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Chemistry 2 > Acids, Bases and Buffers > Flashcards

Acids, Bases and Buffers Flashcards

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1
Q

What is a Bronsted-Lowry acid?

A

A proton donor.

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2
Q

What is a strong acid?

A

An acid that completely dissociates ie it fully ionises when dissolved in water.

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3
Q

What happens when a strong acid reacts with water? What are the products?

A

H+ is transferred to a water molecule to produce a hydroxonium ion and a negative ion depending on what acid you use from the start. HA + H2O H3O+ + A-

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4
Q

Why is it that we assume the dissociation of a strong acid (when it reacts with water) is one wayed?

A

It is a reversible reaction but the forward reaction is must more successful than the backward one i.e. the acid is soo good at giving away H+.

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5
Q

What is the reaction of HCl and H2O? Why is it one wayed?

A

H2O(l) + HCl(g) –> H3O+(aq) + Cl-(aq) So little of the reverse reaction happens hence why we write it one wayed. Virtually 100% of H+ have reacted to form hydroxonium ion so it is 100% ionised/dissociated.

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6
Q

What is pH?

A

The measure of the concentration of H+ ions in a solution. The lower the pH, the higher the concentration of H+.

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7
Q

What is the equation for calculating pH?

A

pH = -log[H+(aq]

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8
Q

How do you calculate [H+] from the pH of a strong acid?

A

[H+] = 10^-pH

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9
Q

What is weak acid?

A

An acid that partially dissociates i.e. it doesn’t fully ionise in water.

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10
Q

When writing the ionisation etc of a weak acid e.g. CH3COOH + H2O H3O+ + Ch3COO-, why do you write an equilibrium sign?

A

The back reaction is more successful than the forward reaction. The further the position is to the left, the weaker the acid is.

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11
Q

What is the equation of the acid dissociate constant, Ka?

A

Ka = [H+][A-] ———— [HA]

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12
Q

What is the acid dissociate?

A

The measure of position of equilibrium.

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13
Q

What is the equation for acid dissociation?

A

HA H+ + A-

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14
Q

How do you calculate pKa?

A

pKa = -log Ka

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15
Q

How do you calculate Ka from pKa?

A

Ka = 10 ^ pKa

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16
Q

What does the pKa tell you? e.g. the higher the pKa…

A

The HIGHER the pKa, the WEAKER the acid. The LOWER the pKa, the STRONGER the acid.

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17
Q

Do Ka and pKa have units?

A

Ka does but pKa doesn’t.

18
Q

What is a base?

A

A proton acceptor.

19
Q

What is a strong base?

A

A base that completely ionises/dissociates when dissolved in water.

20
Q

What are strong bases e.g. KOH or NaOH? I’m referring to ionic stuff.

A

They’re fully ionic e.g. you can think of them being completely split into metal and hydroxide ions.

21
Q

CaOH is insoluable in water. Is it still a base?

A

Yes as it ionises 100%.

22
Q

How do you work out the pH for a strong base?

A

pH = 14 - pOH

23
Q

How do you calculate pOH?

A

pOH = -log [OH-]

24
Q

How do you calculate [OH-] from pOH?

A

[OH-] = 10^ -pOH

25
Q

What is a weak base?

A

A base that partially dissociates?

26
Q

What is Kw?

A

The ionic product of water. Kw = [H+] [OH-]

27
Q

What changes Kw?

A

Temperature

28
Q

What is the value of Kw at room temperature?

A

1x10^14 mol2 dm-6

29
Q

What does the titration curve for strong acid v. strong base look like?

A
30
Q

What does the titration curve for strong acid v. weak base look like?

A
31
Q

What does the titration curve for weak acid v. weak base look like?

A
32
Q

What does the titration curve for weak acid v. strong base look like?

A
33
Q

What is a buffer solution?

A

A buffer solution is one that resists changes in pH when small amounts of acid or alkali are added.

34
Q

What do buffer solutions consist of?

A 
A weak acid and it's salt e.g.
  ethananoid acid (CH3COOH) and sodium ethanoate (CH3COO-Na+).
35
Q

What are acidic buffers? How do they work?

A

They are buffer solutions with a pH of under 7.

  • The acid is a weak acid so partially dissociates and the salt fully dissociates.
  • This means the solution contains: lots of ionised ethanoic acid, lots of ethanoate ions and enought H+ to make the solution acidic.
36
Q

How does a acidic ethanoic acid and sodium ethanoate acid buffer solution work?

A
  • Ethanoic acid partially dissociates: CH3COOH ⇔CH3COO- + H+ pos. of equilibrium left
  • Sodium ethanoate partially dissociates: CH3COONa → CH3COO- + Na+ pos. of equil. further pushed left
  • Plenty of ethanoate ions and undissociated ethanoic acid with enough H+ ions =

CH3COOH(aq) ⇔ CH3COO-(aq) + H+(aq)

37
Q

What happens if you add an alkali to an acidic buffer system?

A

The addiction of OH- raises the concentration of OH-. The buffer solution removes these by reacting the added OH- with H+ ions so OH-(aq) + H+(aq) → H2O

The equilibrium shifts to the right to replace to replace the H+ ions.

38
Q

What happens if you add an acid to an acidic buffer system?

A

The addiction of an acid raises the concentration of H+ ions. The H+ ions react with A- e.g. CH3COO- in the CH3COOH/CH3COO- buffer system. So CH3COO- + H+ <——-===> CH3COOH

The equilibrium shifts to the left, reducing the concentration of H+ ions.

39
Q

BUFFER SOLUTIONS AND BIOLOGICAL ENVIRONMENTS: Why do cells need a constant pH? How is this achieved?

A
  • To allow biochemical reactions to take place. This pH is based on the equilibrium between dihydrogen phosphate ions and hydrogen phosphate ions:
  • H2PO4- <===> H+ + HPO42-
40
Q

BUFFER SOLUTIONS AND BIOLOGICAL ENVIRONMENTS: What pH must blood be kept at? How is this achieved?

A
  • Blood needs to be at constant pH of 7.4.
  • It is buffered using carbonic acid. The levels of H2CO3 are controlled by respiration. By breathing out CO2, levels of H2CO3 is reduced as it moves equilibrium to the right: H2CO3 <==> H2O + CO2
  • The levels of HCO3- are controlled by the kidneys with excess being secreted in the urine: H2CO3 <==> H+ + HCO3-

Chemistry 2 (10 decks)

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