Q: Which of the following is the correct formula for calculating density?

$$\\text{Density} = \\frac{\\text{mass}}{\\text{volume}}$$

Question 1

Which of the following best describes a chemical change?

Accepted Answer

Iron rusting when exposed to air

Question 2

Which of the following is the correct formula to convert a temperature from Celsius to Kelvin?

Accepted Answer

$$K = ^\circ C + 273$$

Question 3

A student measures the mass of a sample as 12.345 g. If the balance used has an uncertainty of $$\pm 0.001 g$$, how many significant figures should the mass be reported with?

Accepted Answer

5 significant figures

Question 4

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 5

Which of the following is the correct formula for calculating density?

Accepted Answer

$$\text{Density} = \frac{\text{mass}}{\text{volume}}$$

Question 6

Which of the following elements is a noble gas?

Accepted Answer

Neon ($$Ne)$$

Question 7

A sample contains 3.0 moles of $$NaCl. $$What is the mass of the sample? (Molar mass of $$NaCl = 58.44 g/$$mol)

Accepted Answer

$$174.32 g$$

Question 8

Which of the following best describes the difference between mass number and atomic number?

Accepted Answer

Mass number is the sum of protons and neutrons; atomic number is the number of protons.

Question 9

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

Accepted Answer

$$CH_2O$$

Question 10

Which of the following is a physical property?

Accepted Answer

Density

Question 11

A student needs to prepare 250 mL of a 0.50 M $$NaCl$$ solution. How many grams of $$NaCl$$ are required? (Molar mass of $$NaCl = 58.44 g/$$mol)

Accepted Answer

$$7.305 g$$

Question 12

Which of the following best explains why the atomic mass of chlorine is not a whole number?

Accepted Answer

It is the average of the masses of all naturally occurring isotopes of chlorine.

Question 13

Which of the following is the correct method for adding $$2.34$$ and $$0.567$$ with the correct number of significant figures?

Accepted Answer

$$2.91 ($$rounded to the hundredths place)

Question 14

A gas occupies a volume of $$2.50 L at a $$temperature of $$27^\circC. $$What is the volume at $$77^\circC$$, assuming constant pressure? (Use $$V_1$$/$$T_1$$ = $$V_2$$/$$T_2$$ and temperatures in Kelvin)

Accepted Answer

$$2.94 L$$

Question 15

Which of the following is the correct electron configuration for a neutral atom of sodium ($$Na$$, atomic number 11)?

Accepted Answer

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

Question 16

Which of the following ions has the same electron configuration as neon ($$Ne$$)?

Accepted Answer

$$Na^+$$

Question 17

Which of the following best describes the process of determining the empirical formula from combustion data?

Accepted Answer

Calculate the moles of $$CO_2$$ and $$H_2O$$ produced, then determine the moles of C and H, and use the remaining mass for O.

Question 18

Which of the following is the correct way to express the result of $$6.022 \times 10$$^{23}$$ molecules in moles?

Accepted Answer

$$1$$ mole

Question 19

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

Accepted Answer

Metals have free-moving valence electrons that allow electric current to flow.

Question 20

A sample of magnesium reacts completely with oxygen to form $$MgO. If$$ $$24.3 g of$$ $$Mg$$ reacts with $$16.0 g of$$ $$O_2$$, what is the empirical formula of the product?

Accepted Answer

$$MgO$$

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