Chapter 3

A reaction having a 90 percent yield may be considered a successful experiment. However, in the synthesis of complex molecules such as chlorophyll and many anticancer drugs, a chemist often has to carry out multiple-step syntheses. What is the overall percent yield for such a synthesis, assuming it is a 30 -step reaction with a 90 percent yield at each step?

A certain sample of coal contains 1.6 percent sulfur by mass. When the coal is burned, the sulfur is converted to sulfur dioxide. To prevent air pollution, this sulfur dioxide is treated with calcium oxide $(\mathrm{CaO})$ to form calcium sulfite $\left({\mathrm{CaSO}}_3\right).$ Calculate the daily mass (in kilograms) of $\mathrm{CaO}$ needed by a power plant that uses $6.60\times {10}^6\mathrm{kg}$ of coal per day.

Aspirin or acetylsalicylic acid is synthesized by combining salicylic acid with acetic anhydride: $${\mathrm{C}}_7{\mathrm{H}}_6{\mathrm{O}}_3+{\mathrm{C}}_4{\mathrm{H}}_6{\mathrm{O}}_3⟶{\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4+{\mathrm{HC}}_2{\mathrm{H}}_3{\mathrm{O}}_2$$ $\begin{array}{l}\text{ salicylic acid acetic anhydride }\\ \text{ aspirin }& \text{ acetic acid }\end{array}$ (a) How much salicylic acid is required to produce $0.400\mathrm{g}$ of aspirin (about the content in a tablet), assuming acetic anhydride is present in excess? (b) Calculate the amount of salicylic acid needed if only 74.9 percent of salicylic is converted to aspirin. (c) In one experiment, $9.26\mathrm{g}$ of salicylic acid reacts with $8.54\mathrm{g}$ of acetic anhydride. Calculate the theoretical yield of aspirin an the percent yield if only $10.9\mathrm{g}$ of aspirin is produced.

Lactic acid, which consists of $\mathrm{C},\mathrm{H},$ and $\mathrm{O},$ has long been thought to be responsible for muscle soreness following strenuous exercise. Determine the empirical formula of lactic acid given that combustion of a 10.0 -g sample produces $14.7\mathrm{g}{\mathrm{CO}}_2$ and $6.00\mathrm{g}{\mathrm{H}}_2\mathrm{O}$.

Calculate the percent composition by mass of all the elements in calcium phosphate $\left[{\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2\right]$, a major component of bone.

Lysine, an essential amino acid in the human body, contains $\mathrm{C},\mathrm{H},\mathrm{O},$ and $\mathrm{N}$. In one experiment, the complete combustion of $2.175\mathrm{g}$ of lysine gave $3.94\mathrm{g}$ ${\mathrm{CO}}_2$ and $1.89\mathrm{g}{\mathrm{H}}_2\mathrm{O}.$ In a separate experiment, $1.873\mathrm{g}$ of lysine gave $0.436\mathrm{g}{\mathrm{NH}}_3$. (a) Calculate the empirical formula of lysine. (b) The approximate molar mass of lysine is $150\mathrm{g}$. What is the molecular formula of the compound?

The compound 2,3 -dimercaptopropanol $\left({\mathrm{HSCH}}_2{\mathrm{CHSHCH}}_2\mathrm{OH}\right),$ commonly known as British Anti-Lewisite (BAL), was developed during World War I as an antidote to arsenic-containing poison gas. (a) If each BAL molecule binds one arsenic (As) atom, how many As atoms can be removed by $1.0\mathrm{g}$ of BAL? (b) BAL can also be used to remove poisonous heavy metals like mercury $(\mathrm{Hg})$ and lead $(\mathrm{Pb})$. If each $\mathrm{BAL}$ binds one $\mathrm{Hg}$ atom, calculate the mass percent of $\mathrm{Hg}$ in a BAL-Hg complex. (An $\mathrm{H}$ atom is removed when a BAL molecule binds an $\mathrm{Hg}$ atom.)

Mustard gas $\left({\mathrm{C}}_4{\mathrm{H}}_8{\mathrm{Cl}}_2\mathrm{S}\right)$ is a poisonous gas that was used in World War I and banned afterward. It causes general destruction of body tissues, resulting in the formation of large water blisters. There is no effective antidote. Calculate the percent composition by mass of the elements in mustard gas.

Myoglobin stores oxygen for metabolic processes in muscle. Chemical analysis shows that it contains 0.34 percent Fe by mass. What is the molar mass of myoglobin? (There is one Fe atom per molecule.)

Hemoglobin $\left({\mathrm{C}}_{2952}{\mathrm{H}}_{4664}{\mathrm{N}}_{812}{\mathrm{O}}_{832}{\mathrm{S}}_8{\mathrm{Fe}}_4\right)$ is the oxygen carrier in blood. (a) Calculate its molar mass. (b) An average adult has about $5.0\mathrm{L}$ of blood. Every milliliter of blood has approximately $5.0\times {10}^9$ erythrocytes, or red blood cells, and every red blood cell has about $2.8\times {10}^8$ hemoglobin molecules. Calculate the mass of hemoglobin molecules in grams in an average adult.