Q: A student is asked to determine the percent yield of copper in an experiment. If the theoretical yield is 2.50 g and the actual yield is 2.10 g, what is the percent yield?

$$\frac{2.10}{2.50} \times 100 = 84\%$$

Question 1

Which of the following best describes the purpose of using significant figures in laboratory measurements?

Accepted Answer

To reflect the precision of the measuring instrument and communicate uncertainty in the measurement.

Question 2

A student separates a mixture of sand and salt by adding water, stirring, and filtering. Which physical property is primarily used in this separation?

Accepted Answer

Solubility

Question 3

Which of the following is a chemical property that can be used to identify a substance?

Accepted Answer

Ability to react with acid

Question 4

During a chemical reaction in the laboratory, a student observes the formation of a precipitate. Which type of reaction is most likely occurring?

Accepted Answer

Metathesis (double displacement) reaction

Question 5

Which equation correctly represents the dissolution of sodium chloride in water as a net ionic equation?

Accepted Answer

$$\mathrm{NaCl}(s) \rightarrow \mathrm{Na}^+(aq) + \mathrm{Cl}^-(aq)$$

Question 6

A student mixes solutions of silver nitrate and sodium chloride. What is the precipitate formed, and what is the net ionic equation for the reaction?

Accepted Answer

Precipitate: $$\mathrm{AgCl}$$; Net ionic: $$\mathrm{Ag}^+(aq) + \mathrm{Cl}^-(aq) \rightarrow \mathrm{AgCl}(s)$$

Question 7

Which of the following best explains why copper metal can be obtained from copper(II) sulfate solution using zinc metal?

Accepted Answer

Zinc is more reactive than copper and reduces copper(II) ions to copper metal.

Question 8

In a redox reaction, which species is oxidized and which is reduced in the following equation?

$$\mathrm{Zn}(s) + \mathrm{Cu}^{2+}(aq) \rightarrow \mathrm{Zn}^{2+}(aq) + \mathrm{Cu}(s)$$

Accepted Answer

Zinc is oxidized; copper is reduced.

Question 9

A student is asked to determine the percent yield of copper in an experiment. If the theoretical yield is 2.50 g and the actual yield is 2.10 g, what is the percent yield?

Accepted Answer

$$\frac{2.10}{2.50} 	imes 100 = 84\%$$

Question 10

Which of the following best describes the activity series of metals?

Accepted Answer

A ranking of metals based on their ability to lose electrons and undergo oxidation.

Question 11

A sample of gas occupies 2.00 L at 1.00 atm and 300 K. What will be its volume at 2.00 atm and 300 K, assuming ideal gas behavior?

Accepted Answer

$$1.00\ \mathrm{L}$$

Question 12

Which equation is used to correct for non-ideal behavior in gases?

Accepted Answer

$$(P + a\frac{n^2$}{V^2$})(V - nb) = nRT$$

Question 13

A student determines the molar mass of a vapor by measuring the mass, volume, temperature, and pressure. Which equation should be used to calculate the molar mass?

Accepted Answer

$$M = \frac{mRT}{PV}$$

Question 14

In gravimetric analysis, which of the following is most important for obtaining accurate results?

Accepted Answer

Careful filtration and drying of the precipitate.

Question 15

Which statistical measure is most useful for expressing the precision of a set of gravimetric analysis results?

Accepted Answer

Standard deviation

Question 16

A calorimeter is used to measure the heat change in a reaction. If 50.0 g of water absorbs 418 J of heat, what is the temperature change? ($$c = 4.18\ \mathrm{J/g\cdot{}K})$$

Accepted Answer

$$0.20\ \mathrm{K}$$

Question 17

Which of the following statements about chemical equilibrium is correct?

Accepted Answer

At equilibrium, the rates of the forward and reverse reactions are equal.

Question 18

A student mixes 0.10 mol of $$\mathrm{HCl}$$ and 0.10 mol of $$\mathrm{NaOH} in $$water. What is the net ionic equation for the reaction?

Accepted Answer

$$\mathrm{H}^+(aq) + \mathrm{OH}^-(aq) \rightarrow \mathrm{H}_2O(l)$$

Question 19

Which of the following best explains why a saturated solution of sodium chloride cannot dissolve more salt at a given temperature?

Accepted Answer

The rate of dissolution equals the rate of precipitation.

General Chemistry Laboratory Schedule and Key Concepts

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