In an acidic buffer, if the concentration of the salt equals that of the weak acid, the pH of the buffer equals ____
Correct answer A. the pKa of the acid
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MDCAT ECAT Chemistry MCQs
Page 9 of MDCAT ECAT Chemistry multiple-choice questions with answers. Tap an option to check yourself.
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- Gases 40
- Liquids 40
- Solids 40
- Chemical Equilibrium 40
- Reaction Kinetics 40
- Thermochemistry and Energetics 40
- Electrochemistry 40
- Fundamental Concepts of Chemistry 40
- Atomic Structure 39
- Chemical Bonding 39
- Alcohols and Phenols 38
- Industrial Chemistry 37
- Aldehydes and Ketones 37
- Alkyl Halides 37
- s- and p-Block Elements 37
- Chemistry of Hydrocarbons 36
- Fundamental Principles of Organic Chemistry 36
- Carboxylic Acids 36
- Transition Elements 35
- Macromolecules 35
Which catalyst is used in the Haber process for the manufacture of ammonia?
Correct answer A. Finely divided iron with promoters
Which statement about the forward reaction N₂(g) + 3H₂(g) → 2NH₃(g) in the Haber process is correct?
Correct answer C. It is exothermic and decreases the number of gas molecules
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The law of mass action states that the rate of a reaction is proportional to ____
Correct answer B. the product of the active masses of the reactants
How does the rate of most reactions change as the reaction proceeds at constant temperature?
Correct answer B. It decreases
How is the instantaneous rate of a reaction found from a graph of concentration against time?
Correct answer A. From the slope of the tangent at that time
The concentration of a reactant falls from 0.80 to 0.20 mol dm⁻³ in 30 s. What is the average rate of reaction?
Correct answer A. 0.020 mol dm⁻³ s⁻¹
Doubling the concentration of reactant B has no effect on the rate of a reaction. What is the order with respect to B?
Correct answer C. Zero
For rate = k, the rate is 6.0 × 10⁻³ mol dm⁻³ s⁻¹ when = 0.10 and = 0.20 mol dm⁻³. What is k?
Correct answer A. 0.30 dm³ mol⁻¹ s⁻¹
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What are the units of the rate constant for a first-order reaction?
Correct answer A. s⁻¹
A first-order reaction is 75% complete in 40 minutes. What is its half-life?
Correct answer B. 20 min
A mixture of H₂ and Cl₂ reacts slowly in the dark but explosively in bright sunlight. Which factor is responsible?
Correct answer D. Light
Why does AgNO₃ solution react almost instantly with NaCl solution to form a white precipitate?
Correct answer D. It is an ionic reaction requiring no bonds to be broken
Which quantity is NOT changed by adding a catalyst to a reaction?
Correct answer A. The enthalpy change, ΔH
According to collision theory, which collisions lead to reaction?
Correct answer D. Collisions with energy at least equal to Ea and proper orientation
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In the Arrhenius equation, a plot of ln k against 1/T gives a straight line. What is its slope?
Correct answer D. −Ea/R
The reaction NO₂ + CO → NO + CO₂ occurs in two steps, the slow first step being 2NO₂ → NO₃ + NO. What is the rate equation?
Correct answer D. rate = k[NO₂]²
In the titration of oxalic acid with acidified KMnO₄, the reaction is slow at first but speeds up later. Why?
Correct answer D. Mn²⁺ ions formed act as an autocatalyst
For 2NO(g) + O₂(g) → 2NO₂(g), rate = k². How does the rate change if the volume of the vessel is halved?
Correct answer D. It increases 8 times
For an endothermic reaction, how does the enthalpy of the products compare with that of the reactants?
Correct answer D. It is greater