Topic 4 - Chemical Changes Flashcards
What is the pH scale?
A measure of how alkaline or acidic a solution is.
How can you measure the pH of a solution?
Use an indicator. A dye that changes colour depending on the pH. Eg universal indicator.
Use a pH probe which is attached to a pH meter and measures the pH manually.
Whats an acid?
A substance that forms aqueous solutions with pH less than 7. They form H+ ions in water.
Whats an alkali?
A base that dissolves in water to form a solution with pH more than 7. Creates OH- ions in water,
What is a base?
A substance with pH greater than 7.
Whats the reaction for neutralisation?
Acid + base —-> salt + water
H+(aq) + OH-(aq) —-> H20(l)
Whats the features of strong acids?
Ionise completely in water. (All ions dissociate to release H+ ions).
Faster rate of reaction since high concentration H+ ions to react with other substances.
Whats the features of weak acids?
Dont ionise fully in water.
The ionisation of a weak acid is a reversible reaction.
How much more does H+ ion concentration increase per 1pH that you go down?
x 10
ph 4 has 10 times the concentration of H+ than pH 5.
pH 3 has 100 times the concentration of H+ ions than pH 5
Whats the difference between a strong acid and concentrated acid?
Acid strength tells you what proportion of the acid molecules ionis in water.
Concentration measures how much acid there is in a certain volume of water. (How watered down your acid is)
What is formed when a metal hydroxide or metal oxide reacts with acid?
Salt and water
Whats formed when a metal carbonate reacts with water?
Salt
Water
Carbon dioxide
What does a metals reactivity depend on?
How easily they lose electrons.
List the metal reactivity series from most reactive to least.
Potassium Sodium Lithium Calcium Magnesium Carbon Zinc Iron Hydrogen Copper
What does a metal reaction with an acid tell you about the metal reactivity?
There will be a faster reaction the more reactive it is.
So vigorous reaction and lots of bubbles produced
Also the greater the temperature change, the more reactive
Whats formed when a metal reacts with water?
Metal hydroxide
Hydrogen
Note: less reactive metals like zinc iron and copper dont react with water.
Whats the reaction called that separates a metal from its oxide?
Reduction reaction
What is oxidation?
Metal reacts with oxygen and forms an oxide
Whats reduction?
When oxygen is lost
How can you extract metals from their ores with carbon? Can all metals be extracted by reduction from carbon?
The ore is reduced as oxygen is removed from it. The carbon gains the oxygen removed from the ore.
The metal has to be lower down the reactivity series than carbon to be able to be reduced
Why are some metals mined it its element form already?
Theyre just so unreactive. Eg gold
Whats a redox reaction?
Oxidation and reduction but in terms of electrons being transferred
Is oxidation loss or gain of electrons? And reduction?
Oxidation is loss of electrons.
Reduction is gain of electrons
Whats a displacement reaction
When a more reactive metal displaces a less reactive one from its compound.
Remember its always the atom that loses electrons and is oxidised and the ion gains the electrons to be reduced
