JAMB UTME - Chemistry - 2007

If the electron configuration of a element is p1s2 2s2 2P5, how many unpaired electron are there?

Détails de la réponse

The electron configuration of an element provides information about the arrangement of electrons in its orbitals. In this case, the element has 1 electron in the 2p sublevel, which means it has one unpaired electron. The remaining 7 electrons are paired up in the other orbitals (2 electrons in the 2s sublevel and 4 electrons in the 2p sublevel). Therefore, the answer is (C) 1 unpaired electron.

A solution which on treatment with hydrochloric acid produces a colourless, odourless gas which turns lime water milky is most likely to be a

Détails de la réponse

The given information tells us that the solution produces a colorless and odorless gas, which turns lime water milky on reaction with hydrochloric acid. This indicates that the gas produced is carbon dioxide (CO2). The only option that contains carbonate ion (CO32-) which produces CO2 on reaction with hydrochloric acid is "trioxocarbonate (IV)" or "carbonate". Hence, the solution is most likely to be a "trioxocarbonate (IV)" or "carbonate" solution.

What is the volume of oxygen required to bum completely 45cm${}^3$ of methane at s.t.p?

Détails de la réponse

When methane burns completely in oxygen, it produces carbon dioxide and water vapor. According to the balanced chemical equation for the combustion of methane: CH4 + 2O2 → CO2 + 2H2O From the equation, we see that 1 mole of methane (16g) reacts with 2 moles of oxygen (32g) to give 1 mole of carbon dioxide (44g) and 2 moles of water vapor (36g). At s.t.p, 1 mole of any gas occupies 22.4 liters or 22,400 cm3. Therefore, the volume of 45cm3 of methane is equal to 45/22,400 = 0.002 moles. Since methane reacts with oxygen in a 1:2 mole ratio, we need twice the number of moles of oxygen to react completely with the given amount of methane. Thus, we need 2 x 0.002 = 0.004 moles of oxygen. At s.t.p, 1 mole of oxygen occupies 22.4 liters or 22,400 cm3. Therefore, the volume of 0.004 moles of oxygen required is 0.004 x 22,400 = 89.6 cm3. Therefore, the correct option is 90.0cm3, which is closest to the calculated volume of oxygen required.

Calculate the mass of chlorine gas which occupies a volume of 1.12dm3 at s.t.p

[Cl = 35.5, molar volume of gas at s.t.p = 22.4 dm3

Détails de la réponse

2 * 35.5g of chlorine has a volume of 22.4 dm3 at s.t.p
∴ xg of chlorine will have a volume of 1.12 dm3x = (1.12 * 35.5 * 2)/22.4 = 3.55g

The reddish-brown rust on iron roofing sheets consists of

Détails de la réponse

How many structural isomers of chlorobutane are possible?

Détails de la réponse

C2H4(g) + H2(g) → C2H6(g) ΔH = -137kJ mol-1

The reaction represented above is

Détails de la réponse

The reaction represented in the given equation involves the reactants carbon dioxide (CO2) and hydrogen gas (H2) to form the product, ethane (C2H6), with the release of energy (enthalpy change, ΔH) of -137 kJ/mol. As the reaction releases energy in the form of heat, it is exothermic. The negative value of ΔH indicates that the reaction is exothermic.

Which of the following sets of metals dissolves in dilute HCl?

Détails de la réponse

Cu2+(aq) + 4NH3(g) ? [Cu(NH3)4]2+(aq)

In the reaction above, what is the effect of precipitating Cu2+(aq) as CuS(s)?

Détails de la réponse

When Cu2+ is precipitated as CuS, it will be removed from the solution, which will cause the equilibrium to shift to the right to replace the lost Cu2+ ions. As a result, more [Cu(NH3)3]4+ will be produced to compensate for the loss of Cu2+ ions. Therefore, the correct option is "The equilibrium will shift to the right."

Which of the following represents an aromatic compound?

Détails de la réponse

The tincture of iodine means iodine dissolved in

Détails de la réponse

The tincture of iodine is a solution that contains iodine dissolved in a solvent. The question asks about the solvent used in the tincture of iodine. The correct answer is "ethanol." Therefore, the tincture of iodine means iodine dissolved in ethanol.

Which experiment led to the measurement of the charge on an electron?

Détails de la réponse

The experiment that led to the measurement of the charge on an electron is the "Oil-drop experiment." In this experiment, Robert Millikan observed oil droplets falling between two charged plates and was able to determine the charge on an electron. He applied an electric field to the charged plates to slow down the motion of the droplets and then calculated the charge on each droplet by measuring the strength of the electric field required to keep the droplets suspended in mid-air. By using this information, he was able to determine the charge on an individual electron.

CH3CH2Cl + KCN → CH3CH2CN + KClIn the reaction above, the cyanide is

Détails de la réponse

Détails de la réponse

The conversion of open chain alkanes into cycloalkanes and aromatic compounds is called "reforming". Reforming is a process used in the petroleum industry to convert low octane gasoline into high octane gasoline or liquid petroleum gas (LPG). The reforming process involves breaking the carbon-carbon bonds of the straight-chain hydrocarbons, then rearranging them into branched or cyclic compounds, which are higher in octane number. This process is carried out in the presence of a catalyst, typically a platinum or palladium catalyst, at high temperatures and pressures.

A metal X forms two bromides with the formulae XBr2 and XBr3. What type of bonding exists between X and bromine in the bromide?

Détails de la réponse

The metal X forms two bromides with the formulae XBr2 and XBr3. The type of bonding between X and bromine in the bromides is ionic bonding. Ionic bonding is a type of chemical bond that occurs when there is a transfer of electrons from one atom to another. In this case, X loses electrons to the bromine atoms to form positive ions, while bromine gains electrons to form negative ions. These positive and negative ions are then attracted to each other by electrostatic forces, forming an ionic bond. Therefore, X and bromine are held together by ionic bonding in the bromides XBr2 and XBr3.

How many electrons are in the L shell of 3115P?

Détails de la réponse

The atomic number of phosphorus (P) is 15, which means it has 15 electrons in total. To determine the number of electrons in the L shell, we need to know the electronic configuration of phosphorus. The electronic configuration of phosphorus is 1s2 2s2 2p6 3s2 3p3. To find out how many electrons are in the L shell, we need to add up the number of electrons in the 2s and 2p subshells. The 2s subshell contains 2 electrons, and the 2p subshell contains 6 electrons. Therefore, the total number of electrons in the L shell of phosphorus is 8. So the answer is 8.

the elements that belong to the third period of the periodic table are

Détails de la réponse

An element used in the production of matches is

Détails de la réponse

The element used in the production of matches is sulfur. Sulfur is used in the match head, which ignites when struck against a rough surface. When sulfur is mixed with an oxidizing agent and a fuel, such as powdered glass and potassium chlorate, it forms a highly flammable mixture that is ignited by the friction of striking the match. The sulfur helps to ignite the match by lowering the temperature at which the mixture will ignite.

A good drying agent should be

Détails de la réponse

A good drying agent is a substance used to remove moisture or water from a solution or compound. A drying agent should be hygroscopic, which means that it should have the ability to absorb or adsorb water molecules from the surroundings. This makes it effective in removing water from a compound or solution. Deliquescent compounds are those that absorb water so vigorously from the atmosphere that they dissolve in their own water of crystallization. Effervescent compounds release gas upon contact with water, while efflorescent compounds lose water of crystallization upon exposure to air. Therefore, the correct option for a good drying agent is hygroscopic.

Trioxonitrate (V) acid is not used for preparing hydrogen gas from metals because it

Détails de la réponse

Trioxonitrate (V) acid, also known as nitric acid, is not used for preparing hydrogen gas from metals because it is strongly oxidizing. This means that it readily gives up oxygen to other substances, including metals. When nitric acid reacts with metals, it can produce metal nitrates instead of hydrogen gas. In addition, nitric acid can also react with the hydrogen gas produced, forming water and nitrogen oxides. Therefore, other acids, such as hydrochloric acid or sulfuric acid, are used for preparing hydrogen gas from metals as they do not have such strong oxidizing properties.

Which of the following compounds is the best possible anti-knock agent for petrol?

Détails de la réponse

If chlorine is bubbled into water and the resulting yellowish-green solution is exposed to bright sunlight for a while, the solution will decompose giving out

Détails de la réponse

When chlorine is bubbled into water, it reacts to form a yellowish-green solution of aqueous chlorine. This solution is unstable and will decompose on exposure to sunlight, forming oxygen gas and aqueous hydrochloric acid. The reaction can be represented as follows: 2Cl2 + 2H2O + sunlight -> 4HCl + O2 Therefore, the correct answer is "oxygen and leaving behind aqueous hydrochloric acid."

How long would it take to deposit 0.08g of copper from CuCl2 solution by passing a current of 0.5A?

[Cu = 64, F = 96500 C mol-1]

Détails de la réponse

Cu2+ + 2e → Cu(s)
2 * 96500C deposit 64g of Cu
∴ x quantity of electricity wil deposit 0.08
x = (2 * 96500 * 0.08)/64 =241.25 coulomb.
Q = It
241.25 = 0.5t
t = 241.25/60 = 8 mins

H3PO4(aq) + H2O(l) ↔ H2PO4-(aq) + H3O+(aq)

ΔH = -13kJ at 298K

In the reaction above, an increase in temperature would

Détails de la réponse

The given chemical equation is a reversible exothermic reaction, and the value of enthalpy change, ΔH, is negative. According to Le Chatelier's principle, an increase in temperature will favor the endothermic reaction to absorb heat and therefore, will shift the equilibrium towards the reactants' side. Thus, an increase in temperature would favor the reverse reaction. Hence, the correct option is: "favor the reverse reaction."

MnO2(s) + xHCl(aq) → MnCl2(aq) + yH2O(l) + zCl2(g)

In theequation above, what are the values of x, y and z respectively

Détails de la réponse

The equation represents a reaction between solid manganese dioxide (MnO2) and hydrochloric acid (HCl) to produce manganese(II) chloride (MnCl2), water (H2O), and chlorine gas (Cl2). The balanced chemical equation for the reaction is: MnO2(s) + 4HCl(aq) → MnCl2(aq) + 2H2O(l) + Cl2(g) Thus, the values of x, y, and z are 4, 2, and 1, respectively. This is because four moles of hydrochloric acid are needed to react with one mole of MnO2, producing two moles of water and one mole of chlorine gas.

Which of the following decreases when a given mass of gas is compressed to half its initial volume?

Détails de la réponse

Copper and silver metals are commonly use as coin because they are

Détails de la réponse

Dissolving some pellets of NaOH in water would result in

Détails de la réponse

When pellets of NaOH are dissolved in water, they ionize into Na+ and OH- ions, which are surrounded by water molecules. This process increases the entropy of the solution, since the Na+ and OH- ions are now dispersed throughout the solution rather than being confined to the pellets. Therefore, the correct answer is: an increase in the entropy of the solution.

When temporary hard water is boiled for sometime in a kettle, the inner surface of the kettle becomes coated with a deposit of

Détails de la réponse

When temporary hard water is boiled for some time in a kettle, the inner surface of the kettle becomes coated with a deposit of calcium trioxocarbonate (IV). This is because temporary hard water contains soluble calcium hydrogen trioxocarbonate (IV) which decomposes upon heating to form insoluble calcium trioxocarbonate (IV) which deposits on the inner surface of the kettle. This deposit is commonly known as limescale and can be difficult to remove.

Certain useful waxes are composed mainly of

Détails de la réponse

The IUPAC nomenclature of compound CH3CH2COOCH2CH3 is

Détails de la réponse

The compound CH3CH2COOCH2CH3 is named using the IUPAC nomenclature system, which follows a set of rules to name organic compounds. The first step is to identify the longest continuous carbon chain, which in this case is a five-carbon chain, so the parent name is pentanoate. The chain has two substituents, which are ethyl and methyl groups, located on the second and fourth carbon, respectively. The complete name of the compound is ethyl 4-methylpentanoate. Therefore, the correct option is "ethyl butanoate."

Smog usually occurs over cities which

Détails de la réponse

Smog usually occurs over cities which burn a lot of fossil fuels. When fossil fuels such as coal, oil, and natural gas are burned, they release pollutants into the air. These pollutants include particulate matter, nitrogen oxides, sulfur dioxide, and volatile organic compounds. When these pollutants react with sunlight, they form a mixture of air pollutants known as smog. Cities with high levels of traffic and industrial activity tend to produce more smog than areas with fewer sources of pollution. Smog can cause a variety of health problems, such as respiratory issues, eye irritation, and cardiovascular problems, so it is important to monitor and manage smog levels in cities.

What happens when zinc rod is immersed in copper (II) tetraoxosulphate (VI) solution

Détails de la réponse

Which of the following alkanes has the highest boiling point?

Détails de la réponse

The boiling point of a compound depends on the strength of the intermolecular forces between its molecules. The stronger the intermolecular forces, the higher the boiling point. In this case, all of the given alkanes are nonpolar molecules and have only weak London dispersion forces between their molecules. Therefore, the boiling point of these alkanes increases with increasing molecular weight (number of carbon atoms). Out of the given alkanes, pentane has the highest molecular weight and therefore, it has the highest boiling point. Hence, the answer is pentane.

A mixture of petrol and water can be separated through

Détails de la réponse

Petrol and water can be separated by using a separating funnel. A separating funnel is a piece of laboratory apparatus used to separate immiscible liquids that have different densities. The mixture is poured into the funnel, and the heavier liquid settles at the bottom, while the lighter one stays on top. The tap at the bottom of the funnel is then opened, allowing the denser liquid to flow out into a separate container.

Tartaric acid is used industrially to

Détails de la réponse

Tartaric acid is used industrially to make baking powder.

Na2S2O3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l)

Which of the following would introduce the greatest increase in the rate of the chemical reaction above?

Détails de la réponse

The reaction given is a neutralisation reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl) to form sodium chloride (NaCl) and water (H2O). The question is asking which of the given options would increase the rate of this reaction the most. suggests an increase in temperature, which generally increases the rate of reaction, but also a decrease in the concentration of the reactant, which would decrease the rate of reaction. Thus, the overall effect is uncertain. suggests a decrease in volume and an increase in pressure of the reactant, which would not have a significant effect on the reaction rate as it is a solution reaction. suggests a decrease in temperature, which would decrease the rate of reaction, and an increase in the concentration of the reactant, which would increase the rate of reaction. Thus, the overall effect is uncertain. suggests an increase in temperature and an increase in the concentration of the reactant, both of which would increase the rate of reaction. Therefore, this option would introduce the greatest increase in the rate of the chemical reaction above.

A supersaturated solution is said to contain

Détails de la réponse

A supersaturated solution is a solution that contains more than the maximum amount of solute that is capable of being dissolved at a given temperature. A saturated solution contains the maximum amount of solute that will dissolve at that temperature while a supersaturated solution contains more than the maximum amount of solute that can be dissolved at that temperature.

The oxidation state of oxygen in tetraoxosulphate(IV) acid is

Détails de la réponse

The oxidation state (or number) of an element is a number that represents the total number of electrons that an atom can gain, lose, or share when forming a chemical compound. In tetraoxosulphate(IV) acid, the formula is H2SO4, which means that there are four oxygen atoms. To determine the oxidation state of oxygen, we can use the rule that hydrogen has an oxidation state of +1 and oxygen has an oxidation state of -2 in most compounds. Since there are two hydrogen atoms in H2SO4, their total oxidation state is +2. To balance this out, the four oxygen atoms must have a total oxidation state of -8. Therefore, the oxidation state of each oxygen atom is -2. Hence, the answer is -2.

The salt formed from strong acid and a strong base is

Détails de la réponse

When a strong acid and a strong base react with each other, they form a salt and water. Since both the acid and base are strong, they will fully dissociate into their respective ions in solution. When they react, the H+ ion from the acid combines with the OH- ion from the base to form water, while the remaining ions combine to form a salt. Since the salt is formed from a combination of cations and anions, it is neutral in nature. Therefore, the answer is "neutral".

What weight of NaCl is needed to make 2.0 dm3 of a 1.5M solution?

[Na = 23, Cl = 35.5]

Détails de la réponse

To find the weight of NaCl required, we need to use the formula: moles = concentration x volume First, we need to find the number of moles of NaCl required to make 2.0 dm^3 of a 1.5 M solution: moles = concentration x volume moles = 1.5 mol/dm^3 x 2.0 dm^3 moles = 3.0 mol Next, we can use the molar mass of NaCl (58.44 g/mol) to convert moles to grams: grams = moles x molar mass grams = 3.0 mol x 58.44 g/mol grams = 175.32 g Therefore, the weight of NaCl required to make 2.0 dm^3 of a 1.5 M solution is approximately 175 g. So, the correct answer is.

The soft solder used for welding and plumbing is alloy of

Détails de la réponse

The soft solder used for welding and plumbing is an alloy of lead and tin. This alloy has a low melting point, which makes it ideal for welding two pieces of metal together. When the solder is heated, it melts and flows into the joint, bonding the two pieces of metal together. The lead provides the ability to flow easily and the tin provides the strength to hold the joint together.

When calcium oxide is heated with carbon, the oxide will

Détails de la réponse

When calcium oxide is heated with carbon, it will be converted to carbide. This is because calcium oxide and carbon undergo a redox reaction in which calcium oxide is reduced to calcium carbide, while carbon is oxidized to carbon monoxide. The balanced chemical equation for this reaction is: CaO + 3C → CaC2 + CO So, the correct option is "be converted to carbide".

The presence of nitrogen in air is to slow down

Détails de la réponse

Calculate the number of moles of HCl present in 20cm3 of a 0.75M solution of the acid

Détails de la réponse

To calculate the number of moles of HCl, we need to use the formula: moles = concentration x volume We are given the volume of the solution as 20 cm^3, and the concentration as 0.75 M. First, we need to convert the volume to liters: 20 cm^3 = 20/1000 L = 0.02 L Then we can plug in the values: moles = 0.75 M x 0.02 L = 0.015 moles Therefore, the number of moles of HCl present in the solution is 0.015 mole. So the correct option is 0.015 mole.

The reaction that takes place in Daniell cell is

Détails de la réponse

The reaction that takes place in a Daniell cell is a redox reaction. In a Daniell cell, zinc metal (Zn) is oxidized to Zn2+ ions at the anode, while copper (Cu2+) ions are reduced to copper metal (Cu) at the cathode. This is a classic example of a redox reaction, where oxidation and reduction occur simultaneously.

The hydrocarbon used in the production of styrene is

Détails de la réponse

The hydrocarbon used in the production of styrene is "ethene." Styrene is produced by the catalytic dehydrogenation of ethylbenzene, which is obtained by the alkylation of benzene with ethene. Therefore, the correct answer is "ethene."