Q: Which of the following is the correct scientific notation for the number 0.0004560, and how many significant figures does it have?

$$4.560 \times 10$$^{-4}$$; 4 significant figures

Q: A sample of a compound contains 12.0 g of carbon and 32.0 g of oxygen. What is the mass percent of carbon in the compound?

$$\frac{12.0}{12.0 + 32.0} \times 100\% = 27.3\%$$

Q: A 50.0 g sample of water is heated from $$25.0^\circ \mathrm{C} to$$ $$75.0^\circ \mathrm{C}. $$The specific heat capacity of water is $$4.18 \ \mathrm{J}/\mathrm{g} \cdot ^\circ \mathrm{C}. $$How much heat ($$q) is $$absorbed by the water?

$$q = m c \Delta T = 50.0 \times 4.18 \times (75.0 - 25.0) = 10,450 \ \mathrm{J}$$

Q: A student is asked to prepare 250.0 mL of a 0.100 M NaCl solution. How many grams of NaCl are required? (Molar mass of NaCl = 58.44 g/mol)

$$0.100 \ \mathrm{mol/L} \times 0.250 \ \mathrm{L} \times 58.44 \ \mathrm{g/mol} = 1.46 \ \mathrm{g}$$

Question 1

Which of the following best describes the difference between a scientific law and a scientific theory?

Accepted Answer

A scientific law describes a consistent relationship observed in nature, often expressed mathematically, while a scientific theory provides an explanation for why those relationships exist.

Question 2

A student measures the mass of a sample three times and records the values: 2.51 g, 2.50 g, and 2.52 g. The true mass is 2.70 g. Which statement best describes the student's measurements?

Accepted Answer

The measurements are precise but not accurate.

Question 3

Which of the following is the correct scientific notation for the number 0.0004560, and how many significant figures does it have?

Accepted Answer

$$4.560 	imes 10$$^{-4}$$; 4 significant figures

Question 4

A sample of a compound contains 12.0 g of carbon and 32.0 g of oxygen. What is the mass percent of carbon in the compound?

Accepted Answer

$$\frac{12.0}{12.0 + 32.0} 	imes 100\% = 27.3\%$$

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

A 50.0 g sample of water is heated from $$25.0^\circ \mathrm{C} to$$ $$75.0^\circ \mathrm{C}. $$The specific heat capacity of water is $$4.18 \ \mathrm{J}/\mathrm{g} \cdot ^\circ \mathrm{C}. $$How much heat ($$q) is $$absorbed by the water?

Accepted Answer

$$q = m c \Delta T = 50.0 	imes 4.18 	imes (75.0 - 25.0) = 10,450 \ \mathrm{J}$$

Question 7

Which of the following compounds is an example of a molecular compound?

Accepted Answer

CO$$_2$$

Question 8

A student is asked to prepare 250.0 mL of a 0.100 M NaCl solution. How many grams of NaCl are required? (Molar mass of NaCl = 58.44 g/mol)

Accepted Answer

$$0.100 \ \mathrm{mol/L} 	imes 0.250 \ \mathrm{L} 	imes 58.44 \ \mathrm{g/mol} = 1.46 \ \mathrm{g}$$

Question 9

Which of the following best explains why ionic compounds generally have higher melting points than molecular compounds?

Accepted Answer

Ionic compounds are held together by strong electrostatic forces between oppositely charged ions.

Question 10

A reaction has an equilibrium constant $$K_{eq} = 1.2 	imes 10^5$. What does this indicate about the position of equilibrium?

Accepted Answer

The reaction strongly favors the formation of products at equilibrium.

Question 11

Which of the following is the correct net ionic equation for the reaction between aqueous solutions of Na$$_2SO$_4$$ and BaCl$$_2$$?

Accepted Answer

$$\mathrm{Ba}^{2+} (aq) + \mathrm{SO}_4$$^{2-}$$ (aq) \rightarrow \mathrm{BaSO}_4 (s)$$

Question 12

Which of the following statements about acids and bases is correct according to the Bronsted-Lowry definition?

Accepted Answer

An acid is a proton donor and a base is a proton acceptor.

Question 13

A sample of gas occupies 2.00 L at 1.00 atm and $$25.0^\circ \mathrm{C}. $$What will be its volume at 0.500 atm and $$25.0^\circ \mathrm{C}$$, assuming the amount of gas remains constant?

Accepted Answer

$$V_2$$ = \frac{$$P_1$$ $$V_1$$}{$$P_2$$} = \frac{1.00 	imes 2.00}{0.500} = 4.00 \ \mathrm{L}$$

Question 14

Which of the following best describes the role of a catalyst in a chemical reaction?

Accepted Answer

A catalyst lowers the activation energy, increasing the reaction rate without being consumed.

Question 15

Which of the following molecules is expected to have a net dipole moment?

Accepted Answer

NH$$_3$$

Question 16

A radioactive isotope has a half-life of 3.0 days. If you start with a 40.0 g sample, how much remains after 9.0 days?

Accepted Answer

$$40.0 \ \mathrm{g} \rightarrow 20.0 \ \mathrm{g} \rightarrow 10.0 \ \mathrm{g} \rightarrow 5.0 \ \mathrm{g}$$

Question 17

Which of the following best explains why water has a higher boiling point than methane (CH$$_4$$)?

Accepted Answer

Water molecules form hydrogen bonds, which are stronger than the London dispersion forces in methane.

Question 18

A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 500.0 mL of solution. What is the molarity of the solution? (Molar mass of NaCl = 58.44 g/mol)

Accepted Answer

$$\frac{10.0}{58.44} = 0.171 \ \mathrm{mol}; \ M = \frac{0.171}{0.500} = 0.342 \ \mathrm{M}$$

General Chemistry Curriculum Map: Structured Study Guide

Guida di studio - Domande di pratica

Study guide - Flashcard