What colour is litmus in acid and alkali?
Red in acid
Blue in alkali
What colour is phenolphthalein in acid and alkali?
Clear in acid
Pink in alkali
What colour is methyl orange is acid and alkali?
Pink/red in acid
Yellow in alkali
What are acids?
- acids neutralises bases
- they dissolve in water
- they release H+ ions
What do the number of H+ ions lost tell you about the acid?
- strong acids disassociate their H+ ions fully
- weak acids disassociate their H+ ions partially
- pH measures the number of H+ ions lost
What are alkalis?
- dissolve in water
* release hydroxide(OH-) ions
What are bases?
• don’t dissolve in water
• neutralise acids
E.g. Copper or iron oxide, zinc carbonate
explain the add excess base method
Add excess base: (e.g. Making copper sulphate)
- Add excess base to the acid until no more dissolves (warm acid if necessary)
- Filter off excess base
- Obtain dry salt from the solution
Explain the titration method
Titration: (e.g. Hydrochloride acid and sodium hydroxide)
- Measure out the alkali using a pipette, and pour into conical flask
- Add acid via a Burnett to alkali, slowly, occasionally mixing, until indicator is neutral
- Add the same volume of acid to the same amount of alkali WITHOUT indicator
- Obtain dry salt from solution
Explain the precipitation method
Precipitation: (e.g. Making lead iodide)
1. Make two solutions each containing an ion of the salt you want to make (these must be soluble)
2. Mix the solutions
3. Filter off the precipitate- the insoluble salt
4. Wash the precipitate with distilled water to remove any other salt solutions
5. Dry on filter paper or warm gauze
Example: sodium iodide + lead nitrate ➯ lead iodide + sodium nitrate
Colourless solution + colourless solution ➯ yellow precipitate + colourless solution
What salts are soluble?
All chlorides except silver and lead
All sulfates except barium lead and calcium
Potassium, sodium and ammonium carbonates
What salts are insoluble?
Silver chloride, lead chloride
Barium sulphate, lead sulphate, calcium sulphate
All carbonates except potassium, sodium, and ammonium
How do you know what method to use to make a salt?
1. Is the salt soluble? No: precipitation Yes: 2:Is the base soluble? (I.e. Is it a hydroxide) No: add excess base Yes: titration
How des the add excess base method work?
- mix acid and base
- add excess base until it no more dissolves
- heat to get rid of some water
- leave to crystallise
- wash w distilled water to get rid of any remaining acid/alkali
How does titration work?
- measure out alkali using pipette and pour into conical flask
- add acid via a burette slowly, mixing occasionally, until indicator turns neutral
- repeat but w/o indicator
- heat solution to get rid of most of water
- filter to remove water
- allow to crystallise
How does precipitation work?
- make two soluble solutions each containing an ion of the salt you want
- filter off the precipitate- the insoluble salt
- wash w distilled water to get rid of any other salt solutions
- dry on filter paper/warm gauze
What is concentration?
Concentration (moldm-3) = moles / volume
How do you work out concentration calculations?
- balance eq
- write in what we know and what we must find out
- work out mols of known
- use ole ratios to find mols of unknown
- using vol of unknown find conc of unknown