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Physical Chemistry Year 2 > Acids And Bases > Flashcards

Flashcards in Acids And Bases Deck (49)
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1

Define a Brønsted-Lowry acid

Proton donor

2

Define a Brønsted-Lowry base

Protons acceptor

3

What ion causes a solution to be acidic
Name and formula

H+ or more accurately H3O+ (Oxonium ion) as protons react with H2O to form it

4

What ion causes a solution to be alkaline

-OH

5

Write an equation for the ionisation of water

2H2O H3O+ + -OH
H2O H+ + -OH

6

Derive Kw using the equation for the ionisation is water

Kc = [H+] [OH-]
[H2O]

As [H2O] is so large compared to the other concentrations the concentration can be considered to be constant

Kw = [H+] [ OH-]

7

What is the value of Kw at 298K

1 x 10^-14

8

What physical factors affect the value of Kw
How do the affect it

Temperature - if temperature is increased the equilibrium moves to the right so Kw increases and the pH of pure water decreases

9

Why is pure water still neutral even if pH does not equal 7

[H+] = [ OH-]

10

Give an expression for pH in terms of H+

pH = -log10[H+]

11

What is the relationship between pH and concentration of H+

Lower pH the higher the concentration of H+

12

Of two solutions have a pH different of 1 what is the difference in [H+]

X10

13

How do you find [H+] from pH

10^-pH

14

How do you find [OH-] from pH in standard conditions

Find [H+] use Kw to calculate [OH-]

15

What is the different when finding [H+] from the concentration of diprotic and triprotic acids

Need to multiply the concentration of the acid by the number of protons to find [H+]

16

How do you calculate the pH of a strong alkaline solution

Use Kw to calculate [H+] from [OH-]
Use pH = -log[H+]

17

Define the term strong acid

One which fully dissociates in water

18

Define the term strong base

One which fully dissociates in water

19

What is the difference between concentrated and strong

Concentrated means many mil per dm3
Strong refers t amount of dissociation

20

What is a weak acid and a weak base

Weak acids and bases do not fully dissociate in water
They only partially dissociate into their ions

21

Examples of strong acids

HCl
H2SO4
H3PO4

22

Examples of strong bases

NaOH
CaCO3
Na2CO3

23

Examples of weak acids

CH3COOH
Any organic acid

24

Examples of weak bases

NH3

25

What is Ka

Ka = [H+][A-]
[HA]

26

How would you work out the pH of a weak acid

Use Ka
Then pH = -log[H+]

27

What is a titration

The addition of an acid/base of known titration to a base/acid of unknown titration to determine the concentration
An indicator is used to show that neutralisation has occurred or a pH meter

28

Describe titration curve for strong acid with a strong base

High
Gradually decrease
Quick decrease then levels off

29

Titration for a strong acid with a weak base

pH of about 9
Slight decrease
Quick decrease
Levels off

30

Titration curve for a weak acid with weak base

Ph of about 9
Slight decrease
Slight increase
Quick decrease
Levels off

31

Titration curve for a weak acid and strong base

High pH
Levels off
Quick decrease
Levels off

32

Define equivalence point

The point at which the exact volume of base has been added to just neutralise the acid

33

What generally happens to the pH of the solution around the equivalence point

There is a large and rapid change in pH

34

What is the end point

The boiling of acid or alkali added when the indicator changes colour
If the right indicator is chosen then the equivalence point = end point

35

What are the properties of a good indicator

Sharp colour Change
End point list be the same as the equivalence point
Distinct colour change

36

What indicator would you use for a strong acid base titration

Phenolphthalein

37

What indicator would you use a strong acid weak base titration

Methyl orange

38

What indicator would you use for a weak acid and strong base titration

Phenolphthalein

39

What indicator would you use for a weak acid weak base titration

Neither methyl orange or phenolphthalein

40

Methyl orange

Red in acid
Yellow in alkali
Changed at pH 4-5

41

Phenolphthalein

Colourless in acid
Red in alkali
Changes at pH 9-10

42

What is the half neutralisation point

When volume = half the volume that has been added at the equivalence point

43

Define a buffer solution

A solution that resists changes in pH when small amount of acid/alkali are added

44

What do acidic buffer solutions contain in general

A weak acid and a soluble salt of that acid that fully dissociates

45

Equation for an acidic buffer with added acid

A- + H+ -> HA

46

Equation for acidic buffer with added alkali

HA + OH- -> H2O + A-

47

What do basic buffer solutions contain in general terms

Weak base and soluble salt of that weak base

48

How can you calculate the pH of buffer solutions

Ka of weak acid
pH = -log[H+]

49

Which buffer system maintains blood pH

H+ + HCO3- CO2 + H2O