CHEM311 Chapter 2: Water and Polarity

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What is the purpose of using buffers in a solution?

To maintain a stable pH by neutralizing small quantities of additional acid or base

In a buffer solution, which component neutralizes a strong base?

The acid

What is a common buffering agent with a pKa value of 6.40?

KH2PO4

In a phosphate buffer system, what is the typical useful pH range?

6.2 to 8.2

What is the general rule regarding the effective range of a buffer in relation to its pKa value?

The effective range is +/- 1 pH unit of the pKa value of the weak acid

What is a key criterion for selecting a buffer?

Matching pKa value with the system

Which of the following is NOT a typical criterion for selecting a buffer?

High solubility

What is the principal buffer in cells?

$H_2PO_4^-/HPO_4^{2-}$

What happens to blood pH if someone hyperventilates?

It increases

If the buffering capacity of a solution is very high, what does that indicate about the concentrations of the weak acid and its conjugate base?

High concentrations

What is the pH of a solution after adding 1.5mL of 2.0M HCl to 10.0mL of water?

5.58

If you add 1.5mL of 2.0M HCl to a buffer solution, what will happen to the buffer's pH?

It will decrease

In a mixture of 0.55M carbonic acid and 0.55M sodium hydrogen carbonate, what is the resulting pH when 1.5mL of 2.0M HCl is added?

5.84

How does the addition of HCl impact the concentration of carbonic acid in the mixture of carbonic acid and sodium hydrogen carbonate?

Increases

What is the significance of maintaining a specific buffer ratio in a buffer system?

To neutralize any added acid or base

What happens when the concentrations of a weak acid and its conjugate base are equal in a solution according to the Henderson-Hasselbalch equation?

The pH of the solution equals the pKa of the weak acid

Which type of buffer contains a weak acid and its salt or a weak base and its salt?

Buffer resistant to pH change

How do buffers work when a strong base is added to a buffer solution?

The weak acid absorbs the H+ to neutralize the base

What happens when a strong acid is added to a buffer solution?

The pH changes only slightly

What characterizes a buffer's resistance to changes in pH?

The ability of the buffer to absorb or release H+ ions without significant changes in pH

What is the role of a weak acid in an aqueous solution?

Exists as a conjugate acid-base pair

How is the strength of an acid described?

Quantified by Ka value

Which concept connects the equilibrium constant (K) to the pH of a solution containing both an acid and a base?

Henderson-Hasselbalch equation

What is the ionization constant for water at 25°C?

[H+] * [OH-] = 10^-7

What is the molar concentration of water used to calculate the ionization constant for water at 25°C?

55.5 M

What determines the polarity of a molecule?

The geometry of the molecule and the polarity of the bonds

What type of bonds are polar covalent bonds?

Bonds where electrons are shared but not equally

What is electronegativity in relation to a compound?

The ability of an atom in a compound to draw electrons to itself

How does the geometry of a molecule affect its polarity?

It can determine whether the molecule is polar or nonpolar

What does a polar covalent bond imply about electron sharing?

Electrons are shared but not equally between atoms

Which type of molecules tend to dissolve in water?

Hydrophilic

What type of interactions are very weak between nonpolar molecules?

Van der Waals interactions

What kind of molecules have characteristics of both hydrophobic and hydrophilic regions?

Amphipathic molecules

What is the term for a spherical arrangement of organic molecules in water solution?

Micelle

Which type of bonds are responsible for the attraction between temporary induced dipoles in micelle formation?

Van der Waals interactions

What does a Brønsted-Lowry acid donate?

Proton (hydrogen ion)

In the context of acids and bases, what does a Brønsted-Lowry base accept?

Proton (hydrogen ion)

What is the term for molecules that contain one or more hydrophobic and one or more hydrophilic regions?

Amphipathic molecules

What is the main type of bond responsible for forming hydrophobic interactions?

Van der Waals interactions

What is the key characteristic of micelles in aqueous solutions?

Hydrophobic parts on the surface of the sphere

Test your knowledge on the second chapter of CHEM311 covering topics such as water and polarity, hydrogen bonds, acids, bases, and pH, titration curves, and buffers. Review the concepts of polarity in molecules and the factors affecting bond polarity.

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