$$2.00 \times 6.022 \times 10$$^{23}$$ = 1.2044 \times 10$$^{24}$$ molecules

$$12.01\ \mathrm{g/mol} + 2 \times 16.00\ \mathrm{g/mol} = 44.01\ \mathrm{g/mol}$$

$$\frac{2 \times 1.008}{18.016} \times 100\% = 11.19\%$$

$$\text{Percent by mass of element} = \frac{(n \times \text{molar mass of element})}{\text{molar mass of compound}} \times 100\%$$

Question 1

Which of the following is the correct SI base unit for temperature?

Accepted Answer

Kelvin (K)

Question 2

A sample has a mass of 0.00560 kg. How many significant figures are in this measurement?

Accepted Answer

4

Question 3

Which metric prefix represents one billionth $$(1 	imes 10$$^{-9}$$)$$?

Accepted Answer

nano-

Question 4

Convert a temperature of $$25\ ^\circ\mathrm{C} to $$Kelvin using the correct formula.

Accepted Answer

$$K = 25 + 273 = 298\ \mathrm{K}$$

Question 5

Which of the following numbers is correctly written in scientific notation?

Accepted Answer

$$6.5 	imes 10$$^{3}$$

Question 6

How many molecules are present in $$2.00$$ moles of water $$(\mathrm{H}_2\mathrm{O})$$?

Accepted Answer

$$2.00 	imes 6.022 	imes 10$$^{23}$$ = 1.2044 	imes 10$$^{24}$$ molecules

Question 7

What is the molar mass of $$\mathrm{CO}_2$$?

Accepted Answer

$$12.01\ \mathrm{g/mol} + 2 	imes 16.00\ \mathrm{g/mol} = 44.01\ \mathrm{g/mol}$$

Question 8

A 250 g sample of $$\mathrm{NaCl} is $$given. What is the number of moles present? (Molar mass of $$\mathrm{NaCl} = 58.44\ \mathrm{g/mol})$$

Accepted Answer

$$\frac{250}{58.44} = 4.28$$ moles

Question 9

What is the mass percent of hydrogen in $$\mathrm{H}_2\mathrm{O}$$? (Molar mass: H = $$1.008\ \mathrm{g/mol}$$, O = $$16.00\ \mathrm{g/mol})$$

Accepted Answer

$$\frac{2 	imes 1.008}{18.016} 	imes 100\% = 11.19\%$$

Question 10

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 11

If the empirical formula of a compound is $$\mathrm{CH}_2$$ and its molar mass is $$56\ \mathrm{g/mol}$$, what is its molecular formula?

Accepted Answer

$$\mathrm{C}_4\mathrm{H}_8$$

Question 12

Which statement about Lewis structures is correct?

Accepted Answer

Atoms achieve stability by having eight electrons in their valence shell, except hydrogen which only needs two.

Question 13

Which of the following is an exception to the octet rule?

Accepted Answer

Phosphorus pentachloride ($$\mathrm{PCl}_5) $$can have more than eight electrons around phosphorus.

Question 14

How many valence electrons are present in a molecule of $$\mathrm{NH}_3$$?

Accepted Answer

10

Question 15

Which of the following best describes the process for determining the number of atoms in a sample using mass and molar mass?

Accepted Answer

Divide the mass of the sample by the molar mass to get moles, then multiply by Avogadro's number.

Question 16

A molecule of $$\mathrm{C}_2\mathrm{H}_6$$ contains how many hydrogen atoms?

Accepted Answer

6

Question 17

Which of the following is the correct formula for calculating mass percent composition?

Accepted Answer

$$	ext{Percent by mass of element} = \frac{(n 	imes 	ext{molar mass of element})}{	ext{molar mass of compound}} 	imes 100\%$$

Question 18

Which step is NOT part of drawing a Lewis structure for a simple molecule?

Accepted Answer

Assigning oxidation numbers to each atom

Fundamental Concepts in General Chemistry: Units, Measurement, Moles, and Molecular Structure

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