Proportions in Chemical Compounds

Transcription

1 Chapter 6 Proportions in Chemical Compounds Section 6.1 Chemical Proportions and Percentage Composition Solutions for Practice Problems Student Edition page Practice Problem (page 260) Calculate the mass percent of oxygen in iron(ii) oxide, FeO(s). You need to determine the mass percent of oxygen in iron(ii) oxide. You know the chemical formula for iron(ii) oxide: FeO Determine the molar mass of FeO(s). Calculate the mass percent of oxygen: Molar mass, M, of FeO(s): M 1 M 1M FeO Fe O g/mol g/mol g/mol mass of iron II oxide mass percent of O mass of iron II oxide g g % 22.27% Chapter 6ProportionsinChemicalCompounds MHR 1

2 The mass percent of oxygen in iron(ii) oxide is 22.27%. The molar mass has been correctly determined. The mass percent is reasonable and is correctly expressed to four significant digits. 2. Practice Problem (page 260) Calculate the mass percent of oxygen in dinitrogen tetroxide, N 2 O 4 (g). You need to determine the mass percent of oxygen in dinitrogen tetroxide. You know the chemical formula for dinitrogen tetroxide: N 2 O 4 Determine the molar mass of N 2 O 4 (g). Calculate the mass percent of oxygen: mass of dinitrogen tetroxide Molar mass, M, of N 2 O 4 (g): M 2 M 4M N2O4 N O g/mol g/mol g/mol mass percent of O mass of dinitrogen tetroxide g g % 69.55% The mass percent of oxygen in dinitrogen tetroxide is 69.55%. The molar mass has been correctly determined. The mass percent is reasonable and is correctly expressed to four significant digits Chapter 6ProportionsinChemicalCompounds MHR 2

3 3. Practice Problem (page 260) A 650 mg sample is analyzed and found to contain 51.0 mg of hydrogen. What is the mass percent of hydrogen in the sample? You need to determine the mass percent of hydrogen in a given mass of sample. You know the mass of the sample: 650 mg You know the mass of the hydrogen: 51.0 mg Calculate the mass percent of hydrogen: mass of hydrogen mass of sample mass of hydrogen mass percent of H mass of sample 51.0 mg 650 mg % 7.8% The mass percent of hydrogen in the sample is 7.8%. The mass has been substituted correctly. The mass percent is reasonable and is correctly expressed to two significant digits. 4. Practice Problem (page 260) Calculate the mass percent of oxygen in acetic acid, CH 3 COOH(). You need to determine the mass percent of oxygen in acetic acid. You know the chemical formula for acetic acid: CH 3 COOH Chapter 6ProportionsinChemicalCompounds MHR 3

4 Determine the molar mass of CH 3 COOH(). Calculate the mass percent of oxygen: mass of acetic acid Molar mass, M, of CH 3 COOH(): M 2 M 4 M 2M CH3COOH C H O g/mol g/mol g/mol g/mol mass percent of O mass of acetic acid g g % 53.28% Chapter 6ProportionsinChemicalCompounds MHR 4 The mass percent of oxygen in acetic acid is 53.28%. The molar mass has been correctly determined. The mass percent is reasonable and is correctly expressed to four significant digits. 5. Practice Problem (page 260) Potassium dichromate, K 2 Cr 2 O 7 (s), is used in the production of safety matches. A 50.0 g sample of potassium dichromate contains 12.8 g of potassium. What is the mass percent of potassium in the potassium dichromate sample? You need to determine the mass percent of potassium in potassium dichromate. You know the mass of the potassium: 12.8 g You know the mass of the potassium dichromate: 50.0 g Calculate the mass percent of potassium: mass of potassium mass of potassium dichromate

5 mass of potassium mass percent of K mass of potassium dichromate 12.8 g 50.0 g 25.6% The mass percent of potassium in the potassium dichromate is 25.6%. The molar mass has been correctly determined. The mass percent is reasonable and is correctly expressed to three significant digits. 6. Practice Problem (page 260) A 30.0 g sample of a compound contains 8.2 g of carbon. What is the mass percent of carbon in the sample? You need to determine the mass percent of carbon in a given mass of sample. You know the mass of the sample: 30.0 g You know the mass of the carbon: 8.2 g Calculate the mass percent of carbon: mass of carbon mass of sample mass percent of C mass of carbon mass of sample 8.2 g 30.0 g % 27% The mass percent of carbon in the sample is 27% Chapter 6ProportionsinChemicalCompounds MHR 5

6 The mass has been substituted correctly. The mass percent is reasonable and is correctly expressed to two significant digits. 7. Practice Problem (page 260) Which substance has the greater mass percent of chromium: chromic acid, H 2 CrO 4 (aq), or dichromic acid, H 2 Cr 2 O 7 (aq)? You need to determine whether chromic acid or dichromic acid has the greater mass percent of chromium. You know the chemical formula for chromic acid: H 2 CrO 4 You know the chemical formula for dichromic acid: H 2 Cr 2 O 7 Determine the molar mass of H 2 CrO 4 (aq) and the molar mass of H 2 Cr 2 O 7 (aq). Calculate the mass percent of chromium in each substance: mass of chromium mass of compound Molar mass, M, of H 2 CrO 4 (aq): M 2 M 1 M 4M H2CrO4 H Cr O g/mol g/mol g/mol g/mol mass percent of Cr mass of chromium mass of chromic acid 1 52 g g % 44.06% The mass percent of potassium in the chromic acid is % Chapter 6ProportionsinChemicalCompounds MHR 6

7 Molar mass, M, of H 2 Cr 2 O 7 (aq): M 2 M 2 M 7M H2Cr2O7 H Cr O g/mol g/mol g/mol g/mol mass percent of Cr mass of chromium mass of dichromic acid 2 52 g g % 47.70% The mass percent of chromium in the dichromic acid is 47.02%. Dichromic acid has the greater mass percent of chromium. The molar masses have been correctly determined. The calculated mass percentages are reasonable and are correctly expressed to four significant digits. 8. Practice Problem (page 260) Which substance has the greater mass percent of sulfur: sulfurous acid, H 2 SO 3 (aq), or peroxodisulfuric acid, H 2 S 2 O 8 (aq)? You need to determine whether sulfurous acid or peroxodisulfuric acid has the greater mass percent of sulfur. You know the chemical formula for sulfurous acid: H 2 SO 3 You know the chemical formula for peroxodisulfuric acid: H 2 S 2 O 8 Determine the molar mass of H 2 SO 3 (aq) and the molar mass of H 2 S 2 O 8 (aq). Calculate the mass percent of sulfur in each substance: mass of sulfur mass of compound Chapter 6ProportionsinChemicalCompounds MHR 7

8 Molar mass, M, of H 2 SO 3 (aq): M 2 M 1 M 3M H2SO3 H S O g/mol g/mol g/mol g/mol mass of sulfur mass percent of S mass of sulfurous acid g g % 39.07% The mass percent of sulfur in the sulfurous acid is 39.07%. Molar mass, M, of H 2 S 2 O 8 (aq): M 2 M 2 M 8M H2S2O8 H S O g/mol g/mol g/mol g/mol mass percent of S mass of sulfur mass of peroxodisulfuric acid g g % 33.03% The mass percent of sulfur in the peroxodisulfuric acid is 33.03%. Sulfurous acid has the greater mass percent of sulfur. The molar masses have been correctly determined. The calculated mass percentages are reasonable and are correctly expressed to four significant digits Chapter 6ProportionsinChemicalCompounds MHR 8

9 9. Practice Problem (page 260) Calcium chloride, CaCl 2 (s), is used as a de-icer. Calculate the mass percent of chlorine in calcium chloride. You need to determine the mass percent of chlorine in calcium chloride. You know the chemical formula for calcium chloride: CaCl 2 Determine the molar mass of CaCl 2 (s). Calculate the mass percent of chlorine: mass of chlorine mass of calcium chloride Molar mass, M, of CaCl 2 (s): M 1 M 2M CaCl2 Ca Cl g/mol g/mol g/mol mass percent of Cl mass of chlorine mass of calcium chloride g g % 63.89% The mass percent of chlorine in the calcium chloride is 63.89%. The molar mass has been correctly determined. The mass percent is reasonable and is correctly expressed to four significant digits Chapter 6ProportionsinChemicalCompounds MHR 9

10 10. Practice Problem (page 260) Many metals are refined from sulfide mineral deposits that were laid down by volcanoes billions of years ago. List the following sulfide compounds in order, from greatest to least mass percent of sulfur: lead(ii) sulfide, PbS(s); zinc sulfide, ZnS(s); copper(i) sulfide, Cu 2 S(s). You need to determine the mass percent of sulfur in three sulfide compounds and order the compounds from greatest to least mass percent of sulfur. You know the chemical formula for the sulfides: lead(ii) sulfide, PbS; zinc sulfide, ZnS; and copper(i) sulfide, Cu 2 S Determine the molar masses of PbS(s), ZnS(s), and Cu 2 S(s). Calculate the mass percent of sulfur in each mass of sulfur substance: mass of compound lead(ii) sulfide Molar mass, M, of PbS(s): M 1 M 1M PbS Pb S g/mol g/mol g/mol mass percent of S mass of sulfur mass of lead II sulfide g g % 13.40% The mass percent of sulfur in lead(ii) sulfide is 13.40% Chapter 6ProportionsinChemicalCompounds MHR 10