Chemical changes Flashcards
What are the 2 ways to measure the pH of a solution
- pH probe
- Chemical indicator
Universal indicator
- acid = red
- alkaline = bluey-purple
2 reasons why the pH probe is more reliable than indicator
- Determining the colour of the
indicator is subjective - produces more accurate results
What is the ion responsible for making an alkaline pH when dissolved
OH-
What is an acid?
any substance that forms an aqueous solution with a pH less than 7
What ions do acids form?
H+ ions in water
What is a base?
any substance with a pH greater than 7
What is an alkali?
A base that dissolves in water to form a solution with a pH greater than 7
What ions do alkalis form?
0H- in water
Neutralization reaction
acids + base –> salt + water
common acids
hydrochloric - HCL
sulfuric - H2SO4
nitric - HNO3
common bases
sodium hydroxide - NaOH
calcium carbonate - CaCO3
What are the 3 types of indicators?
- phenolphthalein
- litmus
- methyl orange
Phenolphthalein
- acids - colourless
- alkalis = pink
Litmus
- acid = red
- alkaline = blue
Methyl orange
- acid = red
- alkaline = yellow
What makes a strong acid?
Ionise completely in water
- all acid particles dissociate to release H+ ions
ionise completely
all of the acid particles will dissociate
(reactants turn completely into products)
examples of strong acids
- hydrochloric acid
- sulfuric acid
- nitric acid
examples of weak acids
- ethanoic acid
- citric acid
- carbonic acid
What makes a weak acid?
do not fully ionise in solution
- only small proportion of acid particles dissociate to release H+ ions
Why are weak acids weak?
Ionisation of weak acid is a reversible reaction which sets up an equilibrium between the undissociate and dissociate acid.
Strength of acids
How much an acid dissociates
Concentration of acids
How much acid there is in a certain volume
pH scale
A measure of the concentration of H+ ions in a solution
Why does a strong acid have a lower pH than weak acids
Higher proportion of the strong acid particles will dissociate to release their hydrogen ions, which the concentration of those ions determine the pH
The reactivity series
potassium
sodium
lithium
calcium
magnesium
carbon
zinc
iron
hydrogen
copper
What is the reactivity series for
How easily it forms positive ions
How to make sure its a fair test when testing how reactive the metal is
- each of the metal sample has :
- same mass/surface area
- use the same type/ concentration of
acid
Metals + acid —->
Salts + hydrogen
Metals + water —->
Metal hydroxide + hydrogen
metal oxide + acid
salt + water
oxidation
gaining of oxygen
Reduction
loss of oxygen
Oxidation in terms of electrons
loss of electrons
Reduction in terms of electrons
Gaining of electrons
Redox reaction
Where oxidation and reduction occurs at the same time
