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Chemistry (A2) > Acids and Bases > Flashcards

Acids and Bases Flashcards

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
How would you work out the PH of a weak acid?
1) Ka = [H+][A-] / [HA] 2) Rearrange to calculate [H+] 3) Ph = -log[H+]
26
What is a titration?
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
27
Draw a labled diagram for the set up for a titration
28
Draw the pH Curve for strong acid into a 1) Strong Base 2) Weak Bace
29
Draw the pH Curve for weak acid into a 1) Strong Base 2) Weak Bace
30
Define the term equivalence point
The point at which the exact volume of base/acid has been added to neutralise the acid/bace
31
What happens to the ph of the solution around the equivalence point
Large and rapid change of Ph (unless weak-weak) When mol of H+ = mol of OH-
32
What are the properties of a well chosen indicator (3)
. 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
What indicator would you use for a strong acid- strong bace titration
Phenolphthalein or methyl orange
34
Explain the properties of methyl orange indicator
Red in acidic solutions yellow in basic solutions Colour changes between: 3.1-4.4
35
Explain the properties of Phenolphthalein
Colourless in acidic solutions and pink in basic solutions Changes colour between 8.3-10.0 ph
36
What is the half-neutralisation point What is it the same as?
Point where the volume of bace/acid added has reacted with half of the molecules of the original solution Pka value = Ph
37
What indicator would you use for a strong acid - weak bace titration
Methyl Orange
38
What indicator would you use for a strong base- weak acid titration
Phenolphthalein
39
What indicator would you use for a weak acid - weak base titration
Neither methyl orange or phenolphthalein is suitable Neither give a sharp change at the end point
40
Why does the ph equal the pka at the half neutralisation point?
41
Define a buffer solution
A solution that resists changes in ph when small amounts of acid/alkali are added
42
What do acidic buffer solutions contain
A weak acids and a soluble salt of that acid that fully dissociates
43
What happens if (H+) are added to an acidic buffer?
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
What happens when we add a base (OH-) to an acidic buffer
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
What does a basic buffer contain?
Weak base and a soluble salt of that weak base that fully dissociates
46
What happens if you add a base (Oh-) to a basic buffer
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
What happens when you had H+ to a basic buffer
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
Write the equibrium reactions for an acidic buffer. Use Ethanoic acid and Sodium ethanoate
49
Write the equilibrium equations for a basic buffer use Ammonia and Ammonium Chloride
50
Write the reaction for an acidic buffer with added acid
A- + H+ —-> HA
51
Write a reaction for an acidic buffer with added alkali
H+ + Oh- —> H2O
52
How to you form an acidic buffer other then mixing the constituents
Neutralise half of a weak acid with an alkali, this forms a weak acid / soluble salt mixture
53
When calculation the ph of a buffer what assumptions do we make?
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
Where are buffer solutions found in commercial products?
Shampoo - stops hair becoming alkali and therefore dry Washing powder - contains enzymes that require specific ph’s Blood
55
Why does KW increase as temperature increases
Equilibrium is endothermic Equilibrium shifts to the right to minimise temperature change H20 (reversible) H+ + OH- which increases the kw equation
56
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
As it hasn’t reacted with anything [H+] = [A-]
58
59
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
Smaller PH Magnesium Hydroxide is less double then Calcium Hydroxide So it will Dissociate until it’s ions less readily in water
61
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
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
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
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
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
Name something you always forget about this topic
Ka expression you need to divide by the total volume!!!!!!!!!!!!!!!!!!!
65
Which structures are held together by disulphide bridges
Tertiary and Quaternary
66
It takes me X Cm^3 of NaOH to neutralise a monoprotic acid Explain a method to calculate the original concentration of HX
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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