Chemical Flashcards
How to decide if a substance is an acid or alkali
Depends on type of ions released when substance is dissolved in water.
Acids from hydrogen ions (H+) when dissolved in water.
Alkalis form hydroxide ions (OH-)
Neutralisation
Acid + Alkali -> Salt + Water
Can be shown in terms of H+ and OH- ions.
H+ + OH- -> H2O
Acid Strength
Proportion of acid particles that’ll dissociate to produce H+ ions in a solution
Strong Acids
An acid (sulphuric, hydrochloride and nitrate acid) that completely dissociates its H+ ions in water (irreversible)
HCl(g) + H2O(aq) -> H+ (aq) + Cl- (aq)
Reactions of acid
A base if a substance that can accept a hydrogen ion (H+) from another substance. Usually metal oxides or metal hydroxides
Acid + Base -> ? + ?
Salt + water
Metal Carbonate + acid -> ? + ? + ?
Metal salt + carbon dioxide + water
Metal carbonates are also bases, react with acids to produce carbon dioxide
Acid + Metal -> ? + ?
Salt + Hydrogen
Reactivity series
Potassium Sodium Lithium Calcium Magnesium Aluminium Zinc Iron Tin Lead Copper Mercury Silver Gold
Why are carbon and hydrogen included in the reactivity series?
They’re used to displace metals from their ores
What does the reactivity series show?
How easily a metal loses an electron and becomes a positive ion
What reactions give evidence of reactivity?
Metal + Acid -> salt + hydrogen
Metal + water -> metal hydroxide + hydrogen
Displacement reactions
Metal A + Metal B compound -> Metal B + Metal A compound
A more reactive metal displaces a less reactive metal from its compound
2HCl + Mg -> MgCl2 + H2
atom + metal oxide ->? What
Salt + water
Acid + metal hydroxide ->?
Salt + water
Explain an experiment for making pure salt
Heat sulphuric acid Stir in copper oxide, until in excess Let it cool Filter the solution to remove the excess copper oxide Evaporate away the liquid
Equation:
Sulphuric acid + Copper oxide -> Copper sulphate + water
H2SO4 + CuO -> CuSO4 + H2O
What does 1 mean on the pH scale?
Acid
What number represents neutral on the pH scale?
Neutral
What number represents Alkali on the pH scale?
14
Neutralisation Equation
H+ + OH- reversible arrows H2O
How do cells work?
Example: Copper in copper sulphate solution Zinc in Zinc sulphate solution Salt bridge between Zinc is high up in the reactivity series so pushes electrons making a potential difference Zn-> Zn2+ + 2e- Cu2+ + 2e- -> Cu
Non rechargeable batteries
The reactants that produces electricity ones it’s used up its dead
Rechargeable batteries
Reversible
Once reactants used up, electricity can pass through causing the reaction to go in reverse direction, recharging reactants
Hydrogen fuel cell
Hydrogen gas reacts with oxygen gas, turning into water
Advantages
Energy released
Water is only product- no carbon emissions
Disadvantages Production of hydrogen uses fossil fuels Not sold everywhere Hydrogen needs to be compressed Explosive Large tank to store Don’t work at low temp
Half equations for hydrogen fuel cell
Negative electrode
H2 - 2e- -> 2H+
Positive electrode
4H+ + O2 + 4e- -> 2H2O
