Physical Chemistry 2)a) - Chemical equilibrium

Question 1

what is meant by a closed system?

Answer 1

when the chemicals are trapped, and nothing is added or removed, but heat is allowed to be transferred to or from the surroundings

Question 2

when is a system in equilibrium?

Answer 2

when the composition of the reactants and products remains constant indefinitely.

Question 3

what is meant by a homogenous equilibrium?

Answer 3

when all the species are in the same gaseous phase

Question 4

what does it indicate if K is less than 1?

Answer 4

equilibrium lies more to the left, reactants side

Question 5

what does it indicate if K is approx 1?

Answer 5

neither products nor reactants is favoured

Question 6

what does it mean if K is greater than 1?

Answer 6

equilibrium lies more to the right, products side

Question 7

what term is used for a hydrogen ion?

Answer 7

hydronium ion

Question 8

in terms of the Bronsted and Lowry theory, what is an acid considered as?

Answer 8

a proton donor

Question 9

in terms of the Bronsted and Lowry theory, what is a base considered as?

Answer 9

a proton acceptor

Question 10

what is the species left when an acid donates a proton?

Answer 10

a conjugate base

Question 11

what is the species left when a base accepts a proton?

Answer 11

a conjugate acid

Question 12

water can behave as an acid and as a base, what is the term used to describe this nature of water?

Answer 12

amphoteric

Question 13

what is the value of Kw at approx 25°C?

Answer 13

1 x 10-14

Question 14

what is meant by the term monoprotic or monobasic?

Answer 14

an acid that is capable of donating one hydrogen ion per molecule

Question 15

diprotic/dibasic is the term used to describe an acid which can donate two hydorgen ions per molecule, give an example of a diprotic/basic acid:

Answer 15

sulfuric acid

Question 16

what is the definition of a strong acid?

Answer 16

an acid which dissociates fully in water

Question 17

what is the definition of a weak acid?

Answer 17

an acid which only partially dissociates in solution

Question 18

name three examples of strong acids:

Answer 18

*sulfuric acid
*nitric acid
*hydrochloric acid

Question 19

what does a weak acid equilibrium consist of?

Answer 19

non-ionised acid molecules, hydrogen ions and the conjugate base of the acid

Question 20

what is an example of a weak acid?

Answer 20

carboxylic acids

Question 21

define a base:

Answer 21

a substance that reacts with an acid by accepting a proton

Question 22

what is a strong base?

Answer 22

a base that dissociates completely in solution

Question 23

what is a weak base?

Answer 23

a base that partially dissociates in solution

Question 24

what are examples of strong bases?

Answer 24

sodium hydroxide
potassium hydroxide

Question 25

what is an example of a weak base?

Answer 25

ammonia

Question 26

what does the equilibrium of a weak base consist of?

Answer 26

non-ionised base molecules, hydroxide ions and the conjugate acid of the base

Question 27

what makes the pH of a salt acidic?

Answer 27

strong parent acid and weak parent base

Question 28

what makes the pH of a salt alkali?

Answer 28

weak acid parent and strong base parent

Question 29

what makes the pH pf a salt neutral?

Answer 29

strong acid parent and strong base parent

Question 30

why would sodium sulfite form an alkaline solution?

Answer 30

solution of strong base and weak acid. the sulfite ions react with the hydrogen ions in the water equilibrium to form sulfurous acid molecules. this means that there are now fewer H ions than OH ions and so the solution will have a pH greater than 7

Question 31

what is a buffer?

Answer 31

solutions that can resist the change in pH on adding small amounts of an acid or base

Question 32

what is an acid buffer?

Answer 32

consists of a solution of a weak acid and one of its salts

Question 33

what is a basic buffer?

Answer 33

consists of a solution of a weak base and one of its salts

Question 34

what is the role of the weak acid in an acid buffer?

Answer 34

provides hydrogen ions when they are removed on addition of small amounts of base

Question 35

what is the role of the salt in acid buffers?

Answer 35

The salt of the weak acid provides the conjugate base, which can absorb excess hydrogen ions produced by the addition of a small amount of acid.

Question 36

what is an indicator?

Answer 36

weak acids or bases that are able to give the measurement of the pH by their colour

Question 37

what is used when deciding what indicator to use in a titration?

Answer 37

equivalence point

Question 38

what is meant by the equivalence point?

Answer 38

the point where the amount of titrant added is enough to neutralise the solution

Question 39

where does the vertical region occur between for a strong acid-strong base titration?

Answer 39

pH3 - pH10

Question 40

where does the vertical region occur between for a weak acid strong base titration?

Answer 40

pH7 - pH10

Question 41

where does the vertical region occur between for a strong acid and weak base titration?

Answer 41

pH3 - pH8

Question 42

how would you choose an indicator based on equivalence point?

Answer 42

an indicator which has a colour change at a pH very close to the pH of the equivalence point