Chemical reactions Flashcards
What is an acid?
Substances that have a pH below 7
All acids contain hydrogen
What do acids produce when dissolved in water?
Hydrogen ions (H+)
What are bases?
Chemicals that can neutralise acids and produce a salt and water
What is an alkali?
A base that is soluble (can be dissolved) in water
For example sodium hydroxide
What do alkalis produce when dissolved in water?
Hydroxide ions (OH-)
What is neutralisation?
A reaction between an acid and a base to form a salt and water
What is the reaction for an acid-alkali neutralisation?
Alkali + Acid ——> Water + Salt
For example:
Sodium hydroxide + sulphuric acid ——> water + sodium sulphate
NaOH + H₂SO₄ ——> 2H₂O + Na₂SO₄
What is the reaction for acid-metal neutralisation?
Acid + Metal ——> Salt + Hydrogen
For example:
Hydrochloric acid + magnesium ——> magnesium chloride + hydrogen
In an acid-metal reaction what does the metal do?
The metal displaces the hydrogen in the acid to form a salt
If the metal is less reactive than hydrogen on the reactive series, there will be no reaction
Oxidation and reduction in acid-metal neutralisations
Metals are oxidised as they lose electrons to form positive metal ions
Hydrogen is reduced as it gains these electrons to form hydrogen atoms with no charge
This is because in aqueos acid solutions, acids produce H+ ions so they gain electrons to become neutral
What are salts made up of?
An ionic compound which has:
A positive metal ion from the base/alkali
Negative non metal ion from the acid
What is the reaction for acid-metal carbonate neutralisation?
Acid + Metal carbonate ——> Salt + Water + Carbon dioxide
For example:
Hydrochloric acid + Sodium carbonate ——> Sodium chloride + Water + Carbon dioxide
Formula for metal oxygen reaction
Metal + oxygen ——> metal oxide
Oxidation reaction in terms of oxygen
When a compound gains oxygen
The reactant atoms become oxidised
Reduction reaction in terms of oxygen
Losing oxygen from a compound
The reactant compound is reduced
Reaction for a metal and water reaction
Metal + water ——> metal hydroxide + hydrogen
How can we test the reactivity of reactive metals?
React them with water at room temp:
Potas, Sodi, lithi = Rapid reaction
Calcium = quite rapidly at room temp
Magnes, zinc, iron, copper = doesn’t have a noticeable reaction
How can we test the reactivity of the less reactive metals?
React them with a dilute acid
Calcium = extremely vigorous
Magn = rapid reaction
Zinc = quite rapid reaction
Iron = quite slow reaction
Copper = no reaction
Reactivity series
Potassium
Sodium
Lithium
Calcium
Magnesium
Carbon (nm)
Zinc
Iron
Hydrogen (nm)
Copper
What determines a metal’s reactivity?
It’s ability to lose an electron and become a positive ion
More shells = less attraction between reacting electron and positive nucleus
This means the as we go down, metals become more reactive
What determined group 7s reactivity?
Ability to gain another electron
Less shells = more attraction between the reacting electron of a metal and the group 7 nucleus
Therefore as we go down the halogen group it becomes less reactive
How can we extract a metal from a compound, such as a metal oxide?
By reacting a more reactive element with that compound to displace the desired metal
Gives us the pure metal
Displacement reaction
A more reactive element displaces a less reactive element from its compound
Reduction and oxidation in a displacement reaction with a metal oxide
Less reactive metal (metal oxide) is reduced as it loses oxygen atoms (displaced from oxide compound)
More reactive metal oxidised and gains oxygen atoms (takes place of metal oxide)
What element do we usually use for displacement?
Carbon as it’s very cheap
Oxidation reaction in terms of electrons
Oxidation is the loss of electrons
Forms a positive ion (metals)
Reduction in terms of electrons
Reduction is the gain of electrons
Forms a negative ion (non metals)
How to remember Oxidation/reduction in terms of electrons?
OIL RIG
Oxidation is loss
Reduction is gain
Hw to determine which elements have been reduced/oxidised (in terms of electrons) in an equation?
Identify the ions present (usually positive metal ions)
Compare them to when it’s on its own as an atom
If during the equation it joined an ionic compound, it lost electrons (oxidised)
If it was displaced from ionic compound it gained electrons (reduced)
Ending of salts formed from hydrochloric acid
-chloride
Eg sodium chloride
Ending of salts formed from sulfuric acid
-sulfate
Eg sodium sulfate
What determines how quickly an acid will react with a metal?
How reactive the metal is compared to hydrogen on the reactivity series
Oxidation in terms of hydrogen
The loss of hydrogen
Reduction in terms of hydrogen
The gain of hydrogen
Redox reactions
Reactions where one compound gains an electron (reduction) and one loses an electron (oxidation)
What ions do salts contain?
Positive ion from base/alkali
Negative ion from acid
What are metal oxides and hydroxides?
Bases
Why are concentrated acids better at conducting electricity?
Because they contain more H+ ions to carry the charge
What is acid strength a measure of?
If the acid fully ionises (strong) or partially ionises (weak) when dissolved in water
Fully ionising
When dissolved in water it completely breaks down to ions
Partially ionising
If when dissolved in water the H+ ions partially seperate
