5.1.3 Acids, Bases And Buffers

Front 1

brownsted lowery acid

Back 1

a substance which can donate a proton

Front 2

bronsted lowry base

Back 2

a substance which can accept a proton

Front 3

what happens in a reaction when both reactants are acid?

Back 3

The acid with the bigger Ka will act as acid

Front 4

what is the diffrence between a weak acid and a strong acid?

Back 4

A week acid partially discociates in aqueous solutions wheras a weak acid completely dissociates

Front 5

why is the value of [H20 (L)] assumed constant?

Back 5

because the concentration of H20 is much bigger than the concentration of the ions

Front 6

how can Le chatelier's principle be used to predict the change of pH at different temperatures?

Back 6

The dissociation of water is endothermic so by increasing the temperature the reaction favour the forward endothermic reaction pushing equilibrium to the right and giving a bigger concentration of H+ ions. The bigger the concentration of H+ ion the lower the pH.

Front 7

what happens when Ka increases?

Back 7

The acid becomes stronger.

Front 8

when calculating the pH of a weak acid what two assumptions are made to simplify the Ka expression?

Back 8

1) [H+ (aq)]eqm = [A- (aq)]eqm because they have dissociated according to the 1:1 acid

2) as the amount of dissociation is small we assume that the initial concentration of the udissociated acid has remained constant. So

[HA (aq)]eqm = [HA (aq)]initial

Front 9

what are the products when you react an acid with a metal?

Back 9

a salt and hydrogen

Front 10

what are the products when you react an acid with an alkali?

Back 10

salt and water

Front 11

what are the products when you react an acid with a carbonate?

Back 11

salt, water and carbon dioxide

Front 12

buffer solution

Back 12

A buffer solution is one where pH does not change significantly when small amounts of acid or alkali are added to it.

Front 13

how do you make a basic buffer solution?

Back 13

A basic buffer solution is made from a weak base and a salt of that weak base (made by reacting the weak base with a strong acid).

Front 14

how do you make a acidic buffer solution?

Back 14

A acidic buffer solution is made from a weak acid and a salt of that weak acid (made by reacting the weak acid with a strong base).

Front 15

how can the salt be added to make the buffer solution?

Back 15

A salt solution or solid salt can be added to the acid or a weak acid can be partially neutralized with an alkali to create a mixture of acid and salt.

Front 16

What substance has the highest concentration in a buffer solution?

Back 16

In a buffer solution the salt has a higher concetration that the the acid

Front 17

What happens to pH when small amount of acid is added to a buffer?

Back 17

In the equilibrium between the acid and the conjugate base (and H+ ion) the equilibrium will shift to the left removing nearly all the H+ added as the there is a large concentration of salt ion the buffer ratio stays almost constant so pH stays the same.

Front 18

what happens to pH when small amount of alkali is added to to a buffer?

Back 18

The OH- ions will react with the H+ ions to form water. Therefore in the equilibrium between the acid and the conjugate base (and H+ ion) the equilibrium will shift to the right to produce more H+ ion. Overall the concentration of H+ ions and the pH will remain constant but some o the acid is changed to the conjugate base.

Front 19

what assumption are made when working out the acid dissociation constant in buffer solutions?

Back 19

1) the [A-] is due to the added salt only

2) the initial concentration of the acid remains constant as the amount that has been dissociated or reacted remains small.

Front 20

what happens to the calculation of pH when small amount of alkali is added to the buffer solution?

Back 20

The moles of the acid would reduce by the number of moles of alkali added and moles of the salt would increase by the same amount so a new calculation would be done with new values.

Front 21

How does adding a carbonic acid control pH of blood?

Back 21

hydrogen carbonate acts as a buffer in blood plasma and maintains the pH between 7.34 - 7.45. An equilibrium is formed when the hydrogen carbonate dissociated into bicarbonate ion and H+. Adding alkali reacts with H+ so the equilibrium will shift right forming new H+ and more HCO3-.

Front 22

Describe this graph

Back 22

Front 23

Describe this graph

Back 23

Front 24

Describe this graph

Back 24

Strong acid - weak base

Front 25

Describe this graph

Back 25

Front 26

how do you choose an indicator?

Back 26

An indicatorwill work if thr yhr ph range ofthe indicator lies on the verticle part of titration curve. In this case the color will change rapidly aand respond to the neutralising point.

Front 27

when do you use phenolphthalein and what is the colour change and pH range?

Back 27

Use phenolphthalein for titration with strong and not weak bases.

pH range: 8.2-10

colour change: colourless acid > pink alkali

Front 28

when do you use methyl orange and what is the colour change and pH range?

Back 28

Use methyl orange for titration with strong and not weak acids.

pH range: 3.1-4.4

colour change: red acid > yellow alkali (orange endpoint)

Front 29

what are the three types of acid?

Back 29

Monobasic – each molecule may release 1 proton (HCl)

Dibasic – Each molecule may release 2 protons (H2SO4)

Tribasic – Each molecule may release 3 protons (H3PO4)

Front 30

how do you show the role of H+ ion a reaction with metals and bases using ionic equations?

Back 30

Write an ionic equation by splitting any aqueous compounds into ions, cancel out the ions to leave the final equation.

Front 31

What is the equation for the acid dissociation?

Back 31

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

Front 32

what is the relationship between Ka and PKa and ph aand H+?

Back 32

pKa = -log10Ka Ka = 10-pKa

pH = –log[H+] [H+] = 10–pH

Front 33

what is the expression for KW?

Back 33

Kw = [H+(aq)][ OH-(aq)]