Reactions of acids Flashcards
• Reactions of acids with metals • Neutralisation of acids and salt production • Soluble salts • The pH scale and neutralisation • Titrations - technique • Strong and weak acids • RP1: Preparation of a pure, dry sample of a soluble salt from an insoluble oxide or carbonate, using a Bunsen burner to heat dilute acid and a water bath or electric heater to evaporate the solution
What is an acid?
When dissolved in water, its solution has a pH value of less than 7. They are proton donors.
What do acids form in water?
H+ ions
What is a base?
a substance that reacts with an acid to produce a salt and water. They are proton acceptors.
What is an alkali?
A base that is soluble in water and has a pH of more than 7.
What is a salt?
A compound formed when some or all of the hydrogen in an acid is replaced by a metal during a neutralisation reaction.
What does soluble mean?
If a substance is soluble it will dissolve in a given amount of liquid (solvent)
What does insoluble mean?
A substance that will not dissolve in a solvent even after mixing
What does HCL stand for
Hydrochloric acid
What is H2SO4?
sulfuric acid
What is HNO3?
nitric acid
acid + metal oxide or base =
salt + water
2HCl + CuO ->
CuCl2 + H2O
H2SO4 + Zn0 ->
ZnSO4 + H2O
2HNO3 + MgO ->
Mg(NO3)2 + H20
metal hydroxide + acid
salt + water
HCl + NaOH ->
NaCl + H2O
H2SO4 + Zn(OH)2 ->
ZnSO4 + 2H20
HNO3 + KOH ->
KNO3 + H2O
acid + metal ->
salt + hydrogen
2HCl + Mg ->
MgCl2 + H2
H2SO4 + Mg ->
MgSO4 + H2
Acid + metal carbonate
salt + water + carbon dioxide
2HCl + Na2CO3 ->
2NaCl + H2O + CO2
H2SO4 + K2CO3 ->
K2SO4 + H2O + CO2
what is the charge of CO3?
2-
what is the charge of OH?
1-
what is the charge of SO4?
2-
what is the charge of NO3?
1-
what is the charge of O?
2-
How to make a pure, dry sample of a soluble salt (acid and insoluble base method)?
1) Heat the acid in a water bath - speeds up the reaction. In a fume cupboard to avoid releasing acid fumes.
2) Then add the insoluble base to the acid. They will react to produce a soluble salt and water. You know when the base in excess when all the acid has been neutralised because the excess solid will sink to the bottom of the flask.
3) filter the excess solid using a filter paper and and funnel. So that the solution is only salt and water.
4) Heat the solution gently using a Bunsen burner to evaporate the water. Leave the solution to cool and allow the salt to crystallise. Leave the salt to dry.
Why is a certain reactant used in excess?
To ensure the other reactant has been used up
H+ (aq) + OH- (aq) ->
H2O (l)
Qualities of a strong acid?
1) an acid that ionizes completely in aqueous solution
2) an acid that dissociates completely in aqueous solution
3) lower pH
BOTH: to produce the maximum amount of H+ ions / protons
Qualities of a weak acid?
1) an acid that is only slightly ionized in aqueous solution
2) an acid that only slightly dissociates in aqueous solution
BOTH: small proportion of the acid molecules dissociate to produce H+ ions.
If an acid is said to be concentrated what does it mean?
An acid with a large number of acid molecules compared to the volume of water is said to be concentrated.
The lower the pH, the …
The higher the H+ concentration
The higher the pH, the…
lower the H+ concentration / higher the OH- concentration
W are the indicators used in titration?
phenolphtalein or methyl orange NOT UNIVERSAL INDICATOR AS IT CHANGES COLOUR GRADUALLY AND IN TITRATION WE WANT A SUDDEN COLOUR CHANGE
color change in methyl orange,when substance goes from acid -> alkali?
red -> blue
color change in phenolphtalein ,when substance goes from acid -> alkali?
colourless -> pink
What is a pipette used for?
Long, narrow tubes used to suck up an accurate volume of liquid and transfer it to another container.
What is a burette used for?
They have a tap at the bottom and can release the liquid into another container. To use it take an initial reading and then a final reading and calculate the difference
What is the difference of use of a burette vs pipette in a titration?
While burette is used to deliver a chemical solution with a known concentration into a flask, pipette is used to measure the quantity of the solution where the concentration is not known.
What is the test for CO2?
If limewater bubbles and turns cloudly, CO2 is present
What is the test for hydrogen?
Put a lighted splint in the test tube.
If hydrogen is present it will make a’squeaky pop.
What are redox reactions? Give an example
Redox means reduction and oxidation at the same time
Metal-acid reactions
Reactivity series (more reactive to less reactive)
Potassium Sodium Lithium Calcium Magnesium Carbon Zinc Iron Hydrogen Copper
What does OIL RIG stand for?
Oxidation Is Loss
Reduction Is Gain (of electrons)
How are acids neutralised?
Acids are neutralised by alkalis and bases to produce salts and water
Acids are neutralised by metal carbonates to produce salts, water and carbon
dioxide
What do alkalis produce in water?
OH-
How to carry out titration?
- Wash burette using dilute hydrochloric acid and then water
- Fill burette to 100cm3 with acid with the meniscus’ base on the 100cm3
line - Use 25cm3 pipette to add 25cm3
of alkali into a conical flask, drawing alkali into the
pipette using a pipette filler - Add a few drops of a suitable indicator to the conical flask (eg: phenolphthalein
which is pink when alkaline and colourless when acidic) - Add acid from burette to alkali until end-point is reached (as shown by indicator)
- The titre (volume of acid needed to exactly neutralise the acid) is the difference
between the first (100cm3
) and second readings on the burette - Repeat the experiment to gain more precise results
What symbol is ammonia?
NH3
what is the point of filtering?
Separate insoluble solid from solution
What is the point of heating the solution?
Evaporate excess water
How to tell if something is a base?
Ends with carbonate or oxide
How to tell if something is an alkali?
Ends with OH-
