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A-level Chemistry > Acids, Bases And Buffers > Flashcards

Acids, Bases And Buffers Flashcards

1
Q

What is a Brønsted-Lowry acid?

A

The are proton donors

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2
Q

What is a Brønsted-Lowry base?

A

Proton accepter

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3
Q

What are mono basic acids?

A

Acids what donate one mole of H+ per mole of acid

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4
Q

What is a di basic acid?

A

Acids which donate 2 moles of H+ per mole of acids

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5
Q

What is a tribasic acid?

A

Acids that donate three moles of H+ per mole of acids

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6
Q

What are conjugate acid base pairs?

A

A pair of two species that transform into each other by gain or loss of a proton

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7
Q

What are the roles of hydrogen ions in reaction of acids?

A

-They react with metals, carbonates and metal oxides and alkalis

-Which form salts

  • active species from acids is H+
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8
Q

What do strong acids do when put into a solution?

A

They fully dissociate in solution donating H+

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9
Q

How do we calculate the pH of strong acids?

A
  1. First calculate the concentration of H+ ions that have dissociated.
  2. In strong acids they completely dissociate so concentration of acid = concerntration of H+
  3. Then once pH is calculate pH can be found using the equation
    pH= -log[H+]
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10
Q

How do you work out the concentration of a strong acid if your given the pH?

A

[H+] = 10^ -pH

If it’s a diprotic acid= divide answer by 2

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11
Q

If the [H+] is greater what happens to the strength of the acid?

A

The acid is stronger

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12
Q

The smaller the pH is the acid weak or strong?

A

It’s stronger

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13
Q

What is the ionic equation for the dissociation of weak acid in a solution?

A

HA -> H+ + A-

H= concentration of H+ ion

A- = concentration of acid ion

HA= equilibrium concentration of acid

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14
Q

What is the Ka expression?

A

Ka= [H+] [A-]
————
[HA]

H+= concentration of H+ ion

A- = concentration of acid ion

HA= equilibrium concentration of acid

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15
Q

What is the relationship between Ka and dissociation?

A

The larger the value for Ka the greater the dissociation

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16
Q

How do you work out pKa from Ka?

A

pKa= -log Ka

17
Q

How do you work out Ka from Pka?

A

Ka= 10^-pKa

18
Q

How do you work out the equilibrium concentration of an acid?

A

(Given concentration) - [H+ ion concentration]

19
Q

How do you work out pKa from the concentration of a weak acid and it’s pH?

A
  1. If you have pH just 10^-pH to find the [H+]
  2. if your given the concentration then, concentration - H+ value
  3. Then form Ka expression
  4. Then -log Ka to find pKa
20
Q

How do you find the pH of weak acids?

A
  1. For an equilibrium calculation l, Ka expression, to find H+
  2. Convert H+ into pH
21
Q

What is the equation used to calculate [H+] of weak acids?

A

[H+]= square root of ka X [HA]

22
Q

What is the assumption made when calculating pH of weak acids?

A

-assumed that the concentration of acid at equilibrium is equal to the concentration of acid after dissociation. This is because only very little of the acid dissociates

23
Q

What is the equilibrium which occurs in pure water and all aqueous solutions?

A

H2O (l) —> H+ + OH-

24
Q

What is the expression for Kw?

A

= [H+ (aq) ] [ OH- (aq) ]

25
Q

When is the kw expression used?

A

To calculate [H+ (aq) ] ions if we know the [OH (aq)] ions and vice versa

26
Q

Why are pure water and neutral solutions neutral?

A

[H+] = [OH-]

27
Q

How do we calculate kw?

A

Kw= [H+]^2

28
Q

How do we work out H+ from kw?

A

Square root of kw

29
Q

What is the value of kw for all aqueous solutions at 25 degrees?

A

1x10 -14 mol^2 dm^-6

30
Q

How do we work out the pH of a strong base?

A
  1. Work out H+ using the kw expression:
    H+= Kw / [OH-]
  2. Then -log H+ to get pH
31
Q

How do we calculate the pH of a diluted strong acid?

A
  1. Find H+ of new acid=

[H+]old X old volume/ new volume

  1. ph= -log[H+]
32
Q

How do you calculate the pH of a diluted base?

A
  1. Find OH conc of new base=
    [OH-]old X old volume / new volume
  2. Then find H+ conc: kw/[OH-]
  3. Then - log H+
33
Q

What is a buffer?

A

A solution that minimises changes in pH when small amounts of acid or base are added

34
Q

How is an acidic buffer solution made?

A

-made from a weak acid and a salt of that weak acid (made from reacting the weak acid with a strong base

35
Q

Describe how a basic buffer is made?

A

Made from a weak base and a salt of that weak base (made from reacting the weak base with a strong acid)

36
Q

How is the pH of a buffer solution calculated?

A
  1. Calculate the moles of both solutions used to make the buffer solution.
  2. Then insert these values into the equation [H+]=ka [HA] / [A-]
  3. Then - log (H+) to get pH

A-level Chemistry (19 decks)

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