Lecture 3

Question 1

Micropipettes

Answer 1

• used for volumes of 10 to 0.0002 mL
• fixed or adjustable volumes with defined ranges
• disposable tips
• two-stop plunger

Question 2

Micropipettes Systematic Errors

Answer 2

• stops not working (spring)

- dial not calibrated properly

Question 3

Solution Concentrations Given as:

Answer 3

• molarity (M), w/v or % (g/L, L/L or g/g)
• mass/molar mass = moles
• moles/volume = molarity (M or mole/L)

Question 4

Dilution Equation

Answer 4

C1V1 = C2V2

Question 5

Acid

Answer 5

• proton donator

- H+ increase

Question 6

Base

Answer 6

• proton acceptor

- H+ decrease

Question 7

pH

Answer 7

• water (at ~55.5 mol/L) dissociates to give 10^-7 mol/L H+ and 10^-7 mo/L OH-
• additional acid/base pushes equilibrium to more H+ or OH-
  product of [H+][OH-] = 10^-14

Question 8

pH Equation

Answer 8

pH = -log[H+]

Question 9

Buffers

Answer 9

• weak acids/bases
• incomplete dissociation gives an equilibrium between acid and conjugate base & H+
• equal amount of acid/base in solution at certain pH
• buffer pair is only effective +/- 1 pH unit from pKa
• buffered solutions reduce pH fluctuations

Question 10

Henderson-Hasselbalch Equation

Answer 10

• used to determine the pH of a given acid/base mixture

pH = pKa + log[A-]/[HA]

Question 11

C x V = n

Answer 11

n = mol