POST UTME UNN 2019 Chemistry | Objective

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Question 1
The half-life of a radioactive subs\tance is 5.0 days. If 100 mg of the subs\tance is present initially, how much will remain after 20 days?
A. 12.5 mg
B. 25 mg
C. 50 mg
D. 100 mg
Question 2
A metal (M) reacts with oxygen (O2) to form a metal oxide (MO). If the balanced equation for the reaction is: 4M + 3O2 → 2MO, what is the mole ratio of metal (M) to oxygen (O2)?
A. 1:1
B. 1:3
C. 4:3
D. 2:3
Question 3
The pH of a solution is 4.5. Calculate the concentration of hydrogen ions in the solution.
A. 10^-4.5 M
B. 10^-5.5 M
C. 10^-6.5 M
D. 10^-7.5 M
Question 4
A sample of an ideal gas is heated at cons\tant volume. Which of the following statements is true?
A. The pressure of the gas increases.
B. The pressure of the gas decreases.
C. The pressure of the gas remains cons\tant.
D. The pressure of the gas becomes zero.
Question 5
A solution of sodium hydroxide is added to a solution of acetic acid. The reaction is as follows: CH3COOH + NaOH → CH3COONa + H2O. If 25.0 mL of 0.100 M acetic acid is added to 50.0 mL of 0.100 M sodium hydroxide, what is the concentration of the resulting solution?
A. 0.0500 M
B. 0.100 M
C. 0.150 M
D. 0.200 M
Question 6
A reaction is represented by the equation: \( 2A + B \rightarrow 2C + D \). If the rate cons\tant for the reaction is 0.0500 s\( ^{-1} \) and the initial concentrations of A and B are 0.100 M and 0.0500 M, respectively, what is the concentration of A after 10.0 s?
A. 0.0500 M
B. 0.0750 M
C. 0.100 M
D. 0.125 M
Question 7
The s\tandard enthalpy of formation of CO2 is -393.5 kJ/mol. What is the s\tandard enthalpy of formation of CO?
A. -110.5 kJ/mol
B. -130.5 kJ/mol
C. -150.5 kJ/mol
D. -170.5 kJ/mol
Question 8
A reaction is represented by the equation: \( A \rightarrow 2B + C \). If the rate cons\tant for the reaction is 0.0500 s\( ^{-1} \) and the initial concentration of A is 0.100 M, what is the concentration of B after 10.0 s?
A. 0.0500 M
B. 0.0750 M
C. 0.100 M
D. 0.125 M
Question 9
The reaction between HCl and NaOH is represented by the equation: HCl + NaOH → NaCl + H2O. If 50 mL of 0.1 M HCl is mixed with 50 mL of 0.1 M NaOH, what is the concentration of the resulting solution?
A. 0.05 M
B. 0.10 M
C. 0.15 M
D. 0.20 M
Question 10
A 25.0 mL sample of 0.100 M HCl is titrated with 0.100 M NaOH. Calculate the pH of the solution after the addition of 25.0 mL of NaOH.
A. 2.00
B. 3.00
C. 4.00
D. 5.00
Question 11
The rate cons\tant (k) for a first-order reaction is given by the equation: k = Ae^\( -Ea/RT \). If the activation energy (Ea) is 100 kJ/mol, the gas cons\tant (R) is 8.314 J/\( mol*K \), and the temperature (T) is 298 K, what is the value of the rate cons\tant (k) if the pre-exponential factor (A) is 1.0 x 10^10 s^\( -1 \)?
A. 1.0 x 10^\( -10 \) s^\( -1 \)
B. 1.0 x 10^\( -9 \) s^\( -1 \)
C. 1.0 x 10^\( -8 \) s^\( -1 \)
D. 1.0 x 10^\( -7 \) s^\( -1 \)
Question 12
A 2.0 L flask contains 1.0 M H2SO4. If 0.10 M NaOH is added to the flask, what is the concentration of the resulting solution?
A. 0.50 M
B. 0.75 M
C. 1.0 M
D. 1.25 M
Question 13
A metal M reacts with chlorine gas to form a white solid product. The reaction is as follows: M(s) + Cl2(g) → MCl2(s). If 2.5 g of MCl2 is obtained from 3.2 g of M, calculate the percentage yield of MCl2.
A. 60%
B. 70%
C. 80%
D. 90%
Question 14
A sample of nitrogen gas occupies a volume of 2.5 L at a pressure of 1.5 atm and a temperature of 298 K. Calculate the number of moles of nitrogen gas present.
A. 0.05 mol
B. 0.1 mol
C. 0.15 mol
D. 0.2 mol
Question 15
Determine the oxidation state of nitrogen in the compound NO2.
A. +1
B. +2
C. +3
D. +4

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