Chemical Changes Flashcards
What is oxidation?
The gaining of oxygen (loss of the electrons)
What is reduction?
The loses of oxygen (gaining of electrons)
What is the reactivity series of metals?
The series shows the metals in order of their reactivity
What are the trends in reactivities of metals in reactions with water/acids?
Metals above H2 -> in reactivity series react with acids to produce H2. The more reactive the metal is, the quicker and more violent reaction with acids occurs
Metals below H2 -> don’t react with acids
(Not all metals above H2 react with water)
What is a displacement reaction?
A reaction where a more reactive metal displaces a less reactive metal from a compound
How are unreactive metals found in earth?
In their natural state
How can metals less reactive carbon be extracted?
Reduction with carbon. Carbon displaces the metal oxide - gets oxidised to carbon oxides. Metals from the metal oxide get reduced to the pure metal
How are metals more reactive than carbon extracted?
By electrolysis
What is the general equation for a reaction between metals and acids? What type of reaction is this?
Metal + acids -> salt + hydrogen
Redox reaction, also a displacement reaction
What metals are in the reactivity series? (Most reactive to least reactive)
Potassium, sodium, calcium, magnesium, aluminium, CARBON, zinc, iron, tin, lead, HYDROGEN, copper, silver, gold and platinum
Which metals in the reactivity series will react with acid?
Those above hydrogen
What is the general equation for a neutralisation reaction?
Base + acid -> salt + water
What is the general equation for the reaction between metal carbonate and acid?
Metal carbonate + acid -> salt + water + carbon dioxide
What is the general equation for the reaction between metal oxides and acids?
Metal oxides + acid -> a salt + water
What is a redox reaction?
A reaction where both oxidation and reduction occur
How is a soluble salt formed?
- reacts the excess acid with some insoluble chemical
- filter off the leftovers
- crystallise the product
What do acids and alkalis produce in aqueous solutions?
Acids produce hydrogen ions, alkalis produce hydroxide ions
What are bases?
Bases are compounds that neutralise acids
What are acids?
Acids produce hydrogen ions in aqueous solution
What are alkalis?
Alkalis are soluble bases - produce hydroxide ions in aqueous solution
What is the pH scale?
The measure of acidity and alkalinity of a solution and a measure of H(+) concentration
What does a pH of 7 show?
Neutral reaction
What does below pH 7 show?
How acidic something is
What does above pH 7 show?
How alkaline something is
State the general equation for a neutralisation reaction in a short ionic form
H(plus) + OH(minus) -> H20
What is a strong acid?
Strong acid is completely ionised in aqueous solution and has a pH of 1-3
What is a weak acid?
Weak acid is only partially ionised in aqueous solution and has a pH 4-6
What happens to pH as concentration of H(plus) increases?
The pH decreases
What is a concentrated acid?
contains very large amount of acid than water in the solution
What is dilute acid?
the acid which contains greater concentrations of water in it (solutions of low concentration)
As the pH is decreased by one unit, what change is seen in the hydrogen ion concentration?
Increases by a factor of 10
What is electrolysis?
The passing of an electric current through ionic substances that are molten or in solution to break them down into elements, ions are discharged (they lose/gain electrons) at electrodes to produce these
What is an electrolyte?
The liquid which conduct electricity
What is a cathode?
Cathode is the negative electrode
What is an anode?
Anode is the positive electrode
What occurs at the cathode during electrolysis?
Reduction
What occurs at the anode during electrolysis?
Oxidation
In aqueous electrolysis, which element is discharged at the cathode? Oxygen is produced at the anode unless what?
The less reactive elements discharges at the cathode. Hydrogen is produced unless there is a less reactive metal, in which case the said metal is produced. Oxygen is produced at the anode unless the solution contains halide ions, in which case halogen molecules are produced
How is aluminium manufactured? Why is it expensive?
Aluminium is made through the electrolysis of aluminium oxide and cryolite
Lots of energy is needed to produce the current in electrolysis which makes the process expensive
What are half equations?
It is used represent the reaction that happens at an electrode during electrolysis (one-half of a redox reaction)
What are some example of half equations?
Al(3+) + 3e(-) —> Al (cathode)
2O(2-) —> O2 + 4e(-) (anode)
Why is cryolite used in the extraction of aluminium?
It lowers the melting point of aluminium oxide, reducing energy costs
What happen when you extract from metals that are less reactive than carbon?
Reduction using carbon
What is the extraction of metals?
Producing metals from their ore
What type of ions are produced by acids?
H(plus)
What type of ions are produced by alkalis?
OH(minus)
What is universal indicator?
An indicator with a different colour for each pH value
What is the concentration of H(pluses) at pH 7?
Concentration of H(minus) = concentration of OH(minus)
What type of ions are in water?
H(plus) and OH(minus)
What is the equation for the discharge of H(plus)?
2H+ + 2e- —> H2
What is H(plus) attracted to?
Cathode
What is the equation for discharge of OH-?
4OH- —> O2 + 2H2O
What is OH(minus) attracted to?
Anode
What is discharged at the cathode in a solution?
The least reactive element
What is discharged at the anode in solution?
Halide ions, if present otherwise OH(minus)
What is a halide ion?
A negative ion formed from a group 7 element
What are the properties of electrolysis?
expensive -> requires lots of energy to melt the compound and to produce the electrical current
What is cryolite?
The substance added to aluminium oxide to lower its melting point
Why is cryolite used?
Lowers melting point so reduces energy required
