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Chemistry
UTME / JAMB 2019
Chemical Energetics & Thermochemistry
The heat of formation of ethene, C\(_2\)H\(_4\) is 50 kJmol\(^{-1}\), and that of ethane, C\(_2\)H\(_6\) is -82kJmol\(^{-1}\). Calculate the heat evolved in the process:
C\(_2\)H\(_4\) + H\(_2\) \(\to\) C\(_2\)H\(_6\)
A
-122kJ
B
-132kJ
C
-88kJ
D
-60kJ
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option B.
Source: Myschool Past Questions Archive (Record #55707)
Chemistry
UTME / JAMB 2019
Reaction Rates & Chemical Equilibrium
Solution
Which of the following statements about catalyst is false?
A
biological catalysts are called enzymes
B
catalyst do not appear in the balanced equation
C
catalyst reduce the activation energy for a reaction
D
catalysts do not alter the mechanism of the reaction and never appear in the rate low
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Option D says catalysts do not alter the mechanism of the reaction and never appear in the rate low. This statement is false; catalysts do alter the mechanism of a reaction by providing an alternative pathway with a lower activation energy, and while they do not appear in the overall balanced chemical equation, they can be involved in individual steps of the reaction mechanism, meaning they may appear in the rate law for a specific step of the reaction.
Source: Myschool Past Questions Archive (Record #55708)
Chemistry
UTME / JAMB 2019
Air & Environmental Chemistry
Solution
Which of the following does not support the fact that air is a mixture?
A
the constituents of air are in a fixed proportion by mass
B
it cannot be represented with a chemical formula
C
the constituents of air can be separated by physical by physical means
D
none of the above
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Having constituents in a fixed proportion by mass is a characteristic property of compounds, governed by the Law of Constant Proportions.
Air is a mixture because its composition can vary depending on location, altitude, and environmental factors such as humidity or pollution. For example, the amount of water vapour in air is not constant and varies with temperature and weather.
Source: Myschool Past Questions Archive (Record #55709)
Chemistry
UTME / JAMB 2019
Nature of Matter & Separation Techniques
What technique is suitable for separating a binary solution of potassium chloride and potassium trioxochlorate (V)?
A
Fractional crystallization
B
Fractional distillation
C
Filtration
D
Evaporation
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #55710)
Chemistry
UTME / JAMB 2019
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
At 27^\circC, 58.5g of sodium chloride is present in 250cm\(^3\) of a solution. The solubility of sodium chloride at this temperature is?
(molar mass of sodium chloride = 111.0gmol\(^{-1}\))
A
2.0 moldm\(^{-3}\)
B
0.25 moldm\(^{-3}\)
C
1.0 moldm\(^{-3}\)
D
0.5 moldm\(^{-3}\)
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Given the Mass of the salt = 58.5g
Volume = 250 cm\(^3\) = 0.25 dm\(^3\)
Mass concentration = \(\frac{Mass}{Volume}\)
= \(\frac{58.5}{0.25}\) = 234 gdm\(^{-3}\)
Solubility (in moldm\(^{-3}\) = \(\frac{234}{111} \)
= 2.11 moldm\(^{-3}\)
\(\approxeq\) 2.0 moldm\(^{-3}\)
Source: Myschool Past Questions Archive (Record #55711)
Chemistry
UTME / JAMB 2019
Periodic Table & Periodicity
Solution
Which of the following properties increases from left to right along the period but decreases down the group in the Periodic Table?
i. Atomic Number ii. Ionization energy iii. Metallic character iv. Electron affinity
A
ii and iii only
B
ii and iv only
C
iii and iv only
D
i and ii only
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Ionization energy and electron affinity increase across a period, and decrease down a group.
Source: Myschool Past Questions Archive (Record #55712)
Chemistry
UTME / JAMB 2019
Chemical Bonding & Intermolecular Forces
Solution
The molecular shape and bond angle of water are respectively
A
linear, 180°
B
bent, 109.5°
C
tetrahedral, 109.5°
D
bent, 105°
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
The shape of water molecule = Bent/ V- shaped
The bond angle of water = 104.5^\circ/ 105^\circ
Source: Myschool Past Questions Archive (Record #55713)
Chemistry
UTME / JAMB 2019
Acids, Bases, pH & Salts
Solution
Na\(_2\)CO\(_3\) + 2HCl \(\to\) 2NaCl + H\(_2\)O + CO\(_2\)
The indicator most suitable for this reaction should have a pH equal to
A
5
B
7
C
3
D
9
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Methyl orange is the best indicator for the reaction with range 3.1 - 4.4.
Source: Myschool Past Questions Archive (Record #55714)
Chemistry
UTME / JAMB 2019
Atomic Structure, Orbitals & Nuclear Chemistry
Solution
A radioactive nucleus has a half-life of 20 years, starting with 100,000 particles, how many particles will be left exactly at the end of 40 years
A
75,000 particles
B
35,000 particles
C
25,000 particles
D
50,000 particles
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Given:
t\(_{\frac{1}{2}\) = 20 years
After the first 20 years, half of the substance (\(\frac{1}{2} \times 100,000 = 50,000\)) will have decayed. Hence, we have 100,000 - 50,000 = 50,000 particles left.
After the second 20 years (being 40 years in all), half of the remaining substance (\(\frac{1}{2} \times 50,000 = 25,000\)) will have decayed.
Remaining particles after 40 years = 50,000 - 25,000
= 25,000 particles.
Source: Myschool Past Questions Archive (Record #55715)
Chemistry
UTME / JAMB 2019
Non-Metals & Their Compounds
Which two gases can be used for the demonstration of the fountain experiment?
A
SO\(_4\) and NH\(_3\)
B
SO\(_3\) and NH\(_3\)
C
HCl and NH\(_3\)
D
SO\(_2\) and CO
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option C.
Source: Myschool Past Questions Archive (Record #55716)
Chemistry
UTME / JAMB 2019
Air & Environmental Chemistry
Which of the following pollutants will lead to the depletion of ozone layer?
A
chlorofluorocarbon
B
carbon (ii) oxide
C
hydrogen sulphide
D
sulphur (iv) oxide
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #55717)
Chemistry
UTME / JAMB 2019
Acids, Bases, pH & Salts
Which of the following describes the chemical property of acids?
A
None of the above
B
Acid + XCO\(_3\) \(\to\) Salt + H\(_2\)O + NH\(_3\)
C
Acid + NaOH \(\to\) Normal salt + CO\(_2\)
D
Acid + X\(_n\)CO\(_3\) \(\to\) Salt + H\(_2\)O + CO\(_2\)
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #55718)
Chemistry
UTME / JAMB 2019
Metals, Transition Elements & Extraction
Which of the following pairs cannot be represented with a chemical formula?
A
air and bronze
B
bronze and sodium chloride
C
copper and sodium chloride
D
caustic soda and washing soda
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option A.
Source: Myschool Past Questions Archive (Record #55723)
Chemistry
UTME / JAMB 2019
Oxidation, Reduction & Redox Reactions
Solution
Consider the equation below:
Cr\(_2\)O\(_7 ^{2-}\) + 6Fe\(^{2+}\) + 14H\(^{+}\) \(\to\) 2Cr\(^{3+}\) + 6Fe\(^{3+}\) + 7H\(_2\)O.
The oxidation number of chromium changes from
A
+5 to +3
B
+6 to +3
C
-2 to +3
D
+7 to +3
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Cr\(_2\)O\(_7 ^{2-}\) + 6Fe\(^{2+}\) + 14H\(^{+}\) \(\to\) 2Cr\(^{3+}\) + 6Fe\(^{3+}\) + 7H\(_2\)O
The oxidation of Cr in Cr\(_2\)O\(_7 ^{2-}\) :
Let the oxidation of Cr = x;
2x + (-2 x 7) = -2 \(\implies\) 2x - 14 = -2
2x = 12 ; x = +6
Hence, the change in oxidation of Cr = +6 to +3
Source: Myschool Past Questions Archive (Record #55728)
Chemistry
UTME / JAMB 2019
Nature of Matter & Separation Techniques
Which of the following is a physical change?
A
Exposing white phosphorus to air
B
Burning kerosene
C
Dissolving calcium in water
D
Freezing ice cream
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
No expanded working has been attached for this question yet. The verified answer is Option D.
Source: Myschool Past Questions Archive (Record #55783)