SC8 Flashcards
What is the pH scale?
Its a measure of how acidic or alkaline a solution is.
How does the pH scale work?
Goes from 0-14.
Neutral is 7
Acidic is below 7
Alkaline is above 7
What is a base?
A substance that reacts with an acid to reduce salt and water.
What is an alkali?
It’s a base that is soluble in water.
What do alkalis form in water?
OH- ions.
What do acids form in water?
H+ ions
What is an indicator?
Its a dye that changes colour depending on whether its above or below a certain pH.
How do you use indicators?
Add a few drops to the solution you’re treating, then compare the colour the solution goes tot he pH chart for that indicator.
What are some indicators?
Universal
Litmus
Methyl orange
Phenolphthalein
What colours show acids on different indicators?
Universal - red
Litmus - red
Methyl orange - red
Phenolphthalein - colourless
What colours show alkalis on different indicators?
Universal - blue
Litmus - blue
Methyl orange - yellow
Phenolphthalein - pink
What colours show neutral on different indicators?
Universal - green
Litmus - blue
Methyl orange - yellow
Phenolphthalein - colourless
What is the reaction between an acid and a base called?
Neutralisation
What does a reaction between an acid and a base form?
Salt and water.
What happens to the ions at neutralisation?
The concentration of H+ ions is equal tot he concentration of OH- ions.
The pH is 7.
Name some common acids and their formula?
Hydrochloric - HCL
Sulfuric - H2SO4
Nitric - HNO3
Ethanoic - CH3COOH
What does acids can ionise (or dissociate) in solution mean?
It means splitting up to produce a hydrogen ion.
H+ and another ion.
What does a strong acid mean?
Ionise almost completely in water.
What are some examples of strong acids?
Sulfuric
Hydrochloric
Nitric
What does a weak acid mean?
It hasn’t fully ionised in solution.
What are some examples of weak acids?
Ethanoic
Citric
Carbonic
What does acid strength tell you?
What proportion of the acid molecules ionise in water.
What type of reaction is the ionisation of a weak acid?
Reversible reaction
This sets up an equilibrium - since only a few of the acid particles release H+ ions the equilibrium lies to the left.
What does the concentration of an acid measure?
How much acid there is in a litre (1dm3) of water.
What is a concentrated acid?
An acid with a large number of acid molecules compared to the volume of water.
What is a dilute acid?
An acid with a small number of acid molecules compared to the volume of water.
What type of reaction forms a salt?
A neutralisation reaction.
What is formed when an acid reacts with a metal oxide?
Salt
Water
What is formed when an acid reacts with a metal hydroxide?
Salt
Water
What is formed when an acid reacts with a metal?
Salt
Hydrogen
What’s the test for hydrogen?
Hydrogen makes a squeaky pop when a lighted splint is put in the test tube.
What is formed when an acid reacts with a metal carbonate?
Salt
Water
Carbon dioxide
What’s the test for carbon dioxide?
Bubbling limewater through it.
If CO2 is present the limewater turns cloudy.
