JAMB UTME - Chemistry - 1993

A balanced chemical equation obeys the law of?

Antwortdetails

A balanced chemical equation obeys the law of conservation of mass. This means that in a chemical reaction, the total mass of the reactants (the substances being combined) must equal the total mass of the products (the substances formed by the reaction). This law is based on the idea that atoms cannot be created or destroyed in a chemical reaction, they can only be rearranged to form new substances. Therefore, the number and types of atoms present in the reactants must be the same as the number and types of atoms present in the products. By balancing the chemical equation, we ensure that the number of atoms of each element is the same on both sides of the equation, and thus the total mass is conserved.

In the diagram above, curve X represents the energy profile for a homogeneous gaseous reaction. Which of the following conditions would produce curve Y for the same reaction?

Antwortdetails

The energy profile curve X represents a reaction with a high activation energy, meaning that the reaction rate is slow at room temperature. To produce curve Y, which represents a faster reaction rate, we need to lower the activation energy of the reaction. This can be achieved by adding a catalyst, which lowers the activation energy without changing the energy difference between reactants and products. Therefore, the correct answer is "Addition of a catalyst". Increasing temperature or pressure or increasing the concentration of a reactant can also increase the reaction rate, but they do not change the activation energy or the energy profile of the reaction.

The phenomenon whereby sodium trioxocarbonate (IV) decahydrate loses some of its water of crystallization on exposure to the atmosphere is known as?

Antwortdetails

The phenomenon described in the question is known as efflorescence. This occurs when a hydrated salt loses some of its water of crystallization when exposed to air. As a result, the salt becomes less hydrated and may even crumble into a powder. Sodium trioxocarbonate (IV) decahydrate is a salt that contains ten molecules of water of crystallization, and when it loses some of these molecules, it undergoes efflorescence. The other options, deliquescence, hygroscopy, and effervescence, refer to different phenomena. Deliquescence is when a substance absorbs moisture from the air and dissolves in it, forming a liquid solution. Hygroscopy is the ability of a substance to absorb moisture from the air without necessarily dissolving in it. Effervescence is the bubbling or fizzing caused by the release of gas from a chemical reaction.

For iodine crystals to sublime on heating, the molecules must acquire energy that is?

Antwortdetails

For iodine crystals to sublime on heating, the molecules must acquire energy that is greater than the forces of attraction in both the solid and liquid phases. Sublimation is the process by which a solid directly turns into a gas without passing through the liquid phase. This requires a significant amount of energy, as the molecules in the solid phase are held together by strong intermolecular forces of attraction. When iodine crystals are heated, the energy from the heat causes the iodine molecules to vibrate faster and increases the distance between them. At a certain temperature, the energy of the iodine molecules becomes great enough to overcome the intermolecular forces holding them together in the solid phase. The molecules break free from the solid and form a gas, bypassing the liquid phase altogether. Therefore, the energy required to sublime iodine is greater than the forces of attraction in both the solid and liquid phases. If the energy is less than the forces of attraction in the solid or equal to the forces of attraction in the solid, the iodine crystals will not sublime but instead remain in the solid phase. If the energy is only enough to melt the solid, the iodine will only melt and not sublime.

The two functional groups in the above compound are

Antwortdetails

The two functional groups in the above compound are alcohol and amine. An alcohol functional group is characterized by an -OH group, while an amine functional group is characterized by an -NH2 group. In the given compound, there is an -OH group and an -NH2 group, indicating the presence of both alcohol and amine functional groups. The other options can be ruled out as there is no carboxylic acid functional group (-COOH) for no aldehyde functional group (-CHO) for and no ketone functional group (-C=O-) for.

NaCI(s) + H2SO4(I) → HCI(g) + NaHSO4(s).

In the reaction above, H2SO4 behaves as?

Antwortdetails

In the given chemical reaction, H2SO4 is reacting with NaCl to form HCl and NaHSO4. H2SO4 is behaving as a strong acid because it donates a proton (H+) to NaCl to form HCl. This is evident from the fact that H2SO4 dissociates completely in water to form H+ and SO4^2-. Additionally, H2SO4 is not involved in any redox reaction and does not act as a solvent in the given reaction. Therefore, the correct option is "a strong acid."

For which salt in the graph above does the solubility increase most rapidly with rise in temperature?

Antwortdetails

From the graph above, the solubility of a salt increases with an increase in temperature. The salt with the steepest slope on the graph has the most rapid increase in solubility with a rise in temperature. By looking at the graph, it appears that the salt with the steepest slope is KNO3. Therefore, KNO3 is the salt that has the most rapid increase in solubility with a rise in temperature.

Which of the following substances is a mixture?

Antwortdetails

A mixture is a combination of two or more substances that are not chemically bonded. Based on this definition, the substance that is a mixture among the options listed is bronze. Bronze is an alloy, which means it is a mixture of two or more metals, typically copper and tin. Sulphur powder, distilled water, and ethanol are all pure substances, meaning they are made up of only one type of atom or molecule.

As the difference in electronegativity between bonded atoms increases, polarity of the bond?

Antwortdetails

As the difference in electronegativity between bonded atoms increases, the polarity of the bond increases. Electronegativity is a measure of an atom's ability to attract electrons in a covalent bond. If the electronegativity difference between the two atoms is large, one atom will have a stronger pull on the shared electrons than the other, creating a polar covalent bond. For example, in a bond between hydrogen and chlorine, chlorine has a higher electronegativity than hydrogen. This means that the electrons in the bond are pulled closer to the chlorine atom than to the hydrogen atom, resulting in a partial negative charge on the chlorine and a partial positive charge on the hydrogen. The bond is polar, and the greater the difference in electronegativity between the two atoms, the more polar the bond will be. Therefore, as the difference in electronegativity between bonded atoms increases, the polarity of the bond increases. If the electronegativity difference between the two atoms is small, the bond is nonpolar. If the difference is large, the bond is polar.

An experiment produces a gaseous mixtures of carbon (IV) oxide and carbon (II) oxide. In order to obtain pure carbon (II) oxide, the gas mixture should be?

Antwortdetails

The active reducing agent in the blast furnace for the extraction of iron is?

Antwortdetails

Which of these salts will produce its metal, oxygen and nitrogen (IV) oxide on heating?

Antwortdetails

The standard enthalpies of formation of CO2(g), H2O(g) and CO(g) in kJ mol- are -394, -242 and -110 respectively. What is the standard enthalpy change for the reaction CO(g) + H2(g)O → CO2(g) + H2(g)?

Antwortdetails

Standard enthalpy change of a process = ∆H° process = ∆H° F reactant - DF° products

4.0 g of sodium hydroxide in 250 cm3 of solution contains?

Antwortdetails

To determine the moles of sodium hydroxide in the solution, we need to use the formula: moles = mass / molar mass The molar mass of sodium hydroxide (NaOH) is approximately 40 g/mol (23 g/mol for Na + 17 g/mol for OH). First, we need to convert the volume of the solution from cm^3 to dm^3: 250 cm^3 = 0.25 dm^3 Then, we can calculate the concentration of the solution in moles per dm^3: concentration = (4.0 g / 40 g/mol) / 0.25 dm^3 = 0.4 mol/dm^3 Therefore, the answer is: - 0.40 moles per dm^3 So, the correct label for this question would be: "concentration"

The oxidation states of chlorine in HOCL, HCLO3 and HCLO4 are respectively?

Antwortdetails

Water can be identified by the use of?

Antwortdetails

Water can be identified by the use of anhydrous copper (II) tetraoxosulphate (VI). Anhydrous copper (II) tetraoxosulphate (VI) is a white crystalline solid that readily absorbs water from the atmosphere to form copper (II) tetraoxosulphate (VI) pentahydrate, which is blue in colour. When anhydrous copper (II) tetraoxosulphate (VI) is added to water, it turns blue as the water molecules hydrate the copper (II) ions to form the blue pentahydrate. This reaction is used as a simple and quick test for the presence of water.

Argon is used in gas-filled electric lamp because it helps to?

Antwortdetails

Palm wine turns sour with time because?

Antwortdetails

Palm wine turns sour with time because of microbial activity that occurs within it. Microorganisms such as bacteria and fungi that are naturally present in the environment and in the sap of the palm tree can enter the palm wine during tapping and fermentation. These microorganisms metabolize the sugar present in the palm wine, producing organic acids such as lactic acid and acetic acid, which give the wine a sour taste. The longer the palm wine is left to ferment, the more pronounced the sour taste becomes as more and more organic acids are produced. Therefore, option d, "microbial activity results in the production of organic acids within it" is the correct answer.

Which group of elements forms hydrides that are pyramidal in structure?

Antwortdetails

The group of elements that form hydrides that are pyramidal in structure is group V. This is because group V elements, also known as the nitrogen group, have five valence electrons in their outermost shell, which allows them to form covalent bonds with hydrogen atoms to create pyramidal-shaped hydrides. Group V elements include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi).

Which of the reactions occurs at the anode during the electrolysis of a very dilute aqueous solution of sodium chloride?

Antwortdetails

10g of a solid is in equilibrium with its own vapour.

When 1 g of a small amount of solid is added, the vapour pressure?

Antwortdetails

Two atoms represented as U and U are?

Antwortdetails

The two atoms represented as U and U are isotopes. Isotopes are atoms of the same element that have the same number of protons in their nuclei, but different numbers of neutrons. In this case, both U atoms have the same number of protons, but they have different numbers of neutrons, which makes them isotopes of each other.

A student prepares 0.5 M solution each of hydrochloric and ethanoic acids and then measured pH. The result would show that the?

Antwortdetails

When a student prepares 0.5 M solutions of hydrochloric acid (HCl) and ethanoic acid (CH3COOH) and measures their pH, the result would show that the ethanoic acid solution has a higher pH than the hydrochloric acid solution. This is because ethanoic acid is a weak acid, which means it does not fully dissociate into its ions in water, resulting in fewer hydrogen ions (H+) being released into solution. On the other hand, hydrochloric acid is a strong acid and fully dissociates into its ions, resulting in a higher concentration of H+ ions in solution and a lower pH. The sum of the pH values is not necessarily 14, and this information cannot be determined from the question.

NH3 + H3O+

→ NH4+ + H2O. It may be deduced from the reaction above that?

Antwortdetails

Al2O3(s) + 3H2SO4(aq) → Al2(SO4(aq)) + 3H2(I)O

Al2O3(s) + 2NaOH(aq)) + 3H2(I)O → 2NaAl(OH)4(aq)).

We can conclude from the equations above that Al2O3(s) is?

Antwortdetails

The given chemical equations show that when Al2O3 reacts with sulfuric acid, it forms a salt, Al2(SO4)3, and water. When Al2O3 reacts with sodium hydroxide, it forms a salt, NaAl(OH)4. These reactions indicate that Al2O3 can react with both an acid and a base, which means it is amphoteric in nature. Therefore, the correct answer is "an amphoteric oxide".

At 25oC and 1atm, a gas occupies a volume of 1.50dm3. What volume will it occupy at 100oC and 1atm?

Antwortdetails

This question is asking for the volume of a gas at a different temperature and pressure, but with the same amount of gas (assuming ideal gas behavior). We can use the combined gas law to solve this problem: (P1 x V1) / T1 = (P2 x V2) / T2 Where P1, V1, and T1 are the initial pressure, volume, and temperature, and P2, V2, and T2 are the final pressure, volume, and temperature. Plugging in the values given in the question: (P1 x V1) / T1 = (P2 x V2) / T2 (1 atm x 1.50 dm3) / (298 K) = (1 atm x V2) / (373 K) Solving for V2: V2 = (1 atm x 1.50 dm3 x 373 K) / (298 K x 1 atm) V2 = 1.88 dm3 Therefore, the answer is 1.88 dm3, which is the first option given.

The function of the copper (ll)tetraoxosulphate (IV) in dilute H2SO4 in the figure above is to

Antwortdetails

Water has a rather high boiling point despite its low molecular mass because of the presence of?

Antwortdetails

Water has a rather high boiling point because of the presence of hydrogen bonding. Hydrogen bonding is a special type of intermolecular force that occurs when a hydrogen atom is bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine. In the case of water, the oxygen atom is highly electronegative and attracts electrons more strongly than the hydrogen atoms. This creates a partial negative charge on the oxygen atom and a partial positive charge on the hydrogen atoms. The partial positive charge on one water molecule can then be attracted to the partial negative charge on another water molecule, creating a hydrogen bond between them. Hydrogen bonds are much stronger than the usual van der Waals forces between molecules, which is why water has a higher boiling point than expected for its molecular mass. The extra energy required to break the hydrogen bonds must be supplied to boil water, hence water has a relatively high boiling point.

Catalytic hydrogenation of benzene produces?

Antwortdetails

Catalytic hydrogenation of benzene produces cyclohexane. In this reaction, benzene reacts with hydrogen gas in the presence of a catalyst to form cyclohexane. The catalyst used is usually a metal, such as platinum or palladium, which helps to break the double bonds in the benzene ring and allow the hydrogen gas to attach to the carbons, forming a cyclohexane ring. Cyclohexane is a cyclic hydrocarbon with the formula C6H12 and is commonly used as a solvent and in the production of nylon.

The dissolution of common salt in water is a physical change because

Antwortdetails

When dilute aqueous solutions of lead (II) nitrate and potassium bromide are mixed, a precipitate is observed.

The products of this reaction are?

Antwortdetails

An element, E, has the electronic configuration 1s22s22p63s2p3. The reaction of E with a halogen X can give?

Antwortdetails

Which of the following represents saponification?

Antwortdetails

Saponification is the chemical reaction that results in the formation of soap. The reaction involves the hydrolysis of an ester in the presence of a strong base, usually sodium hydroxide or potassium hydroxide. The correct option is: - Reaction of alkanoates with sodium hydroxide During the reaction, the ester bond in the alkanoate is broken down by the sodium hydroxide to form a carboxylate ion and an alcohol. The carboxylate ion then reacts with the sodium cation to form soap. The reaction is commonly used in the production of soap.

Bronze is an alloy of?

Antwortdetails

Bronze is an alloy of copper and tin. It is a durable and strong metal that has been used for a variety of purposes throughout history, such as for making tools, weapons, and decorative objects. Copper provides the base metal while tin is added to make the alloy stronger and more resistant to corrosion.

The air around a petroleum refinery is most likely to contain?

Antwortdetails

Topic is Impurities of Crude-oil

Which of the curves above represents the behaviour of 1 mole of an ideal gas?

Antwortdetails

A reaction takes places spontaneously if?

Antwortdetails

Which of the following is a property of ionic chlorides?

Antwortdetails

The property of ionic chlorides is being asked in this question. Ionic chlorides are compounds formed between a metal and a non-metal where the metal donates an electron to the non-metal, resulting in the formation of ions that are held together by electrostatic forces of attraction. Option (a) states that they can be decomposed by heat. This is true for some ionic chlorides, such as those of alkali metals, which can be decomposed into their respective metal and chlorine gas when heated. Option (b) states that they react with aqueous AgNO3 to give a white precipitate which is soluble in excess ammonia. This is a characteristic reaction of the chloride ion, which forms a white precipitate of AgCl when reacted with AgNO3. Option (c) states that they explode when in contact with dry ammonia. This is not a property of ionic chlorides, and in fact, most ionic chlorides are stable in contact with dry ammonia. Option (d) states that they react with concentrated tetraoxosulphate (IV) acid to give white fumes of chlorine gas. This is another characteristic reaction of the chloride ion, which reacts with concentrated H2SO4 to give HCl gas and white fumes of SO2. Therefore, the correct option that describes a property of ionic chlorides is (b), which states that they react with aqueous AgNO3 to give a white precipitate that is soluble in excess ammonia.

Half-cell reaction. From the data above , it can be deduced that the most powerful reducing agent of the four metals is

Antwortdetails

The power of a reducing agent can be determined by its ability to lose electrons and become oxidized. The more easily a metal loses electrons, the stronger the reducing agent it is. To compare the reducing power of Cu, Fe, Ba, and Zn, we can look at their half-cell reactions and standard reduction potentials. The half-cell reaction with the most negative standard reduction potential (E°) is the strongest reducing agent. Looking at the standard reduction potentials: - Cu: Cu²⁺(aq) + 2e⁻ → Cu(s) E° = +0.34 V - Fe: Fe²⁺(aq) + 2e⁻ → Fe(s) E° = -0.44 V - Ba: Ba²⁺(aq) + 2e⁻ → Ba(s) E° = -2.91 V - Zn: Zn²⁺(aq) + 2e⁻ → Zn(s) E° = -0.76 V We can see that Ba has the most negative standard reduction potential, which means it is the strongest reducing agent among the four metals. Therefore, the answer is Ba.

During the electrolysis of a salt of a metal M, a current of 0.5 A flows from for 32 minutes 10 seconds and deposits 0.325 g of M, What is the charge of the metal ion?(M = 65, If = 96,500 C per mole of electron)

Antwortdetails

Ampere = (Coulomb) x (Sec) x 1930 secs = 965 coulombs (unit of current)
But quantity of electricity = current x time = (Coulomb)/(Sec) x time
If 0.5 A for 32 mins 10 secs; Quantity of electricity = (0.5 coulomb)/(Sec x 1930) secs
= 965 coulombs
Since 965 coulombs give 0.325 g M
i.e1 coulombs = (0.325)/(965) g
∴96500 coulombs = (0.30)/(965) x 96500 =32.5 g
∴(65 g)/(32.5) = 2

inference: it takes 2 Faraday of electricity to deposit 1 mole of M. Therefore, the change on M ion = 2.

A gas that will turn orange potassium heptaoxodichromate (lV) solution to clear green is?

Antwortdetails

Which of these gases can be dried with concentrated H2SO4?

Antwortdetails

The fraction of crude oil used as jet fuel is?

Antwortdetails

Jet fuel, also known as aviation turbine fuel (ATF), is a type of fuel designed for use in aircraft with gas turbine engines. Kerosene is the main component of jet fuel. Therefore, the correct answer to this question is "kerosene." The other options, refinery gas, diesel oil, and gasoline, are not typically used as jet fuel.

How many moles of oxygen molecules would be produced from the decomposition of 2.50 moles of potassium trioxochlorate (V)?

Antwortdetails

The decomposition of potassium trioxochlorate (V) can be represented by the following balanced chemical equation: 2KClO3(s) → 2KCl(s) + 3O2(g) From this equation, we can see that 2 moles of KClO3 produce 3 moles of O2. Therefore, to determine how many moles of O2 would be produced from the decomposition of 2.50 moles of KClO3, we need to set up a proportion: 2 moles KClO3 / 3 moles O2 = 2.50 moles KClO3 / x moles O2 Simplifying this proportion, we get: x = (3/2) * 2.50 = 3.75 Therefore, 3.75 moles of O2 would be produced from the decomposition of 2.50 moles of KClO3. Thus, the correct answer is option (C): 3.75.

The confirmatory test for alkanoic acids in organic qualitative analysis is the?

Antwortdetails

It is not desirable to use lead tetraethyl as an anti-knock agent because?

Antwortdetails

The IUPAC nomenclature for the compound above is

Antwortdetails

The carbon atoms on ethane are?

Antwortdetails

The carbon atoms on ethane are sp3 hybridized. This means that each carbon atom is bonded to four other atoms or groups of atoms, including one hydrogen atom. The electron orbitals of the carbon atom are hybridized to form four sp3 hybrid orbitals, which are then used to form covalent bonds with other atoms.