Question 1

Vanadinite has the formula $$\mathrm{Pb_5$(VO_4$)_3Cl}. $$How many oxygen atoms are present in one formula unit of vanadinite?

Accepted Answer

12

Question 2

Given the formula for vanadinite $$\mathrm{Pb_5$(VO_4$)_3Cl}$$, what is the ratio of lead (Pb) atoms to vanadium (V) atoms in one formula unit?

Accepted Answer

$$5:3$$

Question 3

Calculate the mass ratio of lead (Pb) to oxygen (O) in vanadinite $$\mathrm{Pb_5$(VO_4$)_3Cl}. ($$Atomic masses: Pb = 207.2 g/mol, O = 16.00 g/mol)

Accepted Answer

$$\dfrac{1036\ \mathrm{g\ Pb}}{192\ \mathrm{g\ O}}$$

Question 4

If you have a sample of vanadinite containing $$1.00\ \mathrm{g} of Cl$$, how many grams of vanadinite are present? (Atomic mass: Cl = 35.45 g/mol; Molar mass of vanadinite = 1416.3 g/mol)

Accepted Answer

$$39.96\ \mathrm{g}$$

Question 5

Balance the following equation: $$\mathrm{Na_2CO_3(aq) + $$AgNO_3$$(aq) \rightarrow Ag_2CO_3(s) + $$NaNO_3$$(aq)}. $$What are the correct coefficients (in order: Na$$_2CO$_3$$, AgNO$$_3$$, Ag$$_2CO$_3$$, NaNO$$_3$$)?

Accepted Answer

$$1, 2, 1, 2$$

Question 6

Which of the following is the correct empirical formula for a compound containing 76.14% C, 11.18% H, and 12.68% O by mass?

Accepted Answer

$$\mathrm{C_9H_{16}O}$$

Question 7

A freezing point depression experiment gives a molar mass of $$252.4\ \mathrm{g/mol}$$ for hydnocarpic acid. If the empirical formula is $$\mathrm{C_9H_{16}O} ($$molar mass $$140.22\ \mathrm{g/mol}$$), what is the molecular formula?

Accepted Answer

$$\mathrm{C$$_{18}$$H_{32}O_2$}$$

Question 8

Balance the following equation: $$\mathrm{(C_6H_{11}CO_2$)_2(s) + O_2$(g) \rightarrow CO_2$(g) + H_2O(l)}. $$What is the coefficient for $$\mathrm{O_2$}$$?

Accepted Answer

13

Question 9

A student claims that the ratio of Pb to O atoms in vanadinite is $$5:3. Is $$this correct? Why or why not?

Accepted Answer

No, because there are 5 Pb atoms and 12 O atoms, so the ratio is $$5:12.$$

Question 10

Which of the following best describes the process of determining an empirical formula from percent composition?

Accepted Answer

Convert percentages to grams, then to moles, divide by the smallest number of moles, and write the simplest whole-number ratio.

Question 11

If $$1.00\ \mathrm{g} of Cl is $$present in a sample of vanadinite, how many moles of vanadinite does this represent? (Atomic mass: Cl = $$35.45\ \mathrm{g/mol}$$; Molar mass of vanadinite = $$1416.3\ \mathrm{g/mol})$$

Accepted Answer

$$0.0282\ \mathrm{mol}$$

Question 12

Which of the following is the correct balanced equation for the combustion of hydnocarpic acid ($$\mathrm{C$$_{18}$$H_{32}O_2$}$$)?

Accepted Answer

$$\mathrm{C$$_{18}$$H_{32}O_2$} + 26\ \mathrm{O_2$} \rightarrow 18\ \mathrm{CO_2$} + 16\ \mathrm{H_2O}$$

Question 13

A mineral sample contains $$0.500\ \mathrm{mol} of $$vanadinite. How many moles of Pb atoms are present?

Accepted Answer

$$2.50\ \mathrm{mol}$$

Question 14

Which of the following statements about empirical and molecular formulas is correct?

Accepted Answer

The empirical formula shows the simplest whole-number ratio of atoms, while the molecular formula shows the actual number of atoms in a molecule.

Question 15

A chemist isolates a compound with the empirical formula $$\mathrm{C_9H_{16}O}$$ and determines its molar mass is $$252.4\ \mathrm{g/mol}. $$What is the multiplier used to obtain the molecular formula?

Accepted Answer

3

Question 16

Which of the following best explains why balancing chemical equations is necessary?

Accepted Answer

To obey the law of conservation of mass, ensuring the same number of each atom on both sides of the equation.

Question 17

If $$0.250\ \mathrm{mol} of$$ $$\mathrm{Na_2CO_3}$$ reacts with excess $$\mathrm{$$AgNO_3$$}$$, how many moles of $$\mathrm{Ag_2CO_3}$$ will be formed? (Balanced equation: $$\mathrm{Na_2CO_3} + 2\ \mathrm{$$AgNO_3$$} \rightarrow Ag_2CO_3 + 2\ \mathrm{$$NaNO_3$$})$$

Accepted Answer

$$0.250\ \mathrm{mol}$$

General Chemistry Study Guidance: Vanadinite, Chemical Equations, and Hydnocarpic Acid

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