Acids, bases and pH

Question 1

What is a Bronsted-Lowry acid?

Answer 1

-Proton donor

Question 2

What is a Bronsted-Lowry base?

Answer 2

-Proton acceptor

Question 3

Define a strong acid/base

Answer 3

-Almost entirely dissociated in water

Question 4

Define a weak acid/base

Answer 4

-Only slightly dissociated in water

Question 5

What is the expression for the equilibrium constant?

Answer 5

(H+)(OH-)/(H2O)

Question 6

What is the expression for the ionic product of water (Kw)?

Answer 6

(H+)(OH-)

Question 7

What is the expression for pH?

Answer 7

pH=-log10(H+)

Question 8

How do you calculate pH from (H+)?

Answer 8

(H+)=10^-pH

Question 9

What does monoprotic mean?

Answer 9

-Each molecule of an acid will release one proton when it dissociates

Question 10

Name two acids that are monoprotic

Answer 10

-HCl
-HNO3

Question 11

What is a diprotic acid?

Answer 11

-Each molecule of an acid will release two protons when it dissociates

Question 12

How do you calculate the pH of strong bases?

Answer 12

-Kw=(H+)(OH-) to calculate (H+)
-Put in equation -log10(H+)

Question 13

What is the acid dissociation constant?

Answer 13

Ka=(H+)^2/(HA)

Question 14

What is the equation to find out pKa?

Answer 14

pKa=-log10(Ka)

Question 15

What is the equation to find Ka in relation with pKa?

Answer 15

Ka=10^-pKA

Question 16

Describe the graph of a pH curve that is strong acid/strong base

Answer 16

-Starts around 1
-Finishes around pH 13

Question 17

Describe the graph of a pH curve that is strong acid/weak base

Answer 17

-Starts around 1
-Finishes around pH 9

Question 18

Describe the graph of a pH curve that is weak acid/strong base

Answer 18

-Starts around 5
-Finishes around pH 13

Question 19

Describe the graph of a pH curve that is weak acid/weak base

Answer 19

-Starts around 5
-Finishes around 9

Question 20

How do you decide what indicator to use?

Answer 20

-Needs to change colour over a narrow pH range

Question 21

What indicators are often used in acid-base titrations?

Answer 21

-Phenolphthalein
-Methyl orange

Question 22

What colour change occurs when using methyl orange and what pH does it change at?

Answer 22

-Red->Yellow
3.1-4.4

Question 23

What colour change occurs when using phenolphthalein and what pH does it change at?

Answer 23

-Colourless->pink
8.3-10

Question 24

When doing a strong acid/weak base titration, what indicator should you use?

Answer 24

-Methyl orange

Question 25

When doing a weak acid/strong base titration, what indicator should you use?

Answer 25

-Phenolphthalein

Question 26

What is a buffer?

Answer 26

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

Question 27

What is the pH of an acidic buffer?

Answer 27

-Less than 7

Question 28

What is the pH of a basic buffer?

Answer 28

-More than 7

Question 29

Name two everyday objects that buffers are used in

Answer 29

-Shampoo
-Washing powder

Question 30

How do you calculate the pH of an acidic buffer?

Answer 30

-Write out the expression for the Ka of the weak acid
-Rearrange the equation to give the expression for (H+)
-Solve equation to find a value for (H+)
-Substitute your value into pH=-log10(H+)

Question 31

How do you calculate the pH of a basic buffer?

Answer 31

-Write out the equation for the neutralisation reaction
-Calculate the number of moles of acid and base
-Using molar ratios, calculate the moles at the end of the reaction
-Calculate the concentration of the acid and salt in the buffer solution
-Substitute value into pH=-log10(H+)