Lab P

Question 1

`Bronstead-Lowry definition of acid

Answer 1

proton donors

Question 2

Bronstead-Lowry definition of base

Answer 2

proton acceptors

Question 3

Titration curve

Answer 3

plot of acid solution pH against vol of added titrant

Question 4

Create a titration curve with following labelled:
A: Equivalence point
B: midpoint
C: xs OH- controls pH

Question 5

What is significant about equivalence

Answer 5

mol(A-)equiv = mol(HA)init = mol(OH)to reach equiv.

Question 6

what is significant about the midpoint of a weak acid (3)

Answer 6

molHA = molA-

[HA] = [A-]

pH = pKa

Question 7

conjugate acid-base pair

Answer 7

HA+ and A-

Question 8

%dissociation formula

Answer 8

%dissociation formula = [HA]diss / [HA]init

or

[H+]equil / [HA]init

Question 9

how does concentration affect %dissociation

Answer 9

increasing dilution of solution increases %dissociation

increasing concentration of solution decreases %dissociation

Question 10

initial molarity

Answer 10

concentration of HA if no dissociation occurs (before its mixed)

Question 11

How to find [A-] at equivalence if you are titrating a weak acid

Answer 11

[A-] = (HAmol)init / [(volHA)i + (volOH-)added]

Question 12

What is significant about strong acid’s midpoint

Answer 12

[A-] does not equal [HA] because when HA is mixed with water it immediately dissociates meaning that the solution you are titrating has 0 [HA]

Question 13

When do indicators change colour

Answer 13

pH of solution is close to pKa of indicator

Question 14

Acid - base indicator

Answer 14

weak organic acids that have a conjugate bases of a different colour

Question 15

Standardized base solution

Answer 15

base that you know the concentration of

Question 16

How to determine an unknown concentration of a known acid (3)

Answer 16

1. titrate acid to equivalence using a standardized base solution
2. Use acid - base indicator to recognize when you’ve reached equilibrium (solution changes colour)
3. You know how much titrant you had to add to reach equilibrium

Question 17

Why do indicators change colour

Answer 17

• Indicators are substances that undergo their own reaction with H⁺ ions in a solution, with a different coloured conjugate base
  HIn= H^+ + In^-
• The H+ in the solution forces the reaction to reach its midpoint
• At the midpoint of an indicator’s reaction, [HIn] and [In⁻] are equal.
• After, the midpoint, the indicator reaction shifts to favor the formation of the differently coloured conjugate base

Question 18

Experiment P process (4)

Answer 18

1. prepare a beaker of unknown M of acid, add indicator
2. titrate NaOh with the unknown acid
3. while titrating acid, regularly record pH using pH meter to get a titration curve
4. record entire titration curve. Reaction will turn pink at equivalence