Q: A solution has a hydronium ion concentration of $$[H_3O^+] = 2.5 \times 10$$^{-4}$$ M. What is its pH?

$$pH = -\log(2.5 \times 10$$^{-4}$$) = 3.60$$

Q: A 15.0 mL sample of HCl is titrated with 0.09977 M NaOH. If 29.27 mL of NaOH is required to reach the equivalence point, what is the concentration of HCl?

$$C_{HCl} = \frac{0.09977 \times 29.27}{15.00} = 0.1949 M$$

Q: Calculate the energy required to raise the temperature of 250 mL of water from 20.5°C to 95.6°C. (Assume $$c_s = 4.184 J$$ $$g^{-1}$$ $$K^{-1}$$, density = 1.00 $$g/mL)$$

$$q = 250 \times 4.184 \times (95.6 - 20.5) = 78,800 J$$

Q: A gas expands from 1.50 L to 2.18 L against a constant pressure of $$1.01 \times 10^5$ Pa. What is the work done by the gas?

$$w = -p \Delta V = -1.01 \times 10^5$ \times (2.18 - 1.50) = -68,000 J$$

Q: A gas has a density of 1.98 $$g/L at $$STP. What is its molar mass? (STP: $$p = 1$$ atm, $$T = 273 K$$, $$R = 0.0821$$ $$L \cdot atm \cdot $$mol^{-1}$$ \cdot K$$^{-1}$$)

$$M = \frac{dRT}{p} = \frac{1.98 \times 0.0821 \times 273}{1} = 44.4 g/$$mol

Question 1

Which of the following best describes the process of gravimetric analysis as used to determine the amount of Na2SO4 in a mineral sample?

Accepted Answer

Reacting the sample with BaCl2 to precipitate BaSO4, collecting and weighing the solid.

Question 2

A solution has a hydronium ion concentration of $$[H_3O^+] = 2.5 	imes 10$$^{-4}$$ M. What is its pH?

Accepted Answer

$$pH = -\log(2.5 	imes 10$$^{-4}$$) = 3.60$$

Question 3

If a solution has a pH of 9.25, what is its hydroxide ion concentration $$[OH^-]$$?

Accepted Answer

$$[OH^-] = 10$$^{-(14.00 - 9.25)}$$ = 10$$^{-4.75}$$

Question 4

Which equation correctly relates pH and pOH in aqueous solution?

Accepted Answer

$$pH + pOH = 14.00$$

Question 5

A 15.0 mL sample of HCl is titrated with 0.09977 M NaOH. If 29.27 mL of NaOH is required to reach the equivalence point, what is the concentration of HCl?

Accepted Answer

$$C_{HCl} = \frac{0.09977 	imes 29.27}{15.00} = 0.1949 M$$

Question 6

Which of the following statements about exothermic and endothermic processes is correct?

Accepted Answer

In an exothermic process, heat is transferred from the system to the surroundings.

Question 7

Calculate the energy required to raise the temperature of 250 mL of water from 20.5°C to 95.6°C. (Assume $$c_s = 4.184 J$$ $$g^{-1}$$ $$K^{-1}$$, density = 1.00 $$g/mL)$$

Accepted Answer

$$q = 250 	imes 4.184 	imes (95.6 - 20.5) = 78,800 J$$

Question 8

Which equation represents the First Law of Thermodynamics?

Accepted Answer

$$\Delta U = w + q$$

Question 9

A gas expands from 1.50 L to 2.18 L against a constant pressure of $$1.01 	imes 10^5$ Pa. What is the work done by the gas?

Accepted Answer

$$w = -p \Delta V = -1.01 	imes 10^5$ 	imes (2.18 - 1.50) = -68,000 J$$

Question 10

Which equation is used to calculate the enthalpy change of a reaction using standard enthalpies of formation?

Accepted Answer

$$\Delta_r H^\circ = \sum n_i \Delta_f H^\circ (products) - \sum n_i \Delta_f H^\circ (reactants)$$

Question 11

Which equation is the Ideal Gas Law?

Accepted Answer

$$pV = nRT$$

Question 12

A gas has a density of 1.98 $$g/L at $$STP. What is its molar mass? (STP: $$p = 1$$ atm, $$T = 273 K$$, $$R = 0.0821$$ $$L \cdot atm \cdot $$mol^{-1}$$ \cdot K$$^{-1}$$)

Accepted Answer

$$M = \frac{dRT}{p} = \frac{1.98 	imes 0.0821 	imes 273}{1} = 44.4 g/$$mol

Question 13

Which law states that the total pressure of a mixture of gases is the sum of the partial pressures of each gas?

Accepted Answer

Dalton's Law of Partial Pressures

Question 14

Which equation describes the relationship between vapor pressure and temperature for a liquid according to the Clausius-Clapeyron equation?

Accepted Answer

$$\ln(p) = -\frac{\Delta H_{vap}}{RT} + 	ext{Constant}$$

Question 15

Which property is NOT a colligative property?

Accepted Answer

Color of the solution

Question 16

What is the van't Hoff factor ($$i) $$for a strong electrolyte such as Na2SO4?

Accepted Answer

$$i = 3$$

Question 17

Which equation describes the osmotic pressure of a solution?

Accepted Answer

$$\Pi = cRT$$

Question 18

Which factor does NOT affect the rate of a chemical reaction according to collision theory?

Accepted Answer

Color of the reactants

Question 19

For a first-order reaction, which equation gives the half-life ($$t_{1/2}$$)?

Accepted Answer

$$t_{1/2} = \frac{0.693}{k}$$

Question 20

Which equation is the Arrhenius equation relating the rate constant $$k to $$temperature?

Accepted Answer

$$k = Ae$$^{-E_a/RT}$$

General Chemistry: Aqueous Reactions, Thermochemistry, and Kinetics

Guida di studio - Domande di pratica

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