Acids and Bases (C4) Flashcards
What does pH measure?
Acidity or Alkalinity
What is indicator?
A dye that changes colour depending on its pH
Is pH 7 acid or alkali?
Neutral
Is pH 5 acid or alkali?
Acid
Is pH 9 acid or alkali?
Alkali
Is pH 14 acid or alkali?
Strong Alkali
Is pH 1 acid or alkali?
Strong Acid
What can we use to judge pH?
pH probe or indicator
Define Acid
Substances that form aqueous solutions with a pH below 7
They form H+ ions in water
Define Base
A substance with a pH greater than 7
Define Alkali
A base dissolved in water to form a solution greater than 7
Alkalis form OH- ions in water
Neutralisation Reaction
Base + Acid = Water + Salt
BAWS
Neutralisation Reaction in terms of ions
H+(aq) + OH- = H2O(l)
What is titration for?
They allow you to find exactly how much acid is needed to neutralise an alkali or vie versa.
What is the first step of a titrartion?
when you are finding the concentration of an alkali needed for the neutralisation of an acid
Use a pippette and pippette filler, add a set volume (25cm^3) of the alkali to a conical flask. Add a few drops of indicator.
What is the second step of a titrartion?
when you are finding the concentration of an alkali needed for the neutralisation of an acid
Use a funnel to fill a burette with acid. Make sure you do this below eye level. Record the initial volume of the acid in the burette.
What is the third step of a titrartion?
when you are finding the concentration of an alkali needed for the neutralisation of an acid
Add acid slowly from the burette into the conical flask, swirlig constantly until you see the end-point. This is visible when the colour changes.
What is the fourth step of a titrartion?
when you are finding the concentration of an alkali needed for the neutralisation of an acid
Record the final volume of the acid in the burette and use it to calculate the volume of acid needed to neutralise the alkali.
What should you do to increase the accuracy of your titration?
You should take several consstent results. Take only answers within 0.1cm^3 of each other and ignore any anomalous results.
Why is universal indicator not ideal for titrations?
It changes colour gradually
What indicators are best for titrations?
Single indicators
litmus, phenolphthalein, methyl organge
What colour does litmus paper turn?
Blue in alkalis and red in acids.
What colour does phenolphthalein turn?
Pink in alkalis and colourless in acids and neutral
What colour does methyl orange turn?
Yellow in alkalis and red in acids
What is a strong acid?
Fully ionising in an aqueous solution
They produce H+ hydrogen ions
What is a weak acid?
Weak acids do not fully ionise in aqueous solutions. Only a small proportion of acid particles dissociate to release H+ ions.
Examples of strong acids
Sulphuric Acid
Hydrochloric Acid
Nitric Acid
Examples of weak acids
Ethanoic Acid
Citroc Acid
Carbonic Acid
The ionisation of which acids is reversible?
Weak Acids
What is pH?
Concentration of H+ ions
If the concentration of H+ ions in an acid that was pH 4 is increased by a factor of 10, what is the pH now?
pH5
Which has a higher pH, strong acid or weak acid?
Weak acid has a higher pH than strong acid
Reaction between acid and metal oxide
Metal Oxide (Base) + Acid = Water + Salt BAWS
Reaction between acid and metal hydoxide
Metal Hydroxide (Base) + Acid = Water + Salt BAWS
What is salt produced in a reaction between hydrochloric acid and a metal?
Metal chloride
What is salt produced in a reaction between sulphuric acid and a metal?
Metal sulphate
What is salt produced in a reaction between nitric acid and a metal?
Metal nitrate
Reaction between acid and metal carbonate
Metal Carbonate + Acid = Water + Carbon Dioxide + Salt
CAWCS
Name 3 types of bases
Metal oxides
Metal hydroxides
Metal carbonates
Which base does not form a BAWS reaction?
Metal Carbonates form a CAWCS reaction (with carbon dioxide)
How do you make a soluble salt from an insoluble base?
- Gently warm the dilute acid on a bunson burner, then switch off
- Add the base, stirring until it sinks to the bottom (it will be in excess at this point)
- Filter out excess base
- Gently heat the solution in a water bath or electric heater to evaporate water
- Stop heating and allow to cool
- Filter and dry the crystals
What process seperates an insoluble?
Crystallisation
What is the reactivity series?
Order of metal reactivity
Which non-metals are in the reactivity series?
Hydrogen and Copper
How reactive is Potassium (K)
Very
How reactive is Copper (Cu)
Not very
How reactive is Carbon (C)
Fairly
How reactive is Lithium (Li)
Very
How reactive is Hydrogen (H)
Not very
How reactive is Sodium (Na)
Very
How reactive is Magnesium (Mg)
Fairly
How reactive is Iron (Fe)
Fairly
How reactive is Calcium (Ca)
Very
How reactive is Gold (Au)
Not - It’s a native metal
How reactive is Zinc (Zn)
Fairly
Define Native Metal
Usually found in their pure form, pretty much unreactive
What forms if an acid reacts with a metal?
Acid + Metal = Salt + Hydrogen
Test for Hydrogen
Squeaky Pop test
Place a lit splint near it, you should hear a ‘squeaky-pop-
Which metals will readily undergo a reaction with acids?
Anything more reactive than hydrogen
What forms if water reacts with a metal?
Metal + Water = Metal Hydroxide + Hydrogen
Which metals will readily undergo a reaction with water?
Potassium (K)
Sodium (Na)
Lithium (Li)
Calcium (Ca)
Define Oxidation
(Gain of oxygen)
Loss of electrons
Define Reduction
(Loss of oxygen)
Gain of electrons
How do we extract metals with low reactivity from their ores?
Reduction using carbon
anything less reactive than carbon
How do we extract metals with high reactivity from their ores?
Electrolysis
anything more reactive than carbon
Why can highly reactive metals not be extracted with carbon?
This reduction is a displacement reaction, more reactive metals will not be displaced by carbon
What type of reaction is reduction using carbon?
Displacement Reaction
What is a displacement reation?
When a more reactive element takes the place of a less reactive one in a compound
What is a redox reaction?
A reaction where electrons are transferred
Oxygen is essential to an oxidation or reduction reaction. True or False?
False
Any electron loss or gain classifies as a reduction or oxidation
What do we call an ion which does not change in a reaction?
Spectator ions
Define Electrolysis
Using an electrical current to ‘split’ a metal compound into its elements
Why must a metal compound be molten or aqueous during electrolysis?
So that the ions can move freely
Where does the positive ion go during electrolysis?
Cathode (negative electrode)
Where does the negative ion go during electrolysis?
Anode (positive electrode)
What do we call the molten or aqueous solution during electrolysis?
Electrolyte
What happens during electrolysis of a molten solution?
Two rods (electrodes) with electrical current are placed in the electolyte
Metals (positive ions) are attracted to the negative electrode
Non - metals (negative ions) are attracted to the positive electrode
These can then be collected in their pure form
What is used to lower the melting point of metal compounds such as aluminium oxide, to make a molten solution?
Cryolite
What is aluminum ore called?
Bauxite
What happens at the negative elctrode?
The positive metal ion is attracted to the negative electrode. Here it gains electrons (reduction) and becomes its element.
What happens at the positive elctrode?
The negative non-metal ion is attracted to the positive electrode. Here it looses electrons (oxidation) and becomes its element.
What additional ions are involved in the electrolysis of an aqueous solution?
H+ and OH-
When does hydrogen form at the cathode?
Electrolysis of an aqueous solution if hydrogen is less reactive than the metal
When does oxygen form at the annode?
Electrolysis of an aqueous solution if no halide ions are present (Cl2, Br2 etc..)
