Topic 12-Acid/Base Quilibria

Question 1

What does an acid do to be classed as an acid?

Answer 1

Releases protons

Question 2

What does a base do to be classed as a base?

Answer 2

Accepts protons

Question 3

What determines the strength of an acid?

Answer 3

Strong acids dissociate (ionise) almost completely in water- nearly all H+ ions will be released.

Question 4

How do you class a weak acid?

Answer 4

Weak acids only dissociate slightly in water so small numbers of H+ ions are formed. An equilibrium is set up which lies well over to the left.

Question 5

Define a Bronsted Lowry Acid:

Answer 5

Substance that can DONATE a PROTON

Question 6

Define a Bronsted Lowry Base:

Answer 6

Substance that can ACCEPT a PROTON

Question 7

In an equation acids are linked to a ….. …… on the other side of the equation

Answer 7

Acids are linked to a conjugate base

Question 8

Acid base reactions involve the ……… of …….

Answer 8

Acid base reactions involve the transfer of protons

Question 9

Define the term pH

Answer 9

A figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acidic and higher values more alkaline.

Question 10

Define Conjugate acid/base pair

Answer 10

​ Two species that differ by H​ +​ .

Question 11

Give the equation for pH calculations

Answer 11

pH = -log [H+]

Where [H+] is the concentration of hydrogen ions in the solution

Question 12

How do you know if an acid is STRONG?

Answer 12

It will completely dissociate

Question 13

Finding [H+] from pH

Answer 13

[H+] = 1 x 10 ^(-pH)

Question 14

Monoprotic?

Answer 14

Each mole of acid produces 1 mole of hydrogen ions.

Question 15

Polyprotic?

Answer 15

Each molecule of a strong polyprotic acid releases 2 protons when it dissociates.

Question 16

Ka is an example of an …… ……

Answer 16

equilibrium constant

Question 17

Acids and Bases react in …… reactions

Answer 17

Neutralisation Reactions

Question 18

Define a buffer

Answer 18

A solution that minimises changes in pH when a small amount of acid or base is added.

Question 19

Acidic buffers are made from:

Answer 19

a weak acid + it’s salt

Question 20

Basic buffers are made from:

Answer 20

a weak base + it’s salt

Question 21

What do titration curves show?

Answer 21

The change in pH when a volume of an acid or a base is added

Question 22

What is the equivalence point?

Answer 22

The point which the exact volume of base has been added to neutralise the acid or vice versa

Question 23

How can you improve the accuracy of a pH metre?

Answer 23

Maintaining a constant temperature

Question 24

What is the value of Kw at 298K

Answer 24

1.0 x10 ^-14

Question 25

What physical factors affect the value Kw? How?

Answer 25

Temperature- if it increases the eq shifts to the right so Kw increases

Question 26

pKw =

Answer 26

-logKw

Question 27

What is a titration?

Answer 27

The addition of an acid/base of known conc to an unknown acid/base to determine the concentration. Indicator used to show point of neutralisation, as is pH metre

Question 28

List equipment needed for a titration

Answer 28

``` Conical flask White tile Burette Acid/alk of known conc Pipette and filler unknown acid/alk Clamp stand ```

Question 29

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

Answer 29

There is a large and rapid change in pH (except weak/weak titration)

Question 30

3 properties of a good indicator?

Answer 30

Sharp colour change Endpoint must be same as equivalence point Distinct colour change

Question 31

What colour is methyl orange in acid & alkali.

Answer 31

Red in acid | yellow in alkali

Question 32

What colour is phenolphthalein in acid/alkali

Answer 32

Colourless in acid | pink/red in alkali

Question 33

What is the half neutralisation point?

Answer 33

When volume = half the volume added at equivalence point

Question 34

What do acidic buffer solutions contain in general terms?

Answer 34

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

Question 35

What do basic buffer solutions contain in general terms

Answer 35

A weak base and a soluble salt of that weak base.

Question 36

what ion causes a solution to be alkaline

Answer 36

OH-

Question 37

state assumptions that you make when calculating Ka/pH

Answer 37

``` all H+ comes from acid (none from water dissociation) If weak acid only small amount of it will have ionised so that we can approximate that [HA]eqm≈ [HA]original standard temp (298K) ```

Question 38

give the typical range of a weak acid pH

Answer 38

typically pH 2.5 - 6.5.

Question 39

For an acid HA, [H+] = [A-] we can rewrite the Ka expression replacing …. with …..

Answer 39

[H+] = [A-] so can subs in [H+]^2

Question 40

Define a 'neutral solution'

Answer 40

One where the concentration of OH- = H+

Question 41

Phenolphthalein changes from ….. to …… within the pH range …….-.....

Answer 41

colourless to pink within pH 8.3-10

Question 42

Methyl Orange changes from ….. to …… within the pH range …….-.....

Answer 42

red to yellow between pH's 3.1-4.4

Question 43

Which 2 indicators are suitable for strong acid/base titrations?

Answer 43

Methyl Orange (strong acid) and Phenolphthalein (strong base)

Question 44

What assumptions do you make when making Ka calculations with buffers?

Answer 44

That the salt fully dissociates | Acid = (practically) un-ionised