module 6 HSC Flashcards
properties of acids
- sour taste
- burn skin
- blue litmus to red
- pH < 7
properties of bases
- bitter taste
- soapy feel in aqueous solution
- red litmus to blue
- pH > 7
- caustic
acid + base
salt + water
HNO3 + NaOH –> H2O + NaNO3
acid+ carbonate
salt + water + carbon dioxide
2HCl (aq) + Na2CO3 (s) –> CO2 (g) + H2O (l) + 2NaCl(aq)
acid + active metal
salt + hydrogen gas
H2SO4 (aq) + Ba(s) –> H2 (g) + BaSO4(s)
what are indicators
substances which change colour based on the pH of the environment
- methyl orange (orange)
- bromthymol blue (green)
- phenolphthalein (pink)
methyl orange
3.1 - 4.4
red - orange - yellow
bromothymol blue
6.0 - 7.6
yellow - green - blue
phenolphthalein
8.3 - 10.0
colourless - pale pink - pink/magenta
natural indicator
red cabbage
antoine lavoiser
acids contain O
bases neutralise acids
a: raised the need to define acids and bases
d: statement is wrong eg. HCl
humphrey davy
Acids contain replaceable H. Bases neutralise acids.
a: worked for many acids
d: cannot explain acidic or basic oxides
arrhenius
acids release H+ in solution and bases release OH - in solution
a:
- works for many acids and bases
- explains the common mechanism of acid base neutralisations
d:
- does not recognise solvents in determining the acidic/weakness of acid
- cannot explain basic nature of carbonates, acidic or basic salts in not aqueous form
bronsted lowry
acids donate protons, bases accept protons
a:
- recognises role of solvent in determining the strength and weakness of an acid
- explains acidic and basic behaviour in non aqueous solvents
- explains how species can be amphiprotic
- recognises conjugate acids and bases
d:
- cant explain amphoteric substances
- cannot explain acids or bases that dont accept/donate protons
amphoteric substances
can act as both an acid or base
amphiprotic
can act as either an acid or base in different chemical environments
enthalpy of neutralisation
thermal energy change
q = mcat
delta h = -q/n
proticity + what is a protic substance
capacity to act as a proton donor
eg. mono HCl, diprotic H2SO4, triprotic H3PO4
- strong is the first (one directional arrow) , weak is the scond (biodirectinal arrow)
degree of ionisation
how much it ionises
strong acid: fully ionises 100%
weak acid: does not fully ionise <100%
[A-]eq / [HA] initial x 100%
strong acid degree of ionisation
100
weak acid degree of ionisation
<100
strong acids
HCl, HBr, HI, HNO3, H2SO4 (first is strong, second is weak)
strong bases
HF, CH3COOH, H2CO3, H3PO4, C6H8O7
conjugate of base HSO2-
acid H2SO4
conjugate of acid HCl
base Cl-
conjugate of strong …
extremely weak/almost neutral
conjugate of weak …
weak
conjugate of extremely weak …
strong
prove that HCO3 from NaCO3 is amphiprotic
strong base : …
strong acid: …
neutralisation
acid base reaction that goes to completion and does not directly produce H3O+ and OH-
- strong goes to completion
- weak does not go to completion
explain with both le chateliers and bronsted lowry
eg. CH3COOH weak acid in water
- NaOH strong base in water
CH3Cooh + NaOH -> NaCh3CH3COOH + H2O
- since acetic acid is a weak acid relative to water but strong acid relative to sodium hydroxide and sodium hydroxide is a strong base relative to water and acetic acid is stronger than water –> the acetic acid will ionise completely in the presence of sodium hydroxide where neutralisation is complete
changing degree of ionisation
depends on concentration acids however only temperature changes the Ka
pH
-log10[H3O+]
[H3O+]
10^-pH
factors that affect an acids pH
- concentration
- strength
- proticity (strong acids)
- degree of ionisation (weak acids)
concentration impacts on pH
more concentrated acid = lower pH
think about how a log is an inverse
strength impact on pH
strong acids have a lower pH as it completely ionises in water
proticity impact on pH
strong acids only
higher proticity = lower pH
sulfuric acid has a lower pH than HCl as it has both a strong first ionisation and weak second ionisation
degree of ionisation impact on pH
weak acids only
high degree of ionisation = lower pH
citric < acetic < carbonic
- although carbonic acid has more protons readily available to donate, it has a much lower degree of ionisation
what salt does strong acid + strong base produce
neutral salt
what salt does strong base + weak acid produce
acidic salt
what salt does strong acid + weak base produce
basic salt
what salt does weak acid + weak base produce
any of them..?
what is the levelling effect of a solvent
acid: strength of acid is levelled/limited by the ability of a solvent to accept protons
base: strength of base is levelled by the ability of solvent to donate protons
define titration
volumetric analysis which the concentration of a solution is determined by measuring the volumes of solutions involved in a reaction
- uses neutralisation reactions
equivalence point
point at which equal moles of H3O+ ions and OH- ions have been reacted together
endpoint
the point at which a sustained colour change is achieved using an appropriate indicator
titration error
the difference between the equivalence point and the endpoint
titre
the minimum volume required to reach the endpoint of the neutralisation reaction in the titration
titrant
solution which is used to determine the concentration of an unknown solution
analyte
solution whose concentration is to be determined
standard solution
solution with known concentration
qualities looked for in a standard solution (primary standard) + example
- high purity
- stability in air
-high molecular weight - inexpensive and readily obtained
eg.
acid: hydrated oxalic acid (weak acid for strong base)
base: anhydrous sodium carbonate (Na2CO3) / sodium hydrogen carbonate (NAHCO3) -> weak base for strong acid
what to avoid in a primary standard
weak acid and weak base together
deliquescent compounds: absorb water from surrounding environment by reacting with CO2 in air which dissolves in the solution eg. NaOH + KOH
hydroscopic: attract water molecules due to the presence of hydrophilic groups eg. H2SO4
what is al the glassware rinsed with
all glassware rinsed with demineralised water first
pipette + burette = rinsed finally with solution they are to contain to ensure the concentration of substances they are to contain are accurate
(the demin water would dilute the solution)
volumetric flask + conical flask = rinsed thoroughly with demineralised water so the number of moles of the substance can be accurate
beaker
used to dissolve the dry powdered primary standard to make the standard solution
volumetric flask
cleaned with demin and and filled to the gradation line with the standard solution then inverted 20 times to homogenise the solution
FIX TITRATION FLASH CARDS
neutralisation real life applications
antacid tablets:
- antacid tablets contain Mg(OH)2/Al(OH)3 that undergo neutralisation with excess gastric acid in the human stomach eg HCl
tooth decay:
- acids from food and drinks cause tooth decay
- toothpaste is weakly alkaline with undergoes neutralisation with acids present on the cavity
- CaCO3
baking:
- sodium bicarbonate (NaHCO3) (s)
- reacts with acids
- gives cake airy quality and produces CO2 to help rise
industrial:
- sodium hydrogen carbonate is used to neutralise any spills that are acidic.basic that is corrosive and causes harm to the environment and should e cheap, safe and weakly acidic/basic
wastewater:
treatment of waste water
- HF used to neutralise NaOH and Ca(OH)2 and produces a solid that can be removed
antacid tablets
- antacid tablets contain Mg(OH)2/Al(OH)3 that undergo neutralisation with excess gastric acid in the human stomach eg HCl
baking
- sodium bicarbonate (NaHCO3) (s)
- reacts with acids
- gives cake airy quality and produces CO2 to help rise
tooth decay
- acids from food and drinks cause tooth decay
- toothpaste is weakly alkaline with undergoes neutralisation with acids present on the cavity
- CaCO3
industrial
- sodium hydrogen carbonate is used to neutralise any spills that are acidic/basic that is corrosive and causes harm to the environment and should e cheap, safe and weakly acidic/basic
waste water
treatment of waste water
- HF used to neutralise NaOH and Ca(OH)2 and produces a solid that can be removed
styrofoam cup experiment
- imperfect insulator = heat loss ot the environment -> use styrofoam lid
- thermometer should not touch the bottom of the cup as the reading will be wrong
Kw
10^-14 = Ka x Kb
pH + pOH
14
define a buffer
similar/comparable concentrations of a weak acid/base and its conjugate which resists the change in pH if another acid/base is added
how do buffers work
eg. carbonic acid (wa) is mixed with sodium hydrogen carbonate
H2CO3/HCO3- system
- then write the equations showing the addition of H3O+ and addition of OH-
addition of H3O+: acid
- acid consumed by HCO3- shifting the equation to the left to reduce [H3O+] by LCP
- minimal change in [H3O+] , pH remains stable
addition of OH-: base
- base consumed and shifts left to decrease [OH-] by LCP
then link back to buffer: therefore since the solution minimises changes in [OH-] and [H3O+], it can act as a buffer
example of buffers
human blood:
- to maintain homeostasis
acidic through exercise as more carbonic acid is produced:
- shifts left to increase H2CO3
ocean buffer:
HCO3-/CO32- buffer system
- shells and limestone composed of CaCO3 that dissolve into CO32-
