Chemistry
Q. Calculate the pH of a 0.01 M solution of NaHCO3. (2023)
A.
8.3
B.
9.0
C.
7.5
D.
8.0
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Solution
NaHCO3 is a weak base. The pH can be calculated using the formula pH = 7 + 0.5(pKa - log[C]). pKa of HCO3- is about 10.3, so pH ≈ 8.3.
Correct Answer: A — 8.3
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Q. Calculate the pH of a 0.05 M NH4Cl solution (Kb for NH3 = 1.8 x 10^-5).
A.
4.75
B.
5.25
C.
5.75
D.
6.25
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Solution
Using the formula for weak bases, pH = 14 - 0.5(pKb - logC) = 14 - 0.5(4.74 - log(0.05)) = 5.25.
Correct Answer: B — 5.25
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Q. Calculate the pH of a 0.1 M NaOH solution.
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Solution
pOH = -log[OH-] = -log(0.1) = 1, thus pH = 14 - pOH = 14 - 1 = 13.
Correct Answer: C — 14
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Q. Calculate the pH of a 0.2 M solution of KOH.
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Solution
pOH = -log(0.2) = 0.7, thus pH = 14 - 0.7 = 13.3.
Correct Answer: B — 13
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Q. For a monatomic ideal gas, the ratio of specific heats (γ) is approximately: (2019)
A.
1.5
B.
1.67
C.
1.4
D.
2
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Solution
For a monatomic ideal gas, γ = C_p/C_v = 5/3 = 1.67.
Correct Answer: B — 1.67
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Q. For a process at constant volume, which of the following is true? (2023)
A.
Work done is zero
B.
Heat added equals change in internal energy
C.
Both A and B
D.
None of the above
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Solution
At constant volume, no work is done (W=0), and the heat added equals the change in internal energy (Q=ΔU).
Correct Answer: C — Both A and B
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Q. For a reaction with a rate constant of 0.02 M⁻¹s⁻¹ and initial concentration of 0.5 M, what is the time taken to reach 0.25 M in a second-order reaction? (2023)
A.
25 s
B.
50 s
C.
10 s
D.
20 s
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Solution
Using t = 1 / (k[A₀]) * (1/[A] - 1/[A₀]), t = 1 / (0.02 * 0.5) * (1/0.25 - 1/0.5) = 25 s.
Correct Answer: A — 25 s
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Q. For a reaction with an activation energy of 50 kJ/mol, what is the rate constant at 300 K if R = 8.314 J/(mol·K)? (2022)
A.
0.001 M/s
B.
0.01 M/s
C.
0.1 M/s
D.
1 M/s
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Solution
Using the Arrhenius equation, k = Ae^(-Ea/RT). Calculate k using the given values.
Correct Answer: C — 0.1 M/s
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Q. For a reaction with an activation energy of 50 kJ/mol, what will happen to the rate if the temperature is increased by 20°C? (2022)
A.
Rate decreases
B.
Rate remains the same
C.
Rate increases significantly
D.
Rate increases slightly
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Solution
Increasing the temperature generally increases the rate of reaction significantly due to higher kinetic energy.
Correct Answer: C — Rate increases significantly
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Q. For a zero-order reaction, if the initial concentration is 0.5 M and the rate constant is 0.1 M/s, how long will it take to reach 0.2 M? (2021)
A.
3 s
B.
5 s
C.
2 s
D.
4 s
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Solution
For a zero-order reaction, t = [A₀ - A] / k. Here, t = (0.5 - 0.2) / 0.1 = 3 s.
Correct Answer: D — 4 s
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Q. For a zero-order reaction, if the initial concentration is 0.5 M and the rate constant is 0.1 M/s, how long will it take to reach 0 M? (2019)
A.
5 s
B.
10 s
C.
15 s
D.
20 s
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Solution
For a zero-order reaction, t = [A₀] / k. Here, t = 0.5 M / 0.1 M/s = 5 s.
Correct Answer: B — 10 s
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Q. For an ideal gas, the work done during an isobaric process is given by which formula? (2022)
A.
W = PΔV
B.
W = nRT
C.
W = ΔU + Q
D.
W = 0
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Solution
In an isobaric process, the work done is calculated using the formula W = PΔV, where P is pressure and ΔV is the change in volume.
Correct Answer: A — W = PΔV
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Q. For an ideal gas, which law relates pressure, volume, and temperature? (2023) 2023
A.
Boyle's Law
B.
Charles's Law
C.
Ideal Gas Law
D.
Avogadro's Law
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Solution
The Ideal Gas Law (PV = nRT) relates pressure (P), volume (V), and temperature (T) for an ideal gas.
Correct Answer: C — Ideal Gas Law
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Q. For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), what will happen if the volume of the container is increased? (2020) 2020
A.
Equilibrium shifts to the right
B.
Equilibrium shifts to the left
C.
No change in equilibrium
D.
Reaction stops
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Solution
Increasing the volume decreases the pressure, and according to Le Chatelier's principle, the equilibrium will shift to the side with more moles of gas, which is the left side in this case.
Correct Answer: B — Equilibrium shifts to the left
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Q. For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what happens to the equilibrium if the volume of the container is decreased? (2020)
A.
Equilibrium shifts to the right
B.
Equilibrium shifts to the left
C.
No change in equilibrium
D.
Equilibrium shifts to the side with more moles
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Solution
Decreasing the volume increases the pressure, and according to Le Chatelier's principle, the equilibrium will shift to the side with fewer moles of gas, which is the right side in this case.
Correct Answer: A — Equilibrium shifts to the right
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Q. For the reaction: 2SO2(g) + O2(g) ⇌ 2SO3(g), what will happen if the volume of the container is increased? (2020)
A.
Equilibrium shifts to the right
B.
Equilibrium shifts to the left
C.
No change in equilibrium
D.
Equilibrium shifts to the center
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Solution
Increasing the volume decreases the pressure, and according to Le Chatelier's principle, the equilibrium will shift to the side with more moles of gas, which is the left side in this case.
Correct Answer: B — Equilibrium shifts to the left
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Q. How many grams are in 0.5 moles of glucose (C6H12O6)? (2023)
A.
90 g
B.
180 g
C.
45 g
D.
60 g
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Solution
Molar mass of C6H12O6 = 6*12 + 12*1 + 6*16 = 180 g/mol. Mass = 0.5 moles x 180 g/mol = 90 g.
Correct Answer: A — 90 g
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Q. How many grams are in 4 moles of potassium chloride (KCl)? (2022)
A.
74 g
B.
148 g
C.
296 g
D.
37 g
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Solution
Molar mass of KCl = 39 + 35.5 = 74.5 g/mol. Mass = 4 moles x 74.5 g/mol = 298 g.
Correct Answer: C — 296 g
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Q. How many grams are in 4 moles of sulfuric acid (H2SO4)? (2023)
A.
196 g
B.
98 g
C.
392 g
D.
294 g
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Solution
Molar mass of H2SO4 = 2*1 + 32 + 4*16 = 98 g/mol. Mass = 4 moles x 98 g/mol = 392 g.
Correct Answer: C — 392 g
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Q. How many grams of KCl are needed to prepare 0.5 M solution in 500 mL of water? (2023)
A.
14.9 g
B.
7.45 g
C.
29.8 g
D.
3.73 g
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Solution
Molarity = moles/volume(L). Moles = 0.5 mol/L * 0.5 L = 0.25 mol. Mass = moles * molar mass = 0.25 mol * 74.5 g/mol = 18.625 g.
Correct Answer: B — 7.45 g
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Q. How many grams of KCl are needed to prepare 250 mL of a 0.5 M solution? (2023) 2023
A.
7.45 g
B.
12.5 g
C.
9.25 g
D.
5.25 g
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Solution
Molar mass of KCl = 74.55 g/mol. Grams = Molarity * Volume (L) * Molar mass = 0.5 M * 0.25 L * 74.55 g/mol = 9.31 g.
Correct Answer: A — 7.45 g
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Q. How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (2023)
A.
37.25 g
B.
50 g
C.
75 g
D.
25 g
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Solution
Molar mass of KCl = 74.55 g/mol. Grams = moles × molar mass = 0.5 moles × 74.55 g/mol = 37.25 g.
Correct Answer: A — 37.25 g
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Q. How many grams of KCl are needed to prepare 250 mL of a 2 M solution? (Molar mass of KCl = 74.5 g/mol) (2023)
A.
37.25 g
B.
74.5 g
C.
18.625 g
D.
9.25 g
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Solution
Grams = moles × molar mass = (2 moles/L × 0.25 L) × 74.5 g/mol = 37.25 g.
Correct Answer: A — 37.25 g
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Q. How many liters of a 0.5 M NaOH solution are needed to obtain 1 mole of NaOH? (2023)
A.
1 L
B.
2 L
C.
0.5 L
D.
0.25 L
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Solution
Volume = moles / molarity = 1 mole / 0.5 M = 2 L.
Correct Answer: A — 1 L
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Q. How many liters of a 0.5 M solution contain 2 moles of solute? (2023)
A.
2 L
B.
4 L
C.
1 L
D.
0.5 L
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Solution
Volume = moles / molarity = 2 moles / 0.5 M = 4 L
Correct Answer: B — 4 L
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Q. How many liters of a 3 M solution can be made from 6 moles of solute? (2023)
A.
1 L
B.
2 L
C.
3 L
D.
4 L
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Solution
Volume = moles / molarity = 6 moles / 3 M = 2 L.
Correct Answer: B — 2 L
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Q. How many molecules are in 0.1 moles of oxygen gas (O2)? (2021)
A.
6.022 x 10^22
B.
6.022 x 10^23
C.
1.2044 x 10^23
D.
3.011 x 10^23
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Solution
Number of molecules = moles x Avogadro's number = 0.1 moles x 6.022 x 10^23 molecules/mole = 6.022 x 10^22 molecules.
Correct Answer: A — 6.022 x 10^22
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Q. How many molecules are in 0.25 moles of oxygen gas (O2)? (2022)
A.
3.011 x 10^23
B.
6.022 x 10^22
C.
1.2044 x 10^23
D.
1.5055 x 10^23
Show solution
Solution
Number of molecules = moles x Avogadro's number = 0.25 moles x 6.022 x 10^23 molecules/mole = 1.5055 x 10^23 molecules.
Correct Answer: B — 6.022 x 10^22
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Q. How many molecules are present in 2 moles of water (H2O)? (2022) 2022
A.
6.022 x 10^23
B.
1.2044 x 10^24
C.
3.011 x 10^23
D.
1.2044 x 10^23
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Solution
Number of molecules = moles x Avogadro's number = 2 moles x 6.022 x 10^23 molecules/mole = 1.2044 x 10^24 molecules.
Correct Answer: B — 1.2044 x 10^24
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Q. How many moles are in 100 grams of NaOH? (2022)
A.
2.5
B.
1.25
C.
0.5
D.
3
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Solution
Molar mass of NaOH = 23 + 16 + 1 = 40 g/mol. Number of moles = mass/molar mass = 100 g / 40 g/mol = 2.5 moles.
Correct Answer: B — 1.25
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