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A2 Level - Chemistry > Chapter 20 - Acid-base Equilibria > Flashcards

Chapter 20 - Acid-base Equilibria Flashcards

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1
Q

what was the Arrhenius model of an acid

A

Acids dissociate and release H+ ions in aqueous solutions

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2
Q

What was the Arrhenius model of an alkali

A

Alkalis dissociate and release OH- ions in aqueous solutions

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3
Q

What is the Bronsted Lowry model for an acid

A

Acids are proton donors

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4
Q

What is the Bronsted Lowry model for an alkali

A

Alkalis are proton acceptors.

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5
Q

Define conjugate acid-base pairs

A

They contain 2 species that can be interconverted by transfer of a proton

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6
Q

What is a Conjugate acid

A

If it has lost a H+.

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7
Q

What is a Conjugate alkali

A

If it has gained a H+

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8
Q

Define monobasic, dibasic, tribasic

A

They refer to the number of hydrogen ions in the acid that can be replaced per molecule in an acid-base reaction.

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9
Q

What plays an active role in an acid

A

the H+ ion

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10
Q

acid + metal

A

salt + H2

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11
Q

acid + carbonate

A

salt + water + CO2

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12
Q

acid + base

A

salt + water

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13
Q

acid + alkalis

A

salt + water.

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14
Q

Equation for pH

A

ph = -log [H+]

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15
Q

Equation for [H+]

A

[H+] = 10^ -pH.

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16
Q

What is neutral on the pH scale

A

7.

17
Q

What is acid on the pH scale

A

Anything below 7.

18
Q

What is alkali on the pH scale

A

Anything above 7.

19
Q

pH of strong acids

A

In aqueous solutions, a strong mono basic acid will complete dissociate.
So, for any strong acid, the [H+] is equal to the concentration of the acid [HA].

20
Q

Define a strong acid

A

One that completely dissociates in aqueous solutions

21
Q

Define a weak acid

A

One that partially dissociates in aqueous solutions.

22
Q

What is the Ka

A

The acid dissociation constant for weak acids only.

It is equal to the Kc in some ways, but for an equilibrium equation

23
Q

The larger the Ka

A

The further the equilibrium has shifted to the right side, so the greater the dissociation and the acid strength

24
Q

Equation for pKa

A

pKa = -log Ka

25
Q

Equation for Ka

A

10 ^ -pKa

26
Q

Strong acid =

A

Large Ka = Small pKa

27
Q

Weak acid =

A

Small Ka = Large pKa

28
Q

What does a strong acid do in water

A

Completely dissociate

29
Q

What happens when a weak acid in mixed with water

A

It will only partially dissociate and instead, an equilibrium will take place.
[HA] [A-] + [H+]

30
Q

What does the [H+] depend on?

A

Concentration of the acid, [HA]

And the acid dissociation constant, Ka.

31
Q

What are the 2 important approximations to make for the calculation of the Ka?

A
  1. You can assume that the concentration of H+ = Concentration of A-, because they are equal at first.
  2. The equilibrium concentration of HA is smaller than the undissociated concentration. As the dissociation of weak acids is small, you can assume that it is so small, it’s negligible, so that [HA] start = [HA] eqm
32
Q

Equation to calculate Ka for a weak acid

A

Ka = [H+]^2 / [HA]

33
Q

Experimentally, how can you calculate Ka (2 ways)

A
  1. Preparing a standard solution of a weak acid of known concentration.
  2. Measuring the pH of the standard solution using a pH meter.
34
Q

What are the approximations made when calculating with weak acids?

A
  1. The dissociation of water is negligible.

2. The concentration of the acid is much greater than the H+ concentration at equilibrium

35
Q

What is Kw

A

Ionic product of water. The ions in water multiplied together. At 25 degrees C, it is 1 x 10^-14.

36
Q

For whole number pH values, ensure that the indices for [H+] and [OH-] add up to:

A

-14

37
Q

Define an alkali

A

A soluble base that releases OH - ions in aqueous solutions.

A2 Level - Chemistry (11 decks)

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