Chapter 20 - Acids, bases, and PH Flashcards

1
Q

What is the important chemical component in an acid?

A

Hydorgen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Briefly describe the arrhenius model of acids and bases

A
  • Acids dissociate and release H+ ions in aqeous solution (e.g. water)
  • Alkalis (soluble base) dissociate and release OH- ions in aqueous solution
  • H+ ions are neutralised by OH- ions to form water. H+(aq) + OH-(aq) -> H2O(l)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is a Bronsted-lowry acid?

A

Species that donates a proton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is a Bronsted-Lowry base?

A

species that accepts a proton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a conjugate acid-base pair?

A

contains two species that can be interconverted by transfer of a proton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

In the dissociation of HCl to H+ and Cl- , identify the conjugate acid and base

A

HCl releases a proton, so therefore is a conjugate acid

Cl- accepts a proton, so therefore is the conjugate base

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Give the acid base pairs in this equilibria:

HCl(aq) + OH-(aq) H2O(l) +Cl-(aq)

A

HCl - donates H+ - Acid 1

OH - accepts H+ - base 2

H20 - donates H+ - acid 2

Cl - accepts H+ - base 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

When water is the base, what’s formed?

A

H3O+ - hydronium ion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What do the terms monobasic, dibasic and tribasic refer to?

A

total number of hydrogen ions in the acid that can be replaced per molecule in an acid-base reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How can ionic equations be simplified?

A

Cancel the spectator ions (don’t react)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What’s the word equation for reaction of an acid and a metal?

A

Acid + metal -> salt +hydrogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What’s the word equation for reaction of acids and a carbonate?

A

acid + carbonate -> salt + water + CO2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What’s the word equation for reaction of acids with a base?

A

acid + base -> salt + water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What’s the word equation for reaction of an acids with an alkali?

A

acid + alkali -> salt + water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the relationship between PH and concentration of H+?

A

Low value of [H+(aq)] = high PH

high value of [H+(aq)] = low PH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What;s the equation for working out PH from [H+]?

A

PH = -log[H+(aq)]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How do you work out [H+(aq)] using PH?

A

[H+(aq)] = 10-PH

18
Q

What change in [H+] does 1 PH number increase give

A

x10 difference

19
Q

How is the PH calculated for a strong acid?

A

Assume it fully dissociates

20
Q

How is the new PH calculated for a strong acid on dilution?

A

Work out change in concentration of HA and therefore [H+]

[H+] x original vol/ new total vol

or

C1V1 = C2V2

then put back into PH = -log[H+]

21
Q

What is Ka?

A
  • Acid dissociation constant
  • standardised at 25ºC
22
Q

How do you work out Ka?

using HA(aq) H+(aq) +A-(aq)

A

Ka = [H+(aq)] [A-(aq)]/ [HA(aq)]

23
Q

What is pKa value formula? (used to make Ka data more comparible)

A

pKa = -logKa

24
Q

How do you get Ka from pKa?

A

Ka = 10-pKa

25
Why are pKa values used and not Ka?
Much more manageable than Ka. Easier to compare relative acidic strengths using pKa strengths using pKa values than Ka values
26
What does a lower pKa and larger Ka value tell us?
Stronger acid
27
What does a lower Ka value and larger pKa value tell us?
Weaker acid
28
What information is provided by Ka values?
Strength of acid/ extent of dissociation
29
What is Kw?
Ionic product of water Ions in water (H+ and OH-) multiplied together
30
What's the equation for Kw?
Kw = [H+(aq)] [OH-(aq)]
31
What is the value of Kw?
1 x 10-14 mol2dm-6
32
What are monobasic and dibasic bases?
- Monobasic bases are bases that release one OH- ion e.g. NaOH, KOH, NH3 - Dibasic bases are bases that release two OH- ions e.g. Ba(OH)2, Ca(OH)2
33
How do you find PH of a strong base?
[OH-] = [Base] [H+] = Kw/[OH-] PH = -log[H+]
34
How do you calculate PH of reaction between strong acid and a strong base?
1. ) Calculate H+ moles 2. ) Calculate OH- moles 3. ) Calculate XS H+ or OH- (larger mol - small mol) 4. ) Calculate XS [H+] or [OH] 5. ) Calculate PH
35
What are the 2 assumptions made about weak acids?
1. ) [H+]eqm = [A-]eqm 2. ) [HA] ≈ [HA]initial [HA] at equilibrium virtually same as it was before any of it dissociated as so little dissociates
36
How do you calculate [H+] of weak acids using Ka?
[H+]2 = Ka x [HA] [H+] = (Ka x [HA])1/2
37
How do you calculate PH of weak acids?
Ka = [H+]2/[HA] [H+] = (Ka x [HA])1/2 PH = -log[H+]
38
How do you calculate PH for the solution formed from reaction between weak acid and a strong base?
For every mole of OH- added, one mole of HA is used up and one mole of A- is formed. 1. ) calculate moles HA (if it is still HA and not H+ - weak acids) 2. ) Calculate OH- moles 3. ) Calculate XS HA or OH- IF XS is HA: 4. ) Calculate HA mol left + A- formed 5. ) Calculate [HA] left over + [A] formed 6. ) Use Ka to find [H+] 7. ) Find PH If XS OH-: 4. ) Calculate [OH-] 5. ) Use Kw to find [H+] 6. ) Find PH
39
How is the PH of a diluted solution of a weak acid?
Find concentration of weak acid when diluted: using C1V1 = C2V2 Calculate [H+] : [H+]2 = Ka x [diluted weak acid] PH = -log[H+]
40
What's the relation between [H+] and [OH-] in pure water
They're the same