Acid-Base Equilibria

Question 1

Bronsted-Lowry Acid

Answer 1

Proton Donor

Question 2

Bronsted-Lowry Base

Answer 2

Proton Acceptor

Question 3

Species which can act as acid and base

Answer 3

H20, HPO4 2-, H2PO4- , HCO3 2-

Question 4

Monobasic Acid

Answer 4

acid molecules that donate one proton per molecule of acid

Question 5

What are H2O’s conjugate Base and Acid

Answer 5

base: OH-
acid: H3O+

Question 6

Difference in arrows used between dissociation of strong acids and weak acids

Answer 6

strong: full arrow
weak: reversible arrow

Question 7

pH equation

Answer 7

pH= -log[H+]

Question 8

[H+] equation

Answer 8

[H+]= 10(-pH)

antilog

Question 9

pH definition

Answer 9

logarithmic scale that gives measure of H+ conc in a solution

Question 10

Kw equation

Answer 10

Kw= [H+] [OH-]

units= mol2 dm-6

ionic product of water - endothermic

Question 11

Kw at 25C

Answer 11

1.00x10-14 mol2dm-6

Question 12

Equation pKw

Answer 12

pH + pOH = pKw

pKw= -logKw 14 at 25C

Question 13

Ka equation

Answer 13

Ka = [A-] [H+]
[HA]

Question 14

Ka equation for weak acid

Answer 14

[H+]= square root Ka x [HA]

Question 15

conc of diluted solution equation

Answer 15

mol solute
vol new solution/cm3 x 1000

Question 16

What does dilution factor of x mean

Answer 16

Solution is x times less conc than original

Question 17

Neutralisation

Answer 17

adding acid to base or vice versa mean some is neutralised = change in pH

calculate amt moles of acid or base left over

Question 18

Buffer definition

Answer 18

solution that resists change in pH on addition of small amounts of acid or alkali

Question 19

Addition of Dilute Acid as a Buffer

Answer 19

-extra H+ added
-anion in buffer reacts with H+
-extra H+ removed
-maintains pH

A- + H+ -> HA

Question 20

Addition of Alkali as a buffer

Answer 20

-extra OH- added
-react w undissociated acid in buffer
-extra OH- removed
-maintains pH

HA+OH- -> A- + H2O

Question 21

calc pH of buffer

Answer 21

conc anion
use Ka expression for pH
-log[H+]= pH

Question 22

Sodium Hydroxide added to excess Weak Acid

Answer 22

NaOH react with HA to form salt in situ
Weak acid must be in excess so no NaOH remains
resulting solution contains HA and its salt

Question 23

Henderson-Hasselbach equation

Answer 23

pH = pKa + log( [A-] )
[HA]

Question 24

Addition Acid/Alkali to buffer

Answer 24

new pH buffer calc by change in conc of anion and weak acid

amount A- decreases by same amount H+ added
same amount HA increases

new amounts used to recalculate pH

some cases [H+] = Ka

Question 25

Titration Curve

Answer 25

graph of pH against volume of alkali/acid added

Question 26

Typical titration curve shows

Answer 26

Initial pH of acid/alkali in conical flask - vertical region occurs at vol where neutralisation occurs shape of curve hows type of titration - vert region when one additional drop from burette neutralises substance - pH change rapily Indicator must have colour change completely within pH range of vertical region

Question 27

Strong Acid Strong Base Curve

Answer 27

vertical region: pH 3 - 10 initial pH: 1 - strong acid in flask 25cm3 of base solution required to neutralise acid

Question 28

Weak Acid Strong Base Curve

Answer 28

vertical pH: 6 - 10 inital pH: 4 - weak acid in flask 25cm3 required to neutralise

Question 29

Strong Acid Weak Base Curve

Answer 29

vertical: 3 - 8 initial: 1 - strong acid in flask 25cm3 required to neutralise

Question 30

Weak Acid Weak Base Curve

Answer 30

Vertical region: not clear initial: 3< not clear what volume used to neutralise

Question 31

Indicators, Their pH and Suitable titrations

Answer 31

Methyl Orange - 3.1-4.4 - SA-SB, SAWB Methyl Red - 4.4-6.2 - SASB, SAWB Phenolphthalein - 8.3-10 - SASB, WASB

Question 32

Colour change phenolphthalein and methyl orange

Answer 32

p= pink alkali - colourless acid mo= yellow alkali - red acid

Question 33

What is used for Weak Acid Weak Base

Answer 33

pH meter

Question 34

Neutral Salt

Answer 34

solution of **Strong** Acid **Strong** Base neither of ions from the salt react with water

Question 35

Acidic Salt

Answer 35

solution of salt of **Strong** acid **Weak** base + ion reacts with water donating H+ NH4+ + H2O <> NH3 + H3O+

Question 36

Alkaline Salt

Answer 36

solution of salt of **Weak** Acid and **Strong** Base -ion reacts with water, water donates proton to - ions, leaving OH- in solution CN- + H2O <> HCN + OH-

Question 37

Salt of Weak Acid Weak Base

Answer 37

either acidic or alkaline depending on dissociation lower pH than same conc of salt from WASB but higher pH than SA and the same WB