Q: How many atoms are present in 72.6 g of $$\mathrm{K}_2\mathrm{CO}_3$$?

$$1.90 \times 10$$^{24}$$ atoms

Question 1

Which of the following statements best explains why chemical equilibrium is described as 'dynamic'?

Accepted Answer

At equilibrium, the forward and reverse reactions continue to occur at equal rates, so the concentrations remain constant.

Question 2

A 25.00 mL sample of 0.45 M NaOH(aq) is titrated with 0.2750 mol/L HNO$$_3(aq). $$What volume of HNO$$_3 is $$required to neutralize the NaOH(aq)?

Accepted Answer

$$0.04091\ 	ext{L}$$

Question 3

Given the reaction $$2A + 3B \rightarrow 4C + D$$, if initially 10 mol of A and 10 mol of B are mixed and at equilibrium 2 mol of D is present, what is the value of the equilibrium constant $$K$$?

Accepted Answer

$$K = \dfrac{[C]^4[D]}{[A]^2[B]^3} = 3.56$$

Question 4

Which of the following is the correct net ionic equation for the neutralization of a strong acid with a strong base?

Accepted Answer

$$\mathrm{H}^+(aq) + \mathrm{OH}^-(aq) \rightarrow \mathrm{H}_2\mathrm{O}(l)$$

Question 5

A solution contains 45.7 g of sugar per 100.0 mL of water. What is the percentage by mass concentration of solute in this solution?

Accepted Answer

$$31.4\%$$

Question 6

Which of the following is the correct equilibrium constant expression for the reaction $$\mathrm{CaCO}_3(s) \rightleftharpoons \mathrm{CaO}(s) + \mathrm{CO}_2(g)$$?

Accepted Answer

$$K = [\mathrm{CO}_2]$$

Question 7

How many atoms are present in 72.6 g of $$\mathrm{K}_2\mathrm{CO}_3$$?

Accepted Answer

$$1.90 	imes 10$$^{24}$$ atoms

Question 8

Which of the following best describes a Brønsted-Lowry acid?

Accepted Answer

A substance that donates a proton ($$\mathrm{H}^+) to $$another substance.

Question 9

In the reaction $$\mathrm{H}_2(g) + \mathrm{I}_2(g) \rightleftharpoons 2\mathrm{HI}(g) at$$ $$425^\circ\mathrm{C}$$, $$K = 24. If$$ $$[\mathrm{H}_2] = 2.25\ \mathrm{M}$$, $$[\mathrm{I}_2] = 1.37\ \mathrm{M}$$, and $$[\mathrm{HI}] = 1.25\ \mathrm{M}$$, what will happen to the system?

Accepted Answer

The system is not at equilibrium; more products will form until equilibrium is reached.

Question 10

Which of the following changes will increase the value of the equilibrium constant $$K$$ for the exothermic reaction $$4\mathrm{SO}_2(g) + 2\mathrm{O}_2(g) ightleftharpoons 4\mathrm{SO}_3(g) + 	ext{Heat}$$?

Accepted Answer

Decreasing the temperature of the system.

Question 11

What is the empirical formula of a compound with the following analysis: 65.0% Ag, 15.7% Cr, 19.3% O?

Accepted Answer

$$\mathrm{Ag}_2\mathrm{CrO}_4$$

Question 12

Which of the following is a correct set of conjugate acid-base pairs for the reaction $$\mathrm{HCN}(aq) + \mathrm{H}_2\mathrm{O}(l) \rightleftharpoons \mathrm{CN}^-(aq) + \mathrm{H}_3\mathrm{O}^+(aq)$$?

Accepted Answer

$$\mathrm{HCN}/\mathrm{CN}^-$$\ and\ $$\mathrm{H}_3\mathrm{O}^+/\mathrm{H}_2\mathrm{O}$$

Question 13

A student mixes 35.8 g of CuCl with excess H$$_2S $$according to the reaction $$2\mathrm{CuCl} + \mathrm{H}_2\mathrm{S} \rightarrow \mathrm{Cu}_2\mathrm{S} + 2\mathrm{HCl}. $$How many grams of H$$_2S $$are required to react completely with the CuCl?

Accepted Answer

$$6.2\ 	ext{g}$$

Question 14

Which of the following is the correct balanced equation for the reaction between Ca(OH)$$_2$$ and HClO$$_4$$?

Accepted Answer

$$\mathrm{Ca(OH)}_2 + 2\mathrm{HClO}_4 \rightarrow \mathrm{Ca(ClO}_4)_2 + 2\mathrm{H}_2\mathrm{O}$$

Question 15

Which of the following is the correct molar mass of Fe(NO$$_3$$)$$_3$$?

Accepted Answer

$$241.88\ 	ext{g/mol}$$

Question 16

A 45.00 mL sample of Ca(OH)$$_2(aq) is $$titrated with 48.65 mL of 0.18 M HCl(aq). What is the concentration of the Ca(OH)$$_2(aq$$)?

Accepted Answer

$$0.0973\ 	ext{mol/L}$$

Question 17

Which of the following best describes the effect of adding a catalyst to a system at equilibrium?

Accepted Answer

It increases the rate at which equilibrium is reached but does not change the value of $$K or $$the position of equilibrium.

Question 18

Which of the following is the correct percentage composition by mass of Ba in BaSO$$_4$$?

Accepted Answer

$$58.84\%$$

Exam Review Guidance: Introduction to Chemistry (Modules 6–10)

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