Acids/Bases Flashcards

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1
Q

What is the Bronsted-Lowry model?

A
  • states that acids are proton donators / bases are proton acceptors

Monoprotic - dones one H
Polyprotic - donates multiple H
- can be diprotic or triprotic
- the likelihood of H + donation at each stage decreases as the acids become weaker

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2
Q

What are conjugate acids and bases?

A

Conjugate base:
- the product formed from an acid that has donated a proton (H+)

Conjugate acid:
- the product formed from a base that has accepted a proton (H+)

Acid and conjugate base –> conjugate pairs

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3
Q

Whar are amphiprotic substances?

A
  • substances that act as both a base and acid, meaning they can donate and accept protons
  • e.g water
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4
Q

Strong vs Weak acids

A

Strong acids:
- completely ionise in a solution, meaning they readily donate their H+
- HCl, H2SO4

Weak acids:
- do not completely ionise in a solution
- CH3COOH

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5
Q

Strong vs Weak Bases

A

The strength of a base depends on its ability to accept H+ and therefore ionise

Strong:
- readily accept H+ from acids during a reaction
- NaOH, KOH

Weak:
- don’t readily accept H+ from acids
- NH3

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6
Q

Strenght vs Conc.

A

Concentration:
- measures the number of molecules, both ionised and unionised, in a given volume

Strength:
- measures the percentage of molecules that ionise

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7
Q

How does water self-ionise?

A
  • it self-ionises to form hydronium (H30+) and hydroxide (OH-) ions
  • H20 + H2O –> H3O(+) + OH(-)
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8
Q

what is the ionisation constant?

A
  • represents the product of the ions H3O and OH when water self-ionises
  • the Kw value is constant, meaning any changes in the conc. of either ion means fluctuation in the conc of the other ion

Kw = [H3O+] [OH-] = 10^-14 at 25C

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9
Q

What is pH and how is it calculated

A
  • it measures the acidity of the solution

pH = - log [H3O+]
or
[H3O+] = 10^-pH

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10
Q

What is the acid disassociation constant?

A
  • Ka is a measure of the substances ability to reversibly disssociate in a solution
  • can determine the extent of the disassociation of acids at a particular temp at eq.

Ka = [H3O+] [A-] / [HA]

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11
Q

What is the base dissociation constant?

A
  • Kb measures the ability of a base to dissociate

Kb = [BH+] [OH-] / [B]

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12
Q

Strength based on Ka/Kb

A
  • strong acids have a high Ka / weak acids have a low Ka
  • strong bases have a large Kb / weak bases have a low Kb
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13
Q

What are buffers?

A
  • solutions that can resist a slight change in pH when an acid/base is added to a solution
  • they work by neutralising the acid/base added

Made from weak conjugate pairs
- weak acid and/or salt containing the conjugate base
- weak base and/or salt containing the conjugate acid

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14
Q

What salt is primarily used?

A
  • salt is used as a sodium-based salt due to the solubility of sodium
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15
Q

What occurs when a base is added with a buffer?

A
  • the [OH-] ions react with the weak acids to form water and the conjugate base
  • prevents pH from changing too much
  • favours the forward reaction and shifts eq. to the right
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16
Q

What occurs when an acid is added with a buffer?

A
  • the [H+] ions react with the conjugate base to form water and the weak acid
  • due to the inability of weak acids to dissociate fully, there is no large change in pH
  • favours the backward reaction and shifts eq. to the left
17
Q

What is an acid-base indicator

A
  • often weak acids/bases and indicate colour change based on the solution they are added to
  • with the solution acidic and high in [H3O+], there is a shift to the left, causing a colour change
  • with the solution basic and low in [H3O+], there is a shift to the right, causing a colour change
18
Q

Relationship between pH and pKa

A

Indicator will change colour when Ka = [H3O+]
- pKa ( -log of Ka) can be used due to the number being so small
- the smaller the pKa, the stronger the acid

Therefore, when pKa = pH –> there will be a colour change

19
Q

How does Volumetric Analysis work?

solutions of known conc.

A
  • solutions of known concentrations (primary standards) are used to determine the conc. of unknown solutions
20
Q

How does Titration work?

A
  • a solution with a known quantity is titrated against a solution of an unknown conc.
21
Q

Aliquot, Titrant, Analyte?

A

Aliqout:
- an exact amount of a substance

Titrant:
- substance of a known conc. in the burette

Analyte:
- substance of unknown conc. in the conical flask

22
Q

What is the equivalence point?

A
  • point at which the substances in a reaction have reacted according to the stoichiometric ratio, as per the balanced chemical equation
  • this is when neutralisation occurs
23
Q

What is the end point?

A
  • point in an acid-base titration whwere a permanent colour change occurs
24
Q

When will the colour of the indicator change?

A

When pKind = pH

25
Q

The buffer point?

A
  • within the buffer region, there is a half-equivalence point / buffer point
  • it is where half the reactants have reacted –> [HA] = [A-]

Therefore, Ka = [H+]
or
pKa = pH

26
Q

Steps to calculating an unknown conc.

A
  1. determine average titre of known solution
  2. calculate the moles of known solution used
  3. determine the moles of unknown solution used –> molar ratio
  4. calculate the unknown conc
27
Q

Determining conc./vol before and after dilution?

A

C1 x V1 = C2 x V2

28
Q

How to find conc of original undiluted solution

A

Dilution factor in mL:
= volume of diluted solution / volume of concentrated sample

Then:
- you multiply the conc of the aliquot by the dilution factor to calculate the conc of the original concentrated sample