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OCR Chemistry > Chapter 20 - Acids, Bases, and pH > Flashcards

Chapter 20 - Acids, Bases, and pH Flashcards

Bronsted-Lowry acids and bases, The pH scale and strong acids, The acid dissociation constant Ka, The pH of weak acids, pH and strong bases.

1
Q

What is a Bronsted-Lowry acid defined as?

A

A proton donor

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2
Q

What is a Bronsted-Lowry base defined as?

A

A proton acceptor

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3
Q

What is a conjugate acid-base pair?

A

Two species that can be interconverted by transfer of a proton.

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4
Q

In the dissociation of HCl to H+ and Cl-, identify the conjugate acid and base.

A

HCl releases a proton so is therefore the conjugate acid.

Cl- accepts a proton so is therefore the conjugate base.

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5
Q

When water is the base, what is formed?

A

H(3)O+

Hydronium ion

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6
Q

What do the terms monobasic, dibasic and tribasic refer to?

A

The total number of hydrogen ions in the acid that can be replaced per molecule in an acid-base reaction.

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7
Q

How can redox reactions be simplified?

A

Remove the spectator ions

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8
Q

What is the word equation for the reaction of an acid and a metal?

A

acid + metal -> salt + hydrogen

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9
Q

What is the word equation for the reaction of an acid and a carbonate?

A

acid + carbonate -> salt + water + carbon dioxide

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10
Q

What is the word equation for the reaction of an acid and a base?

A

acid + base -> salt + water

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11
Q

What is the word equation for the reaction of an acid and an alkali?

A

acid + alkali -> salt + water

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12
Q

What is the relationship between pH and concentration of H+?

A

Low value [H+] = high pH

High value [H+] = low pH

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13
Q

What is the equation for working out pH from [H+]?

A

pH = -log[H+] (base 10)

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14
Q

How is the pH calculated for a strong acid?

A

Assume it fully dissociates

Therefore [H+] = [HA]

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15
Q

How is the new pH calculated for a strong acid on dilution?

A

Work out change in concentration of HA and therefore [H+]

Then put back into pH = -log[H+]

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16
Q

How is the pH calculated for a weak acid?

A 
Ka = [H+][A-]/[HA]
Ka[HA] = [H+][A-]
[H+] = [A-]
[H+]^2 = Ka[HA]
[H+] = sqrt(Ka[HA])
17
Q

What is Kw?

A

The ionic product of water

18
Q

What is the value of Kw?

A

1x10^-14 mol2dm-3 at 298K

given on data sheet

19
Q

How can pH of strong bases be found when given the concentration of OH-?

A

Kw =[H+][OH-]=1x10^14

Find [H+]
Then pH=-log[H+]

20
Q

How can pH of weak bases be found when given the concentration of OH-?

A

Similar method to weak acids, with the additional step of Kw = [H+][OH-]

21
Q

what is the pOH formula

A

pOH= -log[OH(aq)]

22
Q

What is the formula of [OH-(aq)]

A

10^-pOH

23
Q

pKa value formula

A

pKa = -log ka

24
Q

What is the unlog of pKa

A

Ka = 10^-pKa

25
Q

limitations of using approximations to Ka related calculations for ‘stronger’ weak acids

A

[HA]equilibrium ~ [HA]undissociated may no longer be valid.

The approximation that the concentration of acid is much greater than the H+ concentration at equilibrium is not valid

OCR Chemistry (28 decks)

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