2.1.4 Acids Flashcards
What are the formulae of common acids?
HCl = hydrochloric acid
H2SO4 = sulfuric acid
HNO3 = nitric acid
CH3COOH = ethanoic acid
What are the formulae of common alkalis?
NaOH = sodium hydroxide
KOH = potassium hydroxide
NH3 = ammonia
What is an acid? (Arrhenius theory)
A substance that releases H+ ions in aqueous solution
What is an alkali? (Arrhenius theory)
A substance that releases OH- ions in aqueous solution
- A soluble base
What is a strong acid?
A strong acid will fully dissociate in aqueous solution
e.g. HCl, H2SO4, HNO3
What is a weak acid?
A weak acid will partially dissociate in aqueous solution
- Equilibrium lies to the right so backwards reaction is favoured
E.g. carboxylic acids
What does monoprotic mean?
1mol of acid produces 1mol of H+ ions
What are acids? (Bronsted-Lowry theory)
Proton donors
What are alkalis? (Bronsted-Lowry theory)
Proton acceptors
What are conjugate acid pairs?
They differ by one proton (H+)
What is neutralisation?
- The reaction between the H+ ions from acids and the OH- ions from alkalis
- Forms water which is neutral
- H+ (aq) + OH- (aq) -> H2O (l)
What are salts?
- Produced when acids and bases react
- Neutral
- Made from the metal from the base and the non-metal from the acid
What does ammonia react with acids to form?
Ammonium salts
What do metals react with acids to form?
Salt + hydrogen
What do metal oxides react with acids to form?
Salt + water
What do metal hydroxides react with acids to form?
Salt + water
What do metal carbonates react with acids to form?
Salt + carbon dioxide + water
What is a titration?
A technique used to accurately measure the volume of one solution that reacts exactly with another
What is a standard solution?
A solution of a known concentration
How do you prepare a standard solution?
- Solid is weighed accurately using an electronic balance and weighing boat
- Solid is transferred to a beaker and any solid left behind in the weighing boat is washed into the beaker using distilled water
- Solid is dissolved fully in the beaker using less distilled water than will be needed to fill the volumetric flask and solution is stirred with a glass road
- Solution is transferred to a volumetric flash using a funnel to avoid spillage and the beaker and glass road are rinsed with distilled water
- Volumetric flask is filled to the graduation line with distilled water and a pipette is used at the end to ensure the bottom of the meniscus lines up exactly with the mark, whilst at eye level
- Volumetric flash is slowly inverted several times to the mix the solution thoroughly
How do you carry out an acid-base titration?
- Add a measured volume of one solution to a conical flask using a pipette
- Add other solution to a burette using a funnel and record initial burette reading to the nearest 0.05cm3
- Add a few drops of indicator to the solution in the conical flask
- Run the solution in the burette into the solution in the conical flask and swirl the conical flask throughout to mix the 2 solutions
- Indicator will change colour at the end point of the titration
- Record final burette reading and subtract the initial reading from the final reading to find the titre
- A quick trial titration is carried out first to find the approximate titre
- Titration is then repeated accurately, adding solution dropwise as the end-point is approached
- Further titrations are carried out until at least two titres (excluding initial) are concordant
What does concordant mean?
Agreeing to within 0.1cm3
Why does adding water to the conical flask not have an effect?
It doesn’t change the number of moles added to the flask
What calculation do you need to do in a titration?
- Work out concentration of standard solution
- Calculates moles in conical flask (using pipette volume and known concentration)
- Use equation to calculate mols of other solution
- Work out unknown information
