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chemistry (a2) > Acids and Bases > Flashcards

Acids and Bases Flashcards

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1
Q

Define a Brønsted-Lowry Acid?

A

A proton Donor

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2
Q

Define Brønsted-Lowry Base

A

Proton Acceptor

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3
Q

What ion causes a solution to be acidic

A

The oxonium ion

H3O+

Protons react with H2O to form it

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4
Q

What ion causes a solution to be alkaline

A

-OH

Hydroxide ion

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5
Q

Write the equation for the ionisation of water

A
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6
Q

Derive the Kw Equation using the ionisation of water

A

Ka = [H3O+][OH-] / [H2O]

[H2O] Kw = [H3O+][OH-]
[H2O] is so large in comparison to [H3O+] and [OH-] That it is considered to remain constant

Kw = [H3O+][OH-]

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7
Q

State the value of kw at 298k

A

10^-14

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8
Q

What physical factors affect the value of Kw and explain why

A

Temperature only

If temperature is increased the eqm moves in the endothermic direction (right)

Kw therefore increases and the Ph of pure water decreases

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9
Q

Why is pure water still neutral even if the ph doesn’t equal 7?

A

[H3O+] = [OH-]

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10
Q

What is the equation for Ph?

What bace is the logarithm to

A

Ph = -log(H3O+)

Base 10

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11
Q

A lower ph has a _____________________________

A

Higher concentration of [H+] present

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12
Q

A Ph difference of 1 is a ______________ difference in [H+]

A

A factor of 10

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13
Q

How do you find [OH-] From ph

A

1) PH —-> [H3O+]

2) Kw = [H3O+][OH-]

3) Kw at 298k = 10^-14

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14
Q

Explain the difference between monoprotic, diperotic and triprotic acids?

A

Produce different amounts of Protons per mol of acid

Monoprotic —> 1 Mol of [H+] from 1 mol of acid

DiProtic ——> 2 Mol of [H+] from 1 mol of acid

Triprotic ——> 3 Mol of [H+] from 1 mol of acid

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15
Q

How do you calculate the PH of a strong alkaline solution?

A

1) Kw = [H+][OH-]

2) ph = -log([H+])

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16
Q

Define the term strong acid?

A

An acid which dissociates fully into their ions within aqueous conditions

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17
Q

Define the term strong bace

A

A bace which fully dissociates into their ions in water

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18
Q

What is the difference between a strong acid and a concentrated one?

A

Concentrated acids have many moles per unit volume

Strong acids dissociate fully in water

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19
Q

What is a weak acid and bace

A

Acids and braces which only dissociate partially into their ions in aqueous conditions

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20
Q

Name some strong acid examples

A

H2SO4 - Diprotic
HCl - Monoprotic
H3PO4 - Triprotic

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21
Q

Give some examples of strong bases?

A

NaOH

CaCO3

Na2CO3

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22
Q

Give an example of a weak acid

A

Ethanoic acid - CH3COOH

Any organic acid

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23
Q

Give an example of a weak Base?

A

NH3 Ammonia

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24
Q

Write the expression for Ka

A

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

Where
HA (reversible) [H+][A-]

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25
Q

How would you work out the PH of a weak acid?

A

1) Ka = [H+][A-] / [HA]
2) Rearrange to calculate [H+]
3) Ph = -log[H+]

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26
Q

What is a titration?

A

The addition of a base/acid of know concentration

Titration by adding it to a acid/bace of unknown concentration to determine the unknown concentration

A Indicator (Ph probe) is used to show that neutralisation has occurred

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27
Q

Draw a labled diagram for the set up for a titration

A
28
Q

Draw the pH Curve for strong acid into a

1) Strong Base

2) Weak Bace

A
29
Q

Draw the pH Curve for weak acid into a

1) Strong Base

2) Weak Bace

A
30
Q

Define the term equivalence point

A

The point at which the exact volume of base/acid has been added to neutralise the acid/bace

31
Q

What happens to the ph of the solution around the equivalence point

A

Large and rapid change of Ph (unless weak-weak)

When mol of H+ = mol of OH-

32
Q

What are the properties of a well chosen indicator (3)

A

. Sharp colour change changes colour over a small range of ph values

. Colour change must be at the steep/vertical section of the curve

. Distinct colour change so it is obvious when the endo point has been reached

33
Q

What indicator would you use for a strong acid- strong bace titration

A

Phenolphthalein or methyl orange

34
Q

Explain the properties of methyl orange indicator

A

Red in acidic solutions
yellow in basic solutions

Colour changes between:
3.1-4.4

35
Q

Explain the properties of Phenolphthalein

A

Colourless in acidic solutions and pink in basic solutions

Changes colour between
8.3-10.0 ph

36
Q

What is the half-neutralisation point

What is it the same as?

A

Point where the volume of bace/acid added has reacted with half of the molecules of the original solution

Pka value = Ph

37
Q

What indicator would you use for a strong acid - weak bace titration

A

Methyl Orange

38
Q

What indicator would you use for a strong base- weak acid titration

A

Phenolphthalein

39
Q

What indicator would you use for a weak acid - weak base titration

A

Neither methyl orange or phenolphthalein is suitable
Neither give a sharp change at the end point

40
Q

Why does the ph equal the pka at the half neutralisation point?

A
41
Q

Define a buffer solution

A

A solution that resists changes in ph when small amounts of acid/alkali are added

42
Q

What do acidic buffer solutions contain

A

A weak acids and a soluble salt of that acid that fully dissociates

43
Q

What happens if (H+) are added to an acidic buffer?

A

H+ reacts with the organic acids ion
The organic acids ion is in high concentration due to the soluble salt of that acid
This means that eqm shifts to the left to compensate for the increase in H+
so CH3COOH is produced more

44
Q

What happens when we add a base (OH-) to an acidic buffer

A

The OH- ions react with the h+ ions in the solution producing water
There is a low concentration of these ions within the solution, so to compensate the eqm shifts to the right to utilise more of the organic acid.

45
Q

What does a basic buffer contain?

A

Weak base and a soluble salt of that weak base that fully dissociates

46
Q

What happens if you add a base (Oh-) to a basic buffer

A

OH- reacts with the basic ion
The basic ion is in high concentration due to the soluble salt of that base
This means eqm of weak base has shifted to the left to compensate for the change, producing more of the weak bace and water

47
Q

What happens when you had H+ to a basic buffer

A

The H+ ions react with the OH- ions in the solution producing water
There is a low concentration of these ions within the solution, so to compensate the eqm shifts to the right to utilise more of the Base and water .

48
Q

Write the equibrium reactions for an acidic buffer.

Use Ethanoic acid and Sodium ethanoate

A
49
Q

Write the equilibrium equations for a basic buffer

use Ammonia and Ammonium Chloride

A
50
Q

Write the reaction for an acidic buffer with added acid

A

A- + H+ —-> HA

51
Q

Write a reaction for an acidic buffer with added alkali

A

H+ + Oh- —> H2O

52
Q

How to you form an acidic buffer other then mixing the constituents

A

Neutralise half of a weak acid with an alkali, this forms a weak acid / soluble salt mixture

53
Q

When calculation the ph of a buffer what assumptions do we make?

A

Salts are dissociated fully
and weak acids dissociate very poorly, (conc of acid at start of calc = conc of acid )
[Salt] = [A-] (conc of salt is this initial concentration of A- ions)
[HA start] = [HA Eqm] (conc of acid is taken as it’s initial conc)

54
Q

Where are buffer solutions found in commercial products?

A

Shampoo - stops hair becoming alkali and therefore dry
Washing powder - contains enzymes that require specific ph’s
Blood

55
Q

Why does KW increase as temperature increases

A

Equilibrium is endothermic
Equilibrium shifts to the right to minimise temperature change
H20 (reversible) H+ + OH-

which increases the kw equation

56
Q
A

Both Acids are in the form of RCOOH

ethanoic acid R = CH3
ethanediotic acid R =COOH

COOH on ethanediotic acid contains two very electronegative oxygen atoms

has a negative inductive effect compared with the CH3 group’s positive inductive effect

as a result O-H bond in ethanediotic acid is more polarised resulting into more H+dissociation

ethanediotic acid is stronger

57
Q
A

As it hasn’t reacted with anything [H+] = [A-]

58
Q
A
59
Q
A

C
Propanoic acid has more of the negative inductive effect then Methanol
So there’s the addition of more (OH-) in solution then (H3O+)
So higher PH

60
Q
A

Smaller PH

Magnesium Hydroxide is less double then Calcium Hydroxide

So it will Dissociate until it’s ions less readily in water

61
Q
A

In Pure water [H+] = [OH-]
So Ratio of A- : HA remains constant as Equilibrium shifts equally in both directions

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

H+ stays constant, so Ph stays constant

62
Q

The Ph of barium hydroxide is lower at 50 Degrees then at 10 degrees

At 50 degrees a 25cm^3 sample was neutralised by 22.45Cm^3 of HCL

Would the volume of hydrochloric acid added to 25Cm^3 of Barium hydroxide at 10 degrees be lower/the same/ higher then at 50 degrees

Explain your answer

A

The same —> Same number of [OH] ions

Explanation (No marks) :

Neutralisation is when all of the [H+] ions have reacted with [OH-] ions

Barium hydroxide at different a higher PH means that more OH- ions have been dissociated from the positive barium ion, but the amount of [OH] ions in solution are exactly the same.

So The same amount of Acid is needed

63
Q

State how a buffer solution can be made from solutions of Potassium Hydroxide and Ethanoic acid

How does this solution resist a change in PH if a small acid is added

A

Add sufficient KOH so that the acid contains a mixture of Ethanoic acid and Ethanoate ions.

Soluble salt/weak acid mixture

Ethanoate ion reacts with the H+ to form CH3COO
This shifts the equilibrium to the left as in a weak acid changes in conc of conjugate bace and h+ will has a greater effect then changes in conc of the acid. , utilising more of the H+ ions in solution to form Ethanoic acid. as H+ has a lower conc then A- increase in H+ have the most effect

64
Q

Name something you always forget about this topic

A

Ka expression you need to divide by the total volume!!!!!!!!!!!!!!!!!!!

65
Q

Which structures are held together by disulphide bridges

A

Tertiary and Quaternary

66
Q

It takes me X Cm^3 of NaOH to neutralise a monoprotic acid

Explain a method to calculate the original concentration of HX

A

In the reaction OH- ions react with the Acid to produce a salt + water

Therefore mol of OH- ions = mol of acid in the original solution

chemistry (a2) (15 decks)

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