Q: A sample of a compound contains 12.0 g of carbon and 32.0 g of oxygen. What is the mass percent of oxygen in the compound?

$$\frac{32.0}{12.0+32.0} \times 100 = 72.7\%$$

Question 1

Which of the following statements best describes the difference between a hypothesis and a scientific theory?

Accepted Answer

A hypothesis is a tentative explanation that can be tested, while a theory is a well-substantiated explanation based on a body of evidence.

Question 2

A sample of a compound contains 12.0 g of carbon and 32.0 g of oxygen. What is the mass percent of oxygen in the compound?

Accepted Answer

$$\frac{32.0}{12.0+32.0} 	imes 100 = 72.7\%$$

Question 3

Which of the following is an example of a physical change?

Accepted Answer

Ice melting to form liquid water.

Question 4

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 data?

Accepted Answer

The data are precise but not accurate.

Question 5

Which separation technique would be most appropriate to separate a mixture of sand and salt water?

Accepted Answer

Filtration

Question 6

Which of the following best illustrates the Law of Definite Proportions?

Accepted Answer

Water from any source always contains hydrogen and oxygen in a 2:1 ratio by atoms.

Question 7

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of CO_2$. How many moles of CO_2$ are present?

Accepted Answer

$$0.500$$ mol

Question 8

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 9

Which experiment provided evidence for the existence of the atomic nucleus?

Accepted Answer

Rutherford’s gold foil experiment

Question 10

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

$$24 - 12 = 12$$ neutrons

Question 11

Which of the following is a molecular element?

Accepted Answer

O$$_2$$

Question 12

Which of the following compounds is named correctly?

Accepted Answer

FeCl$$_3 is $$iron(III) chloride

Question 13

A 5.00 g sample of a metal displaces 0.50 mL of water. What is the density of the metal?

Accepted Answer

$$\frac{5.00\ \mathrm{g}}{0.50\ \mathrm{mL}} = 10.0\ \mathrm{g/mL}$$

Question 14

Which of the following best describes the difference between an ionic and a covalent compound?

Accepted Answer

Ionic compounds are formed from metals and nonmetals, while covalent compounds are formed from nonmetals only.

Question 15

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

Accepted Answer

CH$$_2O$$

Question 16

Which of the following is an extensive property?

Accepted Answer

Mass

Question 17

A student needs to convert 250.0 milligrams to grams. What is the correct conversion?

Accepted Answer

$$250.0\ \mathrm{mg} 	imes \frac{1\ \mathrm{g}}{1000\ \mathrm{mg}} = 0.250\ \mathrm{g}$$

Question 18

Which of the following best explains why water (H$$_2O) $$extinguishes flames, while hydrogen and oxygen gases are flammable or support combustion?

Accepted Answer

The chemical combination of hydrogen and oxygen in water results in a substance with very different chemical properties from its elements.

Question 19

A sample of neon contains 90.48% $$^{20}Ne ($$mass = 19.992 amu), 0.27% $$^{21}Ne ($$mass = 20.994 amu), and 9.25% $$^{22}Ne ($$mass = 21.991 amu). What is the average atomic mass of neon?

Accepted Answer

$$(0.9048 	imes 19.992) + (0.0027 	imes 20.994) + (0.0925 	imes 21.991) = 20.18\ \mathrm{amu}$$

Question 20

Which of the following best describes the process of mass spectrometry?

Accepted Answer

Ionized particles are separated based on their mass-to-charge ratio and detected to determine isotopic abundance.

General Chemistry I: Study Guide for Chapters 1–3

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