Acids, Alkali, Bases and salt preperation Flashcards
Red litmus (from acid to alkali)
Blue litmus
Phenolphthalein
Methyl orange
Red, Red, Blue
Red, Blue, Blue REMEMBER IT ONLY CHANGES THE MIDDLE
Colourless, Colourless, Pink
Red/orange, yellow, yellow
Why is universal indicator used to measure the approximate pH value of an aqueous solution
It operates across a broad pH range and is useful for estimating the pH of an unknown solution
Why do acids neutralize alkali and vice versa
Presence of H+ ions make a solution acidic, and OH- ions make an aqueous solution alkali
Neutralisation - H+ OH- becomes H2O
Sodium, potassium and ammonium
Soluble
All nitrates
Soluble
Chlorides
Soluble (except Silver chloride and Lead(II) chloride
Sulfates
Soluble (except Barium sulfate, calcium sulfate and lead(II) sulfate
Carbonates
Insoluble (except sodium, potassium and ammonium carbonates)
Hydroxides
Insoluble (except sodium, potassium and calcium hydroxides [calcium hydroxide is slightly soluble])
Alkali + acid ->
salt + water
base + acid ->
metal oxides and hydroxides are bases
salt + water
metal + acid ->
salt + hydrogen
carbonate + acid ->
salt + carbon dioxide + water
metal + water ->
metal hydroxide + hydrogen
metal oxide + water ->
metal hydroxide BALANCE IT
Ammonia + water ->
NH4+ (aq) + OH-
Titration method (example sodium hydroxide + water)
- Pipette 25cm^3 of alkali (NaOH) into a conical flask
- Add indicator
- Titrate the acid through the burette in small portions and swirl, until there is a sharp color change
- Quickly close the tap and record the volume (eye level with meniscus)
- Repeat the experiment without indicator given the volume of acid needed (no impurities)
- Transfer to evaporating basin and heat the solution, and allow it to cool so that crystals form (remove H2O, saturate salt)
- Dry by leaving in a warm place
Precipitation method (example forming silver chloride)
silver nitrate + potassium chloride (two soluble salt solutions) -> silver chloride(s) + potassium nitrate(aq) one sol. one insol.
1. mix the two salt solutions together in a beaker
2. stir with a glass rod (ensure all reactants have reacted)
3. filter the insoluble salt using filter paper and funnel
4. wash the insoluble salt with distilled water (to remove all of the remaining soluble salt)
5. Dry by leaving in a warm place
Neutralisation/Excess Solid method (example forming copper(II)sulfate from copper(II) oxide)
CuO + H2SO4 -> copper sulfate + water
1. Heat acid in a beaker (speed up reaction)
2. Add base (CuO) in excess (until no more CuO dissolves) and stir with glass rod
3. Filter the mixture using filter paper and funnel
4. Gently heat the filtered solution until crystals form (check if they form on end of a glass rod to show saturated solution)
5. Dry by leaving in a warm place
When to use titration:
Soluble, sodium or potassium salt
When to use precipitation:
Insoluble salt
When to use neutralisation:
Soluble, not sodium or potassium salt
