JAMB UTME - Chemistry - 1994

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The number of electrons in the valence shell of an element of atomic number 14 is?

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The atomic number of an element tells us the number of protons in its nucleus, which is also equal to the number of electrons in the neutral atom. The element with atomic number 14 is Silicon (Si). To determine the number of electrons in the valence shell, we need to look at the electron configuration of Silicon. The electron configuration of Silicon is 1s2 2s2 2p6 3s2 3p2. The valence shell of an atom is the outermost shell containing electrons, and in the case of Silicon, this is the 3rd shell (3s2 3p2). The number of electrons in the valence shell of Silicon is equal to the sum of the electrons in the s and p orbitals of that shell, which is 2 + 2 = 4. Therefore, the correct answer is 4, which means that Silicon has 4 valence electrons.

MnO4(aq) + 8H + 5Fe2+ $\to$ Mn2+(aq) + 5Fe3+(aq) + H2O. The oxidation number of maganese in the above reaction changed from

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2HCL(ag) + CaCO3(ag) ? CaCL2(ag) + H2O(1) + CO

From the reaction above, which of the following curves represents the consumption of calcium trioxocarbonate (IV) as dilute HCL is added to it?

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To what temperature must a gas 273 K be heated in order to double both its volume and pressure?

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According to the Ideal Gas Law, PV = nRT, where P is the pressure, V is the volume, n is the number of moles of gas, R is the gas constant, and T is the temperature in Kelvin. If we want to double both the volume and pressure of the gas while keeping the number of moles constant, then we can use the combined gas law, which states: (P1V1)/T1 = (P2V2)/T2 where P1 and V1 are the initial pressure and volume, and P2 and V2 are the final pressure and volume. Since we want to double both the pressure and volume, we can set: P2 = 2P1 V2 = 2V1 Substituting these values into the combined gas law, we get: (P1*2V1)/T1 = (2P1*2V1)/T2 Simplifying, we get: T2 = T1*4 So, the temperature must be quadrupled in order to double both the pressure and volume. Since the initial temperature is 273 K, we can multiply it by 4 to get the final temperature: T2 = 273 K * 4 = 1092 K Therefore, the answer is 1092 K.

Which of the following is NOT true of metals?

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The statement that is NOT true of metals is: "Their oxides are acidic". Metals are elements that tend to have certain characteristics such as good conductivity of heat and electricity, high melting points, and the ability to lose electrons to form positively charged ions or cations. When a metal reacts with oxygen, it forms metal oxide, which may be either basic or amphoteric, but not acidic. Basic oxides react with acids to form salts and water, while amphoteric oxides can react as either an acid or a base. Therefore, their oxides are not acidic, but either basic or amphoteric in nature.

For a gas, the relative molecular mass is equal to 2Y. What is Y?

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Which of these metals CANNOT replace hydrogen from alkaline solutions?

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20 cm3 of a 2.0 M solution of ethanoic acid was added to excess of 0.05 M sodium hydroxide. The mass of the salt produced is?(Na = 23, C = 12, O = 16, H = 1)

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Which of the following is the correct order of decreasing activity of the metals Fe, Ca, Al and Na?

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The reactivity of metals is related to their tendency to lose electrons and form positive ions. Metals that lose electrons easily are more reactive, while metals that don't lose electrons easily are less reactive. The order of decreasing activity of the metals Fe, Ca, Al, and Na can be determined by their position in the reactivity series. In the reactivity series, metals are listed in order of decreasing reactivity. The most reactive metals are at the top, and the least reactive metals are at the bottom. The reactivity series is based on how readily the metals react with water and dilute acids. The correct order of decreasing activity of the metals Fe, Ca, Al, and Na is: Na > Ca > Al > Fe This is because Na is the most reactive metal, followed by Ca, Al, and Fe. Therefore, is the correct answer. Na (s) + H2O (l) -> NaOH (aq) + 1/2H2 (g) Ca (s) + H2O (l) -> Ca(OH)2 (aq) + H2 (g) Al (s) + 3H2O (l) -> Al(OH)3 (aq) + 3/2H2 (g) Fe (s) + H2O (l) -> Fe(OH)2 (s) + H2 (g)

What volume of oxygen measured at s.t.p would be liberated on electrolysis by 9650 coulombs of electricity?

(Molar volume of gas = 22.4 dm3, F = 96,500 C mol-)

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Which of the following compounds is NOT an isomers of 2,2 dimethylbutane?

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The diagram above represents an atom of

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8g CH4 occupies 11.2 dm3 at s.t.p. What volume would 22 g of CH3CH3 occupy under the same condition?

(C = 12, H = 1)

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MnO4(aq) + 8H + (aq) + 5Fe2+ → Mn2+(aq) + 4H2O(I). The oxidation number of manganese in the above reaction changed from?

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In the given chemical reaction, MnO₄^- ion is reduced to Mn²⁺ ion, indicating a decrease in the oxidation number of manganese. To determine the change in oxidation number, we need to know the oxidation state of manganese in the reactant and product side. In MnO₄^-, oxygen has an oxidation state of -2, so the oxidation state of Mn can be calculated as follows: (+4) + 4(-2) = -8 x + (-8) = -1 (the net charge of MnO₄^-) Solving for x, the oxidation state of Mn in MnO₄^- is +7. On the product side, there are two H₂O molecules, so the oxidation state of Mn can be calculated as follows: x + 4(+2) + 2(-2) = 0 (the net charge of Mn2+) Solving for x, the oxidation state of Mn in Mn²⁺ is +2. Therefore, the oxidation state of Mn changes from +7 to +2 in the given reaction, which means that the correct answer is "+7 to +2".

H- + H2(I)O → H2(g) + OH-(aq). From the equation above, it can be inferred that the?

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A mixture of sand, ammonium chloride and sodium chloride is best separated by?

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The best method to separate the mixture of sand, ammonium chloride, and sodium chloride is "sublimation followed by addition of water and filtration". The mixture contains two sublimating components, sand and ammonium chloride, and one non-sublimating component, sodium chloride. Therefore, sublimation can be used to separate the mixture into two components. By heating the mixture, ammonium chloride sublimes, and can be collected on a cool surface as solid. The remaining mixture will contain sand and sodium chloride. Next, water can be added to dissolve the sodium chloride, leaving the sand as a residue. The solution containing sodium chloride can then be filtered to remove any insoluble impurities, leaving behind a clear solution of sodium chloride. Therefore, the correct option for separating the given mixture is "sublimation followed by addition of water and filtration".

From the above diagram, the caustic soda in the conical flask serves to

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Use the diagram above to answer this question.

The reaction taking place in the flask above is known as

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The reaction taking place in the flask above is dehydration. Dehydration is a chemical reaction that involves the removal of water from a molecule or compound. In the diagram, there is a reactant (the pink molecule) that loses a water molecule (H2O) and forms a new compound (the blue molecule). This process is known as dehydration, and it is represented by the removal of water (H2O) from the pink molecule, leaving behind a double bond (represented by the black line) between the two carbon atoms.

The ∆H for the reaction represented by the energy profile above is

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In the diagram above the activation energy is represented by

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In the diagram, the activation energy is represented by the vertical distance between the reactants (energy level x) and the maximum point in the curve (energy level y). Therefore, the answer is "y - x".

SO3 is NOT directly dissolved in water in the preparation of H2SO4 by the contact process because?

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A solid that absorbs water from he atmosphere and forms an aqueous solution is?

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Crude copper could be purified by the electrolysis of concentrated copper (II) chloride if the crude copper is?

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The densities of two gases, X and Y, are 0.5 g dm-3 and 2.0 dm-3 respectively.

What is the rate of diffusion of X relative to Y?

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An increase in temperature causes an increase in the pressure of a gas because?

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Which of the following is TRUE of Le Chatelier's Principle for an exothermic reaction?

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Le Chatelier's Principle states that if a system at equilibrium is subjected to a change in temperature, pressure, or concentration of reactants or products, then the equilibrium shifts in the direction that tends to undo the effect of the change. For an exothermic reaction, increasing the temperature will cause a shift in the equilibrium towards the reactants, in order to reduce the effect of the added heat. This means that the equilibrium constant will decrease since it is a ratio of the concentrations of products to reactants at equilibrium. Therefore, the correct answer is "Increase in temperature will cause a decrease in the equilibrium constant." The addition of a catalyst will not affect the position of the equilibrium, but it will increase the rate at which the reaction reaches equilibrium. Therefore, the statement "Addition of a catalyst will cause an increase in the equilibrium constant" is false.

Which of these solutions will give a white precipitate with a solution of barium chloride acidified with hydrochloric acid?

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The solubility, in moles per dm3 of 20.2 g of potassium trioxonitrate (V) dissolve in 100 g of the resulting mixture is?(K = 39, O = 16, N =14).

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The first step to solve the problem is to calculate the molar mass of potassium trioxonitrate (V), which is given by: KNO₃ = (1 x 39) + (1 x 14) + (3 x 16) = 101 g/mol Next, we need to calculate the number of moles of potassium trioxonitrate (V) that are present in 20.2 g: moles of KNO₃ = mass / molar mass = 20.2 / 101 = 0.2 mol Now, we need to calculate the total mass of the resulting mixture. This is given by: mass of resulting mixture = mass of KNO₃ + mass of water = 20.2 + 100 = 120.2 g Finally, we can calculate the solubility of potassium trioxonitrate (V) in moles per dm³ by dividing the number of moles of KNO₃ by the volume of the resulting mixture in dm³. The volume of the resulting mixture is equal to 0.1 dm³ (since 100 g of water is equal to 0.1 dm³): solubility = moles / volume = 0.2 / 0.1 = 2.0 Therefore, the solubility of potassium trioxonitrate (V) in moles per dm³ is 2.0 mol/dm³, which corresponds to option (D).

Sodium chloride has no solubility product value because of its?

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An anhydride is an oxide of non-mental?

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A pure solid usually melts?

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In general, a pure solid usually melts over a narrow range of temperature. This is because a pure solid has a well-defined melting point, which is the temperature at which the solid transitions into its liquid state. The melting point of a pure solid is determined by its chemical composition and the strength of the intermolecular forces between its molecules. Impurities in a solid can disrupt the intermolecular forces and change the melting point of the solid. This is why impure solids may melt over a wider range of temperature or at a lower temperature than the corresponding pure solid. Therefore, if we compare the melting behavior of a pure solid and an impure solid, we can expect the pure solid to have a well-defined melting point and melt over a narrow range of temperature, while the impure solid may melt over a wider range of temperature or at a lower temperature.

A major effect of oil pollution in coastal waters is the?

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One mole of a hydrocarbon contains 48 g of carbon. If it vapour density is 28, the hydrocarbon is?

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When sodium ethanoate is treated with a few drops of concentrated tetraoxosulphate(vi)acid. one of the products is

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When sodium ethanoate (also known as sodium acetate) is treated with concentrated tetraoxosulphate (VI) acid (also known as sulfuric acid), one of the products formed is ethanoic acid (CH3COOH). This is due to the fact that the sulfuric acid protonates the acetate ion in the sodium ethanoate solution, leading to the formation of ethanoic acid and sodium sulfate as the other product. Therefore, the correct option is: CH3COOH.

A few drops of concentrated PCI are added to about 10cm3 of a solution of pH 3.4. The pH of the resulting mixtures is?

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The set-up above would be useful for determining the amount of

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Clothes should be properly rinsed with water after bleaching because?

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At the same temperature and pressure, 50 cm3 of nitrogen gas contains the same number of molecules as?

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Which of the following atoms represents deuterium?

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Deuterium is an isotope of hydrogen which has one proton and one neutron in its nucleus. Therefore, the correct answer would be the option that has one proton and one neutron, and one electron to balance the charge of the nucleus. The only option that satisfies this requirement is "No protons = 1, No of neutrons = 1, No of electrons = 1". So, the answer is.

Which of the following physical properties decreases down a group in the periodic table?

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Which of the following compounds is a base?

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A base is a substance that can accept hydrogen ions (H+) or donate hydroxide ions (OH-) in a chemical reaction. Among the given options, CaO is a base. When CaO dissolves in water, it reacts with water to form Ca(OH)2, a strong base that dissociates into calcium ions (Ca2+) and hydroxide ions (OH-) in solution. Therefore, CaO is a base.

Which of the following reagents will confirm the presence of unsaturation in a compound?

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Bromine water can confirm the presence of unsaturation in a compound. Unsaturated compounds contain multiple bonds between carbon atoms, and these double or triple bonds can readily react with bromine water (an aqueous solution of bromine) by breaking the double or triple bond and forming a colorless dibromo compound. As a result, if the compound has unsaturation, bromine water will lose its characteristic orange color upon reaction with the compound, indicating the presence of unsaturation. The other reagents listed are used for different types of chemical tests, such as reducing sugars (Fehling's and Benedict's solutions) or identifying aldehydes or ketones (Tollen's reagent).

The general formula of alkanoates is?

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Element X, Y and Z belong to a groups I, V and VII respectively. Which of the following is TRUE about the bond types of XZ and YZ3?

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The bond types of XZ and YZ can be determined based on the electronic configuration of the elements. Group I elements, such as X, have one valence electron, while Group V elements, such as Y, have five valence electrons. Group VII elements, such as Z, have seven valence electrons. To achieve stability, Group I elements tend to lose one electron to achieve a stable noble gas configuration, while Group V elements tend to gain three electrons to achieve a stable noble gas configuration. Group VII elements tend to gain one electron to achieve a stable noble gas configuration. Therefore, in the case of XZ, element X will lose one electron to element Z to form an electrovalent or ionic bond. In the case of YZ, element Y will share three electrons with element Z to form a covalent bond. Thus, the correct option is: XZ is electrovalent and YZ is covalent.

When sodium is added to ethanol, the products are?

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When sodium is added to ethanol, the products are sodium ethoxide (NaC2H5O) and hydrogen gas (H2). This is because sodium is a highly reactive metal that reacts with ethanol to displace the hydrogen atom attached to the carbon atom in the -OH group. As a result, the hydrogen atom combines with another hydrogen atom to form hydrogen gas, while the remaining ethoxide ion combines with the sodium cation to form sodium ethoxide. Therefore, the correct option is: sodium ethoxide and hydrogen gas.

The shape of ammonia molecule is?

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Which of the following are produced when ammonium trioxonitrate (V) crystals are cautiously heated in a hard glass round bottomed flask?

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