Chapter 4 Flashcards
What happens when acids are dissolved in water (aqueous)?
They release H+ ions into the solution
HCl dissolve in water equation
HCl (g) + aq (excess of water to form solution with gas) -> H+ (aq) + Cl- (aq)
Carboxylic acids functional group
(Methyl, ethyl etc) COOH
What is a strong acid?
HCl - releases all its hydrogen atoms into solution as H+ ions and completely DISSOCIATES in aqueous solution
Complete dissociation of HCl?
HCl (aq) -> H+ (aq) + Cl- (aq)
Weak acid?
CH3COOH - only releases a small proportion of its available hydrogen atoms into solution as H+ ions - PARTIALLY DISSOCIATES
Partial dissociation of Ethanoic acid
CH3COOH (aq) -> <- H+ (aq) + CH3COO- (aq)
Most organic acids are…
Weak acids
What are bases?
Metal oxides, hydroxides, carbonates and Ammonia (NH3)
What do bases do?
Neutralise acids to form a salt
What is an alkali?
A base that dissolves in water by releasing OH- ions
Sodium Hydroxide Alkali Dissolving
NaOH (s) + aq -> Na + (aq) + OH- (aq)
Neutralisation reaction?
H+ ions react with a base to form a salt and water
Ammonium ion
NH4+
Ammonium ethanoate
NH4+ , CH3COO- therefore CH3COONH4 (ACID GOES FIRST IN THIS INSTANCE)
Acid + metal oxide/hydroxide
Salt + water
Acid + metal carbonate
Salt + water + carbon dioxide
Ionic equation of sodium hydroxide and hydrochloric acid?
OH- + H+ -> H2O (ONLY WORKS WITH ALKALIS AS THEY ARE AQUEOUS)
What is special about dissociation of H2SO4
It is a strong acid but this is only true for 1 of the 2 hydrogen atoms - when mixed with water H2SO4 dissociates but releases JUST ONE of its two hydrogen atoms as an H+ ion
What would dissociation of H2SO4 look like?
At first it is a strong acid
H2SO4 (aq) -> H+ (aq) + HSO4- (aq)
Now it partially dissociates
HSO4- (aq) ->
What is a titration?
Technique used to accurately measure the volume of one known solution that reacts with another solution
What are they used for?
Finding the concentration of a solution
Identification of unknown chemicals
Finding purity of a substance
Why is checking purity important?
Quality control for compounds manufactured for human use - pharmaceuticals should have high level of ourity
How to prepare standard solution?
Solution of known concentration - volumetric flask is used to make it very accurately
100 cm cubed - 0.20 cm cubed +/-
250 cm cubed - 0.30 cm cubed +/-
Stages in preparing standard solution?
Solid weighed accurately
Dissolved in a beaker using less distilled water than will be needed to fill volumetric flask to mark
Transferred to volumetric flask and washings rinsed with distilled water
Drip by drip distilled water until graduation line (bottom of meniscus) - eye level for accuracy (if too much then becomes dilute)
Volumetric flask slowly inverted several times to mix thoroughly - makes sure titration results are consistent
Burette apparatus used
50 cm cubed - +/- 0.1 cm cubed
Nearest half division therefore always ends in 5 or 0
Acid base titration procedure
Add measured volume of alkali or acid to conical flask using pipettes
Add other solution to burette (0.05 cm cubed)
Add indicator to solution in flask
Swirl conical flask as you run burette solution to mix evenly - eventually indicator changes colour to end point ; record final reading
Titre = final - initial ; approximate tire first and the repeated
until they are concordant (within 0.1)
Mean titre
Repeat titres until they are within 0.1 and reject any inaccurate titres
If you include all tires then lost accuracy of titration technique
Original values you have from results of titration
Both concentration and reacting volume of one solution
Only reacting volume of other solution
What is oxidation number?
Number fo electrons involved in bonding to a different element
What is oxidation number for elements?
For pure elements - always 0 as it is bonding to atoms of same element
How to write oxidation number?
Sign placed before the number and each atom in compound has oxidation number
H in metal hydrides
Usually +1 but now -1
O in peroxides (H2O2)
-1 (usually -2)
O bonded to F
+2
Oxidation numbers on ions?
Sum of oxidation numbers = charge
What do Roman numbers show?
Oxidation number of an element without the charge
NO2-
Oxidation number of nitrogen is +3 therefore nitrate (III)
NO3-
Nitrate - oxidation number of nitrogen is +5 so nitrate (V)
Oxidation
Addition of oxygen
Loss of electrons
Gain in oxidation number
Reduction
Removal of oxygen
Gain of electrons
Loss in oxidation number
Does oxidation number apply to each atom or whole compound?
EACH ATOM - do not look at balancing numbers
