Question 1

A compound is found to contain 40.00% carbon, 6.71% hydrogen, and 53.29% oxygen by mass. If the molar mass of the compound is $$90.08\ \mathrm{g/mol}$$, what is its molecular formula?

Accepted Answer

$$\mathrm{C}_3\mathrm{H}_6\mathrm{O}_3$$

Question 2

Which of the following best describes the difference between an empirical formula and a molecular formula?

Accepted Answer

The empirical formula gives the simplest whole-number ratio of atoms in a compound, while the molecular formula gives the actual number of atoms of each element in a molecule.

Question 3

A chemist combusts 0.250 g of a compound containing C, H, and Cl, producing 0.451 g of CO$$_2$$ and 0.0617 g of H$$_2O. $$What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{CH}_2\mathrm{Cl}$$

Question 4

A sample of a compound weighing 4.30 g is combusted, producing 8.59 g of CO$$_2$$ and 3.52 g of H$$_2O. If $$the molar mass of the compound is 176.22 g/mol, what is its molecular formula?

Accepted Answer

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

Question 5

Which of the following is the correct systematic name for the polyatomic ion $$\mathrm{NO}_3^-$$?

Accepted Answer

Nitrate

Question 6

A compound is found to be 72.2% C, 8.50% H, and the remainder is O. If 0.250 moles of the compound weighs 41.5 g, what is the molecular formula?

Accepted Answer

$$\mathrm{C}_{10}\mathrm{H}_{12}\mathrm{O}_2$$

Question 7

The formula for the sulfate ion is $$\mathrm{SO}_4$$^{2-}$$. If the term 'thio' means the replacement of an oxygen by a sulfur, what is the formula for the thiosulfate ion?

Accepted Answer

$$\mathrm{S}_2\mathrm{O}_3$$^{2-}$$

Question 8

A combustion analysis of a hydrocarbon produces 2.80 g of CO and 1.44 g of H$$_2O. $$What is the empirical formula of the hydrocarbon?

Accepted Answer

$$\mathrm{CH}_2$$

Question 9

Which of the following is the correct systematic name for the polyatomic ion $$\mathrm{CO}_3$$^{2-}$$?

Accepted Answer

Carbonate

Question 10

A compound contains 3.12 g of potassium and $$1.922 	imes 10$$^{23}$$ oxygen atoms. If the total mass of the sample is 12.61 g, what is the empirical formula?

Accepted Answer

$$\mathrm{KMnO}_4$$

Question 11

Which of the following is the correct systematic name for the polyatomic ion $$\mathrm{PO}_4$$^{3-}$$?

Accepted Answer

Phosphate

Question 12

A combustion reaction of a compound containing only C, H, and O produces 7.79 g CO$$_2$$ and 3.18 g H$$_2O $$from a 4.16 g sample. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{C}_2\mathrm{H}_4\mathrm{O}_2$$

Question 13

Which of the following is the correct systematic name for the polyatomic ion $$\mathrm{IO}_3^-$$?

Accepted Answer

Iodate

Question 14

A combustion analysis of a 12.01 g sample of an acid produces 14.08 g CO$$_2$$ and 4.32 g H$$_2O. $$The acid contains only C, H, and O. What is the empirical formula?

Accepted Answer

$$\mathrm{C}_4\mathrm{H}_6\mathrm{O}_4$$

Question 15

Which of the following is the correct systematic name for the polyatomic ion $$\mathrm{AsO}_4$$^{3-}$$?

Accepted Answer

Arsenate

Question 16

A combustion chamber experiment burns 5.00 g of an organic molecule (MW = 233.07 g/mol) containing C, H, and O. The mass of the CO$$_2$$ absorber increases from 75.30 g to 78.15 g, and the mass of the H$$_2O $$absorber increases from 49.14 g to 50.11 g. What is the molecular formula of the compound?

Accepted Answer

$$\mathrm{C}_{12}\mathrm{H}_{12}\mathrm{O}_3$$

Question 17

Which of the following is the correct systematic name for the polyatomic ion $$\mathrm{FO}^-$$?

Accepted Answer

Fluorate

Question 18

Which of the following best describes a polyatomic ion?

Accepted Answer

A tightly bound group of two or more atoms that acts as a single ion with an overall charge

Empirical and Molecular Formulas, Combustion Analysis, and Polyatomic Ions

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