chemical changes

• acids and alkalis are on the opposite ends of the pH scale and combine to form water, which is neutral
• acids are substances that form hydrogen ions when they dissolve in water
• alkalis are substances that form hydroxide ions when they dissolve in water
• an alkali is a type of base
• the pH scale is used to measure how acidic or alkaline a substance is
• oxidation is the gaining of oxygen in a reaction and reduction is the loss of oxygen in a reaction
• we can also describe oxidation and reduction in terms of electrons
• when a substance is oxidised, it always loses electrons
• when a substance is reduced, it always gains electrons
• a useful way of remembering the different between oxidation and reduction reactions in terms of electrons is 'OIL RIG': Oxidation Is Loss Reduction Is Gain
• when reacting with other substances, metal atoms always form positive ions
• the reactivity of a metal is linked to how easy it is for a metal to form a positive ion
• metals can be arranged in order of their reactivity
• gold and platinum are examples of highly unreactive metals which can be found in the earth's crust as pure metals and call them native metals
• a more reactive metal can remove a less reactive metal from a compound, called a displacement reaction
• a metal can only displace another metal from a compound if it is located above it in the reactivity series
• more reactive substances can displace less reactive substances from compounds
• spectator ions are the ions that are unchanged during displacement reactions
• potassium, sodium and lithium all react quickly with cold water to produce a metal hydroxide and hydrogen gas
• potassium is the most reactive so reacts very quickly s the hydrogen produced ignites instantly nd the metal also sets alight, sparking and burning with a lilac flame
• sodium fizzes rapidly and melts to form a ball that moves around on the water surface
• lithium fizzes steadily and floats, becoming smaller until it eventually disappears
• most metals react with dilute acids to give a salt and hydrogen gas
• metals don't have to be that reactive to react with dilute acids
• the metals that react with dilute acids but not cold water are magnesium, aluminium, zinc, iron and lead
• the only metals that aren't reactive enough are copper, silver, gold and platinum
• most metals are only found as compounds because the metal has reacted with other elements in the past, due to this the metal has to be extracted from the pre where the metal compound is found
• reducing a metal with carbon will result in the extraction of the metal if the metal is lower in the reactivity series than carbon
• carbon is used because it is cheap and abundant
• in the reduction, the metal oxide loses oxygen to form a pure metal
• reduction with carbon normally involves heating the metal oxide in the presence of the carbon, which is often used in the form of coal
• when acids react with metals, hydrogen and a salt are always formed - the first part of the salts name comes from the metal involved, the second part of the name comes from the acid
• redox reactions involve a reduction reaction and an oxidation reaction
• acids can be neutralised by reacting with bases
• metal carbonates, metal oxides and metal hydroxides are all examples of bases
• acid + carbonate = salt + water + carbon dioxide
• acid + metal oxide = salt + water
• acid + hydroxide = salt + water
• soluble salts are salts which dissolve in water
• we can produce soluble salts through a reaction between acids and solid, insoluble substances such as pure metals, metal oxides, metal hydroxides, or metal carbonates