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chemistry y13 > acids and bases > Flashcards

acids and bases Flashcards

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1
Q

What is a Bronsted-Lowry acid?

A

Protons donors- release H+ ions when they’re mixed with water

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2
Q

What is a Bronsted-Lowry base?

A

Proton acceptors

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3
Q

What does dissociate mean?

A

Break up into positively and negatively charged ions in water.

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4
Q

What do strong acids/bases do in terms of dissociation?

A

Fully dissociate/ionise in water

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5
Q

What do weak acids/bases do in terms of dissociation?

A

Partially dissociate/ionise in water so equilibrium lies well to the left

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6
Q

What is the ionic product of water at 25ºC?

A

1 x 10^-14 mol^2dm^-6

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7
Q

What is the equation for Kw?

A

Kw= [H+][OH-]
OR
Kw= [H+]^2

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8
Q

How do you calculate pH?

A

pH= -log [H+]

[H+] = 10 ^ -pH

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9
Q

What is the pH scale?

A

0 (very acidic) to 14 (very alkaline)
pH 7 is neutral

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10
Q

What does monoprotic mean?

A

Each molecule of an acid will release one proton when it dissociates
e.g HCl or HNO3

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11
Q

What does diprotic mean?

A

Each molecule of an acid will release two protons when it dissociates
e.g H2SO4

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12
Q

How do you calculate the acid dissociation constant?

A

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

when dealing with weak acids [H+]=[A-] so Ka= [H+]^2 / [HA]

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13
Q

What does the pH curve look like for a strong acid/strong base reaction?

A

The pH starts around 1 as theres as excess of strong acid. It finishes around pH 13, when you have an excess of strong base

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14
Q

What does the pH curve look like for a strong acid/weak base reaction?

A

The pH starts around 1 as there’s an excess of strong acid. It finishes around pH 9, when you have an excess of weak base

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15
Q

What does the pH curve look like for a weak acid/strong base?

A

The pH starts around 5, as there’s an excess of weak acid. It finishes around pH 13 when you have an excess of strong acid

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16
Q

What does the pH curve look like for a weak acid/weak base?

A

The pH starts around 5 as there is an excess of weak acid. Finishes around pH 9, when you have an excess of weak base

17
Q

What is the point of equivalence?

A

When the pH graph is almost vertical also known as end point

18
Q

What is the range of pH for the colour change of phenalphthalein, and what is the colour change?

A

8.3-10
Colourless to pink

19
Q

What is the range of pH for the colour change of methyl orange, and what is the colour change?

A

3.1-4.4
red to yellow

20
Q

What is a buffer?

A

A solution that resists change in pH when small amounts of acid or alkali are added

21
Q

What is an acidic buffer?

A

Have a pH of less than 7. Contain a mixture of weak acid with one of its salts

22
Q

Why can acidic buffers resist an acid?

A

The large number of A- ions make sure that the buffer can cope with the added acid. If you add a small amount of acid, [H+] increases. Most of the extra H+ ions combine with the A- ions to form HA. This shifts the equilibrium to the left, reducing [H+] conc close to original so pH stays roughly the same

23
Q

Why can acidic buffers resist a base?

A

If you add a small amount of base, [OH-] increases. Most of the extra OH- ions combine with the H+ ions to form water, causing more HA to dissociate into H+ ions, shifting equilibrium to the right. [H+] increases until close to original so pH stays roughly the same

24
Q

What is a basic buffer?

A

Have a pH greater than 7, contain a mixture of a weak base with one of its salts.

25
Q

How does a basic buffer resist an acid?

A

If you add a small amount of acid, [H+] increases. Some of the H+ ions react with OH- to form H2O. This shifts the equilibrium to the right, replacing the OH- ions. this will remove most of the added H+ ions so pH stays roughly the same

26
Q

How does a basic buffer resist a base?

A

If a small amount of base is added, [OH-] increases making the solution more alkaline. Most of the OH- will react with the salt so the equilibrium shifts to the left removing OH- ions from solution. pH stays roughly the same

27
Q

Why do buffers resist changes in pH when diluted by water?

A

If a small amount of water is added, the water dissociates slightly. The extra H+ and OH- ions push the equilibrium the same amount in both directions, leaving it unchanged

28
Q

What are some real life applications of buffers?

A

Shampoos have a pH of around 5.5 to keep hair smooth and shiny as alkaline conditions make surface of individual hairs rougher

Bio washing powders contain buffers to keep pH at right level for enzymes to work

chemistry y13 (6 decks)

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