Intro, Neutralization, Salts

Seite 1

Properties of Acids:

- turns litmus paper red

- destroys the chemical properties of bases = neutralizes bases

- conducts electricity

Properties of Bases

- turns litmus paper blue

- destroys the chemical properties of acids = neutralizes acids

- conducts electricity

Bases neutralize acids

- usually metal oxides, hydroxides, or carbonates

- not all are soluble in water

- soluble base = alkali

hydroxide = OH

carbonate = CO3

nitrate = NO3

oxide = O

Indicators

Indicators are used to find out if a liquid is acidic

they change colour when added to acids or alkalis

Litmus is a dye that turns red when added to acid and blue when added to alkali

Universal indicator (mix of several indicators)

pH scale

- devised to let chemists measure the strength of an acidic or alkaline solution

- measures on a 14 point scale

- can change into several colours depending on the pH of the solution

- each units represents 10x in acidity

- can also be found using a pH meter

Salts can be formed when a base neutralises an acid

when sodium hydroxide neutralizes hydrochloric acid = solution of the salt sodium chloride is formed (and water)

Acid + reactive metal --> Salt + Hydrogen

Acid + Metal Oxide --> Salt + water

Acid + metal hydroxide --> salt + water

acid + metal carbonate --> salt + water + carbon dioxide

acid + excess metal --> salt + water + unreactive metal

Acid + Ammonia --> Ammonium salt

zinc did not react with any of the acid solutions

magnesium reacted most strongly

product of:

salt + water

salt + hydrogen

salt + water + carbon dioxide

means that it was acidic

Normal Salts:

compound that has been formed when all the hydrogen ions have been replaced by metal ions or by the ammonium ion (NH4)

Soluble Salts:

- all nitrates

- all common sodium, potassium and ammonium salts

- all chlorides except lead, silver and mercury

- all sulphates but lead, barium and calcium

Excess metal or base is added to an acid until all of the acid has reacted -- no more solid will dissolve

excess solid is removed by filtration

^suitable for making soluble salts when the solid reactants are insoluble

filtering is only suitable for making soluble salts -- if it was insoluble it would get stuck in the filter paper

1. Metal with a dilute acid

METAL + ACID --> SALT + HYDROGEN GAS

do not use this is the metal is very reactive eg sodium or very unreactive eg copper

2. Insoluble base (metal oxide) with an acid

Do not use this if the base is soluble (an alkali) -- when filtering the excess base it will not get stuck in the filter paper and will not separate from the salt

ACID + METAL OXIDE --> SALT + WATER

3. Insoluble base (metal carbonate) with an acid

Do not use if the carbonate is soluble

CARBONATE + ACID --> SALT + CARBON DIOXIDE + WATER

Soluble Salts:

React an excess of the solid with an acid to make sure that all the acid has been neutralized.

Acid + Metal

Method:

Measure out some acid into a beaker

Add the solid metal in excess into the beaker

Filter the mixture to remove the excess metal

Heat the filtrate to evaporate some water

Leave to cool and crystallize

Wash with a little distilled water & pat dry with filter paper

Only suitable for making soluble salts because if insoluble it wouldn't separate from the excess metal and would get stuck in the filter paper

Titration

in other method soluble bases cannot be filtered out

Sodium, potassium, calcium react with cold water = alkalis

ALKALI + ACID --> SALT + WATER

Use: To find the amount of acid needed to neutralize a certain amount of alkali or vice versa.

Equipment:

Set limit of acid/alkali in a CONICAL FLASK

Burette to find the amount to neutralize the acid/alkali

Indicator

Pipette

Method:

Fill the burette with acid/alkali and take note of the reading. Read it to the nearest 0.05 cm3

Pipette 25cm3 of the alkali/acid into a conical flask

Add a few drops of indicator

Add the acid to the alkali swirling the mixture constantly

The end point is determined by the colour the indicator reaches. If phenolphthalein than the end point colour will be a light pink. If univeral indicator than the solution colour will be green. If methyl-orange is used than the colour will be salmon pink.

Record the reading of the end point on the burette.

Repeat without adding the indicator

Pour the neutral solution into an evaporating basin and evaporate about half the water

Pour the concentrated solution into a petri dish set aside to cool and crystallize

crystals form because salts are less soluble in colder liquids

Precipitation

precipitate = insoluble solid that forms out of a mixture of solutions

when solutions of two soluble salts are mixed -- two new combinations of ions are possible

if either of these new combinations produce an insoluble salt then a precipitate will form

spectator ions are left

Method:

Prepared by using a precipitation reaction

Two soluble solutions of the insoluble salt are mixed together. One with the cation, one with the anion

Stir the mixture until a precipitate forms

Filter the mixture to obtain the insoluble salt

Rinse with a little bit of distilled water and pat dry with filter paper

Precipitate: insoluble product in a reaction

Spectator Ion: ions that don't change their state in a reaction ie. ions that don't react

Ionic Equation: equation without spectator ions ie. showing the real reaction

Neutralisation

acids and bases = chemical opposites

when they react together they destroy each other’s characteristics = neutralisation

heat is produced (Exothermic reaction)

HCl + NaOH --> NaCl + H2O

remove spectator ions = H+OH --> H2O

Phenolphthalein Indicator

acid: colorless

base: pink

sodium c

All soluble:

sodium compounds

nitrates

ammonium salts

potassium compounds

Properties and Indicators

Salts and Neutralisation

Making a Soluble Salt

Making a Soluble Salt II (soluble reactants)

Making Insoluble Salts