chem: sec3: salts

what are the 3 methods to prepare salts

• titration

• reacting acid with excess insoluble solids

• precipitation

what would happen when acid + group 1 metal?

will cause explosion as its too reactive

(group 1 = very reactive)

what salts can be prepared using titration?

• group 1 metals and Ammonium salts, NH4 1+

whats the only reactants for titration

• acid + alkali / aqueous carbonate

what salts can be prepared by acid reacts with excess insoluble solids

• non-group 1 metals

what are some excess insoluble salts and what do they prepare

• metals

• insoluble bases

• insoluble carbonates

are used to prepare soluble salts

what the reactants for excess insoluble solids reacts with acid

• acid + excess reactive metal

OR

• acid + excess base

OR

• acid + excess metal carbonate

what salts can be prepared by precipitation

• insoluble salts

Soluble compound + soluble compound → insoluble salt (precipitate) + soluble compound

what are the reactants for precipitation

• one containing the positive ion of the insoluble salt

• one containing the negative ion of the insoluble salt.

What do you add to the positive and negative ions to make the reactants?

• positive ion (Cation) - add nitrate (NO3 1-)

• negative ion (Anion) - add sodium (Na 1+)

• acids can be considered

what are the soluble salts for carbonates (CO3 2-)

• Sodium carbonate (Na2 CO3)

• Potassium carbonate (K2 CO3)

• Ammonium carbonate ( CO3 (NH4)2)

what are the insoluble salts for carbonates (CO3 2-)

• all the other carbonates

what are the soluble salts for nitrates (NO3 1-)

all nitrates

what are the insoluble salts for nitrates (NO3 1-)

none

what are the soluble salts for chlorides (Cl 1-)

• all chlorides except 2

what are the insoluble salts for chlorides (Cl 1-)

• Lead (II) chloride (PbCl2)

• Silver chloride (AgCl)

what are the soluble salts for sulfates (SO4 2-)

• all sulfates except 3

what are the insoluble salts for sulfates (SO4 2-)

• Calcium sulfate (CaSO4) (only slightly soluble)

• Lead (II) sulfate (PbSO4)

• Barium sulfate (BaSO4)

what are the soluble salts for Ammonium (NH4 1+) salts & group 1 metals salts

all

what are the insoluble salts for Ammonium (NH4 1+) salts and group 1 metal salts

none

steps for titration

• Pipette 25.0 cm cube of alkali/base (eg, sodium hydroxide) into a conical flask.

• Add 2 - 3 drops of indicator into the conical flask

• titrate the solution in the conical flask with acid (eg, hydrochloric acid) until the indicator changes colour and note the volume of the acid added

• swirl the solution each time the acid was added

• when its at the endpoint, all of the alkali has been neutralised by the acid

• repeat the titration without the indicator using the known volume of the acid

• the salt produced (eg. sodium chloride) solution is heated until saturation

• cool the saturation to allow crystals to form

• filter to obtain the salt’s crystals

• wash the crystals with cold distilled water to remove any soluble impurities

• dry the crystals between pieces of filter paper

why the repeat the titration without the indicator

to remove the impurity from the salt solution

how do u check for saturation?

dip a cool glass rod into the hot solution, small crystals should form on the glass rod

steps for excess insoluble solids reacts with acid

• add excess base / carbonate / metal (eg. aluminium oxide (B), aluminium carbonate (C) / aluminium (M)) to a beaker containing warm dilute acid (eg warm dilute nitric acid)

• filter the mixture to remove the unreacted B/C/M

• collect the filtrate, which is the salt (eg, aluminium nitrate) solution

• gently heat the fitrate to form a saturated solution

• allow it to cool and crystals will be formed

• filter to obtain the salt’s crystals (eg aluminium nitrate) as the residue

• wash the crystals with cold distilled water to remove any soluble impurities

• dry the crystals between the pieces of filter paper to obtain dry crystals

why is excess insoluble B/C/M added

to make sure that all acid has completely reacted in the reaction

steps for precipitation

• add a soluble compound containing a negative ion (eg, hydrochloric acid / sodium chloride) to soluble compound containing the positive ion (eg, silver nitrate) into a beaker and stir until no more salt (which is insoluble and is a precipitate) (eg, silver chloride) forms.

• flter the solution to collect the salt precipitate as a residue

• wash the salt precipitate with cold distilled water to remove any soluble impurities

• dry the precipitate between pieces of filter paper to obtain dry salt