Q: How many atoms are present in $$0.25$$ mol of neon gas?

$$3.01 \times 10$$^{23}$$ atoms

Question 1

A sample of a compound is analyzed and found to contain 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 the difference between a physical and a chemical change? Select the correct example.

Accepted Answer

Burning wood is a chemical change because new substances are produced.

Question 3

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 2.00 g. Which statement best describes the accuracy and precision of the measurements?

Accepted Answer

The measurements are precise but not accurate.

Question 4

Which experiment provided evidence for the existence of the nucleus in the atom?

Accepted Answer

Rutherford's gold foil experiment

Question 5

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

Accepted Answer

$$0.500$$ mol

Question 6

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 7

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

Accepted Answer

Filtration

Question 8

A compound contains only sodium and chlorine. If a sample contains $$4.60 g of $$sodium and $$7.10 g of $$chlorine, what is the empirical formula?

Accepted Answer

$$\mathrm{NaCl}$$

Question 9

Which of the following is a correct nuclide symbol for an isotope of carbon with 7 neutrons?

Accepted Answer

$$^{13}_{6}\mathrm{C}$$

Question 10

Which of the following elements is a metalloid?

Accepted Answer

Silicon ($$\mathrm{Si})$$

Question 11

What is the mass percent of oxygen in $$\mathrm{H}_2\mathrm{O}$$? (Atomic masses: H = 1.01, O = 16.00)

Accepted Answer

$$88.8\%$$

Question 12

Which of the following compounds is an ionic compound?

Accepted Answer

$$\mathrm{Na}_2\mathrm{O}$$

Question 13

A mass spectrum of an element shows two peaks at mass numbers 63 and 65 with relative abundances of 69% and 31%, respectively. What is the average atomic mass of the element?

Accepted Answer

$$64.0$$ amu

Question 14

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

Accepted Answer

Iron(III) oxide

Question 15

How many atoms are present in $$0.25$$ mol of neon gas?

Accepted Answer

$$3.01 	imes 10$$^{23}$$ atoms

Question 16

Which of the following is a correct example of a homonuclear diatomic element?

Accepted Answer

$$\mathrm{O}_2$$

Question 17

A student needs to prepare $$250.0 mL of a$$ $$0.100 M$$ $$\mathrm{NaCl}$$ solution. How many grams of $$\mathrm{NaCl}$$ are required? (Molar mass of $$\mathrm{NaCl}$$ = $$58.44 g/$$mol)

Accepted Answer

$$1.46 g$$

Question 18

Which of the following is the correct formula for dinitrogen pentoxide?

Accepted Answer

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

Question 19

Which of the following is a property of metals?

Accepted Answer

They are good conductors of electricity.

Question 20

Which of the following is an organic compound?

Accepted Answer

$$\mathrm{CH}_4$$

Study Guide: Matter, Atoms, and Molecules (Chapters 1–3, CHEM 134)

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