Acids, Bases and Salts
Acids: Hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, ethanoic acid, methanoic acid, citric acid, carbonic acid.
1. Corrosive: Have a look https://www.youtube.com/watch?v=gEqHJ1tomnk
2. Turns blue litmus paper red
Alkali: Sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia,
1. Can burn skin.
2. Feels slippery.
The pH value
Acidic: less than 7 Alkali: more than 7 Neutral: Exactly 7
Methyl orange: https://www.youtube.com/watch?v=jEvhhxg2yKA
11.2 A closer look at acids and alkalis
Acids: how do they show their acidity?
Definition of strong and weak acid. Measure by conductivity meter or pH meter.
The reactions of acid and base
Reaction of acids
Acid + metals -> salt + hydrogen gas
Acid + base -> salt + water
Acid + carbonates -> salt + water + carbon dioxide
Reaction of bases
calcium hydroxide + ammonium chloride -> calcium chloride + water + ammonia
Strong alkali and weak alkali
Special case of ammonia!
Making use of neutralisation
Acidity of soil comes from : rotting of vegetation, heavy use of fertilisers
If soil is too acidic, plants can't grow.
To reduce acidity, (increase the pH), soil is treated with
limestone ( calcium carbonate )
Lime ( calcium oxide )
Slaked lime ( calcium hydroxide )
11.4 A Closer Look at Neutralisation
Neutralisation by alkali (soluble base)
hydrochloric acid + sodium hydroxide -> sodium chloride + water
Since both (acid and alkali) is in aqueous form, let look at the amount of ions in the solution on both side.
Reactant: H+, Cl-, Na+, OH-
Product: Na+, Cl-, H2O
Change the chemical formula into ionic form. Eliminate ions that appears on both sides of the equation. (They are called spectator ions). What is left?
H+ + OH- -> H2O
This is the ionic equation for neutralisation of acid and alkali.
Neutralisation by insoluble base (metal oxide)
Hydrochloric acid + magnesium oxide -> magnesium chloride + water
Ions of both side:
Reactant: H+ , Cl-, Mg2+, O2-
Product: Mg2+, Cl- , H2O
Eliminate ions that appears on both sides of equation.
2H+ + O2- -> H2O
ACID ARE PROTON DONORS.
BASES ARE PROTON ACCEPTORS.
Oxides are compounds containing oxygen and another element. Or, any element that is oxidised.
Basic oxide: Magnesium oxide, Iron(III) oxide, Copper (II) oxide
Acidic oxide: Carbon dioxide, sulfur dioxide, phosphorus (V) oxide
Amphoteric oxide: Aluminium oxide, zinc oxide
Neutral oxide: carbon monoxide, dinitrogen oxide