Acids and Bases

Question 1

What is a Bronsted-Lowry acid?

What is released when you mix an acid with water?

Answer 1

A proton donor

H+ ions (H3O+)

Question 2

What is a Bronsted-Lowry base?

What is released when you mix a base with water?

Answer 2

A proton acceptor

OH-

Question 3

Difference between strong and weak acids/bases?

Answer 3

Strong acids and bases dissociate almost entirely

Weak acids and bases dissociate poorly

Question 4

Example of weak acids?

Where does equilibrium lie in a reversible reaction?

Answer 4

Carboxylic acids

Well over to the left

Question 5

Example of strong acid?

Where does equilibrium lie in a reversible reaction?

Answer 5

HCl
H2SO4
HNO3

Right

Question 6

Example of strong base?

Where does equilibrium lie in a reversible reaction?

Answer 6

NaOH
KOH

Right

Question 7

Example of weak base?

Where does equilibrium lie in a reversible reaction?

Answer 7

NH3

Left

Question 8

What does water dissociate into?

How strongly does it dissociate?

Answer 8

H2O ⇌ H+ + OH-

It dissociates very weakly so equilibrium lies well to the left - to the extent that we assume water has a constant value

Question 9

What is the ionic product of water?

Answer 9

The constant you get when the constant of Kc is multiplied by the concentration of H2O you get Kw.

Question 10

Kw =

Units?

Answer 10

[H+][OH-]

As you get a 1:1 can be simplified to
[H+]^2.

mol^2dm^-6

Question 11

Is Kw effected by temperature?

Answer 11

Yes

Question 12

pH =

Answer 12

-log10[H+]

Question 13

[H+] =

Answer 13

10^-pH

Question 14

How is [H+] different for diprotic acids?

Answer 14

x2

Question 15

How do you calculate the pH of strong bases?

Answer 15

Kw = [H+][OH-]

Question 16

What is Ka used for?

Answer 16

Acid dissociation constant - use for weak acids

Question 17

Ka =

Answer 17

[H+][A-]/[HA]

[H+]^2/[HA] - Can’t do this with buffers, use for weak acids only.

Question 18

What’s pKa?

Answer 18

Another way of measuring the strength of an acid.
Lower the value the stronger the acid

Question 18

pKa =

Ka=

Answer 18

pKa = -log10(Ka)

Ka = 10^-pKa

Question 19

In titrations the known conc goes in the?

Answer 19

Burette

Question 20

Shape of strong acid, strong base titration graph?

Answer 20

Starts at pH 1

Very large vertical section

Finishes at pH 13 when you have an excess of strong base

Question 21

Shape of weak acid strong base titration graph?

Answer 21

Graph starts around pH 5

Smaller vertical section

Ends at around pH 13

Question 21

Shape of strong acid, weak base titration graph?

Answer 21

Graph starts at pH 1

Smaller vertical section

Finishes around pH 9

Question 22

Shape of weak acid, weak base titration graph?

Answer 22

Starts around pH 5 and finishes around pH9

Very small vertical section/ less pronounced S shape.

Question 23

What is the equivalence/ end point?

Answer 23

The point at which the acid/ base has been neutralised - shown by the steep gradient as pH rapidly changes.

Question 24

What is the half neutralisation point? What is it used for?

Answer 24

The point halfway between 0 and the equivalence point. Can be used to calculate pKa by taking the pH at this point. Because [HA] = [A-] Ka = [H+] pKa = pH

Question 25

How to choose the correct indicator using a titration curve?

Answer 25

Pick an indicator with a pH range that lies entirely within the equivalence point (vertical section).

Question 26

How do you measure pH for weak acid weak base titrations?

Answer 26

Use a pH meter as the pH change is too gradual and too small for an indicator to be effective.

Question 27

What is a buffer?

Answer 27

A chemical that resists the change in pH when small amount of acid or base are added

Question 28

What is an acidic buffer made from? How does it work?

Answer 28

Made from a weak acid and its salt. Designed to keep pH below 7 Weak acid only slightly dissociates so eq is to the left. Salt strongly dissociates so eq is to the right. The two equilibrium equations coexist in the same beaker. The position of equilibrium shifts accordingly to Le Chatelier's principle.

Question 29

What is a basic buffer made from? How does it work?

Answer 29

Made from weak base and its salt. The weak base only slightly dissociates The salt strongly dissociates These from 2 equilibrium reactions which coexist together

Question 30

Uses of buffers?

Answer 30

**Shampoo** - Prevents acidic shampoo damaging the hair **Washing powders** - Enzymes within need to work at their optimum pH **Blood** - needs to maintained at pH 7.4 so enzymes can operate at their optimum.