Biochemistry Chapter 2: Water as a Solvent

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Questions and Answers

What is the net equation for the reaction of carbon dioxide and water?

CO2(g) + H+(aq) ⇌ HCO3−(aq)

CO2(g) + O2(l) ⇌ H2CO3(aq)

CO2(g) + H2O(l) ⇌ H+(aq) + HCO3−(aq) (correct)

CO2(aq) + H2(g) ⇌ H2CO3(aq)

What is a common example of an in vitro buffer system?

Phosphate buffer system

Zwitterion buffer system

Bicarbonate buffer system

Tris buffer system (correct)

Which of the following describes zwitterions?

Compounds with only a positive charge

Compounds with only a negative charge

Compounds that can act as both acids and bases

Compounds that have both a positive and negative charge (correct)

Which buffer system is known to be prevalent in the living body?

Phosphate buffer system Signup and view all the answers

What is the main role of buffers in biochemical reactions?

To prevent drastic changes in pH Signup and view all the answers

Which statement about buffers is false?

Buffers can only neutralize acids. Signup and view all the answers

What is the pH of a 1×10–3 M HCl solution?

3 Signup and view all the answers

What is the pH of a 1×10–4 M NaOH solution?

10 Signup and view all the answers

Which hydronium ion concentration corresponds to a pH of 10.0?

1×10–10 M Signup and view all the answers

Why does pepsin have maximum activity under very acidic conditions?

It is a digestive enzyme found in the stomach. Signup and view all the answers

Which enzyme has maximum activity near pH 5?

Lysozyme Signup and view all the answers

What concentration of hydroxide ions is found in a solution with a pH of 3?

1×10–11 M Signup and view all the answers

What determines the effective range of a buffer solution?

The pKa of the weak acid Signup and view all the answers

Which of the following options describes buffering capacity?

The concentration of the weak acid and its conjugate base Signup and view all the answers

How can a buffer solution be prepared in the laboratory starting from the weak acid?

By adding NaOH until the pH is correct Signup and view all the answers

What is the principal buffer pair found in cells?

H2PO4–/HPO42– Signup and view all the answers

What is the pKa value of carbonic acid in the blood buffering system?

6.37 Signup and view all the answers

What happens to the pH of a buffer when OH– is added?

It converts HA to A− Signup and view all the answers

Which enzyme catalyzes the conversion of CO2 to bicarbonate in the blood?

Carbonic anhydrase Signup and view all the answers

What is the general effect of increasing the concentrations of a weak acid and its conjugate base on buffering capacity?

It increases the buffering capacity Signup and view all the answers

What is the pKa value used in the example for calculating the new pH?

7.20 Signup and view all the answers

What does the Henderson–Hasselbalch equation help calculate in a buffer system?

New pH Signup and view all the answers

What determines the polarity of a bond in a water molecule?

Difference in electronegativity of atoms Signup and view all the answers

Which atom in a water molecule has a negative charge due to electron sharing?

Oxygen Signup and view all the answers

According to Le Chatelier’s principle, what happens when H+ ions are added to a buffer system?

The equilibrium shifts to produce more buffer Signup and view all the answers

At the inflection point of a titration curve, what proportion of the original acid has been converted to the conjugate base?

Half of the acid Signup and view all the answers

How does the geometry of a molecule affect its polarity?

It can make polar bonds nonpolar if symmetrically arranged. Signup and view all the answers

Which of the following molecules is considered nonpolar despite having polar bonds?

CO2 Signup and view all the answers

When the pH is one unit higher than pKa, what is the ratio of conjugate base to conjugate acid?

10:1 Signup and view all the answers

Which ion concentrations are used in the Henderson–Hasselbalch equation in this example?

H2PO4− and HPO42− Signup and view all the answers

Which type of bond is held together by positive and negative ions?

Ionic bond Signup and view all the answers

What is the effect of stress on a buffer system according to Le Chatelier’s principle?

It causes the equilibrium to shift Signup and view all the answers

What is the primary role of water as a solvent in living systems?

Facilitating biochemical reactions Signup and view all the answers

Which stage of phosphoric acid ionization is the focus of the buffer mentioned in this example?

Second stage Signup and view all the answers

What describes a nonpolar bond?

Electrons are shared evenly Signup and view all the answers

What is the result of differences in electronegativity between atoms in a bond?

Creation of a polar bond Signup and view all the answers

Study Notes

Water and Polarity

Water is a vital component of most cells and its molecular geometry significantly influences biological properties.
Electronegativity refers to an atom's ability to attract electrons; oxygen and nitrogen are more electronegative than carbon and hydrogen.
Polar bonds arise when electrons are shared unequally, resulting in a molecule having a positive end and a negative end.
A molecule can contain polar bonds but remain nonpolar overall, as seen in CO2 due to its linear geometry.

Solvent Properties of Water

Ionic bonds form when positive and negative ions attract each other, facilitating various biochemical reactions.
In pure water, the concentration of hydrogen ions ([H+]) is 1×10–7 M, leading to a neutral pH of 7.0.
Example calculations show that 1×10–3 M HCl gives a pH of 3, while 1×10–4 M NaOH gives a pH of 10.0.
pH levels are crucial for enzyme activity; enzymes like pepsin and trypsin show optimal activity within specific pH ranges.

Buffers and Their Mechanisms

Buffers maintain a stable pH by resisting changes when acids or bases are added, following Le Chatelier's principle.
Buffer systems are crucial in maintaining homeostasis, with the equilibrium defined by reactions involving weak acids (HA) and their conjugate bases (A−).
The Henderson-Hasselbalch equation can be used to calculate pH based on the ratio of acid and base concentrations.

Titration and Buffer Action

Titration curves provide insights into buffer effectiveness, showing pH stability in the presence of added acids or bases.
At an inflection point on a titration curve, equal concentrations of acid and conjugate base exist, allowing effective buffering capacity.

Biological Buffers

The H2PO4–/HPO42– buffer system is prominent in biological systems, providing stability in cellular environments.
Carbonic acid (H2CO3) dissociates in blood to maintain pH around 7.4, with carbonic anhydrase catalyzing CO2 to bicarbonate ion (HCO3−) conversion.
Phosphate buffer systems, such as TRIS, are commonly utilized in laboratory settings, both in vitro and in vivo.

Key Buffer Properties

Buffers are effective within two pH units of the pKa of the acid component, with greater concentrations of weak acid and conjugate base increasing buffering capacity.
Biological buffers include zwitterions, which possess both positive and negative charges, and are less likely to interfere with biochemical processes compared to older buffer systems.

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Description

Explore the critical role of water in biochemical reactions in this quiz based on Chapter 2. Topics include water's polarity, hydrogen bonding, acids, bases, pH, and buffers. Test your understanding of how these concepts interact within biological systems.