salts Flashcards
solubility of grp I and ammonium salts?
ALL are soluble
solubility of common nitrates
ALL are soluble
solubility of common sulfates?
ALL are soluble EXCEPT: PbSO4, CaSO4, BaSO4
soloubility of common chlorides/bromides/iodides
ALL are soluble EXCEPT Pb: Cl2, Br2 and I2
Ag: Cl2, br2, I2
Solubility of common carbonates
ALL are insoluble EXCEPT Group 1 and ammonium carbonates
Solubility of common oxides
ALL are insoluble EXCEPT Group 1 and ammonium oxides. CaO is sparingly soluble
Titration method questions:
1. whi is phenolphthalein added?
2. how do we ensure that salt produced is pure without the presence of indicator?
- because of its more easily seen colour change
- To ensure purity, after initially using the indicator to estimate the volume, we repeat the titration using the estimated volume without the indicator, as its presence could make the salt impure.
how to prepare a pure and dry sample of Lead (II) chloride?
precipiation method
- Mix equal volumes of lead(II) nitrate (Pb(NO₃)₂) solution and sodium chloride (NaCl) solution in a beaker.
- A soid precipitate of lead(II) chloride (PbCl₂) will form.
- Filter the mixture to separate the precipitate from the solution.
4 Wash the precipitate with cold distilled water to remove any soluble impurities. - Dry the lead(II) chloride precipitate between sheets of filter paper.
SPAN salts and their solubility
ALL Sodium Potassium Ammonium and Nitrates salts are soluble
rule for precipitation method
starting mateials must be soluble and it form a insoluble solid.
Solubility of common hydroxides
ALL are insoluble EXCEPT Group 1 and ammonium hydroxides.
Ca(OH)2 is sparingly soluble
titration method is for WHO
SPAN salts (basically grp 1 and ammonium salts)
Some excess method questions:
1. why is zinc added in excess?
2. Why might crsytalisation be more suitabel than evap/heating to dryness?
3. why is crystals washed in cold distilled water
- To ensure that all the acid is entirely reacted, since it is easier to filter out excess solid metal than to separate excess acid from the solution.
- heating may decompose the salt, while crystallisation allows the salt to form pure, intact crystals without decomposition.
3.to remove soluble impurities without dissolving the crystals themselves, as hot water could dissolve some of the salt.
Rules for excess method
- preparing soluble salts
- insoluble starting material
- Acid + excess INSOLUBLE base/carbonate OR Acid + excess metal
preparing a pure and dry sample of soium sulfate ?n
titration method
1. Draw up 25.0 cm³ of sulfuric acid (H₂SO₄) into a pipette.
2. Place the sulfuric acid solution into a titration flask.
3. Add a few drops of phenolphthalein to the sulfuric acid solution in the flask.
4. Draw up to 25.0 cm³ of sodium hydroxide (NaOH) into the burette, then run the alkali into the sulfuric acid solution until the indicator changes color from pink to colorless when all the acid has reacted. Record the volume of alkali used.
5. To ensure purity, after initially using the indicator to estimate the volume, we repeat the titration using the estimated volume without the indicator, as its presence could make the salt impure.
6. Heat the solution, of sodium sulfate, gently to concentrate the salt solution
7. When filtrate is saturated, leave it to cool so sodium sulfate crystals can form.
8. Wash the crystals with cold distilled water to remove impurities + Dry the crystals between a few sheets of filter paper.
How to prepare a pure and dry sample of zinc sulfate and What method is this
Excess method [crystalisation]
- Add dilute sulfuric acid to a beaker.
- Add zinc metal in excess to the acid and stir constantly.
- Wait for the effervescence to stop or until no more zinc dissolve as this means the reaction is complete.
- Filter the mixture to remove the excess unreacted zinc.
- Heat the filtrate, zin sulfate, gently to concentrate the salt solution
- When filtrate is saturated, leave it to cool so zinc sulfate crystals can form.
- Wash the crystals with cold distilled water to remove impurities + Dry the crystals between a few sheets of filter paper.
What preperation method do we use for insouble salts?
Precipitation
