Chemical Changes

What is oxidation/reduction ?

Oxidation is the loss of electrons and gain of oxygen.

Reduction is the gain of electrons and loss of oxygen.

What is the reactivity series in order of highest to lowest reactivity?

Potassium

Sodium

Lithium

Calcium

Magnesium

Aluminium

Zinc

Iron

Tin

Lead

Copper

Silver

Gold

Why is the reactivity series in that order ?

When metal atoms react they lose electrons to form positive ions. The easier it is for the metal to lose electrons the more reactive it is.

What is a displacement reaction ?

A reaction where a more reactive metal displaces a less reactive metal from a compound.

How can metals less reactive than carbon be extracted ?

Reduction with carbon. Carbon displaces the metal in metal oxides - gets oxidised to carbon oxides. Metals from the metal oxide gets reduced to the pure metal.

How are metals more reactive than carbon extracted ?

By electrolysis.

What is the general equation for a neutralisation reaction ?

Base + acid = salt + water

What is a redox reaction ?

A reaction where both oxidation and reduction occurs.

How is a soluble salt formed ?

1) Heat sulfuric acid gently until slmodt boiling with Bunsen burner, then turn it off

2) Remove from tripod and add a small amount of copper (II) oxide powder to hot acid

3) Stir with glass rod and it should turn blue

4) Keep adding copper (II) oxide until some remains after stirring

5) Filter into conical flask and pour into evaporating basin

6) Set up a water bath and evaporate filtrate gently

7) When crystals start to form stop heating and pour remaining solution into crystallising dish and leave for 24 hours

8) Remove crystals and gently pat dry

What do acids and alkalis produce in aqueous solutions ?

Acids produce hydrogen ions, alkalis produce hydroxide ions.

What is a strong acid ?

Substance that completely ionises into H+ ions in aqueous solution.

What is a weak acid ?

Partially ionises in water releasing only a small proportion of H+ ions.

What happens to pH as H+ increases ?

The pH decreases.

What is a concentrated acid ?

An acid solution that contains a relatively large amount of dissolved acid solute in a given volume of water

What is a dilute acid ?

A solution that contains a relatively small amount of dissolved acid molecules in a given volume.

What is electrolysis ?

Passing of an electric current through ionic substances that are molten or in solution to break them down into elements - ions are discharged at electrodes to produce these

What is an electrolyte ?

The liquid which conducts electricity

What is a cathode and what is an anode ?

Cathode is the negative electrode and anode is the positive electrode.

What occurs at the cathode and what occurs at the anode ?

Reduction at the cathode and oxidation at the anode

In aqueous electrolysis which element is discharged at the cathode ?

The less reactive element discharges at the the cathode. Hydrogen is produced unless there is a less reactive metal in which case the disc metal is produced

Oxygen is produced at the anode unless what ?

The solution contains halide ions which then produce halogen molecules.

How is aluminium manufactured and why is it expensive ?

Made through the electrolysis of aluminium oxide and cryolite. Lots of energy is needed to produce the current in electrolysis which makes this process expensive.

Why is cryolite used ?

It lowers the melting points.

How is oxygen formed from water during electrolysis ?

Water molecules split which forms OH- and H+ ions, OH- ions can move to the anode and the ions get oxidised resulting in the gain of oxygen

What is the method for titration ?

1 )use a pipette and pipette filler to add 25 ml of sodium hydroxide to a clean conical flask

2) add a few drops of phenolphthalein indicator and place the conical flask on a white tile

3) fill the burette with hydrochloric acid and record the starting volume

4) slowly open the tap of the burette, and add the acid to the conical flask, swirling to mix

5) stop adding the acid when the end-point is reached (when the colour permanently changes from pink to colourless) and record your final volume 

6) repeat steps 1-5 until you get concordant titres