Q: Which of the following statements about the mole is correct?

One mole of any substance contains $$6.022 \times 10$$^{23}$$ representative particles.

Question 1

Which of the following best describes the scientific method as used in modern chemistry?

Accepted Answer

A systematic approach involving observation, hypothesis formation, experimentation, and revision of hypotheses based on experimental results.

Question 2

A student measures the mass of a sample three times and records the values: 5.12 g, 5.13 g, and 5.11 g. The true mass is 5.50 g. Which statement best describes the accuracy and precision of these measurements?

Accepted Answer

The measurements are precise but not accurate.

Question 3

Which of the following statements about the mole is correct?

Accepted Answer

One mole of any substance contains $$6.022 	imes 10$$^{23}$$ representative particles.

Question 4

Which of the following best explains why sodium (Na) reacts vigorously with water, while magnesium (Mg) reacts much less so?

Accepted Answer

Sodium has a lower ionization energy than magnesium, making it easier to lose its outer electron.

Question 5

A sample of methane ($$\mathrm{CH_4$}) is $$combusted in excess oxygen. Which of the following balanced equations correctly represents this reaction?

Accepted Answer

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

Question 6

Which of the following aqueous compounds is most likely to be insoluble in water?

Accepted Answer

$$\mathrm{AgCl}$$

Question 7

A balloon contains $$2.00 L of $$helium gas at $$1.00$$ atm and $$300 K. If $$the temperature increases to $$600 K at $$constant pressure, what will be the new volume of the balloon?

Accepted Answer

$$4.00 L$$

Question 8

Which of the following is a redox reaction?

Accepted Answer

$$\mathrm{2Na} + \mathrm{Cl_2$} \rightarrow 2\mathrm{NaCl}$$

Question 9

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

Accepted Answer

Atomic radius decreases due to increasing effective nuclear charge.

Question 10

A $$10.0 g $$sample of calcium carbonate ($$\mathrm{$$CaCO_3$$}) is $$heated and decomposes according to the equation $$\mathrm{$$CaCO_3$$} \rightarrow \mathrm{CaO} + \mathrm{CO_2$}. $$What is the theoretical yield of $$\mathrm{CO_2$} (in $$grams)? (Molar masses: $$\mathrm{$$CaCO_3$$} = 100.1 g/$$mol, $$\mathrm{CO_2$} = 44.0 g/$$mol)

Accepted Answer

$$4.40 g$$

Question 11

Which of the following statements about the quantum-mechanical model of the atom is correct?

Accepted Answer

Electrons occupy orbitals, which are regions of space where there is a high probability of finding an electron.

Question 12

Which of the following is the correct Lewis structure for carbon dioxide ($$\mathrm{CO_2$}$$)?

Accepted Answer

O=C=O, with each O atom having two lone pairs

Question 13

Which of the following best explains why water ($$\mathrm{H_2O}) $$has a bent molecular shape?

Accepted Answer

The two lone pairs on oxygen repel the bonding pairs, resulting in a bent shape.

Question 14

A $$50.0 mL $$sample of $$0.200 M$$ $$\mathrm{HCl} is $$mixed with $$50.0 mL of$$ $$0.200 M$$ $$\mathrm{NaOH}. $$What is the resulting solution?

Accepted Answer

A neutral solution of $$\mathrm{NaCl}$$ and water

Question 15

Which of the following best describes the energy change in an exothermic chemical reaction?

Accepted Answer

Energy is released to the surroundings, and the enthalpy change $$\Delta H is $$negative.

Question 16

Which of the following is the correct electron configuration for a neutral atom of nitrogen ($$Z=7$$)?

Accepted Answer

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

Question 17

A real gas deviates most from ideal behavior under which conditions?

Accepted Answer

Low temperature and high pressure

Question 18

Which of the following is a correct application of the law of conservation of mass in a chemical reaction?

Accepted Answer

The total mass of reactants equals the total mass of products.

Question 19

Which of the following best explains why noble gases are generally unreactive?

Accepted Answer

They have a complete valence electron shell.

Question 20

A $$0.500$$ mol sample of $$\mathrm{O_2$}$$ gas is confined in a $$10.0 L $$container at $$300 K. $$What is the pressure of the gas? $$(R = 0.0821\ \mathrm{L\cdot atm\cdot $$mol^{-1}$$\cdot K$$^{-1}$$})$$

Accepted Answer

$$1.23$$ atm

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