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physical chemistry > acids bases and pH > Flashcards

acids bases and pH Flashcards

(46 cards)

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1
Q

What is a Bronsted-Lowry Acid?

A

Proton donor

This definition emphasizes the role of acids in proton transfer reactions.

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2
Q

What is a Bronsted-Lowry Base?

A

Proton acceptor

Bases are defined by their ability to accept protons in acid-base reactions.

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3
Q

What characterizes a monoprotic acid?

A

One H+ per molecule

Examples include hydrochloric acid (HCl).

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4
Q

What characterizes a diprotic acid?

A

Two H+ per molecule

An example is sulfuric acid (H2SO4).

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5
Q

How do weak acids behave in solution?

A

Only a small fraction of molecules break apart to form ions

Examples include ethanoic acid and citric acid.

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6
Q

What is the equilibrium position of weak acids?

A

Lies very to the left

This indicates that most of the acid remains undissociated.

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7
Q

What are strong acids characterized by?

A

All molecules break apart to form ions

Examples include HCl and H2SO4.

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8
Q

What defines a weak base?

A

Only slightly ionises in water

An example is ammonia (NH3).

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9
Q

What defines a strong base?

A

Ionises completely in water

An example is sodium hydroxide (NaOH).

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10
Q

What is the general form of an acid-base reaction?

A

HA(aq) + B(aq) ⇌ BH+(aq) + A-(aq)

This represents the transfer of protons between acid (HA) and base (B).

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11
Q

What does the H+ ion represent in aqueous solutions?

A

A proton

It is often associated with water molecules as hydronium ions (H3O+).

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12
Q

What is the formula for pH?

A

pH = -log10[H+(aq)]

This equation shows the relationship between pH and hydrogen ion concentration.

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13
Q

What does a lower pH indicate?

A

Greater concentration of [H+(aq)]

A difference of one pH unit corresponds to a tenfold difference in hydrogen ion concentration.

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14
Q

What is the pH of strong monoprotic acids?

A

[H+] = [acid]

Example: For HCl, the concentration of H+ ions equals that of the acid.

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15
Q

What is the dissociation of strong diprotic acids in water?

A

[H+] = 2[acid]

Example: H2SO4 dissociates to produce two moles of H+ ions per mole of acid.

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16
Q

What happens when an acid is added to water?

A

Forms hydroxonium ions H3O+

Water acts as a base, accepting protons from the acid.

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17
Q

What is the ionic product of water (Kw)?

A

Kw = [H+][OH-]

In pure water, [H+] = [OH-], leading to Kw = [H+]².

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18
Q

How does temperature affect Kw?

A

Kw is temperature dependent

For endothermic reactions, an increase in temperature raises Kw.

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19
Q

What defines the neutral point of water?

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A

[H+] = [OH-]

This means pure water is neutral with equal concentrations of H+ and OH- ions.

20
Q

What is the relationship between pH and temperature in water?

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A

pH of water is different at different temperatures

Changes in temperature affect the ionization of water.

21
Q

What is the pH calculation method for strong bases?

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A

[H+] = Kw / [OH-]

The relationship between hydroxide ions and hydrogen ions is utilized to calculate pH.

22
Q

What is the acid dissociation constant (Ka)?

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A

Equilibrium constant for weak acids

A larger Ka value indicates a stronger acid.

23
Q

What does pKa represent?

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A

Measure of how strong a weak acid is

Smaller pKa values indicate stronger acids.

24
Q

What is the half neutralization point?

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A

Point halfway between zero and the equivalence point

It is significant in titration processes and indicates stability in pH.

25
What is a buffer?
Solution that resists changes in pH ## Footnote Buffers maintain pH stability when small amounts of acid or alkali are added.
26
What is the significance of the half neutralisation point in buffer solutions?
At the half neutralisation point, half the HA has been converted into A- so half remains.
27
What is the equation for the acid dissociation constant (Ka)?
Ka = [HA][A-] / [H+]
28
What is the relationship between pKa and pH at the half-neutralisation point?
pKa = pH
29
Define a buffer.
A buffer is a solution that resists changes in pH when small amounts of acid or alkali are added or when it is diluted.
30
How do buffers maintain pH?
Buffers keep the concentration of hydrogen ions and hydroxide ions in a solution almost unchanged.
31
What happens to the pH of a buffer when small amounts of acid are added?
The equilibrium shifts left, reacting H+ with A- to form more undissociated weak acid HA.
32
What is an acidic buffer made from?
A mixture of weak acid and soluble salt of that acid.
33
Give an example of an acidic buffer.
Ethanoic acid and sodium ethanoate.
34
What is the function of weak acid in an acidic buffer?
To act as a source of HA which can remove any OH- added.
35
What is the function of the salt of a weak acid in an acidic buffer?
To act as a source of A- ions which can remove any H+ ions added.
36
What happens when small amounts of OH- are added to an acidic buffer?
OH- reacts with H+ ions to form water and A-, shifting equilibrium right.
37
Define a basic buffer.
A basic buffer is a mixture of a weak base and a salt of that base to maintain a pH above 7.
38
What is an example of a basic buffer?
A mixture of aqueous ammonia and ammonium chloride.
39
What happens to the pH when small amounts of H+ are added to a basic buffer?
H+ reacts with OH- to make H2O, and equilibrium moves to the right.
40
What happens when small amounts of OH- are added to a basic buffer?
OH- reacts with NH4+ to form NH3 and H2O, shifting equilibrium left.
41
What are the steps for buffer calculations when acid is added?
Initial HA moles + added moles; Initial A moles - added moles.
42
What are the steps for buffer calculations when alkali is added?
Initial HA moles - added moles; Initial A moles + added moles.
43
What is the typical pH of blood?
Approximately 7.4.
44
What is a potential consequence of a 0.5 change in pH in blood?
It may be fatal.
45
Fill in the blank: Most shampoos contain a pH ______ buffer.
5.5
46
How do biological washing powders relate to pH?
They keep pH for enzymes to work most efficiently.

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