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what is an inorganic Acids and give examples
simple and have a hydrogen and an ion: HCl, HNO3, H3PO4
define Organic Acids
compounds that are organic but have acidic properties (e.g. alkanoic acids: have -COOH)
what is the nature of Alkalis
Bases soluble in water → include soluble hydroxides and ammonia (all Group 1 metals)
Monoprotic
Not all hydrogens in an acid molecule are ionizable: monoprotic = can donate one H+
define Diprotic
Can donate two H+
hydronium ion
Is the more stable version of an aqueous H+(aq): H+(aq)+ H2O(l) → H3O+(aq)
H+(aq) = H3O+(aq)
properties of acids (6)
Produce H+ ions in water |
Have a pH < 7 |
Sour taste |
Conducts electricity in solution |
Turns blue litmus red |
Corrosive |
acid dissociation equation
HA → H+ + A-
base properties (6)
Produce hydroxide ions (OH-) in solution |
pH > 7 |
Soapy feel, bitter taste |
Conducts electricity in solution (if soluble) |
Turns red litmus blue |
Corrosive (caustic) |
types of bases and an example (4)
Metal Hydroxides | Metal Oxides (non-metal oxides like CO2 and SO2 are acidic) | Metal Carbonates/Hydrogen Carbonates | Organic Bases (include amines: -NH2) |
NaOH, Ba(OH)2 | Na2O, CuO | K2CO3, NaHCO3 | caffeine, nicotine, morphine |
what is the nature of ammonia?
a weak base
metal oxides are either:
bases or amphoteric
what is the acetate ion and its nature?
a weak base, CH3COO-
what is amphoteric
can act as either an acid or a base (Al2O3) → will be the opposite of whatever it is reacting with
base: Al2O3 (s) + 6HCl(aq) → 2AlCl3 (aq) + 3H2O(l)
acid: Al2O3 (s) + 2NaOH(aq) → 2AlCl3 (aq) + 2Na(Al(OH)4)(aq)
what is amphiprotic:
Amphiprotic: can donate or accept a proton
H2O(l) + HCl → H3O+(aq) + Cl-(aq) (water accepted the H+, HCl donated)
H2O(l) + NH3 (aq) → NH4+(aq) + OH-(aq) (water donated H+, NH3 accepted)
what is the purpose of an indicator and what is an indicator’s nature?
used to measure how acidic or basic something is
An indicator in any substance that will be different colours in different pH conditions (qualitative change)
Indicators are weak acids or bases = exist in two forms
what is a universal indicator?
most commonly used → useful because it is a whole range of different colours depending on the pH - combination of indicators
purpose of the pH
Describes the acidity of a solution [H+]
Acids have a high [H+] = low pH
Bases have a low [H+] = high pH
pH =7: neutral solution
pH formula
pH = -log10[H+]
how does an indicator work?
Indicators are weak acids or bases = exist in two forms that are different colours due to its reversibility
HInd ⇌ H+ + Ind-
H is the hydrogen atom and Ind is the indicator - the rest of the organic molecule
A chemical equilibrium exists in solution between HInd and Ind-: and they are different colours
Qualitatively shows where the equilibrium lies
If a base is added, [H+] ↓, so eqm shifts right
If acid is added, [H+] ↑, so eqm shifts left
methyl orange’s pH range and colour at each pH
Methyl orange | red | 3.1- 4.4 | yellow |
litmus’s pH range and colour at each pH
Litmus (vegetable extract) | red | 4.5-8.3 | blue |
bromothymol blue’s pH range and colour at each pH
Bromothymol blue | yellow | 6.0-7.6 | blue |
phenolphthalein’s pH range and colour at each pH
Phenolphthalein | colourless | 8.2-10 | pink |
how to you prepare and test a natural indicator?
Preparing the Natural Indicator
Tear or slice one red cabbage leaf/flower petal/tea/fruit leaf into small pieces and place them in a beaker
Cover it in 250mL boiling water for 15 minutes
Pour the mixture through a strainer and collect the indicator solution in a clean beaker
Testing the Natural Indicator(observe colour of indicator in solutions with a KNOWN pH)
Pour indicator into 3 small test tubes until they are half-full
Add 1mL of 0.5 HCl into the first tube and agitate to mix (acid)
Add 1mL of 0.5 NaOH into the second tube and agitate to mix (base)
Add 1mL of water into the third tube and agitate to mix (neutral)
Record the colour of each solution
Acid + base
salt + water
acid + metal hydroxide
salt + water
Acid + Metal Oxides →
salt + water
Acid + Metal Carbonate →
salt + water + carbon dioxide
Acid + hydrogen carbonate →
salt + water + carbon dioxide
Dilute Acid + reactive metal →
salt + hydrogen gas
reactive metal is higher than hydrogen on the standard potential table
Acid + ammonia
ammonium salt
what is the nature of the ammonium ion
a weak acid
what is the nature of ammonia
weak base
what does enthalpy mean
how much energy is found within a substance or groups of substances
the change of enthalpy (∆H) is measured in kJ/mol
∆H = H(products) - H(reactants)
what is the enthalpy of neutralisation?
change in enthalpy per one mole of H2O formed
what is the net ionic equations of strong acids and bases?
H+(aq) + OH-(aq) → H2O(l) ∆Hn = -57kJ/mol
what is the overall enthalpy of neutralisation of weak acids/bases?
less exothermic, possibly endothermic
They don't completely dissociate in water
Heat produced is used to dissociate the weak acid/base into ions
∆H (observed) = ∆H (neutralisation) + ∆H (dissociation of acid/base): negative + positive
how do you find the heat produced?
q=mc∆T
q= heat produced (J)
m = mass of reaction (kg)
c= specific heat capacity of water (4.18 x 103)
∆T = change in temp of water (units don’t matter)
how do you find the change in enthalpy (formula)
∆H = -q/n
∆H=enthalpy change (kJ/mol)
q= heat produced (kJ)
n = moles of water produced
what is acid strength?
the extent of ionisation/dissociation in water (NOT based on the concentration - its the nature of the particle)
Acids are covalent molecular compounds that split into ions (ionises) when it interacts with water
what do strong acids do?
Dissociation goes to completion/ionises further (→ ) |
HA(aq) + H2O(l) → H3O+(aq) + A-(aq) HA(aq) → H+(aq) + A-(aq) |
Strong electrolytes (conductors of electricity in solution) |
what do weak acids do?
Dissociation is reversible: reaches a dynamic equilibrium (⇌) % of products/reactants formed depends on the concentration |
HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq) HA(aq) ⇌ H+(aq) + A-(aq) |
Weak electrolytes |
what are the 5 main strong acids?
HCl, HBr, HI, H2SO4, HNO3
what does a strong base do?
Strong Base ~ ionic |
Dissociates completely in water when it dissolves, producing free OH- ions (→) |
Strong electrolytes |
NaOH(s) → Na(aq)+ + OH(aq)- |
what does a weak base do?
Weak Base |
Reacts partially with water to form hydroxide ions in solution (⇌) (include water in equation)
Some weak bases are anions inside an ionic compound
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Weak electrolytes |
Ionic NH3 (aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq) Anions in an ionic compound Na2CO3 (s) → 2Na+(aq) + CO32-(aq) CO32-(aq) + H2O(l) ⇌ HCO3-(aq) + OH-(aq) |
examples of strong bases
Group 1, 2 metal hydroxides: NaOH, KOH, Ca(OH)2
what is Ka?
Equilibrium constant for the dissociation (ionisation) of an acid into a hydrogen or hydronium ion and anion
Indicates the extent of dissociation/strength of an acid
The stronger the acid, the ↑ Ka (eqm lies on the right, more ionisation)
Polyprotic acids have more than one Ka value (for each H+ they donate)
what is Kb?
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water is both
amphoteric and amphiprotic (acts as both base and acid and can donate/accept a proton)
Water can acts as either a B/L acid or a B/L base
give an example of water acting as an acid
Molecular acids dissolve in water to produce ions -- according to the Bronsted/Lowry theory this occurs because a proton is donated from the acid to the water molecule to produce the hydronium ion
NH3 (g) + H2O(l) ⇌ NH4+(aq) + OH-(aq)
give an example of water acting as a base
HCl(g) + H2O(l) → H3O+(aq) + Cl-(aq)
The HCl = B/L acid as it it a proton donor, water is the B/L base as it is a proton acceptor
pH =
-log10[H+]
pOH =
-log10[OH-]
pH + pOH =
14 (for aqueous solutions at 25℃)
what does the pOH range look like?
what did Lavoisier propose for the definition of acids?
Acids contain oxygen - the presence of oxygen gives acids their properties
Based on compounds like HNO3 and H2SO4
what is the limitations of Lavoisier’s definition
Couldn't explain acids that didn’t contain oxygen (HCl)
what is Davy’s definition of an acid?
Stated acidity is due to the presence of hydrogen
Showed that HCl is strongly acidic
what is Davy’s limitation in his definition?
Doesn’t define a base
Lacks an explanation of the chemical behaviour of bases
Didn’t explain why other compounds that contained H weren’t acidic (CH4)
what is arrhenius’ definition of acids and bases?
Acids as substances that increases the concentration of H+ ions in aqueous solutions HCl → H+ + Cl-
Bases are substances that increase the concentration of OH- ions in aqueous solutions NaOH → Na+ + OH-
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what is the limitation of arrhenius’ definition?
Only for aqueous solutions
Doesn’t explain reactions in non-aqueous solvents or gas phase reactions
Cannot explain bases that don’t contain OH- like NH3
Couldn’t explain why some neutralisation reactions produced unneutral solutions
what is bronsted and Lowry’s definition of acids and bases?
Acids are proton (H+) donors
Bases are proton acceptors (H+)
Explains a wide range of acid-base behaviour
Explains how ammonia works as a base because it accepts a proton
Explains that ionic compounds are basic because they dissolve first and then ionise
what is the benefit of bronsted lowry defintions?
Works in both aqueous and non-aqueous environments (any solvent)
Introduces the idea of conjugate acid-base pairs
NH3 (g) + HCl(g) → NH4Cl(s)
NH3 + H2O ⇌ NH4+ + OH-
what is the B/L base and the B/L acid
NH3 acts as a B/L base as it accepts a proton to become NH4+
H2O acts as a B/L acid as it donates a proton to become OH-
what is the limitation of B/L definition
Doesn’t explain acid-base reactions that don’t involve proton transfer (Lewis acid-base theory) e.g. AlCl3 and BF3
Can’t explain reactions between acidic oxides and basic oxides that occur without a solvent
HOWEVER, it is still used because it is sufficient in covering most situations
what is the lewis acid-base theory?
Lewis acid: an electron pair acceptor
Lewis base: an electron pair donor
what is the order of acid/base definitions from old to new?
lavoisier, davy, arrhenius, bronsted-lowry, lewis
explain the self-ionisation of water at 25 degrees?
H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)
its pH = 7, so the [H+] = 10-7 mol/L
Kw = [H3O+][OH-] = 10-14 (from data sheet)
∴ [OH-] = 10-7
Kw =
[H3O+][OH-] = 10-14 (at 25℃)
what is conjugate acid-base pairs?
If something is an acid, something else is a base
When a B/L acid donates its proton to the base, the anion of the acid is proton deficient - this species can act as a base as it could accept a proton and reform the original acid
when writing a conjugate acid base pair what do you write first?
When writing the pairs, write the acid first: so here: H2O/ OH- and NH3/ NH4+
what is the base dissociation formula?
AB —> A+ + B-
B- + H2O → HB + OH-
what is the strength of an acid?
the degree of ionisation of an acid or dissociation of a base → can be determined by calculating the [H+] of equal concentration of acids
how does the dissociation of polyprotic acids work?
in subsequent reactions (NOT all at once)
the reactions strength can be different
what is the advantages and disadvantages of using a pH probe?
advantages | disadvantages |
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what is the experiment to indicate the difference in strengths between acids and bases
Add 100mL of 0.1mol/L of each solution in three separate, dry, 250mL beakers
Label the beakers with the solutions it contains
Place the calibrated pH probe into the first beaker, and record the pH
Remove the probe from the solution and rinse it with distilled water and blot dry
Repeat steps 2 and 3 for the remaining solutions
Repeat the procedure for 0.01M and 0.001M of the solutions
what is the relative strength of conjugate pairs?
The pairs have inverse strength: strong acid has extremely weak (almost neutral) conjugate base
Weak acid will have relatively strong conjugate base
Weak acid | Relatively strong conjugate base |
Weak base | Relatively strong conjugate acid |
Strong acid | Relatively weak/neutral conjugate base |
Strong base | Relatively weak/neutral conjugate acid |
why do conjugate pairs have inverse strength?
A strong acid has a strong tendency to give up H+ and completely ionises in water
Equilibrium lies far to the right
The reverse reaction will barely proceed as the conjugate base has no tendency to accept H+ as the reaction is not reversible
what is concentration?
Concentration = the amount of solute in a specified amount of solution (oft. Expressed as moles/L)
Concentrated = total concentration is high
A dilute solution is one which the total concentration is low (e.g 0.1M)
what is the strength of a solution?
The degree of ionisation of an acid or dissociation of a base → can be determined by calculating the [H+] of equal concentration of acids
draw a model of a concentrated weak acid, concentrated strong acid, dilute weak acid, dilute strong acid?
is the pH of the final solution in a neutralisation always neutral?
Acid + Base → salt + water
pH of final solution is not always neutral
The salt could also be acidic or basic.
The excess acid/base would react with water to produce ions
what type of salt is formed if: strong acid + strong base
neutral salt
what type of salt is formed if: strong acid + weak base
acidic salt
what type of salt is formed if: weak acid + strong base
basic salt
what type of salt is formed if: weak acid + weak base
Depends on which is the stronger of the acid and base
Compare the dissociation value
If Ka > Kb = acidic
If Kb > Ka = basic
how to calculate the pH of a weak acid/base?
Write equation and Ka expression
Use ICE table to determine eqm conc
Let x be the change in concentration
Assume Ka is small, so it = 1 (prove it later)
Solve for x
Check assumption is < 5%
Calculate pH
if an acid is multiprotic how do you calculate the pH?
If the acid is multiprotic, do calculations of the H+ concentrations of each dissociation and then add the concentrations together
what is the formula for degree of ionisation?
% ionised = ([H+]eqm / [HA] initial) x 100
how to calculate the pH of diluted strong acids/bases?
Find the concentration of the solution diluted (use C1V1 = C2V2)
Find the concentration of diluted H+
Calculate the pH
how to find the pH of diluted weak acids/bases?
Write the equation (⇌) and the Ka formula
Determine the new diluted concentration (use C1V1 = C2V2)
Use a Ka or Kb calculation (using an ICE table) to find the concentration of diluted H+
Calculate the pH
how to calculate the pH of the mixing of a strong acid and base (no reaction)
Calculate the moles of H+ or OH- from each solution
Calculate the total moles of H+
Calculate the final volume
Calculate the final [H+] and find the pH
how to calculate the pH of a neutralisation reaction b/w strong acid and strong base?
Write a balanced equation
Find the moles of the acids and bases
Find the limiting reagent/ excess reagent
Calculate the leftover moles of the excess reagent
nexcess = ninitial - nexcess used with limiting reagent - use mole ratio
Calculate the concentration of excess reagent using the total volume
Calculate the pH