Acids, Bases And pH

Question 1

Bronsted Lowry acids

Answer 1

Proton donors

Question 2

Bronsted Lowry bases

Answer 2

Proton acceptors

Question 3

What does it means when acids and bases both dissociate in water

Answer 3

They break up into positively and negatively charged ions

Question 4

Does a strong acids completely or partially dissociate in water

Answer 4

Completely

Question 5

Do strong bases completely or slightly ionise in water

Answer 5

Completely

Question 6

What is the ionic product of water

Answer 6

Kw= [H+][OH-]

Question 7

Why is there no [H2O] in Kw

Answer 7

As water only dissociates a tiny amount, so the equilibrium lies well over to the left of (H2O H+ + OH-)
There’s so much water compared to the amounts of H+ and OH- ions that the concentration of water is considered to have a constant value.

Question 8

Calculating pH

Answer 8

-log[H+]

Question 9

[H+] = ?

Answer 9

10^-pH

Question 10

Steps to find pH of a strong base

Answer 10

1) find the values of Kw and [OH-]
2) rearrange the equation to find [H+]
3) pH = -log[H+]

Question 11

What is the acid dissociation constant

Answer 11

Ka= [H+][A-]
———-
[HA]

Question 12

Steps to find the pH of weak acids

Answer 12

1) write an equation for Ka
2) rearrange the equation and substitute the values you know to find [H+]^2
3) take the root of both sides
4) -log[H+] = pH

Question 13

Finding the concentration of weak acids

Answer 13

1) substitute the pH into the inverse pH equation to calculate [H+]
2) write an expression for Ka
3) rearrange the equation to give the concentration of the acid
4) substitute the values for Ka and [H+] into the equation and solve it

Question 14

pKa = ?

Answer 14

-log(Ka)

Question 15

Ka = ?

Answer 15

10^-pKa

Question 16

Approx colour change pH for methyl orange

Answer 16

3.1 - 4.4
Colour at low pH - red
Colour at high pH - yellow

Question 17

Approx pH colour change for phenolphthalein

Answer 17

8.3-10
Colour at low pH - colourless
Colour at high pH - pink

Question 18

How do you make titration results as accurate as possible:

Answer 18

• measure the neutralisation volume as precisely as you possibly can
• it’s a good idea to repeat the titration until you get concordant results
• use the 2 concordant results to calculate the mean titre

Question 19

Calculating concentrations of monoprotic acids

Answer 19

1) write out a balanced equation for the titration reaction
2) decide what you know already and what you need to know
3) calculate the number of moles of the reagent where you know the concentration and volume
4) use the molar ratios in the balanced equation to find out how many moles of the other reagent reacted
5) concentration = moles X 1000
—————-
Volume in cm^3

Question 20

What is a buffer

Answer 20

A solution that resists changes in pH when small amounts of acid or alkali are added

Question 21

Acidic buffers have a pH of a less than ?

Answer 21

7

Question 22

Basic buffers have a pH greater than ?

Answer 22

7