Topic 4 - Chemical Changes
- Created by: Zuha7375
- Created on: 03-11-18 19:21
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- Topic 4 - Chemical Changes
- Acids & Bases
- pH Scale = measure of how acidic or alkaline a solution is
- Acid = substance that forms aqueous solutions with pH of less than 7 - form H+ ions
- Base = substance with pH greater than 7
- Alkali = base that dissolves in water to form solution with pH greater than 7 - form OH- ions in water
- Neutralisation - acid + base GIVES salt + water
- Strong Acids & Weak Acids
- Strong Acid = ionise completely in water & all acid particles dissociate to release H+ ions
- Weak Acid = don't fully ionise in solution & only small proportion of acid particles dissociate to release H+ ions
- Ionisation of weak acid = reversible reaction = sets up equilibrium (position of this = left) between undissociated & dissociated acid
- If concentration of H+ ions is higher, rate of reaction = faster so strong acids = more reactive than weak acids of same concentration
- pH = measure of concentration of H+ ions in solution
- Acid strength = tells what proportion of acid molecules ionise in water WHERE AS Concentration = measures how much acid is in certain volume of water
- Reactions of Acids
- Metal Oxides & Metal Hydroxides = Bases
- Acid + Metal Oxide GIVES Salt + Water
- Acid + Metal Hydroxide GIVES Salt + Water
- Acid + Metal Carbonate GIVES Salt + Water + Carbon Dioxide
- Metal Oxides & Metal Hydroxides = Bases
- Reactivity Series
- How well a metal reacts
- The higher up the reactivity series a metal is, the more easily they form positive ions (by losing electrons)
- Higher a metal is in the reactivity series, the more easily it reacts with water or acid
- acid + metal GIVES salt + hydrogen
- metal + water GIVES metal hydroxide + hydrogen
- More reactive the metal, the faster the reaction will go
- Investigate reactivity of metals by measure temp change of reaction with acid or water over set time period
- If use same mass & surface area of metal each time - more reactive the metal, the greater temp change should be
- Separating Metals from Metal Oxides
- Metals often have to be separated from their oxides
- Reduction Reaction
- Formation of Metal Ore: Oxidation = Gain of Oxygen
- Extraction of Metal: Reduction = Loss of Oxygen
- Some metals = Extracted by Reduction with Carbon
- Metals HIGHER THAN CARBON in Reactivity Series = extracted using electrolysis
- Metals BELOW CARBON = extracted by Reduction using Carbon
- Redox Reactions
- If electrons = transferred
- OILRIG
- Displacement Reactions are Redox Reactions
- Rule - A more reactive metal will DISPLACE a less reactive metal from its COMPOUND
- Metal ion = gains electrons and is reduced - metal atom = loses electrons and is oxidised
- Acids & Bases
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