Q: Given the balanced equation: $$2 \mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2 \mathrm{H}_2\mathrm{O}$$, how many grams of water are produced from 4.00 g of hydrogen gas and excess oxygen?

$$n_{H_2$} = \frac{4.00}{2.02} = 1.98$$ mol; \newline n_{H_2O} = 1.98$$ mol; m = 1.98$$ \times 18.02 = 35.7$ g

Q: A 20.0 g piece of iron (specific heat $$c = 0.45 J/g$\cdot$$°C) is heated to 250°C and placed in 100.0 mL of water at 18.0°C. What is the final temperature? ($$c_{H_2O} = 4.18 J/g$\cdot$$°C, $$d_{H_2O} = 1.00 g/mL)$$

Set $$q_{Fe} = -q_{H_2O}$$: $$20.0 \times 0.45 \times (T_f - 250) = -100.0 \times 4.18 \times (T_f - 18)$$; $$T_f = 18.9$$°C

Q: A hydrated ionic compound has the formula $$\mathrm{CuSO}_4 \cdot 5\mathrm{H}_2\mathrm{O}. $$What is the percent by mass of water in this compound? ($$M_{$$CuSO_4$$} = 159.6 g/$$mol, $$M_{5H_2O} = 90.1 g/$$mol)

$$\frac{90.1}{249.7} \times 100 = 36.1\%$$

Q: A sample contains 3.01 $$\times$$ $$10^{23}$$ molecules of $$\mathrm{CO}_2. $$What is the mass of this sample? ($$M_{CO_2$} = 44.01 g/$$mol)

$$n = \frac{3.01 \times 10$$^{23}$$}{6.022 \times 10$$^{23}$$} = 0.500$$ mol; $$m = 0.500 \times 44.01 = 22.0 g$$

Question 1

Which of the following best describes the classification of matter in the image labeled (a) in the first figure, and what is the correct reading of the liquid volume to the appropriate number of significant figures?

Accepted Answer

The liquid is a homogeneous mixture; the volume is 72.5 mL.

Question 2

Using the standard curve in the second image, estimate the concentration (in mg/dL) of a solution that gives an absorbance of 0.4. Use the equation of the line provided.

Accepted Answer

$$x = \frac{0.4 + 0.03}{0.027} = 15.9 mg/dL$$

Question 3

Which of the following best describes the physical state and classification of the substance in image (c) of the first figure, and what is the correct reading of the liquid volume to the appropriate number of significant figures?

Accepted Answer

The substance is a liquid; the volume is 610 mL.

Question 4

Which scientist is credited with the discovery of the electron, and what experiment led to this discovery?

Accepted Answer

Thomson; cathode ray tube experiment

Question 5

A student measures the temperature of a solution as shown in image (b) of the first figure. If the thermometer reads 8.0°C, what is this temperature in Kelvin?

Accepted Answer

$$T = 8.0 + 273.15 = 281.2 K$$

Question 6

Which of the following best describes the law illustrated when 10.0 g of calcium reacts with 17.8 g of chlorine to produce 27.8 g of calcium chloride?

Accepted Answer

Law of Conservation of Mass

Question 7

Which of the following is the correct empirical formula for a compound that contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 8

A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 250.0 mL of solution. What is the molarity of the solution? ($$M_{NaCl} = 58.44 g/$$mol)

Accepted Answer

$$M = \frac{10.0}{58.44} \div 0.250 = 0.684 M$$

Question 9

Which of the following best describes the type of chemical reaction when aqueous solutions of sodium sulfate and barium chloride are mixed, forming a white precipitate?

Accepted Answer

Precipitation reaction

Question 10

Given the balanced equation: $$2 \mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2 \mathrm{H}_2\mathrm{O}$$, how many grams of water are produced from 4.00 g of hydrogen gas and excess oxygen?

Accepted Answer

$$n_{H_2$} = \frac{4.00}{2.02} = 1.98$$ mol; 
ewline n_{H_2O} = 1.98$$ mol; m = 1.98$$ 	imes 18.02 = 35.7$ g

Question 11

Which of the diagrams (a, b, c, or d) in the third and fourth images best represents a mixture where neither reactant is in excess for the reaction $$\mathrm{CH}_4 + 2\mathrm{O}_2 \rightarrow \mathrm{CO}_2 + 2\mathrm{H}_2\mathrm{O}$$?

Accepted Answer

Diagram c

Question 12

A 20.0 g piece of iron (specific heat $$c = 0.45 J/g$\cdot$$°C) is heated to 250°C and placed in 100.0 mL of water at 18.0°C. What is the final temperature? ($$c_{H_2O} = 4.18 J/g$\cdot$$°C, $$d_{H_2O} = 1.00 g/mL)$$

Accepted Answer

Set $$q_{Fe} = -q_{H_2O}$$: $$20.0 	imes 0.45 	imes (T_f - 250) = -100.0 	imes 4.18 	imes (T_f - 18)$$; $$T_f = 18.9$$°C

Question 13

Which of the following is the correct name for the compound $$\mathrm{Fe}_2\mathrm{O}_3$$?

Accepted Answer

Iron(III) oxide

Question 14

A hydrated ionic compound has the formula $$\mathrm{CuSO}_4 \cdot 5\mathrm{H}_2\mathrm{O}. $$What is the percent by mass of water in this compound? ($$M_{$$CuSO_4$$} = 159.6 g/$$mol, $$M_{5H_2O} = 90.1 g/$$mol)

Accepted Answer

$$\frac{90.1}{249.7} 	imes 100 = 36.1\%$$

Question 15

Which of the following best describes the type of bond and the elements involved in sodium chloride ($$\mathrm{NaCl}$$)?

Accepted Answer

Ionic bond between a metal and a nonmetal

Question 16

A sample contains 3.01 $$	imes$$ $$10^{23}$$ molecules of $$\mathrm{CO}_2. $$What is the mass of this sample? ($$M_{CO_2$} = 44.01 g/$$mol)

Accepted Answer

$$n = \frac{3.01 	imes 10$$^{23}$$}{6.022 	imes 10$$^{23}$$} = 0.500$$ mol; $$m = 0.500 	imes 44.01 = 22.0 g$$

Question 17

Which of the following is the correct balanced equation for the combustion of pentanol ($$\mathrm{C}_5\mathrm{H}_{11}\mathrm{OH}$$)?

Accepted Answer

$$2 \mathrm{C}_5\mathrm{H}_{11}\mathrm{OH} + 15 O_2$ \rightarrow 10 CO_2$ + 12 H_2O$$

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