Q: A sample of water is heated from $$25^\circ\mathrm{C} to$$ $$75^\circ\mathrm{C}. If $$the mass of water is $$100.0\ \mathrm{g}$$ and the specific heat of water is $$4.18\ \mathrm{J/g\cdot ^\circ C}$$, how much energy is absorbed?

$$q = m \cdot c \cdot \Delta T = 100.0\ \mathrm{g} \times 4.18\ \mathrm{J/g\cdot ^\circ C} \times (75-25)\ ^\circ\mathrm{C} = 20,900\ \mathrm{J}$$

Q: Convert $$0.0250\ \mathrm{kg} to $$milligrams ($$\mathrm{mg}).$$

$$0.0250\ \mathrm{kg} \times \frac{1,000,000\ \mathrm{mg}}{1\ \mathrm{kg}} = 25,000\ \mathrm{mg}$$

Q: A sample of gold has two naturally occurring isotopes: $$^{197}\mathrm{Au} ($$abundance 98.93%, mass 196.967 u) and $$^{198}\mathrm{Au} ($$abundance 1.07%, mass 197.968 u). What is the average atomic mass of gold?

$$(0.9893 \times 196.967) + (0.0107 \times 197.968) = 196.98\ \mathrm{u}$$

Question 1

Which of the following best describes the difference between a compound and a mixture?

Accepted Answer

A compound has a fixed composition with elements chemically combined, while a mixture contains substances physically combined in variable proportions.

Question 2

A student measures the mass of a metal sample as 12.45 g and its volume as 4.10 mL. What is the density of the metal, and which of the following is the correct answer with the proper number of significant figures?

Accepted Answer

$$\frac{12.45\ \mathrm{g}}{4.10\ \mathrm{mL}} = 3.04\ \mathrm{g/mL}$$

Question 3

Which of the following is the correct electron configuration for a neutral atom of magnesium ($$Z=12$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$

Question 4

A sample of water is heated from $$25^\circ\mathrm{C} to$$ $$75^\circ\mathrm{C}. If $$the mass of water is $$100.0\ \mathrm{g}$$ and the specific heat of water is $$4.18\ \mathrm{J/g\cdot ^\circ C}$$, how much energy is absorbed?

Accepted Answer

$$q = m \cdot c \cdot \Delta T = 100.0\ \mathrm{g} 	imes 4.18\ \mathrm{J/g\cdot ^\circ C} 	imes (75-25)\ ^\circ\mathrm{C} = 20,900\ \mathrm{J}$$

Question 5

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 6

Which of the following phase transitions is endothermic?

Accepted Answer

Melting (fusion)

Question 7

A radioactive isotope of iodine, $$^{131}\mathrm{I}$$, undergoes beta decay. Which of the following correctly represents the nuclear equation for this process?

Accepted Answer

$$^{131}_{53}\mathrm{I} \$$rightarrow ^{131}$$_{54}\mathrm{Xe} $$+ ^{0}$$_{-1}\beta$$

Question 8

Which of the following best explains why metals are good conductors of electricity?

Accepted Answer

Metals have delocalized electrons that can move freely throughout the structure.

Question 9

Convert $$0.0250\ \mathrm{kg} to $$milligrams ($$\mathrm{mg}).$$

Accepted Answer

$$0.0250\ \mathrm{kg} 	imes \frac{1,000,000\ \mathrm{mg}}{1\ \mathrm{kg}} = 25,000\ \mathrm{mg}$$

Question 10

Which of the following elements is a metalloid?

Accepted Answer

Silicon ($$\mathrm{Si})$$

Question 11

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties because they have the same number of valence electrons.

Question 12

A sample of gold has two naturally occurring isotopes: $$^{197}\mathrm{Au} ($$abundance 98.93%, mass 196.967 u) and $$^{198}\mathrm{Au} ($$abundance 1.07%, mass 197.968 u). What is the average atomic mass of gold?

Accepted Answer

$$(0.9893 	imes 196.967) + (0.0107 	imes 197.968) = 196.98\ \mathrm{u}$$

Question 13

Which of the following best describes the trend in atomic size across a period from left to right?

Accepted Answer

Atomic size decreases due to increasing nuclear charge pulling electrons closer.

Question 14

A patient receives 250 mL of a saline solution at $$25^\circ\mathrm{C}. If $$the solution is heated to body temperature ($$37^\circ\mathrm{C}$$), how much energy is required? (Assume the density of the solution is $$1.00\ \mathrm{g/mL}$$ and the specific heat is $$4.18\ \mathrm{J/g\cdot ^\circ C}.)$$

Accepted Answer

$$q = 250\ \mathrm{g} 	imes 4.18\ \mathrm{J/g\cdot ^\circ C} 	imes (37-25)\ ^\circ\mathrm{C} = 12,540\ \mathrm{J}$$

Question 15

Which of the following is the correct shorthand electron configuration for chlorine ($$Z=17$$)?

Accepted Answer

$$[Ne]\ 3s^2$\ 3p^5$

Question 16

Which of the following best describes the process of sublimation?

Accepted Answer

A solid changes directly to a gas without passing through the liquid state.

Question 17

Which of the following is the correct symbol, mass number, and charge for an alpha particle?

Accepted Answer

$$^{4}_{2}\mathrm{He}^{2+}$$

Question 18

A sample of ethanol ($$C_2H_5OH) is $$heated from $$20^\circ\mathrm{C} to$$ $$78^\circ\mathrm{C}$$, its boiling point. If the mass is $$50.0\ \mathrm{g}$$ and the specific heat is $$2.44\ \mathrm{J/g\cdot ^\circ C}$$, how much energy is required for this temperature change?

Accepted Answer

$$q = 50.0\ \mathrm{g} 	imes 2.44\ \mathrm{J/g\cdot ^\circ C} 	imes (78-20)\ ^\circ\mathrm{C} = 7,054\ \mathrm{J}$$

Question 19

Which of the following best describes ionization energy?

Accepted Answer

The energy required to remove an electron from a gaseous atom.

Unit Exam 1 Study Guide: Introductory Chemistry Topics

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