Topic 4 - Acid and Alkali Flashcards
acidic pH
less than 7
alkali pH
more than 7
neutral pH
7
how can you find the pH of a solution
using indicators
indicator
a substance that changes colour depending on the pH
name common acids
- hydrochloric acid (HCl)
- sulfric acid (H2SO4)
- nitric acid (HNO3)
name a common alkali
- sodium hydroxide (NaOH)
what ion does acids contain
H+
what ion does alkalis contain
OH-
what ion does neutral solutions contain
even concentration of H+ and OH- ions
concentrated solution
contains a lot of dissolved solute per unit volume
dilute solution
contains only a small amount of solute
difference in concentration of H+ ions in acid pH
each time (each number) you go down in pH the concentration of H+ ions i increases by 10x
concentration equation
amount dissolved / volume of solution
bases
substances that neutralise acids to form a salt and water only
base + acid reaction
base + acid -> salt + H20 (BASH20)
during neutralisation reactions explain why the pH becomes neutral
the hydrogen ions combine with oxide ions to form water; this removes the’” hydrogen ions ans so the pH increases
during neutralisation reactions explain how is a salt produced
salts are produced by replacing the hydrogen ions with metal ions
method to prepare a solute
1) add excess of base
2) gently warm the mixture to speed up reaction
3) filter to remove the untracked solid from the solution
4) heat to evaporate water and concentrate the salt solution
5) leave to evaporate water slowly for crystallisation to occur
what’s the difference between base and an alkali
base is insoluble, alkali is soluble
what happens in a titration
- acid is added from à burette to a fixed volume of alkali in a conical flask “)
- a few drops of indicator are added to the alkali so you can follow the reaction
- eventually the solution will reach end-point
end-point
when the indicator changes colour
how to make a pure dry salt
- carry out a titration
- note the exact volume of acid needed to neutralise the alkali
- use the burette to add the correct volume of acid without the indicator
- evaporate the water from the solution formed
general equation for reaction of metal and an acid
metal + acid -> salt + H2 (MASH2)
general equation for reaction of metal carbonate and an acid
metal carbonate + acid -> salt + H20 + CO2 (CASH2OCO2)
precipitation reaction
in a precipitation reaction is one in which a soluble substance in a solutions* i cause an insoluble precipitate to form
precipitate
cause (a substance) to be deposited in solid form from a solution
what is the test for carbon dioxide
limewater
what happens to the hydrogen ions in neutralisation?
They combine with oxide ions to form water. This removes the hydrogen ions instead of pH increases.
Difference between single indicator and universal indicator
Single indicator only tells if substance is acidic or basic however universal indicator provides a more detailed indication of how acidic or basic substances by displaying a variety of colours of the pH scale
spectator iron
An ion from the acid that does not change during a reaction
Oxidation
Loss of electrons in a reaction
reduction
gain of electrons in a reaction
how do you work at the ionic equation?
Crossover method
what happens when two solutions containing soluble cells react together?
The endings swap
e.g. Copper sulphate + potassium carbonate -> copper carbonate + potassium sulphate
how to prepare insoluble salts
- mix the two solutions in a beaker, then filter the mixture
- Rinse the beaker with a little distilled water and pour this through the funnel
- Pour a little distilled water over the precipitate in the funnel
- Carefully remove the food paper containing the precipitate and dry in a warm oven
What chloride are in soluble water?
Silver, lead chlorides
What sulphates are in soluble in water?
Lead barium calcium sulphate
what nitrates are insoluable water?
all of them
name a piece of equipment that could be used to measure the pH of a substance more accurately than universal indicator paper
pH meter
