Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$$\text{Average Atomic Mass} = (\text{Fraction}_1 \times \text{Mass}_1) + (\text{Fraction}_2 \times \text{Mass}_2)$$

Q: A student is asked to calculate the number of moles in $$18.0\ \mathrm{g} of $$water ($$\mathrm{H}_2\mathrm{O}). $$Which equation should they use?

$$\text{Moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$$

Question 1

Which of the following best distinguishes a chemical change from a physical change?

Accepted Answer

A chemical change results in the formation of new substances with different chemical properties, while a physical change does not alter the chemical identity of a substance.

Question 2

A sample of water is heated from $$25\ ^\circ\mathrm{C} to$$ $$75\ ^\circ\mathrm{C}. $$Which of the following equations correctly converts the final temperature to Kelvin?

Accepted Answer

$$K = 75 + 273$$

Question 3

Which of the following is an example of an intensive property?

Accepted Answer

Density

Question 4

A student measures the mass of a metal sample as $$12.34\ \mathrm{g}$$ and the volume as $$4.1\ \mathrm{mL}. $$What is the density of the metal, reported with the correct number of significant figures?

Accepted Answer

$$3.0\ \mathrm{g/mL}$$

Question 5

Which of the following correctly describes the difference between an atom and an ion?

Accepted Answer

An ion has a different number of electrons than protons, resulting in a net charge, while an atom has equal numbers of protons and electrons.

Question 6

Which of the following elements is a noble gas?

Accepted Answer

Neon ($$\mathrm{Ne})$$

Question 7

A compound contains $$40.0\%$$ carbon, $$6.7\%$$ hydrogen, and $$53.3\%$$ oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

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

Question 8

Which of the following best describes the law of conservation of mass?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 9

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Average Atomic Mass} = (	ext{Fraction}_1 	imes 	ext{Mass}_1) + (	ext{Fraction}_2 	imes 	ext{Mass}_2)$$

Question 10

A patient receives a dose of $$250\ \mathrm{mg} of a $$medication. How many grams is this?

Accepted Answer

$$0.25\ \mathrm{g}$$

Question 11

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 12

Which of the following is the correct formula for density?

Accepted Answer

$$d = \frac{m}{V}$$

Question 13

A sample of gas occupies $$2.50\ \mathrm{L} at$$ $$25\ ^\circ\mathrm{C}. $$What is the volume in milliliters?

Accepted Answer

$$2500\ \mathrm{mL}$$

Question 14

Which of the following best describes a cation?

Accepted Answer

An ion with more protons than electrons, resulting in a positive charge.

Question 15

Which of the following is the correct way to report the result of $$4.56 	imes 1.4$$ using the rules for significant figures?

Accepted Answer

$$6.4$$

Question 16

A student is asked to calculate the number of moles in $$18.0\ \mathrm{g} of $$water ($$\mathrm{H}_2\mathrm{O}). $$Which equation should they use?

Accepted Answer

$$	ext{Moles} = \frac{	ext{mass (g)}}{	ext{molar mass (g/mol)}}$$

Question 17

Which of the following is the correct empirical formula for a compound with a molar ratio of $$2$$ moles of nitrogen to $$3$$ moles of oxygen?

Accepted Answer

$$\mathrm{N}_2\mathrm{O}_3$$

Question 18

Which of the following best describes the difference between mass number and atomic number?

Accepted Answer

Mass number is the sum of protons and neutrons, while atomic number is the number of protons.

Question 19

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of carbon dioxide. How many moles of carbon dioxide are present?

Accepted Answer

$$0.5$$ moles

Question 20

Which of the following is the correct formula for converting Celsius to Kelvin?

Accepted Answer

$$K = ^\circ\mathrm{C} + 273$$

General Chemistry I: Study Guide and Objectives Overview

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