Q: A compound contains 40 g of element A and 60 g of element B. What is the percent composition of element A?

$$\frac{40}{40+60} \times 100\% = 40\%$$

Q: What is the molar mass of water ($$\mathrm{H}_2\mathrm{O}$$)?

$$2 \times 1.01\ \mathrm{g/mol} + 16.00\ \mathrm{g/mol} = 18.02\ \mathrm{g/mol}$$

Q: A gas occupies a volume of 2.0 L at a pressure of 1.0 atm and temperature of 273 K. Using the ideal gas law $$PV = nRT$$, how many moles of gas are present? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

$$n = \frac{PV}{RT} = \frac{1.0 \times 2.0}{0.0821 \times 273} \approx 0.089\ \mathrm{mol}$$

Q: A solution is prepared by dissolving 5.0 g of NaCl in enough water to make 250 mL of solution. What is the molarity of the solution? ($$\mathrm{NaCl}$$ molar mass = $$58.44\ \mathrm{g/mol})$$

$$M = \frac{\text{moles of solute}}{\text{liters of solution}} = \frac{5.0/58.44}{0.250} \approx 0.34\ \mathrm{M}$$

Question 1

Which of the following best describes a homogeneous mixture?

Accepted Answer

A mixture in which the composition is uniform throughout, such as saltwater.

Question 2

A student measures the mass of a sample as 12.5 g and its volume as 5.0 mL. What is the density of the sample?

Accepted Answer

$$\frac{12.5\ \mathrm{g}}{5.0\ \mathrm{mL}} = 2.5\ \mathrm{g/mL}$$

Question 3

Which statement about covalent bonds is correct?

Accepted Answer

Covalent bonds involve the sharing of electrons between nonmetals.

Question 4

What is the correct chemical formula for carbon dioxide?

Accepted Answer

$$\mathrm{CO}_2$$

Question 5

Which of the following is a physical change?

Accepted Answer

Boiling water to produce steam.

Question 6

A compound contains 40 g of element A and 60 g of element B. What is the percent composition of element A?

Accepted Answer

$$\frac{40}{40+60} 	imes 100\% = 40\%$$

Question 7

Which of the following is NOT a type of chemical reaction?

Accepted Answer

Evaporation

Question 8

What is the molar mass of water ($$\mathrm{H}_2\mathrm{O}$$)?

Accepted Answer

$$2 	imes 1.01\ \mathrm{g/mol} + 16.00\ \mathrm{g/mol} = 18.02\ \mathrm{g/mol}$$

Question 9

Which of the following best describes an acid according to the study materials?

Accepted Answer

An acid produces $$\mathrm{H}^+$$ ions in water.

Question 10

A gas occupies a volume of 2.0 L at a pressure of 1.0 atm and temperature of 273 K. Using the ideal gas law $$PV = nRT$$, how many moles of gas are present? ($$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$n = \frac{PV}{RT} = \frac{1.0 	imes 2.0}{0.0821 	imes 273} \approx 0.089\ \mathrm{mol}$$

Question 11

Which statement about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties.

Question 12

Which of the following is a correct example of a chemical symbol and its element?

Accepted Answer

Na for sodium

Question 13

A solution is prepared by dissolving 5.0 g of NaCl in enough water to make 250 mL of solution. What is the molarity of the solution? ($$\mathrm{NaCl}$$ molar mass = $$58.44\ \mathrm{g/mol})$$

Accepted Answer

$$M = \frac{	ext{moles of solute}}{	ext{liters of solution}} = \frac{5.0/58.44}{0.250} \approx 0.34\ \mathrm{M}$$

Question 14

Which of the following is a correct balanced chemical equation for the reaction of hydrogen and oxygen to form water?

Accepted Answer

$$2\mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2\mathrm{H}_2\mathrm{O}$$

Question 15

Which of the following is a property of a solid?

Accepted Answer

Definite shape and definite volume.

Question 16

Which of the following is a correct statement about limiting reactants?

Accepted Answer

The limiting reactant is the reactant that is completely consumed first in a chemical reaction.

Question 17

Which of the following is the correct formula for calculating pH?

Accepted Answer

$$\mathrm{pH} = -\log[\mathrm{H}^+]$$

Question 18

Which of the following is a safety precaution that should always be followed in a chemistry laboratory?

Accepted Answer

Always follow proper lab safety precautions.

Question 19

Which of the following is a correct statement about ions?

Accepted Answer

Ions are atoms or groups of atoms that have gained or lost electrons.

Introduction to Chemistry: Matter, Atoms, Measurement, Chemical Bonding, and Reactions

Guida di studio - Domande di pratica

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