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Edexcel A-Level Chemistry > Topic 12 - Acid Base reactions > Flashcards

Topic 12 - Acid Base reactions Flashcards

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1
Q

What are the products when an acid reacts with a base?

A

The salt and water

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2
Q

What are the products when an acid reacts with a metal?

A

salt + hydrogen

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3
Q

What are the products when an acid reacts with a carbonate?

A

salt + water + carbon dioxide

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4
Q

What are the products when an acid reacts with an alkali?

A

Salt + Water

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5
Q

How can you group Acids?

A

By the number of hydrogens

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6
Q

What does Monobasic Mean?

A

The acid contains one hydrogen

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7
Q

What does Dibasic mean?

A

The acid contains two hydrgens

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8
Q

What does Tribasic mean?

A

The acid contains three hydrogens

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9
Q

What does the number of hydrogens in an acid affect?

A

The PH

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10
Q

What is the definition of a Bronsted and Lowry acid?

A

proton donor

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11
Q

What is the definition of a Bronsted and Loweys Base?

A

proton acceptor

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12
Q

What do acids contain?

A

Hydrogen ions.

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13
Q

What do bases do?

A

accept H+ to try and produce water

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14
Q

What do strong acids do?

A

Fully dissociate. All the hydrogen ions will be released

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15
Q

What do weak acids do?

A

Only partially dissociate. Only some of the hydrogen ions will be released

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16
Q

What are conjugate acid-base pairs?

A

Two species that can be interconverted via an exchange of a proton.

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17
Q

How do you show conjugate acid-base pairs?

A

Write acid under those that loose hydrogen. Write Base under those that gain hydrogen. Numbers show the linking molecules. Where one hydrogen is lost and then ends up is shown with the same number.

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18
Q

What does PH mean?

A

Potential Hydrogen

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19
Q

What is PH a measure of?

A

The concentration of hydrogen ions (H+) in a substance.

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20
Q

What is the formula for calculating PH?

A

-log([H+])

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21
Q

What do [ ] mean?

A

[ ] means concentration

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22
Q

What does [H+] mean?

A

Concentration of Hydrogen Ions

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23
Q

What is the formula to calculate [H+]?

A

10^-PH

24
Q

How do you calculate the PH of a strong acid?

A

Calculate the concentration of hydrogen ions ([H+]). Then perform -log() on that value.

25
Q

Why is it harder to calculate PH of a weak acid?

A

As they don’t fully dissociate it means that the [H+] is not the same as the acid concentration.

26
Q

How can the dissociation of weak acids be represented?

A

HA = Weak acid. H = Hydrogen. A = Other parts of the acid. HA <-> H+ + A-.

27
Q

What is the symbol for the Acid Dissociation Constant?

A

ka

28
Q

What does Ka show?

A

The extent of acid dissociation. The larger the Ka value the stronger the acid (more dissociation)

29
Q

How do you calculate Ka?

Formula

A

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

30
Q

What is Pka?

A

Another measure for the dissociation constant.

31
Q

How do you calculate Pka?

A

pKa = -logKa

32
Q

Why do we use Pka?

A

It is the log() of ka so is a larger number which is more useful and easier to use.

33
Q

How do you calculate the PH of a weak acid?

A

Use the value of Ka to calculate [H+] using the formula: [H+] = (²root) Ka*[HA]. You can then use -log([H+]) to get the PH

34
Q

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

A

That the concentration of the weak acid doesnt change. As so little dissociates it is easier to assume that nothing is lost from the [HA]

35
Q

How does water dissociate

A

It slightly dissociates into Hydrogen and Hydroxide ions. H2O <-> H+ + OH-

36
Q

Is water an acid or a base?

A

Both.

37
Q

What is the Ionic Product of Water?

A

The extent to which water dissociates. As water only dissociates a small amount it is said to be constant at a certain temperature.

38
Q

What is the symbol for the Ionic Product of Water?

A

Kw

39
Q

What is the formula for Kw?

A

Kw = [H+][OH-]

40
Q

What is Kw at standard conditions?

A

At PH7 and 25°C: [H+] = [OH-] = 10^-7. So Kw = 10^-7 *10^-7. Kw = 10^-14

41
Q

What are strong bases?

A

Bases that fully dissociate to form OH-ions.

42
Q

What are some examples of strong bases?

A

sodium hydroxide (NaOH)

43
Q

What is the dissociation ratio of strong bases?

A

1:1. For every mole of base one mole of OH- ions are released.

44
Q

How do you get the [H+] of a strong base?

A

From the [OH-] using the Kw.

45
Q

What is the formula for [H+] from [OH-]?

A

[H+] = Kw/[OH-]

46
Q

How do you calculate the PH of a strong Base?

A

[H+] = Kw / [OH-]. then do -log([H+])

47
Q

What is a buffer solution?

A

A solution that resists the change in PH when a small amount of Acid or Alkali is added.

48
Q

How do you make a buffer solution?

A

From a weak acid and its conjugate base - (or its salt).

49
Q

Example of the formation of a Buffer solution:

A

Weak acid - CH3COOH. Its salt - CH3COONa. CH3COONa -> CH3COO- + Na+. So the buffer solution will have this formula:. CH3COOH <-> H+ + CH3COO-. Na+ are spectator ions and do not form part of the buffer solution reaction.

50
Q

What will happen if you add Hydrogen Ions to a buffer solution?

A

The hydrogen ions will react with the conjugate base and form more of the acid - Reducing the [H+] and so the equlibrium shifts to the left.

51
Q

What happens if you add OH- ions to a buffer solution?

A

They react with H+ to produce water (H2O). This reduces the number of H+ ions so the acid disociates more to produce more. The equilibrium shifts to the Right.

52
Q

What do you need to calculate the PH of a Buffer?

A

The Ka (Acid Dissociation Constant) and the concentrations of the weak acid and the salt.

53
Q

How do you calculate the [H+] of a buffer?

A

[H+] = Ka * [HA] / [A-]. HA = Weak Acid. A- = Conjugate Base/salt

54
Q

Why do you need to calculate the concentrations in a buffer?

A

When you create the buffer the concentrations of everything wont be the same as some things will react.

55
Q

What is the formula for Concentration in a buffer?

A

(Initial Concentration of thing * Initial Volume of thing) / Total Buffer Volume

56
Q

What is the formula for PH from buffer volumes?

A

PH = PKa + log([A-]/[HA])

57
Q

How do you use the formula to calculate the concentrations needed create a buffer at a specific PH?

A

Rearrange so that the PH and the PKa (which should be known) are on one side of the equation: PH - Pka = log([A-]/[HA]). This will let you find the total of the log(x). Use 10^log(x) to get the total for the fraction without the log. (z in this case). You can then substitute in one of the concentrations (Which should be known) (Here the conjugate base

Edexcel A-Level Chemistry (9 decks)

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