Q: How many atoms are present in $$2.00\ \mathrm{mol} of $$sodium ($$\mathrm{Na}$$)?

$$1.20 \times 10$$^{24}$$ atoms

Q: A $$0.250\ \mathrm{mol}$$ sample of $$\mathrm{CO}_2$$ contains how many molecules?

$$1.51 \times 10$$^{23}$$ molecules

Question 1

Which of the following statements best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 2

A sample contains two isotopes of bromine: $$^{79}\mathrm{Br} ($$abundance 50.7%, mass = 78.918 amu) and $$^{81}\mathrm{Br} ($$abundance 49.3%, mass = 80.916 amu). What is the average atomic mass of bromine?

Accepted Answer

$$79.92\ \mathrm{amu}$$

Question 3

Which of the following best explains why the periodic table is organized by increasing atomic number rather than atomic mass?

Accepted Answer

Atomic number determines the number of protons, which defines the element.

Question 4

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

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 5

Which of the following is a correct statement about metals and nonmetals?

Accepted Answer

Metals are generally good conductors of electricity, while nonmetals are poor conductors.

Question 6

A sample of glucose ($$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6) $$has a mass of $$180.16\ \mathrm{g}. $$How many moles of glucose are present?

Accepted Answer

$$1.00\ \mathrm{mol}$$

Question 7

Which of the following best describes the law of definite proportions?

Accepted Answer

A chemical compound always contains the same proportion of elements by mass.

Question 8

How many atoms are present in $$2.00\ \mathrm{mol} of $$sodium ($$\mathrm{Na}$$)?

Accepted Answer

$$1.20 	imes 10$$^{24}$$ atoms

Question 9

A student determines that a $$5.00\ \mathrm{g}$$ sample of magnesium reacts with oxygen to form $$8.30\ \mathrm{g} of $$magnesium oxide. What mass of oxygen reacted?

Accepted Answer

$$3.30\ \mathrm{g}$$

Question 10

Which of the following is the correct formula for aluminum sulfate?

Accepted Answer

$$\mathrm{Al}_2(\mathrm{SO}_4)_3$$

Question 11

A $$0.250\ \mathrm{mol}$$ sample of $$\mathrm{CO}_2$$ contains how many molecules?

Accepted Answer

$$1.51 	imes 10$$^{23}$$ molecules

Question 12

Which of the following is a property of ionic compounds?

Accepted Answer

They conduct electricity when dissolved in water.

Question 13

A compound is found to contain 27.3% carbon and 72.7% oxygen by mass. What is the empirical formula?

Accepted Answer

$$\mathrm{CO}_2$$

Question 14

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed by the sharing of electrons between two nonmetals.

Question 15

How many grams of $$\mathrm{NaCl}$$ are present in $$0.500\ \mathrm{mol}$$?

Accepted Answer

$$29.2\ \mathrm{g}$$

Question 16

Which of the following is the correct name for $$\mathrm{Fe}_2\mathrm{O}_3$$?

Accepted Answer

Iron(III) oxide

Question 17

A $$10.0\ \mathrm{g}$$ sample of a compound contains $$2.68\ \mathrm{g} of $$nitrogen and $$7.32\ \mathrm{g} of $$oxygen. What is the empirical formula?

Accepted Answer

$$\mathrm{N}_2\mathrm{O}_5$$

Question 18

Which of the following statements about Avogadro's number is correct?

Accepted Answer

It is the number of particles in one mole of a substance.

Question 19

Which of the following is the correct formula for calcium phosphate?

Accepted Answer

$$\mathrm{Ca}_3(\mathrm{PO}_4)_2$$

Question 20

A $$0.100\ \mathrm{mol}$$ sample of $$\mathrm{H}_2\mathrm{O}$$ contains how many molecules?

Accepted Answer

$$6.02 	imes 10$$^{22}$$ molecules

Atoms, Elements, Isotopes, and Chemical Quantities: Study Notes

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