TOPIC C4 CHEMICAL CHANGES Flashcards
what does the pH scale go from
0-14
pH acidity
-lower the pH of a solution, the more acidic it is
-higher the pH of a solution, the more alkaline it is
what is the neutral substance of a pH
7
e.g pure water
how to measure the pH of a solution
-indicator is a dye that changes colour depending on whether its above or below a certain pH
-named wide range indicators and are useful for estimating the pH of a solution
-pH probe attatched to the pH meter
whats an acid
-a substance that forms aqueous solution with a pH of less than 7
acids form H+ ions in water
whats a base
a substance with a pH greater than 7
whats an alkali
a base that dissolves in water to form a solution, with a pH over 7
-they form OH- in water
whats the reaction between acids and bases called
show the reaction
H+ + OH- —– H20
-NEUTRALISATION
do strong acids ionise in solutions
strong acids ionise completely in water and all acid particles dissociate to release H+ ions
do weak acids ionise
they do not fully ionise in solution
-only small proportiond of acid particles dissociate to release H+ ions
do weak acids or strong acids form reversible reactions
-reversible reactions, which sets up an equilibrium between the undissociated and undissociated acid
what does the pH mean
of an acid or alkali is the measure of the concentration of H+ ions in the solution
state the elements in the reactivity series
potassium
sodium
lithium
calcium ALL 4 VERY REACTIVE
magnesium
carbon
zinc
iron ALL 4 FAIRLY REACTIVE
hydrogen
copper 2 NOT REACTIVE
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how do metals react with acids
to produce salt and hydrogen gas
-speed of reaction is indicated by the rate of bubbles
-more reactive the metal, the faster the reaction will go
show the equation for metals reacting with water
metal + water ____ metal hydroxide +hydrogen
state what elements DO react with water and which dont
DO
-potassium
-sodium
-lithium
-calcium
DONT
-zinc
-iron
-copper
seperating metals from metal oxides
-most metals react with oxygen to form oxides and this process is an example of oxidation
-oxides are often the ores that the metals are extracted from
-a metal that seperates a metal from its oxide is a reduction reaction
Formation of metal ore
e.g magnesium
oxidation=gain of oxygen
magnesium is oxidised to make magnesium oxide
2Mg + O2 —- 2MgO
displacement meaning
where a more reactive element takes the place of a less reactive element in a compound
use of displacement
to extract a pure metal from a compound
oxidation
when a substance reacts to lose electrons
reduction
when a substance reacts to gain electrons
metal extraction
hydrogen and carbon are used to extract metals by displacement
electrolysis meaning
the method used to extract metals more reactive than carbon
why can ionic solids not undergo electrolsysis
as the ions are in fixed positions and cant move
why can molten ionic compounds undergo electrolysis
as the ions move freely and conduct electricity
-positive metal ions are reduced to the element
-negative non metal ions are oxidised to the element
METAL- cathode
NON METAL- anode
electrolsysi of aqueous solutoons
