Q: How many atoms are present in $$18.0\ \mathrm{g} of $$water ($$\mathrm{H}_2\mathrm{O}$$)? (Molar mass of $$\mathrm{H}_2\mathrm{O} = 18.0\ \mathrm{g/mol})$$

$$1.81 \times 10$$^{24}$$ atoms

Question 1

A sample of a compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula of this compound?

Accepted Answer

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

Question 2

Which of the following best describes a homogeneous mixture?

Accepted Answer

A mixture in which the composition is uniform throughout, such as salt water.

Question 3

A student measures the mass of a metal sample as $$12.34\ \mathrm{g}$$ and its volume as $$4.56\ \mathrm{cm}^3. $$What is the density of the metal, reported with the correct number of significant figures?

Accepted Answer

$$2.7\ \mathrm{g/cm}^3$$

Question 4

Which of the following statements about the Rutherford gold foil experiment is correct?

Accepted Answer

It showed that atoms are mostly empty space with a small, dense, positively charged nucleus.

Question 5

Which separation technique would be most effective for separating a mixture of sand and salt water?

Accepted Answer

Filtration

Question 6

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of water. How many moles of water does this represent?

Accepted Answer

$$0.500\ \mathrm{mol}$$

Question 7

Which of the following is a chemical change?

Accepted Answer

Burning wood

Question 8

Which group on the periodic table contains elements that are all gases at room temperature and are chemically inert?

Accepted Answer

Noble gases (Group 8A)

Question 9

A neutral atom of chlorine has an atomic number of 17 and a mass number of 35. How many neutrons does it have?

Accepted Answer

18

Question 10

Which of the following best describes the Law of Constant Composition?

Accepted Answer

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

Question 11

Which of the following is the correct name for $$\mathrm{Na}_2\mathrm{SO}_4$$?

Accepted Answer

Sodium sulfate

Question 12

A student needs to convert $$25.0\ ^\circ\mathrm{C} to $$Kelvin. What is the correct temperature in Kelvin?

Accepted Answer

$$298\ \mathrm{K}$$

Question 13

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 14

Which of the following best describes a cation?

Accepted Answer

An atom that has lost one or more electrons and has a positive charge.

Question 15

A sample of magnesium reacts with oxygen to form magnesium oxide. If $$24.3\ \mathrm{g} of $$magnesium reacts completely with $$16.0\ \mathrm{g} of $$oxygen, what is the percent composition by mass of magnesium in magnesium oxide?

Accepted Answer

$$60.3\%$$

Question 16

Which of the following is a binary acid?

Accepted Answer

Hydrochloric acid ($$\mathrm{HCl})$$

Question 17

Which of the following best explains why metals are good conductors of electricity?

Accepted Answer

They have delocalized electrons that can move freely throughout the structure.

Question 18

How many atoms are present in $$18.0\ \mathrm{g} of $$water ($$\mathrm{H}_2\mathrm{O}$$)? (Molar mass of $$\mathrm{H}_2\mathrm{O} = 18.0\ \mathrm{g/mol})$$

Accepted Answer

$$1.81 	imes 10$$^{24}$$ atoms

Question 19

Which of the following is the correct electron configuration for a neutral atom of sodium ($$Z=11$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^1$$

Question 20

Which of the following best describes the difference between a physical and a chemical property?

Accepted Answer

A physical property can be observed without changing the substance's identity, while a chemical property describes the substance's ability to undergo a specific chemical change.

General Chemistry Study Guide: Matter, Atomic Theory, and Chemical Compounds

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