Chapter 23

Consider a polymer made from tetrachloroethylene. (a) Draw a portion of the polymer chain. (b) What is the molar mass of the polymer if it contains \(3.2 \times 10^{3}\) tetrachloroethylene molecules? (c) What are the mass percents of \(\mathrm{C}\) and \(\mathrm{Cl}\) in the polymer?

Consider Teflon, the polymer made from tetrafluoroethylene. (a) Draw a portion of the Teflon molecule. (b) Calculate the molar mass of a Teflon molecule that contains \(5.0 \times 10^{4} \mathrm{CF}_{2}\) units. (c) What are the mass percents of \(\mathrm{C}\) and \(\mathrm{F}\) in Teflon?

Show the structure of the monomer used to make the following addition polymers.

The following condensation polymer is made from a single monomer. Identify the monomer. CNCCC(=O)NCC(C)=O

Write a chemical equation, using molecular formulas, for the reaction of sucrose with water to form glucose and fructose.

Write a chemical equation, using molecular formulas, for the reaction of maltose with water to form glucose.

Cellulose consists of about \(10,000 \mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{5}\) units linked together. (a) What are the mass percents of \(\mathrm{C}_{2} \mathrm{H}\), and \(\mathrm{O}\) in cellulose? (b) What is the molar mass of cellulose?

Starch has the same empirical formula as cellulose and a molar mass of about \(1.0 \times 10^{5} \mathrm{~g} / \mathrm{mol}\). (a) What are the mass percents of \(\mathrm{C}, \mathrm{H}\), and \(\mathrm{O}\) in starch? (b) How many \(\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{O}_{5}\) units are linked together in a starch molecule?

Mannose has the same molecular formula as glucose and the same geometry except at carbon-2, where the \(\mathrm{H}\) and \(\mathrm{OH}\) groups are interchanged. Draw the structures of \(\alpha\) - and \(\beta\) -mannose.

How many chiral carbon atoms are there in \(\alpha\) -glucose? in fructose?

How many chiral carbon atoms are there in sucrose? maltose?

Give the structural formula of two different dipeptides formed between arginine and serine.

Give the structural formulas of two different dipeptides formed between leucine and lysine.

(a) How many tripeptides can be made from glycine, alanine, and leucine, using each amino acid only once per tripeptide? (b) Write the structural formulas of these tripeptides and name them in the shorthand abbreviation used for showing amino acid sequences.

WEB A tripeptide contains valine, lysine, and phenylalanine residues. (a) How many tripeptides are possible from these amino acids? (b) Draw a structural formula for a possible form of the tripeptide and name it, using the shorthand form.

For alanine, \(K_{\mathrm{al}}=5.1 \times 10^{-3}, K_{\mathrm{a} 2}=1.8 \times 10^{-10}\), Calculate the ratios \([\mathrm{Z}] /\left[\mathrm{C}^{+}\right]\) and \([\mathrm{Z}] /\left[\mathrm{A}^{-}\right]\) at \(\mathrm{pH}\) (a) \(2.00\). (b) \(6.00\). (c) \(10.50\).

On complete hydrolysis, a polypeptide gives two alanine, one leucine, one methionine, one phenylalanine, and one valine residue. Partial hydrolysis gives the following fragments: Ala-Phe, Leu-Met, Val-Ala, Phe-Leu. It is known that the first amino acid in the sequence is valine and the last one is methionine. What is the complete sequence of amino acids?

Which of the following monomers could form an addition polymer? A condensation polymer? (a) \(\mathrm{C}_{2} \mathrm{H}_{6}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{4}\) (c) \(\mathrm{HO}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{OH}\) (d) \(\mathrm{HO}-\mathrm{CH}_{2}-\mathrm{CH}_{3}\)

Explain the difference between (a) a synthetic and natural polymer. (b) a polyester and polyamide. (c) \(\alpha\) -and \(\beta\) -glucose.

Explain the difference between (a) linear and branched polyethylene. (b) glucose and fr?ctose. (c) maltose and sucrose

Sketch the tetrapeptide obtained from four molecules of the \(\alpha\) -amino acid glycine.

How many tripeptides could one make from glycine, valine, and lysine, using any number of each amino acid?

A \(1.00\) -mg sample of a pare protein yielded on hydrolysis \(0.0165 \mathrm{mg}\) of leucine and \(0.0248 \mathrm{mg}\) of isoleucine. What is the minimum possible molar mass of the protein? (MM leucine \(=\) MM isoleucine \(=131 \mathrm{~g} / \mathrm{mol}\) )

Describe what is meant by (a) the primary structure of a protein. (b) the secondary structure of a protein. (c) the tertiary structure of a protein.

Gycolysis is the process by which glucose is metabolized to lactic acid according to the equation $$ \begin{gathered} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q) \longrightarrow 2 \mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{3}(a q) \\ \Delta G^{6}=-198 \mathrm{~kJ} \text { at } \mathrm{pH} 7.0 \text { and } 25^{\circ} \mathrm{C} \end{gathered} $$ Glycolysis is the source of energy in human red blood cells. In these cells, the concentration of glucose is \(5.0 \times 10^{-3} M_{3}\) while that of lactic acid is \(2.9 \times 10^{-3} M\). Calculate \(\Delta G\) for glycolysis in human blood cells under these conditions. Use the equation \(\Delta G=\Delta G^{\circ}+\mathrm{RT} \ln Q\), where \(Q\) is the concentration quotient, analogous to \(K\).

Plants synthesize carbohydrates from \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) by the process of photosynthesis. For example, $$ 6 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(t) \longrightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q)+6 \mathrm{O}_{2}(g) $$ \(\Delta G^{\circ}=2.87 \times 10^{3} \mathrm{~kJ}\) at \(\mathrm{pH} 7.0\) and \(25^{\circ} \mathrm{C}\). What is \(K\) for the reaction at \(25^{\circ} \mathrm{C} ?\)

Aspartic acid acts as a triprotic acid with successive dissociation constants of \(8.0 \times 10^{-3}, 1.4 \times 10^{-4}\), and \(1.5 \times 10^{-10}\). Depending upon \(\mathrm{pH}\), aspartic acid can exist in four different forms in water solution. Draw these forms and calculate the pH range over which each form is the principal species.