# A2 Chem 4 Acid-Bases

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- Created by: Victoria Fry
- Created on: 09-04-14 17:46

Definition of a Bronsted-Lowry Acid?

Proton Donor

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Definition of a Bronsted-Lowry Base?

Proton Acceptor

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How do you calculate pH?

-log[H+]

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How many decimal places do you pH to?

2 decimal places

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How do you calculate [H+] from pH?

1 x 10 -pH

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What is the pH of 0.115moldm3 of H2S04?

-log(0.115x2) = 0.64

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What is the expression for kw?

Kw= [H+][OH-]

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At 25 degrees what is the value of Kw?

1x10-14 mol2dm-6

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What is the expression of Kw with pure water?

Kw= [H+]2 as [H+]=[OH-]

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How would you calculate [H+] from Kw?

[H+]= √Kw

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At 318K Kw is 4.02x10-14 calculate the pH of water?

-log(√4.02x10-14 = 6.70

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What equation would you use to go about calculating the pH of a strong base using Kw?

[H+]= Kw divided by [OH-]

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Calculate the pH of 0.1 moldm3 of NaOH?

-log(1x10-14 divided by 0.1 = 13.00

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What is the Ka expression for a weak acid?

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

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What is the simplified Ka expression for a weak acid?

Ka= [H+]2 divided by [HA]

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How would you calculate [H+] for a weak acid from Ka?

[H+]= √Ka x [HA]

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Calculate the pH of 0.1moldm-3 of chloroethanoic acid with a Ka of 1.38x10-3?

-log(√0.1 x 1.38x10-3 = 1.93

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What is the expression for pKa?

pKa= -logKa

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How would you get Ka from pKa?

10-pKa

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How would you calculate the [H+] from diluting a strong acid?

[H+]old x (old volume divided by new volume)

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How would you calculate the [OH-] from diluting a strong base?

[OH-]old x (old volume divided by new volume)

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Calculate the pH when 100cm3 of H20 is added to 25cm3 of 0.5moldm-3 of KOH?

0.5 x (25/100+25) = 1x10-14/0.10 = 13.00

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What is an example of a strong acid?

HCl

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What is an example of a strong base?

NaOH

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What is an example of a weak acid?

Ch3COOH

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What is an example of a weak base?

NH3

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What can't methylorange be used for?

A weak acid

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What pH range does methylorange have?

3.1-4.4

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What can't phenolphthalein be used for?

A weak base

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What pH range does phenolphthalein have?

8.3-10

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How would you know if the question was a strong acid/base question?

The Ka isn't given

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How would you go about calculating a strong acid question?

Balance eqauation, Work out initial moles, find out remaining moles, divide by total volume, then -log

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How would you go about answering a strong base question?

Balance equation, work out initial moles, find remaining moles, divide by total volume, divide by Kw (1x1o-14) and then -log

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How would you know the question is a weak acid question?

The Ka is given

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What is the Ka expression for a weak acid?

Ka= [H+]2/[HA]

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How would you calculate [H+] from Ka in a weak acid question?

[H+] = √Ka x [HA]

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How would you go about answering a weak acid question?

Find out original moles, find out which is in excess - if acid proceed, take away to find remaining, divide moles by salt (limiting factor), times by Ka and then -log

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What do you do in a weak acid question if the base is in excess?

Answer it as if it was a strong base question

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How do you know it's a buffer question?

The ka is given

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What is the Ka expression for a buffer question?

Ka= [H+][X-]/[HX]

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How would you find [H+] in a buffer question?

[H+]= Ka x acid/salt

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How would you go about answering a buffer question?

Find out original moles, calculate moles remaining, times by Ka, take away from salt/smallest number and then -log

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## Other cards in this set

### Card 2

#### Front

Definition of a Bronsted-Lowry Base?

#### Back

Proton Acceptor

### Card 3

#### Front

How do you calculate pH?

#### Back

### Card 4

#### Front

How many decimal places do you pH to?

#### Back

### Card 5

#### Front

How do you calculate [H+] from pH?

#### Back

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