Lab Guide 2: pH and Buffers

Acids on the pH scale

0-6

What is the molar concentration of H+ in pure water?

1x10^-7

What is the molar concentration of OH- in pure water?

1x10^-7

What is the product of the molar concentrations of H+ and OH- in pure water?

1x10^14

If we say that one solution has 100 times as many hydrogen ions as another solution, how many pH units of difference exist between the two solutions?

2 units of pH

Bases on the pH scale

8-14

Bases

A solution that increases the number of OH- ions and decreases the number of H+ ions

What is a buffer composed of?

An acidic-base conjugate pair of a weak acid or a weak base in a solution

Reactants when water ionizes

H+ + OH -

What are the OH-, H+, and pH of a 0.01 M Solution of NaOH?

H+ = 10^-2 OH- = 10^-12 pH=2

What is the H+ of a solution whose pH is 8? What is [OH-] of this solution?

H+ concentration is 10^-8; OH- concentration is 10^-6

Example of a weak acid

H2CO3 (carbonic acid)

Example of a strong acid

HCl

Example of weak base

NH3 (ammonia)

Example of a strong base

NaOH (sodium hydroxide)

Write the equation for the neutralization of NaOH by HCl

NaOH + HCl → Na+ +OH- + H+ + Cl- → NaCl + H20

What are the OH, H, and pH of a 0.1 M solution of KOH?

OH= 10^1 H= 10^-13 pH=13

If solution A contains 1x10^-6 M H+ ions and solution B contains 1x10^-8 H+ ions, which solution contains more H+ ions?

Solution A has more H+ ions; Solution B is more basic and therefore has more OH- ions than H+ ions

What happens to pH when you increase H+ ions?

The acidity increases because there is a decrease in OH-

What happens to pH when you decrease OH- ions?

The solutions gets more basic because there are less H+ ions

HCl ionizes completely in water. What is the H+ of a 0.01 M Solution of HCl? What is the pH

[H+}= 10^-2; pH is 2

pH

a measure of the concentration of hydrogen ions in an aqueous solution -- how acidic or alkaline the solution is

Acids

a substance that increases the number of H+ ions and decreases the number of OH- ions

Is the hydrogen ion concentration of a pH 3.8 solution higher or lower than that of a solution with a pH of 6.2?

the 3.8 pH has a higher concentration of hydrogen ions because it is more acidic, so it has more H+ and less OH-

HA is a hypothetical acid that ionizes 10% in solution. What is the H+ of a 0.01 M solution of HA? What is its pH?

the H+ is 10^-3, the pH is 3