Acids And alkalis Flashcards
What is an acid
These are proton donors; when mixed with water, they all dissociate, releasing H+ ions
H+ ions are just protons (they only have one electron remember)
These always combine with H2O to form H3O+
What is a base
These are proton acceptors; they accept H+ ions
What is an alkali
These are bases which are soluble in water
They release OH- ions in aqueous solution.
Examples of Acids
HCl
H2SO4
HNO3
CH3COOH
Examples of bases
NaOH
KOH
Reaction between acids and water
A for acid
HA + H2O produces H3O + and A-
These reactions are reversible
Reaction between bases and water
B + H2O produces BH+ and OH-
This reaction is reversible
What is a strong acid and base
For strong acids, very little reverse reaction occurs (H3O+ and A- changing back to HA and H2O)
So nearly all of the acid will disassociate ( or ionise) in the water, releasing H+ ions.
Similarly in strong bases, the forward reaction is favoured ( B + H2O reacting to produce BH+ and OH- ions)
So nearly all of the base disassociates in the water, releasing OH- ions.
What is a weak base and acid
For weak acids, the reverse reaction is favoured ( the A- and H3O+ ions reacting to form H2O and HA)
So very little acid disassociates in water and release H+ ions.
Similarly for weak bases, the reverse reaction is favoured (the BH+ and OH- ions react to produce H2O and B) so very little base disassociate in the water, releasing OH- ions.
What is a salt
Salt is produced when acids and bases neutralise each other.
How is a salt formed
When the H+ ions are replaced by the metal or ammonium (NH4+) ions from the alkali
What does metal and acid produce
Salt and Hydrogen
What does an acid and alkali produce
Salt and water
What does an acid and carbonate produce
Salt+ hydrogen + carbon dioxide
Different examples of bases and alkalis
Bases (insoluble in water)- oxides
Alkalis(soluble in water)- hydroxides
Metal and acid reaction process
Add a magnesium ribbon in a small volume of acid in a test tube
Observations
- fizzing or effervescence
- the test tube will be heating up
- magnesium will no longer be seen
Don’t usually use this method to produce a salt because the metal is usually more expensive to extract than the salt; most metals are extracted through electrolysis which is a very expensive process
Acid and alkali reaction process
Titration required
For the first titration, use an indicator to find the volume of acid required to neutralise the alkali
For the Second titration, don’t use an indicator to attain an uncontaminated salt.
Acid and base reaction process
Pour out 25/30/50ml of acid. Add excess base to the acid. For example, copper oxide
Heat it to speed up the rate of reaction; this reaction is exothermic
The copper oxide solution will turn blue.
The excess base will ensure that all of copper oxide has reacted and avoids having 2 solutes (water and acid).
Then filter it
Observations:
Excess solute particles will be seen at the bottom of the beaker
Fizzing
Acid and carbonate reaction process
In a beaker of known amount of carbonate (for ex: copper carbonate), add a certain volume of acid.
In this example, the green copper carbonate power will turn into a pale blue solution when acid is added.
Add excess carbonate to ensure that all of the acid has reacted.
The reaction will be completed when there is excess unreacted green powder at the bottom of the beaker. It has stopped fizzing too.
Stirring speeds up the reaction.
Observations
Fizzing and effervescence
Bubbles
Heating and crystillisation
All of these reactions will involve heating the salt to dryness which is different to crystallisation.
When heating a product to dryness, a lot of heat is exposed and over a short period of time.
This is done because sometimes, base or carbonate crystals will have water as well (hydrated). To attain pure salt or dehydrated salt we need to heat it strongly.
Crystallisation involves heating the product slowly until there is little amount of solution left.
Then it is left to dry over a mat.
