Q: How many particles are present in one mole of any substance, and what is this number called?

$$6.02 \times 10$$^{23}$$ particles; this is Avogadro's number.

Question 1

When sodium reacts to form an ion, which of the following best explains the process in terms of electron configuration and periodic trends?

Accepted Answer

It loses one electron to achieve the electron configuration of neon, a noble gas.

Question 2

A patient is given potassium iodide (KI) as a supplement. When iodine forms its ion in this compound, what is its charge and how does it achieve this?

Accepted Answer

Iodine gains one electron to form a $$\mathrm{I^-}$$ ion.

Question 3

Which of the following is the correct chemical formula for iron(III) sulfide, and what does the Roman numeral indicate?

Accepted Answer

$$\mathrm{Fe_2S_3}$$; the Roman numeral indicates iron has a $$+3$$ charge.

Question 4

Which of the following best describes a polyatomic ion?

Accepted Answer

A group of covalently bonded atoms with an overall charge.

Question 5

What is the correct name for the compound $$\mathrm{Fe_2$(SO_4$)_3}$$, and why?

Accepted Answer

Iron(III) sulfate, because iron has a $$+3$$ charge and sulfate is $$\mathrm{SO_4$^{2-}}.$$

Question 6

Which of the following compounds contains an ionic bond, and what is the main evidence for this?

Accepted Answer

$$\mathrm{CaO}$$; it is formed from a metal and a nonmetal.

Question 7

The shape of a water molecule ($$\mathrm{H_2O}) is $$best described as:

Accepted Answer

Bent (109°), due to two lone pairs on the oxygen atom.

Question 8

Which type of intermolecular force is primarily responsible for the high boiling point of ammonia ($$\mathrm{NH_3$}$$)?

Accepted Answer

Hydrogen bonding, due to the N-H bonds.

Question 9

How many particles are present in one mole of any substance, and what is this number called?

Accepted Answer

$$6.02 	imes 10$$^{23}$$ particles; this is Avogadro's number.

Question 10

How many moles of carbon atoms are present in $$0.500$$ mole of $$\mathrm{C_2H_6}$$?

Accepted Answer

$$1.00$$ mole, because each molecule contains two carbon atoms.

Question 11

A patient receives an IV containing $$75.0 g of $$water. How many moles of water is this? ($$\mathrm{H_2O}$$ molar mass = $$18.0 g/$$mol)

Accepted Answer

$$4.16$$ moles, calculated as $$\frac{75.0}{18.0}.$$

Question 12

How many grams of glucose ($$\mathrm{C_6H_{12}O_6$}$$, molar mass $$= 180 g/$$mol) are in $$3.55$$ moles of glucose?

Accepted Answer

$$640 g$$, calculated as $$3.55 	imes 180.$$

Question 13

Given the reaction $$2\mathrm{Al} + 6\mathrm{HCl} \rightarrow 3\mathrm{H_2$} + 2\mathrm{$$AlCl_3$$}$$, how many moles of HCl are required to react with $$0.345$$ mole of Al?

Accepted Answer

$$1.04$$ moles, using the ratio $$0.345 	imes \frac{6}{2}.$$

Question 14

In the combustion of methane: $$\mathrm{CH_4$} + 2\mathrm{O_2$} \rightarrow \mathrm{CO_2$} + 2\mathrm{H_2O}$$, how many grams of $$\mathrm{CO_2$}$$ are produced from $$125 g of$$ $$\mathrm{O_2$}$$ and excess $$\mathrm{CH_4$}$$? ($$\mathrm{O_2$}$$ molar mass $$= 32 g/$$mol, $$\mathrm{CO_2$}$$ molar mass $$= 44 g/$$mol)

Accepted Answer

$$85.9 g$$, calculated using stoichiometry.

Question 15

A gas sample has an initial volume of $$380 mL at$$ $$20.0\ ^\circ\mathrm{C}. If $$the temperature increases to $$120.0\ ^\circ\mathrm{C} at $$constant pressure, what is the final volume? (Use $$V_1$$/$$T_1$$ = $$V_2$$/$$T_2$$, temperatures in Kelvin)

Accepted Answer

$$590 mL$$, using $$V_2$$ = $$V_1$$ 	imes \frac{$$T_2$$}{$$T_1$$}$$.

Question 16

A sample of nitrogen gas has a volume of $$500 mL at$$ $$740$$ torr and $$25\ ^\circ\mathrm{C}. $$What is the new volume if the temperature increases to $$50\ ^\circ\mathrm{C}$$ and the pressure increases to $$760$$ torr? (Use the combined gas law: $$\frac{P_1V_1}{T_1$} = \frac{P_2V_2}{T_2$})$$

Accepted Answer

$$530 mL$$, calculated using the combined gas law.

Question 17

A gas sample contains $$4.0 g of$$ $$\mathrm{CH_4$}$$ and $$2.0 g of He. $$What is the total volume at STP? ($$\mathrm{CH_4$}$$ molar mass $$= 16 g/$$mol, He molar mass $$= 4 g/$$mol, $$1$$ mole gas at STP $$= 22.4 L)$$

Accepted Answer

$$17 L$$, calculated as $$(0.25 + 0.5)$$ moles $$	imes 22.4 L.$$

Question 18

An oxygen sample with a mass of $$8.0 g $$has a volume of $$2.6 L. If$$ $$10 g of $$neon is added at constant pressure and temperature, what is the new total volume? ($$\mathrm{O_2$}$$ molar mass $$= 32 g/$$mol, Ne molar mass $$= 20 g/$$mol, $$1$$ mole gas at STP $$= 22.4 L)$$

Accepted Answer

$$7.8 L$$, calculated by adding the volumes of both gases.

Question 19

A gas at $$5.00$$ atm pressure is stored at $$5.0\ ^\circ\mathrm{C}. If $$the temperature increases to $$40.0\ ^\circ\mathrm{C} at $$constant volume, what is the new pressure? (Use $$P_1$$/$$T_1$$ = $$P_2$$/$$T_2$$, temperatures in Kelvin)

Accepted Answer

$$5.63$$ atm, calculated using the gas law.

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