pH Calculations/Acids/Bases

Question 1

Outline the equation for pH

Answer 1

pH=-log10[H+]

Question 2

Outline the equation for [H+]

Answer 2

[H+]=10^-pH

Question 3

Define a Strong Acid

Answer 3

Fully dissociates (Ionises) in H2O

Question 4

Outline the Strong Acids

Answer 4

HCl
HNO3
H2SO4
H3PO4

Question 5

Define Monoprotic Acids

Answer 5

1 mol of protons per mole of acid

Question 6

Define Diprotic Acids

Answer 6

2 mol of protons per mole of acid

Question 7

Define Weak Acids

Answer 7

Partially dissociates (Ionises) in H2O

Question 8

Outline Weak Acids

Answer 8

All Organic Acids - COOH, HF

Question 9

Outline the 3 pH calculation steps for Dilutions

Answer 9

1. Find [H+] of OG Acid
2. [H+] of diluted = OG [H+] X OG volume(cm3)/Diluted volume(cm3)
3. Diluted pH=-log[H+] of Diluted

Question 10

Define Ka

Answer 10

Equilibrium Constant for Acids

Question 11

Outline the Equation for Ka

Answer 11

E.G: HCl -> H+ + Cl-
Ka= [H+] [Cl-]/[HCl]

Question 12

When do you use Ka?

Answer 12

Used for weak acids

Question 13

Outline the equation for pKa

Answer 13

pKa=-log10(Ka)

Question 14

Outline the equation of Ka in regards of pKa

Answer 14

Ka = 10^-pKa

Question 15

What happens to pKa when at 1/2 neutralisation

Answer 15

pKa=pH

Question 16

Outline the feature of H2O

Answer 16

It’s amphoteric (can be acid & base)

Question 17

Outline the pH of pure H2O at 298K only

Answer 17

pH 7

Question 18

Outline the Kw equation

Answer 18

Kw(mol2dm6) = [H+] [OH-]

Question 19

When do you use Kw?

Answer 19

Neutral or strong base solutions

Question 20

What is the value of Kw when pure H2O is neutral at 298K

Answer 20

Kw= 1x10^-14 mol2dm6

Question 21

What is the new definition of neutral when H2O is neutral at 298K

Answer 21

[H+] = [OH-]
Therefore
Kw = [H+]^2

Question 22

What is the definition of a base by Bronsted-Lowry?

Answer 22

A proton acceptor

Question 23

Define a Strong Base

Answer 23

A base that fully dissociates in H2O

Question 24

Define a Weak Base

Answer 24

A base that partially dissociates in H2O

Question 25

Define Monobasic Bases

Answer 25

1 mol of OH- per mole of base

Question 26

Define Dibasic Bases

Answer 26

2 mol of OH- per mole of base

Question 27

Outline the steps for finding the pH of a buffer when the weak H+ is in excess

Answer 27

1. Find excess moles of Weak H+ by - all OH- moles
2. Use Ka=[H+][A-]/[HA] & C = (1000 X n)/new V to find [A-] and [HA] with new moles
3. Find [H+] and then -log10[H+]

Question 28

Outline the steps for finding the pH of a buffer when the base is in excess

Answer 28

1. Find excess moles of OH- by - all weak H+ moles
2. Use Kw=[H+][OH-] & C = (1000 X n)/new V to find [OH-]
3. Find [H+] and then -log10[H+]

Question 29

How do Acidic buffers minimise the effect of added H+ ions?

Answer 29

Weak acids and salt concentration is high so salt ions react with H+ ions to remove them