Q: A solution has a pH of 3.0. What is the hydronium ion concentration $$[\mathrm{H_3O^+}]$$?

$$1.0 \times 10$$^{-3}$$\ \mathrm{M}$$

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 2.80 g. Which statement best describes the measurements?

Accepted Answer

The measurements are precise but not accurate.

Question 3

Which of the following is the correct way to express 0.0004560 in scientific notation, including the correct number of significant figures?

Accepted Answer

$$4.560 	imes 10$$^{-4}$$

Question 4

A sample of a metal has a mass of 13.5 g and a volume of 1.50 cm$$^3. $$What is its density?

Accepted Answer

$$9.00\ \mathrm{g/cm^3$}$$

Question 5

Which of the following best describes an endothermic process?

Accepted Answer

A process in which the system absorbs heat from the surroundings.

Question 6

A chemical reaction absorbs 150 J of heat and does 50 J of work on the surroundings. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = 100\ \mathrm{J}$$

Question 7

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 8

A neutral atom of magnesium has an atomic number of 12 and a mass number of 24. How many neutrons does it have?

Accepted Answer

12

Question 9

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

Accepted Answer

CO$$_2$$

Question 10

How many oxygen atoms are present in 2.00 moles of H$$_2SO$_4$$?

Accepted Answer

$$4.82 	imes 10$$^{24}$$

Question 11

A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

Accepted Answer

CH$$_2O$$

Question 12

Which of the following is a balanced equation for the combustion of methane ($$\mathrm{CH_4$}) in $$oxygen?

Accepted Answer

$$\mathrm{CH_4$} + 2\mathrm{O_2$} \rightarrow \mathrm{CO_2$} + 2\mathrm{H_2O}$$

Question 13

Which of the following best explains why water (H$$_2O) $$has a higher boiling point than methane (CH$$_4$$)?

Accepted Answer

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

Question 14

A 0.250 L sample of gas at 1.00 atm and 273 K contains how many moles of gas? (Use $$R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$0.0112\ \mathrm{mol}$$

Question 15

Which of the following statements about solutions is correct?

Accepted Answer

A solution is a homogeneous mixture of two or more substances.

Question 16

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

Accepted Answer

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

Question 17

For the reaction $$\mathrm{N_2$}(g) + 3\mathrm{H_2$}(g) \rightleftharpoons 2\mathrm{NH_3$}(g)$$, which of the following is the correct expression for the equilibrium constant $$K_{eq}$$?

Accepted Answer

$$K_{eq} = \dfrac{[\mathrm{NH_3$}]^2}{[\mathrm{N_2$}][\mathrm{H_2$}]^3}$$

Question 18

A solution has a pH of 3.0. What is the hydronium ion concentration $$[\mathrm{H_3O^+}]$$?

Accepted Answer

$$1.0 	imes 10$$^{-3}$$\ \mathrm{M}$$

Question 19

Which of the following types of radiation has the greatest penetrating power?

Accepted Answer

Gamma rays

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