Chemical changes

• The Ph scale goes from 1 to 14 - 1 being the most acidic and 14 the most alkaline. Ph 7 is neutral.
• Universal indicator is a wide range indicator as it contains a mixture of dyes that can gradually change colour and it estimates the Ph of a solution.
• A Ph probe gives you a numerical value so is more accurate.
• An acid is a substance that forms aqueous solutions with a Ph of less than 7. They form H+ ions in water.
• A base is a substance with a Ph greater than 7 and an alkali is a base that dissolves in water to form a solution with a Ph greater than 7. Alkalis form OH- ions in water.

Neutralisation:
Acid + Base ➡️ Salt + Water
H+ + OH- ➡️ H2O
When acids and bases react their product is neutral, an indicator can be used to show this.

For metals, their reactivity is how easily they lose electrons to form positive ions.
The higher a metal is in the reactivity series, the easier it is for them to react with water or an acid. This is because when metals react with water or an acid, the lose electrons to form positive ions.
The reactivity series (the relative reactivity of metals when reacting with an acid or water):
Potassium
Sodium
Lithium
Calcium
Magnesium
Carbon
Zinc
Iron
Hydrogen
Copper

• Acid + Metal ➡️ Salt + Hydrogen
  The more reactive the metal, the greater the temperature change will be and the faster the reaction will be. You can measure the rate by how any bubbles of hydrgen gas are given off or by measuring the temperature change.
• Metal + Water ➡️ Metal hydroxide + Hydrogen
  Metals like potassium, calcium, sodium and lithium will all react with water.
  Less reactive metal like zinc, iron and copper won't.

Some metals react with oxygen to form oxides (oxidation) and must be extracted from these ores to get the pure metal.
A reaction that separates a metal from its oxide is called a reduction reaction.

Example of oxidation: 2Mg + O2 ➡️ 2MgO

Example of reduction: 2CuO + C ➡️ 2Cu + CO2

Some metals can be extracted from their ores chemically by reduction using carbon. The ore is reduced as oxygen is removed from it, and carbon gains oxygen so it is oxidised. For example:
Iron (III) oxide + Carbon ➡️ Iron + Carbon dioxide.

Metals higher than carbon on the reactivity series have to be extracted using electrolysis.
Metals below carbon can be extracted by reduction using carbon.
This is because carbon can only take oxygen away from the metals which are less reactive than carbon itself.

• A loss of electrons is called oxidation and a gain is reduction. (OILRIG)
  Reduction and oxidation happen at the same time. For example:
  Iron atoms are oxidised, becoming Fe2+ ions when they react with dilute acid.
  Fe +2H+ ➡️ Fe2+ +H2.
  The iron atoms lose electrons, they're oxidised by the hydrogen ions.
  Fe - 2e- ➡️ Fe2+
  The hydrogen ions gain electrons. They're reduced by the iron atoms.
  2H+ + 2e- ➡️ H2
• A more reactive metal will displace a less reactive metal from its compound.
  If you put a reactive metal into the solution of a dissolved metal compound, it will displace the less reactive metal in the compound. For example
  Fe + CuSo4 ➡️ FeSO4 + Cu
  Fe ➡️ Fe2+ 2e-
  Cu2+ 2e- ➡️ Cu
  It is always the metal ion that gains oxygen and is reduced. The metal atom always loses electrons and is oxidised
• In an ionic equation only the particles which react and the products they form are shown. For exaple                               Mg + Zn2+ -> Mg2+ +Zn

These ions that don't change are called spectator ions.

During electrolysis an electric current is passed through an electrolyte (a molten or dissolved ionic compound). The ions move towards the electrodes where they react and the compound decomposes.
The positive ion will move towards the cathode and gain electrons, they are reduced. For example: Pb2+ 2e- ➡️ Pb
The negative ions move towards the anode and lose electrons, they are oxidised.
For example: 2Br- ➡️ Br2 +2e-
This creates a flow of charge through the electrolyte as ions travel to the electrodes.
As these ions become uncharged elements they are dishchaged from the electrolyte.

Extracting metals using this method is very expensive as it requires a lot of energy to melt the ore and produce the required current.
Metals are sometimes mixed with compounds to lower the melting pint and reduce the cost.
The anode is made of carbon and needs to be replaced regularly as it reacts with oxygen to produce carbon dioxide.

In aqueous solutions, as well as the ions from the ionic compound there will be hydrogen ions (H+) and hydroxide ions (OH-) from the water: H2O ↩️ H++ OH-.

At the cathode, if H+ atoms and metal ions are present and if the reactant is more reactive than hydrogen then hydrogen gas will be produced. For example
2H+ 2e- ➡️ H2
If the metal ions form an element that is less reactive than hydrogen (copper) a solid layer of pure metal will be produced instead. For example Cu2 + 2e- ➡️ Cu

At the anode, if OH- and Hallide ions (Cl-, Br-,I-) are present, molecules of these ions will be produced. For example 2Cl- ➡️ Cl2 +2e-
If no Hallide ions are present the OH- ions are discharged and oxygen will be formed. For example 4OH- ➡️ O2 + 2H2O + 4e-

When writing half equations the number of electrons must stay the same for both equations so as to be balanced out in the final equation.

Acids ionise in aqueous solution and produce hygrogen ions, for example HCl -> H+ + Cl-

• Strong acids ionise compleatly in water and all particles dissosciate to release H+ ions. Their reaction will be more reactive than that of weak acids.
• Weak acids do not fully ionise as only a small percentage of the particles dissociate. This reaction is reversible and sets up an equilibrium between the dissociated and undissociated acid. As only a few of the particles release H+ ions, the position of equilibrium lies to the left.

The pH of an acid or alkali is is a measure of the concentration of H+ ions in the solution. For every decrease of 1 on the pH scale, the concentration of H+ ions increases by a factor of 10. Therfore, the pH of a strong acid is always less than a weak acid in the same concentration.

Factor H+ ion concentration changes by = 10^-difference in pH

Acid strength tells you what proportion of the acid molecules ionise in water. The concentration is a measure of how much acid there is to a certain volume of water.

Acid + Metal Oxide  -> Salt +Water

Acid + Metal Hydroxide -> Salt + Water

For example:

• hydrochloric acid + copper oxide -> copper chloride + water.
• sulfuric acid + potassium hydroxide -> potassium sulfate + water.
• nitric acid + sodium hydroxide -> soidium nitrate + water.

Acid + Metal Carbonate -> Salt + Water + Carbon Dioxide

For example:

• hydrochloric acid + sodium carbonate -> sodium chloride + water + carbon dioxide
• sulfuric acid + calcium carbonate -> calcium sulfate + water + carbon dioxide

• Pick an insoluble metal oxide, hydroxide or carbonate as a base. E.g. if you want to make copper chloride mix hydrochloric acid (dilute acid) and copper oxide (base).
• Gently warm the dilute acid using a bunsen burner and turn off when finished.
• Add the insoluble base to the acid a bit at a time until the base is in excess (no more reacts), you can tell when the slid sinks to the bottom of the flask even after stirring.
• Filter out the excess solid to get the salt solution.
• To get pure, solid crystals of the salt use crystalisation: heat gently to make the solution more concentrated, leave to cool for about 24 hours, filter solution and dry.