that fits this description is PH3 (phosphine gas), which is being oxidized (its oxidation state is increasing) and thus acting as a reducing agent. Therefore, the answer is "PH3(g)".

Détails de la réponse

Drying agents are substances used to remove moisture from other substances. The most suitable drying agents are usually hygroscopic, meaning they attract and hold onto water molecules. Therefore, the correct answer is "hygroscopic". Amphoteric substances can react as both acids and bases, efflorescent substances lose water when exposed to air, and acidic substances have a pH less than 7.

Détails de la réponse

When potassium chlorate (KClO3) is heated in the presence of manganese dioxide (MnO2), oxygen gas is produced. The role of MnO2 is to act as a catalyst in the reaction, meaning that it increases the rate of the reaction without being consumed itself. In this case, the catalyst works by lowering the energy barrier of the reaction, allowing it to occur at a lower temperature than it would without the catalyst. Therefore, the correct option is "lowering the energy barrier of the reaction."

Détails de la réponse

The droplets of water observed around a bottle of milk taken out of the refrigerator is due to the fact that the water vapor in the air around the bottle loses some of its energy to the bottle. When the temperature of the milk drops as it loses heat into the surroundings, the air around the bottle cools down as well. The water vapor in the air then loses some of its energy and condenses into liquid droplets on the surface of the bottle. This is called condensation, and it occurs when the temperature of the air is lowered to the point where the water vapor in it can no longer remain in its gaseous state.

Détails de la réponse

The L shell is the second electron shell in an atom, which can hold up to 8 electrons. Therefore, the correct answer is 8.

Détails de la réponse

Détails de la réponse

Détails de la réponse

When the temperature is increased, the equilibrium constant of the reaction will decrease. This is because the reaction is exothermic, meaning it releases heat. According to Le Chatelier's principle, when a stress is applied to a system at equilibrium, the system will shift in a way that counteracts the stress. In this case, an increase in temperature is a stress that causes the equilibrium to shift in the direction that absorbs heat, which is the reverse reaction. As a result, the concentration of reactants will increase and the concentration of products will decrease, leading to a decrease in the equilibrium constant. Therefore, the correct option is "it decreases."

Détails de la réponse

Détails de la réponse

Coffee stains can be stubborn to remove from fabrics, but there are several options you can try. Among the options given, a solution of borax in water can be effective in removing coffee stains. Borax is a natural mineral compound that has cleaning and bleaching properties, making it useful for removing stains. To use it, you can mix a small amount of borax with water to form a paste and then apply it to the stain. Let the paste sit for a few minutes before washing the fabric as usual.

Détails de la réponse

Détails de la réponse

The stability of the noble gases is due to the fact that they have a complete valence electron shell, also known as an octet configuration. This means that their outermost shell is completely filled with electrons, making them unreactive and chemically stable. They do not need to gain or lose electrons to form compounds, and they exist in their elemental form as single atoms. This property is the reason why they are called "noble" gases. The correct answer choice is "have duplet or octet electron configurations".

Détails de la réponse

Détails de la réponse

Détails de la réponse

Trioxocarbonate (IV) salts of sodium, potassium, ammonium are soluble in water.
Tetraoxosulphate (VI) salts of sodium, potassium, ammonium are soluble in water while that of calcium is slightly soluble in water.

Détails de la réponse

Explanation provided by Dr. Chuma Odachi

Détails de la réponse

Iron can be protected from corrosion by coating the surface with zinc. This process is called galvanization. When iron is coated with zinc, it forms a protective layer over the iron surface that prevents water and oxygen from coming into contact with the iron. This protective layer is able to withstand most environmental conditions and can last for a very long time. This is why galvanized iron is used in many outdoor applications, such as in the construction of buildings, bridges, and highways, and in the manufacturing of vehicles, appliances, and many other products.

Détails de la réponse

The first ionization energy is the energy required to remove the most loosely held electron from an atom in the gaseous state. As one moves across a period from left to right, the number of protons in the nucleus increases, which results in an increase in the nuclear charge. This increase in nuclear charge causes the electrons to be held more tightly to the nucleus, which means that more energy is required to remove an electron. Therefore, the general rise in the first ionization energy across a period can be attributed to the increase in nuclear charge. Option (B) - "increase in nuclear charge" is the correct answer.

Détails de la réponse

Out of the options given, "blood" is an example of a mixture. A mixture is formed by the combination of two or more substances, where each substance retains its own chemical properties. Blood is a mixture of different components, such as red blood cells, white blood cells, plasma, and platelets. Each component of the blood has its own chemical and physical properties, and they can be separated through various techniques. In contrast, common salt and washing soda are pure substances, and sand is a heterogeneous mixture.

Détails de la réponse

The given reaction involves the combination of two light nuclei, deuterium (D) and tritium (T), to form a heavier nucleus, helium (He), and a neutron (n), along with the release of a significant amount of energy. This type of nuclear reaction is known as nuclear fusion. Therefore, the correct option is "nuclear fusion."

Détails de la réponse

When hydrocarbons react with bromine water, the bromine is added across the double or triple bond of an unsaturated hydrocarbon. This reaction is called addition reaction. Alkenes and alkynes are unsaturated hydrocarbons which can undergo addition reactions while alkanes are saturated hydrocarbons which cannot undergo addition reactions. Hence, the hydrocarbon Y that did not decolorize the solution is an alkane.

Détails de la réponse

Détails de la réponse

The fuel used in miners' lamp is ethyne. Ethyne is a colorless gas with a faint sweet odor that burns with a bright, white flame. It is commonly used as a fuel for welding and cutting metals due to its high flame temperature. In miners' lamps, the flame produced by burning ethyne is used to provide light in dark and enclosed spaces like mines. It is also known as acetylene and is produced by the reaction of calcium carbide with water.

Détails de la réponse

When a compound is heated in a flame, the heat excites the electrons in the compound, causing them to jump to higher energy levels. When these electrons return to their original energy levels, they release energy in the form of light, which gives a characteristic color to the flame. The orange-red color is typically associated with the presence of calcium (Ca2+) ions in a compound. Therefore, the compound is most likely to contain Ca2+ ions.

Détails de la réponse

Détails de la réponse

The gas that contains the highest number of atoms at standard temperature and pressure (s.t.p) is the gas with the highest number of moles. Neon is a noble gas that exists as single atoms and has an atomic number of 10. Therefore, 6 moles of neon would contain 6 times Avogadro's number (6.02 x 10^23) of atoms, making it the gas with the highest number of atoms at s.t.p. Oxygen exists as a diatomic molecule (O2), so 3 moles of oxygen would contain 3 times Avogadro's number of molecules, which is half the number of atoms in 6 moles of neon. Chlorine is a diatomic molecule like oxygen, but its atomic number is 17, which is higher than that of oxygen. However, 2 moles of chlorine would still contain fewer atoms than 6 moles of neon. Ethane (C2H6) is a compound made up of multiple atoms, so 1 mole of ethane would contain fewer atoms than any of the other options. Therefore, the gas that contains the highest number of atoms at s.t.p is 6 moles of neon.

Détails de la réponse

Ethene is used to hasten the ripening of fruit. When ethene gas is released by a fruit, it can cause nearby fruits to ripen as well. This is because ethene triggers a ripening process in fruit by signaling the fruit to produce enzymes that break down complex molecules into simpler ones. As a result, the fruit becomes softer, sweeter, and more flavorful. Therefore, ethene is commonly used in the agricultural industry to ripen fruits such as bananas, tomatoes, and avocados. Ethanol, ethyne, and ethane are not typically used to hasten the ripening of fruit.

Détails de la réponse

Bronze and solder have copper as a common constituent. Bronze is an alloy made from copper and tin, while solder is a low-melting-point alloy used to join two metals together, typically made from a mixture of tin and lead.