# Chapter 3 Lecture Problems

1. Hydrogen, Oxygen, and Water

2. Chemical Bonds
3. .
4. Representing Compounds: Chemical Formulas and Molecular Models

5. An Atomic-Level View of Elements and Compounds

6. Ionic Compounds: Formulas and Names

7. Chemical Nomenclature Handout
8. Molecular Compounds: Formulas and Names

9. Chemical Nomenclature Handout
10. Formula Mass and the Mole Concept for Compounds
1. Calculate the molecular weight of:
1. NaCl
2. H2O
3. CFCl3
4. C2H6O

2. Beer has about 10. grams of ethanol (C2H6O), how many moles of ethanol? How many ethanol molecules? How many carbon atoms? How many hudrogen atoms? How many oxygen atoms?

3. One cup of Coffee has about 50 mg of caffeine (C8N4O2H10). How many moles of caffeine? How many Moles of carbon? How many moles of nitrogen? How many moles of oxygen? How many moles of hydrogen?

4. It is possible to measure a picomole of CCl4. How many grams is this?

5. It is possible to measure an attomole of sodium. How many grams is this? How many atoms?

6. A friend of mine from graduate school worked on a laser fluorescence experiment that measured a special dye compound at a concentration of 10 yoctomoles (10-24). If the dye has a molecualr weight of 300 g/mole, how many grams of dye is this? How many dye atoms?

7. In a laboratory experiment, it is routine to measure out 0.0154 mole of sodium chloride. How many grams is this?

Solutions
11. Composition of Compounds

12. Calculate the percent mass of each element for the given chemical formula:
1. NaCl
2. H2O
3. CFCl3

13. Determining a Chemical Formula from Experimental Data
1. What is the emperical formula of a salt. 100.0000 grams of salt is analyzed and found to contain:
1. 39.3374 grams of sodium
2. 60.6626 grams of chloride

2. What is the emperical formula of an alcohol. 69.8457 grams of AN alcohol is analyzed and found to contain:
1. 41.9124 grams carbon
2. 9.3234 grams hydrogen
3. 18.6100 grams oxygen

3. What is the molecular formula of the alcohol if:
1. MW = 60.05 grams/mole
2. MW = 120.10 grams/mole

4. 1 asprin tablet contains 325 mg of acetylsalicylic acid (C9H8O4, see page 220 in textbook for structure).
1. How many moles of asprin, carbon, hydrogen, and oxygen are in a single tablet?
2. How many atoms(molecules) of asprin, carbon, hydrogen and oxygen are in a single tablet?
3. What is the percent composition of acetylsalicylic acid?

5. Pamoic acid is one compound I study extensively. Based on the 3D model determine the following:
1. The Molecular Formula
2. The Emperical Formula
3. The Molecular Mass
4. The Emperical Mass
5. The number of moles in 1.34 mg of pamoic acid
6. The number of moles of C, H, and O in 1.34 mg of pamoic acid
7. The number of molecules in 1.34 mg of pamoic acid
8. The mass of 9.35 nano moles of pamoic acid

6. The elemental analysis for another compound I will discuss is given below.

Elemental Analysis Results
ElementPercent Composition
Carbon 59.96
Hydrogen 13.42
Nitrogen 0
Oxygen 26.62
Chlorine 0

1. What is the Emperical Formula for this compound?
2. The Mass Spectrometry analysis of this compound shows that it has a molecular weight of 60 u. What is the Molecular Formula?
3. Based upon the emperical formula this compound could be 1-propanol or 2-propanol.
• From the CRC Handbook of Chemistry and Physics the density of 1-propanol is 0.8035 and the density of 2-propanol is 0.7855.
• Measure the mass of a beaker (69.2543 g). Use a 50.000 mL pipet to add the unknown liquid to the beaker and measure the mass (109.4293 g).
• What can you determine?

Solutions

1. 1 cup of Coffee has about 50 mg caffeine, (C8N4O2H10),
1. How many moles of caffeine, C, N, O, and H
2. How many atoms/molecules of caffeine, C, N, O, and H
3. What is the percent elemental composition of caffeine
4. If 89.6475 grams of caffeine is analyzed, how much C, N, O, and H

2. A confiscated white substance, suspected of being cocaine, was purified by a forensic chemist and subjected to elemental analysis. Combustion of a 50.86-mg sample yielded 150.0 mg CO2 and 46.05 mg H2O. Analysis for nitrogen showed that the compound contained 9.39% N by mass. The formula of cocaine is C17H21NO4. Can the forensic chemist conclude that the suspected compound is cocaine?
1. 150.0 mg CO2 (this is the carbon from the sample)
1. 0.1500 g CO2 at 44 g/mol = 3.41*10-3 moles CO2
2. 1 mole CO2 contains 1 mole C, so 3.41*10-3 moles C
3. 3.41*10-3 moles * 12.01 g/mol = 4.09*10-2 g or 40.9 mg C

2. 46.05 mg H2O (this is the Hydrogen from the sample)
1. 0.04605 g H2O at 18.01 g/mol = 2.56*10-3 moles H2O
2. 1 mole H2O contains 2 moles H, so sample has
3. 2.56*10-3 * 2 = 5.11*10-3 moles H
4. 5.11*10-3 moles * 1.008 g/mol = 5.15*10-3 grams or 5.15 mg H

3. The nitrogen analysis gave 9.39% by mass so that
1. N is 0.0939 * 50.86 mg = 4.78 mg
2. 0.00478 g * 14.01 g/mol = 3.41*10-4 mol

4. The total of C, H, and N = 50.8 mg so the O is the difference
1. 50.86 - 50.83 mg = 0 mg O

5. Mole ratios:
1. C 3.41*10-3 10
2. H 5.11*10-3 15
3. N 3.41*10-4 1
4. O 0 0

6. Does not support that the compound is cocaine.

3. Writing and Balancing Chemical Equations