2.1.4 acids Flashcards
Acid
Releases H+ ions in aqueous solutions
Proton donor
Most common: HCl, H2SO4, HNO3
Bases
Neutralise acids
Proton acceptor
Most common: metal oxides, metal hydroxides, ammonia
Alkali
Soluble base that releases OH- ions in aqueous solution
Most common: NaOH, KOH, NH3
Strong acids
Completely dissociate when dissolved in water
Weak acids
Slightly dissociate when dissolved in water, giving an equilibrium mixture
Salt
Formed from neutralisation reactions
Formed when H+ ion of an acid is replaced by a metal ion or an ammonium ion
Common neutralisation reaction equations
Acid + base > salt + water
Acid + carbonate > salt + water + CO2
Acid + base
Salt + water
Acid + carbonate
Salt + water + CO2
- effervescence due to CO2 gas evolved and solid carbonate dissolves
Titration method
Pipette 25cm3 of alkali into conical flask
Add acid solution from burette
Add a few drops of indicator and refer to colour change
White tile underneath to help observe colour change
Add acid to alkali whilst swirling mixture and add acid dropwise at end point
Note burette reading before and after
Repeat until at least 2 concordat titres
Phenolphthalein colour change
Pink (alkali) to colourless (acid)
Use if NaOH is used
Methyl orange colour change
Yellow (alkali) to red (acid), end point orange
Use if HCl is used
Safety and precautions for titrations
Acids and alkalis are corrosive
Wear eye protection and gloves
if spilled immediately wash affected parts
Recording titration results
Should be clearly recorded in a table
Result should be recorded in full
Record titre volumes to 2dp
Dealing with excess acid
sodium hydrogen carbonate (NaHCO3) and CaCO3 good for neutralising excess acid in the stomach or acid spills as not corrosive
Percentage error calculation
% uncertainty = (uncertainty / measurement made on apparatus) x 100
Percentage error calculation
% uncertainty = (uncertainty / measurement made on apparatus) x 100
Reducing uncertainties in titration
Replacing measuring cylinders with burettes or pipettes which have lower apparatus uncertainty
Titrate a larger volume - increase volume and concentration of substance in conical flask
Decrease apparatus uncertainties
Decrease sensitivity uncertainty by using apparatus with greater resolution (finer scale divisions) or increase size of measurement made
Calculating percentage difference between actual value and calculated value
Difference between values / original x 100
