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Pergunta 1 Relatório
Elements in the periodic table are arranged in the order of their
Detalhes da Resposta
Elements in the periodic table are arranged in the order of their atomic numbers. The atomic number of an element is the number of protons in the nucleus of an atom of that element. The elements are arranged in order of increasing atomic number from left to right and from top to bottom in the periodic table. The elements in each row, also known as a period, have the same number of electron shells, while the elements in each column, also known as a group or family, have the same number of valence electrons. This arrangement makes it possible to predict the chemical and physical properties of an element based on its position in the periodic table. Therefore, the correct answer is: - atomic numbers
Pergunta 2 Relatório
The IUPAC nomenclature of the compound
H3 C - CH(CH3 ) - CH(CH3 ) - CH2 - CH3
Detalhes da Resposta
Pergunta 3 Relatório
The two ions responsible for hardness in water are
Detalhes da Resposta
The ions responsible for hardness in water are Ca2+ and/or Mg2+. Hardness in water refers to the presence of calcium and magnesium ions, which are commonly found in natural water sources such as rivers, lakes, and groundwater. These ions can react with soap to form insoluble compounds, reducing the effectiveness of soap and causing scaling in pipes and appliances. The hardness of water is often measured in terms of the concentration of calcium and magnesium ions, expressed as calcium carbonate equivalents (CaCO3).
Pergunta 4 Relatório
The cost of discharging 6.0g of a divalent metal, X from its salt is ₦12.00. What is the cost of discharging 9.0g of a trivalent metal, Y from its salt under the same condition?
[X = 63, Y = 27, 1F = 96,500C]
Detalhes da Resposta
For X: X2+
+ 2e−
→
X
2F = 63g
xF = 6g
x = 6×263=421F
421
F = N12.00
1F = 12421
= N63.00
1F is equivalent to N63.00.
For Y: Y3+
+ 3e−
→
Y
3F = 27g
xF = 9g
x = 3×927
= 1F
1F = N63.00
Pergunta 5 Relatório
Consider the reaction: A + 2B(g)⇌ 2C + D(g) (Δ H = +ve)
What will be the effect of decrease in temperature on the reaction?
Detalhes da Resposta
The effect of a decrease in temperature on the reaction will be that the rate of the backward reaction will increase. In a chemical reaction, the rate of the forward and backward reactions are determined by the activation energy required for each step and the temperature of the system. When the temperature is decreased, the rate of the reaction decreases, and the rate of the backward reaction increases. This shift in the rate of the backward reaction means that there will be a shift in the position of the equilibrium of the reaction. As the rate of the backward reaction increases, the concentration of the reactants will increase and the concentration of the products will decrease, leading to a decrease in the overall yield of the products. In this reaction, as ΔH (the change in enthalpy) is positive, which means that the reaction is endothermic. Endothermic reactions absorb heat from the surroundings to proceed, so a decrease in temperature will lead to a decrease in the rate of the forward reaction and an increase in the rate of the backward reaction. This shift in the rate of the backward reaction will shift the position of the equilibrium of the reaction to the left, leading to an increase in the concentration of the reactants and a decrease in the concentration of the products.
Pergunta 6 Relatório
Which of the following pairs cannot be represented with a chemical formula?
Detalhes da Resposta
The pair that cannot be represented with a chemical formula is air and bronze. Air is a mixture of several gases, primarily nitrogen (N₂) and oxygen (O₂), with small amounts of other gases such as argon (Ar), carbon dioxide (CO₂), and neon (Ne). Since air is a mixture and not a pure substance, it cannot be represented by a chemical formula. Bronze, on the other hand, is an alloy composed mainly of copper (Cu) and tin (Sn) with small amounts of other metals. The composition of bronze can vary depending on the specific alloy, but it can be represented by a chemical formula such as CuSn. Sodium chloride (NaCl) is a compound composed of sodium (Na) and chlorine (Cl) in a fixed ratio of 1:1, and it can be represented by a chemical formula. Similarly, copper (Cu) and sodium chloride (NaCl) can each be represented by a chemical formula. Cu is an element, so its chemical formula is simply its symbol, while NaCl is a compound with a fixed ratio of sodium and chlorine atoms. Caustic soda (sodium hydroxide, NaOH) and washing soda (sodium carbonate, Na₂CO₃) are both compounds that can be represented by chemical formulas. NaOH consists of one sodium atom, one oxygen atom, and one hydrogen atom, while Na₂CO₃ consists of two sodium atoms, one carbon atom, and three oxygen atoms.
Pergunta 7 Relatório
Which of the following will give a precipitate with an aqueous solution of copper (I) chloride?
Detalhes da Resposta
Pergunta 8 Relatório
Which of the following alkaline metals react more quickly spontaneously with water?
Detalhes da Resposta
The alkaline earth metals (Be, Mg, Ca, Sr, Ba, and Ra) are the second most reactive metals in the periodic table, and, like the Group 1 metals, have increasing reactivity in the higher periods. Beryllium (Be) is the only alkaline earth metal that does not react with water or steam, even if metal is heated to red heat. Additionally, beryllium has a resistant outer oxide layer that lowers its reactivity at lower temperatures.
Magnesium shows insignificant reaction with water, but burns vigorously with steam or water vapor to produce white magnesium oxide and hydrogen gas:
A metal reacting with cold water will produce metal hydroxide. However, if a metal reacts with steam, like magnesium, metal oxide is produced as a result of metal hydroxides splitting upon heating.
The hydroxides of calcium, strontium and barium are only slightly water-soluble but produce sufficient hydroxide ions to make the environment basic, giving a general equation of:
| Order of reactivity | Metal | Reactions with water or steam |
|---|---|---|
| most reactive | potassium (K) | very vigorous reaction with cold water |
| ↑ | sodium (Na) | vigorous reaction with cold water |
| ↓ | calcium (Ca) | less vigorous reaction with cold water |
| least reactive | magnesium (Mg) | slow reaction with cold water, vigorous with steam |
Pergunta 10 Relatório
What mass of magnesium would be obtained by passing a current of 2 amperes for 2 hours, through molten magnesium chloride?
[1 faraday = 96500C, Mg = 24]
Detalhes da Resposta
Current (I) = 2A; Time (t) = 2 hours = 7200 secs
Q = It
= 2 x 7200 = 14400C
1 F = 96500C
x = 14400C
x = 1440096500
= 0.15F
Mg2+
+ 2e−
→
Mg
2F →
24g
0.15F →
x
2x = 24 x 0.15
x = 24×0.152
= 1.8g
Pergunta 11 Relatório
Which process(es) is/are involved in the turning of starch iodide paper blue-black by chlorine gas?
Detalhes da Resposta
The process involved in the turning of starch iodide paper blue-black by chlorine gas is option number 3: chlorine oxidizes the iodide ion to produce iodine which attacks the starch to give the blue-black color. When chlorine gas comes in contact with iodide ions on the starch iodide paper, it oxidizes the iodide ion to form iodine. The iodine that is produced in this reaction is then able to react with the starch present on the paper to form a blue-black complex. This blue-black complex is formed due to the arrangement of the starch molecules and the iodine atoms in a way that causes them to absorb light at a specific wavelength, giving the blue-black color. Therefore, the blue-black color that is observed on the starch iodide paper is due to the reaction between iodine and starch, which is made possible by the oxidation of iodide ions by chlorine gas.
Pergunta 12 Relatório
The velocity, V of a gas is related to its mass, M by (k = proportionality constant)
Detalhes da Resposta
Recall:
V = √3RTM
∴V∝1√M
V=k√M
V = kM12
Pergunta 13 Relatório
Which of the following is a physical change?
Detalhes da Resposta
A physical change refers to a change in a substance that does not result in a change in its chemical composition. Out of the options provided, freezing ice cream is a physical change. This is because when ice cream is frozen, it changes from a liquid state to a solid state without any chemical reaction occurring. Exposing white phosphorus to air is a chemical change, as it reacts with oxygen in the air to form a new substance, phosphorus oxide. Burning kerosene is also a chemical change, as it undergoes combustion to form new substances, such as carbon dioxide and water vapor. Dissolving calcium in water is a physical change, as it simply involves the physical mixing of two substances without any chemical reaction occurring. Therefore, the only option that is a physical change is freezing ice cream.
Pergunta 14 Relatório
SO3 is not directly dissolved in water in the industrial preparation of H2 SO4 by the contact process because
Detalhes da Resposta
Pergunta 15 Relatório
Which of the following statements does not show Rutherford's account of Nuclear Theory? An atom contains a region
Detalhes da Resposta
Rutherford's account of Nuclear theory does not include the fact that atoms contain a massive region and cause deflection of from projectiles.
Pergunta 16 Relatório
Which of the following metals is the most essential in the regulation of blood volume, blood pressure and osmotic equilibrium?
Detalhes da Resposta
The metal that is most essential in the regulation of blood volume, blood pressure, and osmotic equilibrium is sodium. Sodium is a key electrolyte that helps maintain the balance of fluids in the body, including blood volume and blood pressure. Sodium ions are positively charged and are attracted to negatively charged ions, such as chloride (Cl-) and bicarbonate (HCO3-), which together help regulate the pH of the blood. Sodium is also essential for maintaining osmotic equilibrium, which refers to the balance of solutes between cells and the extracellular fluid. Osmotic equilibrium is critical for proper cellular function and is regulated by the movement of water and electrolytes, including sodium, in and out of cells. While the other metals listed (zinc, manganese, and iron) are important for various functions in the body, such as enzyme activity and oxygen transport, they are not directly involved in regulating blood volume, blood pressure, and osmotic equilibrium in the same way that sodium is. Therefore, the answer is not options 1, 2, or 4, and the correct answer is: sodium.
Pergunta 17 Relatório
A certain hydrocarbon on complete combustion at s.t.p produced 89.6dm3 of CO2 and 54g of water. The hydrocarbon should be
Detalhes da Resposta
In the question above an Hydrocarbon combust to give CO2 and H20
Let Hydrocarbon be
CxHy + x+Y/4O2= xCO2 + Y/2H2O
Mass of C0=44g and H2O=18g
at STP vol= 22.4
Therefore, 1mole of CO2 contains 44g and 22.4dm³ at STP
1mole = 22.4dm³
xmole = 89.6dm³
Cross multiplying x=89.6/22.4 =4mole of CO2 produce
1mole of H2O = 18g
Xmole = 56g
Cross multiplying
X = 56/18 = 3mole of H20
Then....
CxHy + X + y/4O2 = 4CO2+ 3H2O
Balancing
C4H6 + 6O2 = 4CO2 + 3H2O
Pergunta 18 Relatório
The IUPAC name for CH3 CH2 COOCH2 CH3 is
Detalhes da Resposta
The IUPAC name for the given molecule is ethyl propanoate. To arrive at the IUPAC name, we first identify the longest continuous chain of carbon atoms, which in this case is a 4-carbon chain (propane). We then identify and name the substituent groups attached to this chain, which are a methyl group (CH3) attached to the second carbon atom and an ethoxy group (OC2H5) attached to the third carbon atom. The ethoxy group is named as an ethyl group, and the entire molecule is named as ethyl propanoate, following the standard IUPAC naming conventions for esters.
Pergunta 19 Relatório
The part of the total energy of a system that accounts for the useful work done in a system is known as
Detalhes da Resposta
The part of the total energy of a system that accounts for the useful work done in a system is known as "Gibbs free energy". Gibbs free energy is a thermodynamic property that represents the amount of energy that can be converted into useful work in a system. It takes into account both the energy of the system and the entropy, or disorder, of the system. In other words, Gibbs free energy is a measure of the energy available to do work, taking into account the energy that is unavailable due to entropy. In simple terms, if a system has a high Gibbs free energy, it has a lot of energy available to do work, and if a system has a low Gibbs free energy, it has little energy available to do work.
Pergunta 20 Relatório
The heat of formation of ethene, C2 H4 is 50 kJmol−1 , and that of ethane, C2 H6 is -82kJmol−1 . Calculate the heat evolved in the process:
C2 H4 + H2 → C2 H6
Detalhes da Resposta
The heat evolved in a chemical reaction can be calculated by subtracting the heat of formation of the reactants from the heat of formation of the products. In this case, the reactants are ethene (C2H4) and hydrogen (H2), and the product is ethane (C2H6). The heat of formation of ethene is 50 kJ/mol and that of hydrogen is 0 kJ/mol (because hydrogen is a reference element). The heat of formation of ethane is -82 kJ/mol. So, the heat evolved in the reaction is given by: Heat evolved = (Heat of formation of products) - (Heat of formation of reactants) = (-82 kJ/mol) - (50 kJ/mol + 0 kJ/mol) = -82 kJ/mol - 50 kJ/mol = -132 kJ/mol. Therefore, the heat evolved in the process is -132 kJ.
Pergunta 21 Relatório
Consider the equation below:
Cr2 O2−7 + 6Fe2+ + 14H+ → 2Cr3+ + 6Fe3+ + 7H2 O.
The oxidation number of chromium changes from
Detalhes da Resposta
Cr2
O2−7
+ 6Fe2+
+ 14H+
→
2Cr3+
+ 6Fe3+
+ 7H2
O
The oxidation of Cr in Cr2
O2−7
:
Let the oxidation of Cr = x;
2x + (-2 x 7) = -2 ⟹
2x - 14 = -2
2x = 12 ; x = +6
Hence, the change in oxidation of Cr = +6 to +3
Pergunta 22 Relatório
If the cost of electricity required to discharge 10g of an ion X3+ is N20.00, how much would it cost to discharge 6g of ion Y2+ ?
[1 faraday = 96,500C, atomic masses are X = 27, Y = 24]
Detalhes da Resposta
X3+
+ 3e−
→
X
3F = 27g
xF = 10g
x3=1027⟹x=109F
109
F ≡
N20.00
1F is equivalent to x
1109=x20
910=x20⟹x=N18.00
1F is equivalent to N18.00.
Y2+
+ 2e−
→
Y
2F = 24g
xF = 6g
x = 6×224=12F
1F = N18.00
12
F = 12×N18.00
= N9.00
Pergunta 23 Relatório
Na2 CO3 + 2HCl → 2NaCl + H2 O + CO2
The indicator most suitable for this reaction should have a pH equal to
Detalhes da Resposta
Methyl orange is the best indicator for the reaction with range 3.1 - 4.4.
Pergunta 24 Relatório
Which of the following factors will speed up the rate of evolution of carbon (iv) oxide in the reaction below?
2HCl + CaCO3 → CaCl2 + H2 O + CO2
Detalhes da Resposta
The following factors increase a reaction rate
- Increase in concentration of reactants
- Increase in temperature
- Addition of catalyst
- Increase in the surface area of reactant(s)
Pergunta 25 Relatório
Which of the following could not be alkane?
Detalhes da Resposta
An alkane is a type of hydrocarbon with only single bonds between the carbon atoms. It follows the general formula CnH2n+2, where "n" is the number of carbon atoms in the molecule. To determine whether a molecule is an alkane or not, we can calculate its molecular formula and check if it fits the general formula of alkane. Out of the given options, the third one (C7H14) cannot be an alkane. To see why, let's use the general formula of alkane, which is CnH2n+2. For C7H14 to be an alkane, it should have 2n+2 = 2(7) + 2 = 16 hydrogen atoms. However, C7H14 has only 14 hydrogen atoms, which means it does not follow the general formula of alkane. Therefore, C7H14 cannot be an alkane. The other options are as follows: - C4H10: This is butane, which is an alkane with four carbon atoms. - C5H12: This is pentane, which is an alkane with five carbon atoms. - C8H18: This is octane, which is an alkane with eight carbon atoms. In summary, the molecule C7H14 cannot be an alkane because it does not follow the general formula of alkane, while the other options are all examples of alkanes.
Pergunta 26 Relatório
Which of the following conditions will most enhance the spontaneity of a reaction?
Detalhes da Resposta
The condition that will most enhance the spontaneity of a reaction is when ΔH is negative (i.e., the reaction releases heat) and ΔS is positive (i.e., the reaction increases the disorder or randomness of the system). This is because a negative ΔH indicates that the reaction releases energy, which is favorable for a spontaneous reaction, while a positive ΔS indicates that the system becomes more disordered, which is also favorable for spontaneous reactions. Among the given options, the first condition of a negative and greater ΔH than ΔS is the best option for enhancing the spontaneity of a reaction. The other options have either a positive ΔH or a zero ΔS, which is not favorable for spontaneous reactions.
Pergunta 27 Relatório
When the end alkyl groups of ethyl ethanoate are interchanged, the compound formed is
Detalhes da Resposta
The compound formed when the end alkyl groups of ethyl ethanoate are interchanged is ethyl propanoate. This is because ethyl ethanoate consists of two parts: the "ethyl" group and the "ethanoate" group. The ethyl group is a two-carbon chain, and the ethanoate group is a combination of a one-carbon chain and a carbonyl group (C=O) that is also attached to an oxygen atom. When the end alkyl groups are interchanged, the "ethyl" group is moved from the second carbon to the first carbon of the ethanoate group, and the "propanoate" group is formed. The "propanoate" group consists of a three-carbon chain and the carbonyl group. Therefore, the resulting compound is ethyl propanoate, which has a chemical formula of CH3CH2COOCH2CH3. This compound is commonly used as a flavoring agent and has a fruity odor reminiscent of pears.
Pergunta 28 Relatório
What volume of 0.100M sodium trioxonitrate (V) solution contains 5g of solute.
[Na = 23, N = 14, O = 16]
Detalhes da Resposta
To calculate the volume of a solution, we need to use the formula: moles of solute = concentration x volume First, let's find the number of moles of sodium trioxonitrate (V) in 5g of the solute. The molar mass of NaNO3 is: Na = 23 N = 14 3 x O = 3 x 16 = 48 Molar mass = 23 + 14 + 48 = 85 g/mol The number of moles of NaNO3 in 5g is: moles = mass / molar mass = 5 / 85 = 0.0588 moles Now, we can use the formula above to find the volume of the solution: moles of solute = concentration x volume volume = moles of solute / concentration volume = 0.0588 moles / 0.100 M volume = 0.588 litres Therefore, the correct answer is 0.588 litres of 0.100M sodium trioxonitrate (V) solution contains 5g of solute.
Pergunta 29 Relatório
A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen. If the molar mass of the compound is 180. Find the molecular formula.
[H = 1, C = 12, O = 16]
Detalhes da Resposta
The molecular formula of a compound is determined by the number of atoms of each element present in the molecule. To find the molecular formula, we need to determine the number of atoms of each element in the compound. First, we convert the percent composition to grams. For example, 40.0% carbon means 40.0 g of carbon per 100 g of compound. Then we divide the number of grams of each element by the molar mass of each element. For example, 40.0 g of carbon divided by the molar mass of carbon (12 g/mol) gives us 3.33 mol of carbon. Next, we convert the number of moles of each element to the number of atoms by multiplying the number of moles by Avogadro's number (6.022 x 10^23 atoms/mol). Finally, we balance the numbers of atoms of each element by dividing them by the smallest number of atoms of all the elements and rounding to the nearest whole number. In this case, the smallest number of atoms is 2, which is the number of hydrogen atoms. So, we divide the number of atoms of carbon and oxygen by 2 to balance the numbers of atoms of all the elements. Therefore, the molecular formula of the compound is C6H12O6.
Pergunta 30 Relatório
X is a substance which liberates CO2 on treatment with concentrated H2 SO4 . A warm solution of X can decolorize acidified KMnO4 . X is
Detalhes da Resposta
It should be noted that for X to liberate CO2
, X must be a carbonate or an oxalate. Since X decolorizes KMnO4
, X must be an oxalate.
Therefore, X is H2
C2
O4
.
Pergunta 31 Relatório
Which of the following is the best starting material for the preparation of oxygen? Heating of trioxonitrate (v) with
Detalhes da Resposta
Pergunta 32 Relatório
Which of the following pollutants will lead to the depletion of ozone layer?
Detalhes da Resposta
The pollutant that leads to the depletion of the ozone layer is chlorofluorocarbon (CFCs). CFCs are man-made chemicals that were widely used in the past as refrigerants, solvents, and propellants. When CFCs are released into the atmosphere, they rise into the stratosphere, where they come into contact with ozone molecules. The chlorine atoms in CFCs react with ozone, breaking apart the ozone molecules and causing a reduction in the overall amount of ozone in the stratosphere. This process continues until all of the ozone-depleting chlorine atoms have been depleted. The resulting decrease in ozone in the stratosphere leads to an increase in the amount of harmful ultraviolet radiation that reaches the Earth's surface, which can have negative impacts on human health and the environment.
Pergunta 33 Relatório
Which of the following statements about catalyst is false?
Detalhes da Resposta
The false statement about catalysts is: "catalysts do not alter the mechanism of the reaction and never appear in the rate law." Catalysts are substances that speed up chemical reactions without being consumed in the process. They achieve this by reducing the activation energy needed for the reaction to occur. Enzymes are a type of biological catalysts. In a chemical reaction, a catalyst is not consumed and does not appear in the overall balanced equation. However, catalysts can alter the mechanism of a reaction by providing an alternative pathway with a lower activation energy. This alternative pathway can have a different rate-determining step, which means that the presence of the catalyst can change the rate law of the reaction. Therefore, the statement that catalysts do not alter the mechanism of the reaction and never appear in the rate law is false.
Pergunta 34 Relatório
The following are isoelectronic ions except
Detalhes da Resposta
Two or more ions are said to be isoelectronic if they have the same electronic structure and the same number of valence electrons.
Na+
= 10 electrons = 2, 8
Mg2+
= 10 electrons = 2,8
O2−
= 10 electrons = 2,8
Si2+
= 12 electrons = 2,8,2
⟹
Si2+
is not isoelectronic with the rest.
Pergunta 35 Relatório
A cell shorthand notation can be written as A / A+ // B2+ /B. The double slash in the notation represents the
Detalhes da Resposta
The double slash in the cell shorthand notation represents the salt bridge. A salt bridge is a component of an electrochemical cell that connects the two half-cells and allows the flow of ions between them. It consists of an inert electrolyte solution (usually a salt) that is placed between the two half-cells. The purpose of the salt bridge is to maintain electrical neutrality in each half-cell by allowing the flow of ions to balance the charge buildup in the half-cells. In the cell shorthand notation, the double slash "//" represents the salt bridge that connects the two half-cells of the electrochemical cell. The first half-cell is represented on the left-hand side of the slash and the second half-cell is represented on the right-hand side of the slash. The anode (where oxidation occurs) is represented on the left side, and the cathode (where reduction occurs) is represented on the right side. Therefore, the correct answer is option number 3: salt bridge.
Pergunta 36 Relatório
Elements X and Y have electronic configurations 1s2 2s2 2p4 and 1s2 2s2 2p6 3s2 3p1 respectively. When they combine, the formula of the compound formed is
Detalhes da Resposta
Pergunta 37 Relatório
The oxidation state(s) of nitrogen in ammonium nitrite is/are
Detalhes da Resposta
Ammonium nitrite = NH4
NO2
NH+4
: Let the oxidation number of Nitrogen = x
x + 4 = 1 ⟹
x = 1 - 4
x = -3
NO−2
: x - 4 = -1
x = -1 + 4 ⟹
x = +3.
The oxidation numbers for Nitrogen in Ammonium Nitrite = -3, +3.
Pergunta 38 Relatório
Which of the following represents the kind of bonding present in ammonium chloride?
Detalhes da Resposta
Ammonium chloride contains both ionic and covalent bonds. In ammonium chloride, the ammonium ion (NH4+) is positively charged and the chloride ion (Cl-) is negatively charged. These ions are held together by ionic bonds, which are formed between positively and negatively charged ions. However, the bond between the hydrogen atom in the ammonium ion and the nitrogen atom in the ammonium ion is also a covalent bond. This type of covalent bond is known as a dative covalent bond, or a coordinate covalent bond, because the electron pair being shared is supplied by one atom only (the nitrogen atom in this case). So, the kind of bonding present in ammonium chloride is both ionic and dative covalent. In simple terms, ammonium chloride contains both ionic bonds between its positive and negative ions, and a dative covalent bond between the hydrogen atom and nitrogen atom within the ammonium ion.
Pergunta 39 Relatório
When chlorine water is exposed to bright sunlight, the following products are formed
Detalhes da Resposta
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