Topic 8 Acids, Bases And Salts Flashcards
Universal indicator at acidic, neutral and alkaline
Acidic - red
Neutral - green
Alkaline - purple
Phenolphthalein indicator at acidic, neutral and alkaline
Acidic - colourless
Neutral - colourless
Alkaline - pink
Methyl Orange indicator at acidic, neutral and alkaline
Acidic - red
Neutral - orange
Alkaline - yellow
Red litmus paper at acidic, neutral and alkaline
Acidic - red
Neutral - red
Alkaline - blue
Blue litmus at acidic, neutral and alkaline
Acidic - red
Neutral - blue
Alkaline - blue
Where are strong acids on the PH scale
0-2. Examples are hydrochloric, sulfuric or nitric acid
Where are weak acids on in the pH scale
3-6. Examples are ethanoic or carbonic
Where is neutral on the pH scale
7
Where are weak alkalis on the pH scale?
8-11. Examples are ammonia
Where are strong alkalis on the pH scale
12-14. Examples are sodium hydroxide or potassium hydroxide
What do acids produce when dissolved?
H+ (aq) ions. The higher the concentration of hydrogen ions, the stronger the acid is
What do alkalis produce when dissolved?
OH- (aq) ions
What do weak acids and alkalis do in water?
Only partially ionise
What do strong acids and alkalis do in water?
Completely ionise
Dilute
contains a Small number of particles dissolved per unit volume
Concentration
A measure of the number of moles of acid/alkali molecules dissolved in 1dm3 of water. Measured in mol/dm3. The higher the concentration the more acid/alkali molecules that have been dissolved
Neutralisation
The reaction between an acid and an alkali which produces salt and water
What is the ionic equation for neturalisation
H+ (aq) + OH- (aq) = H2O (l)
Is neutralisation an exothermic reaction?
Yes
Base
Metal oxide/hydroxide which neutralises an acid
Alkali
A soluble base
Acid + metal =
Salt + hydrogen
Acid + base =
Salt + water
Acid + alkali =
Salt + water
What are bases and alkali?
Oxides/hydroxides
Acid + carbonate =
Salt + water + carbon dioxide
Acid + hydrogencarbonate =
Salt + water + carbon dioxide
Acid + ammonia =
Ammonium salt
Salt
A compound formed when some or all of the hydrogen ions in an acid are replaced by metal/ammonium ions
How to test for hydrogen gas
Apply a lighted splint - if hydrogen is present there will be a squeaky pop
How to test for carbon dioxide?
Limewater will turn from colourless to milky/cloudy if carbon dioxide is present there
Facts about group 1 and 2 salts
Most group 1 and 2, aluminium and zinc salts are white. Dissolved in water they give colourless solutions.
What are transition metals? What do they look like?
They are metals between groups 2 and 3 and are generally coloured
How do you prepare a salt from an acid and base?
- Measure 25cm3 of dilute acid and place in beaker
- Warm dilute acid. Do not allow to boil
- Add the base and stir. Continue adding until there is no further reaction and the unreacted base is in excess at the bottom of the beaker
- Allow to cool then filter the mixture and collect the filtrate in an evaporating basin
- Heat the filtrate in the evaporating basin until half of it has evaporated (to make it more concentrated)
- Allow basin to cool and crystals will form
- When crystals have formed, dry between 2 pieces of filter paper/desiccator/low temperature oven
What is the first method to prepare a salt from an acid and alkali (soluble base)?
- Fill burette with acid
- Using pipette and pipette filler place 25cm3 of alkali solution into a conical flask
- Add 3 drops of phenolphthalein into the conical flask until solution turns pink
- Add acid from the burette the into the conical flask, swirl gently
- Stop adding acid when indicator turns colourless
- Record volume by reading burette
- The reaction is repeated for a more accurate result, then again without indicator and using the more accurate result of acid
- Pour solution into evaporating basin
- Heat gently until half of the solution remains
- Leave to cool and crystallise, remove crystals and dry
What is the second method to prepare a salt from an acid and alkali (soluble base)?
Follow steps 1-5 of first method:
1. Fill burette with acid
2. Using pipette and pipette filler place 25cm3 of alkali solution into a conical flask
3. Add 3 drops of phenolphthalein into the conical flask until solution turns pink
4. Add acid from the burette into the conical flask and swirl gently
5. Stop adding acid when indicator turns colourless
Then:
6. Add 2 spatulas of decolourising charcoal to conical flask
7. Heat gently - do not boil
8. Allow to cool slightly, then filter mixture into evaporating basin
9. Heat again until half of the solution remains
10. Leave to cool and crystallise, remove crystals and dry
