- Created by: abbiedye
- Created on: 25-07-18 14:11
What is the pH scale?
- A measure of how acidic or alkaline a solution is
- The lower the pH, the more acidic and the higher the pH, the more alkaline
- A neutral substance has a pH of 7
- A universal indicator indicates red, orange, or yellow for an acid, green for a neutral substance, and blue or green for an alkali
How do acids and bases neutralise each other?
- An acid is a substance that forms aqueous solutions in a pH less than 7 and forms H+ ions in water
- A base is a substance with a pH greater than 7
- An alkali is a base that dissolves in a solution that has a pH greater than 7. It forms OH- ions in water
- acid + base -> salt + water
What are strong and weak gases?
- Concentration is different to strength
- Strong acids (like sulphuric, hydrochloric and nitric acids) ionise completely in water and all acid particles dissociate to release H+ ions
- Weak acids (like ethanoic, citric and carbonic acids) do not fully ionise in solution, only a small amount of acid particles dissociate to release H+ ions and the reactions are reversible
How do metal oxides/hydroxides react with acids?
- acid + metal oxide -> salt + water
- acid + metal hyrdroxide -> salt + water
- hydrochloric acid + copper oxide -> copper chloride + water
How do acid and metal carbonates produce CO2?
- Metal carbonates are also bases. They react with acids to produce a salt, water and carbon dioxide
- acid + metal carbonate -> salt + water + carbon dioxide
- hydrochloric acid + sodium carbonate -> sodium chloride + water + carbon dioxide
What is the Reactivity Series?
- Potassium - K
- Sodium - Na
- Lithium - Li
- Calcium - Ca
- Magnesium - Mg
- Carbon - C
- Zinc - Zn
- Iron - Fe
- Hydrogen - H
- Copper - Cu
Potassium, sodium, lithium, and calcium are very reactive
Magnesium, carbon, zinc, and iron are very reactive
Hydrogen and copper are not very reactive
How do metals react with acids?
- Metals react with acids to produce a salt and hydrogen gas
- acid + metal -> salt + hydrogen
- The speed of a reaction is indicated by the rate at which bubbles of hydrogen are given off
- The more reactive the metal, the faster the reaction
How do metals react with water?
- metal + water -> metal hydroxide + hydrogen
- example - Ca(s) + 2H2O(l) -> Ca(OH)2(aq) + H2(g)
- The metals potassium, sodium, lithium and calcium react with water and the metals zinc, iron and copper won't react with water
How are metals separated from their oxides?
Formation of metal ore:
- Oxidation = Gain of Oxygen
- E.g. magnesium is oxidised to make magnesium oxide
- 2Mg + O2 -> 2MgO
Extraction of metal:
- Reduction = Loss of Oxygen
- E.g. copper oxide is reduced to copper
- 2CuO + C -> 2Cu + CO2
What metals are extracted by reduction with Carbon
Some metals can be extracted from their ores chemically by reduction using carbon
- In the reactivity series, if a metal is below carbon, it can be extracted by reduction using carbon. These metals are zinc, iron, and copper
- In the reactivity series, if a metal is above carbon, it can be extracted by electrolysis. These metals are potassium, sodium, lithium, calcium, and magnesium
What are redox reactions?
- Displacement reactions
- A more reactive metal will displace a less reactive metal from its compound
- iron + copper sulfate -> iron sulfate + copper (iron is more reactive)
What is electrolysis?
- An electric current is passed through an electrolyte. Ions move towards the electrodes where they react and the compound decomposes
- Positive ions move towards the cathode (negative electrode) and gain electrons (reduced)
- Negative ions move towards the anode (positive electrode) and lose electrons (oxidised)
- It creates a flow of charge and as they gain or lose electrons, they are discharged from the electrolyte
How does electrolysis of aqueous solutions occur?
- As well as ions, there is hydrogen ions and hydroxide ions from the water
- Cathode - if H+ ions and metal ions are present, hydrogen gas will be produced is the metal is more reactive - if not, a solid layer of pure metal is produced
- Anode - if OH- and halide ions are present, molecules of chlorine, bromine or iodine will be formed - if no halide ions, OH- ions are discharged and oxygen is formed