Acids And Bases

Question 1

Bronsted – Lowry acid

Answer 1

Bronsted – Lowry acid proton donor

Question 2

Bronsted – Lowry base

Answer 2

Bronsted – Lowry base proton acceptor

Question 3

pH

Answer 3

Measure of acidity by measuring concentration of H+ ions

Question 4

Low pH means

Answer 4

Acidity

Question 5

High pH means

Answer 5

Alkalinity

Question 6

Calculating pH equation

Answer 6

pH = -log[H+]

Question 7

Calculating [H+]

Answer 7

-pH

[H+] = 10

Question 8

What does an acid/base reaction involves

Answer 8

Transfer of the H+ ions from the acid to the base

Question 9

Strong acid ful..

Answer 9

Strong acid fully dissociates in water

Question 10

Weak acid

Answer 10

Only very Slightly dissociates in water

Question 11

Ka weak acid dissociation constant

Answer 11

Ka= [H+] [A-]

[HA]

Question 12

The more a weak acid dissociates…

Answer 12

The more H+ ions are formed

the stronger the acid the larger the Ka volume

Question 13

Calculating pKa

Answer 13

pKa = -log (ka)

Question 14

Calculating Ka from pKa

Answer 14

-pKa

Ka=10

Question 15

Dissociation of water

Answer 15

H2O (reverse sign) H+/H3O+OH-

Question 16

When water boils what happens to its pH

Answer 16

Water dissociating is endothermic and the reverse reaction is exothermic
Le chatliers principal
equilibrium shifts to rights to lower temperature more H+ ions So pH lower

Question 17

Oxonium ion

Answer 17

H3O+

Question 18

The ionic product of water at 298 Kelvin

Answer 18

Kw = [H+][OH-] = 1.0 x 10^-14

Question 19

Calculating pH of a base

Answer 19

[H⁺] = Kw

[OH⁻]

Question 20

Buffer

Answer 20

Buffer

Solution that maintains an almost constant pH on addition of small amounts of strong acid or strong base.

Question 21

What does an acidic buffer consist of?
Weak acid (HA) with its salt (Na⁺A⁻)

Answer 21

What does an acidic buffer consist of?
Weak acid (HA) with its salt (Na⁺A⁻)

Question 22

What does a basic buffer consist of

Answer 22

What does a basic buffer consist of?

Weak base with its salt.

Question 23

How can an acidic buffer be made?

Answer 23

How can an acidic buffer be made?
Mix HA with Na⁺A⁻.
Part-neutralise HA with NaOH.

Question 24

How can a basic buffer be made?

Answer 24

How can a basic buffer be made?
Mix weak base with its salt (e.g. NH₃ with NH₄Cl).
Part-neutralise weak base with HCl.

Question 25

When H⁺ added to acidic buffer...

Answer 25

``` When H⁺ added to acidic buffer... Unbalances equilibrium. Higher concentration of H⁺. Le Chatelier's principle. H⁺ + A⁻ → HA ```

Question 26

When OH⁻ added to acidic buffer...

Answer 26

``` OH⁻ + H⁺ → H₂O Unbalances equilibrium. Lower concentration of H⁺. Le Chatelier's principle. HA → H⁺ + A⁻ ```

Question 27

When H⁺ added to basic buffer...

Answer 27

``` OH⁻ + H⁺ → H₂O Unbalances equilibrium. Higher concentration of H₂O. Le Chatelier's principle. NH₃ + H₂O → NH₄⁺ + OH⁻ ```

Question 28

When OH⁻ added to basic buffer...

Answer 28

Unbalances equilibrium. Higher concentration of OH⁻. Le Chatelier's principle. NH₄⁺ + OH⁻ → NH₃ + H₂O1.

Question 29

How is a pH titration carried out?

Answer 29

How is a pH titration carried out? 1. Calibration curve of pH meter and electrode using buffer solutions. 2. Prepare graph of pH (y-axis) against volume of alkali added (x-axis). 3. Pipette 25cm³ 0.1M acid into 250cm³ beaker. Measure pH and record as initial pH. 4. Add 0.1M alkali from burette in appropriate portions, measuring and plotting pH after each addition. 5. Repeat up to 50cm³. 6. Plot curve of best fit.

Question 30

Equivalence volume/endpoint

Answer 30

Equivalence volume/endpoint | Mi-point of "vertical section".

Question 31

At half equivalence...

Answer 31

At half equivalence... [A⁻] = [HA] Ka = [H⁺] pKa = pH

Question 32

Buffer region

Answer 32

Buffer region | Around pa where pH changes very little, despite acid/base being constantly added.

Question 33

Acid-base indicators | Weak acids.

Answer 33

Acid-base indicators Weak acids. Conjugate acid and base forms have different colours

Question 34

An indicator colour change must...

Answer 34

An indicator colour change must... Be rapid Occur at exactly the same time as the equivalence point.

Question 35

What colour changes does methyl orange show?

Answer 35

What colour changes does methyl orange show? Yellow - pH5 Orange - pH4 Red - pH3

Question 36

What colour changes does phenolphthalein show?

Answer 36

What colour changes does phenolphthalein show? Pink - pH10 Pale pink - pH9 Colourless - pH8

Question 37

When can you NOT use phenolphthalein?

Answer 37

When can you NOT use phenolphthalein? | With a weak base.

Question 38

When can you NOT use methyl orange?

Answer 38

When can you NOT use methyl orange? | With a weak acid.