Chemical Changes Flashcards
Acids
compounds that have a pH less than 7 and form hydrogen ions (H+) when dissolved in water
Bases
A substance with a pH greater than 7
Alkali
A base that dissolves in water forming Hydroxide ions (OH-).
Neutralisation reaction
Acid + base —> salt + water
Titration
A solution of known concentration is used to determine the concentration of another solution. Usually finding the exact amount of acid needed to neutralise a quantity of alkali or vice versa using an indicator such as methyl orange that is yellow in all acids and red in all alkalis.
Titration method
1) Rinse and fill a burette with alkali
2) Using a standard 25.00cm3 pipette, place acid into a conical flask
3) Add a few drops of acid-base indicator to the conical flask
4) Add the alkali slowly from the burette into the conical flask and swirl the contents
5) Determine the EXACT volume of alkali required to turn the solution a very pale pink
6) Rinse out the conical flask with purified water and repeat the experiment
7) Repeat the experiment until you have 2 concordant results that are within 0.2
Strong acid
an acid that ionizes completely in aqueous solution
Weak acid
an acid that is only slightly ionized in aqueous solution
Acid + metal oxide=
Salt + water
Acid + metal hydroxide=
Salt + water
Acid + metal carbonate=
Salt + water + carbon dioxide
Reactivity series
Potassium sodium lithium calcium magnesium aluminium (carbon) zinc iron Tin lead (hydrogen) copper silver gold
Acid + Metal=
Salt + hydrogen
metal + water=
Metal hydroxide + hydrogen
What is everything below carbon in the reactivity series extracted by?
Reduction with carbon
What is everything above carbon in the reactivity series extracted by?
Electrolysis
Redox reactions
A chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction.
Oxidation is loss
Reduction is gain
(OIL RIG).
Displacement reactions
a reaction in which an element reacts with a compound, displacing an element from the compound. It is a redox reaction. For example in the case of metals, the metal ion that is in the compound gains electron (reduction) and the metal atom loses electrons (oxidation).
Ionic equation
used to show details of reactions that involve ions (just the things that have changed).
Ionic equation example
Iron and hydrogen
Fe—> Fe2+ + 2e-
2H++ 2e- —> H2
Fe + 2H+ —> Fe2+ + H2
Electrolysis
A process by which a dc electric current breaks chemical bonds:
a dc electric current is passed through an electrolyte. The ions move towards the opposite charged electrodes and lose or gain electrons to become the uncharged element and are discharged from the electrolyte.
Electrolyte
a molten or dissolved ionic compound
Metal extraction by electrolysis
must be in molten form (to have free ions to conduct electricity) so heated at very high temperatures (in the case of aluminium cryolite is added to reduce melting point).
metal ions are reduced (gain electrons) by the cathode to form element. Sinks to bottom of tank.
non-metal ions are oxidised (lose electrons) by the anode. If oxygen from ore is released as gas.
Electrolysis of aqueous solutions - copper sulphate solution
At the cathode (negative electrode):
If the metal ion forms metal more reactive than hydrogen it will stay in the aqueous solution as the hydrogen (from the H+ in water) is released. If it is less reactive than hydrogen (e.g. copper) a solid layer of the pure metal will be produced on the negative electrode.
At the anode (positive electrode):
If the solution contains a group 7 ion (halide ion), it is released, otherwise oxygen (from the OH- ion in water) is released.
