Biochemistry Week 4: Water and pH Properties

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Questions and Answers

What is primarily responsible for the unique physical properties of water?

Its dipolar structure and ability to form hydrogen bonds (correct)

Its solid state at ambient temperature

Its high molecular weight

The presence of multiple oxygen atoms

How does water function as a solvent?

It forms strong covalent bonds with solutes

It can solvate a wide range of organic and inorganic molecules (correct)

It has a low viscosity that prevents solvation

It has a high boiling point

What is the role of a hydrogen bond in water molecules?

It causes water to have a high density

It facilitates the self-association of water (correct)

It creates stable covalent bonds between water molecules

It weakens water's solvent capacity

What effect does water's strong dipole have on solvation?

It facilitates the dissolution of charged and polar species Signup and view all the answers

What type of shape does a water molecule have?

Skewed tetrahedron Signup and view all the answers

How long do hydrogen bonds in water typically last?

A few picoseconds Signup and view all the answers

What characteristic of the oxygen atom in a water molecule influences its dipolar nature?

It attracts electrons due to high electronegativity Signup and view all the answers

What is the dielectric constant of water's dipole responsible for?

Decreasing the attraction between charged and polar species Signup and view all the answers

What type of bond requires less energy to rupture in liquid water compared to covalent bonds?

Hydrogen bonds Signup and view all the answers

Which functional groups can serve as hydrogen acceptors in hydrogen bonding?

Aldehydes Signup and view all the answers

What interaction stabilizes the complex three-dimensional conformations of polypeptides?

Hydrogen bonding Signup and view all the answers

What term describes the tendency of nonpolar compounds to self-associate in an aqueous environment?

Hydrophobic effect Signup and view all the answers

What is the primary role of salt bridges in biomolecules?

To facilitate the binding of charged molecules Signup and view all the answers

Which type of interaction is characterized by attractions between transient dipoles generated by the movement of electrons?

Van der Waals forces Signup and view all the answers

Which of the following biomolecules can both accept and donate hydrogen atoms?

Amines Signup and view all the answers

Which type of bond is considered the strongest in biological molecules?

Covalent bond Signup and view all the answers

What is the relationship between the distance separating atoms and the strength of van der Waals forces?

They decrease as the sixth power of the distance. Signup and view all the answers

Which statement accurately describes nucleophiles?

Nucleophiles attack electron-poor atoms. Signup and view all the answers

How is pH defined mathematically?

pH = -log[H+] Signup and view all the answers

What does a low pH value indicate about the concentration of hydrogen ions?

High hydrogen ion concentration. Signup and view all the answers

What distinguishes strong acids from weak acids?

Strong acids completely dissociate into anions and protons. Signup and view all the answers

What does the term pKa represent?

The relative strength of weak acids. Signup and view all the answers

Which of the following is true for strong bases?

Strong bases completely dissociate in solution. Signup and view all the answers

What happens to the pKa value as the strength of an acid increases?

pKa decreases. Signup and view all the answers

Study Notes

Properties of Water

Water is the primary chemical component in living organisms and is known as an ideal biological solvent.
Unique physical properties arise from water's dipolar structure and its capacity for hydrogen bonding.
Water molecules are irregular, tetrahedral with oxygen at the center, leading to a strong dipole.
The electronegative oxygen attracts electrons, creating a partial positive charge on hydrogen and a region of local negative charge on oxygen.

Hydrogen Bonding

Water's high dielectric constant allows it to dissolve various organic and inorganic molecules by decreasing the attraction between charged and polar species.
Hydrogen bonds are formed between a partially unshielded hydrogen atom and unshared electron pairs on oxygen or nitrogen in other molecules, enabling water’s self-association.
These bonds are weak and transient, with a half-life of a few picoseconds; breaking a hydrogen bond requires about 4.5 kcal/mol.

Solvent Power

Water can dissolve organic biomolecules through hydrogen bonds, particularly with functional groups in aldehydes, ketones, amides, alcohols, carboxylic acids, and amines.

Interactions in Biomolecules

Covalent bonds are the strongest forces holding molecules together, while weaker non-covalent interactions stabilize the structure of macromolecules.
Hydrophobic interactions involve the self-association of nonpolar compounds in an aqueous environment, not driven by attraction.
Salt bridges form between oppositely charged groups and are comparable in strength to hydrogen bonds, facilitating the binding of ions and charged molecules.
Van der Waals forces arise from transient dipoles in neutral atoms, acting over very short distances (2 to 4 Å).

Nucleophiles and Electrophiles

Metabolic reactions involve nucleophiles, molecules rich in electrons, attacking electron-poor electrophiles, which may not have formal charges.

pH Concept

pH is defined as the negative log of hydrogen ion concentration: pH = -log[H+].
Low pH indicates high H+ concentrations (acidic), while high pH indicates low H+ concentrations (basic).
Acids donate protons, with strong acids completely dissociating in solutions, whereas weak acids partially dissociate.
Bases accept protons; strong bases do this completely, while weak bases do not.

pKa and Acid Strength

pKa is used to represent the strength of weak acids, where lower pKa values indicate stronger acids.
pKa is related to the acid dissociation constant (Ka), similar to the relationship between pH and hydrogen ion concentration [H+].

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Description

This quiz focuses on the key properties of water, including surface tension, viscosity, and solvent power, as well as the relationship between pH, acidity, and alkalinity. It is designed to test your understanding of these concepts and their significance in biochemistry.