Acids and Salts Bases

What do all these acids have in common: Strong Acids The Formula Sulphuric acid Hydrochloric acid Hydrobromic acid Hydroiodic acid Nitric acid Perchloric acid H2SO4 HCl HBr HI HNO3 HClO4 Weak Acid The Formula Acetic acid (vinegar) HC2H3O2 Carbonic acid HCO3

Acid: A substance that ionises (breaks down into ions) and releases H+ ions in an aqueous solution “aqueous” means: water

Characteristics of Acids: Acids have a sour taste Acids react with metals (to produce hydrogen gas) Acids have a pH of 1-6 Acids turn universal indicator yellow, orange or red Acids turn litmus red Many are corrosive or poisonous

You need to know three acids Sulfuric acid H2SO4 hydrochloric acid HCl Nitric acid HNO3

All are Strong Acids Ionise (break down into ions) completely to give off many H+ ions

Weak Acids (only partially breaks down (ionise), gives less H+)

What do these bases have in common: Strong Bases The Formulae Lithium hydroxide Sodium hydroxide Potassium hydroxide Rubidium hydroxide Caesium hydroxide Barium hydroxide Calcium hydroxide Strontium hydroxide LiOH NaOH KOH RbOH CsOH Ba(OH)2 Ca(OH)2 Sr(OH)2

Base: A substance that ionises and releases OH- ions in an aqueous solution Alkali: A base that dissolves in water

OH- Characteristics of Bases: Bases usually taste bitter Bases feel slippery Bases have a pH of 8 – 14 Bases turn universal indicator blue or purple Bases turn litmus blue OH-

BUT AREN’T METAL OXIDES BASES? Yes!!!!!! Metal oxide + water  metal hydroxide Metal oxides release hydroxide ions in solution

Some bases (VERY FEW) don’t have or produce OH- Examples include: ammonia NH3 Carbonates (CO3 and HCO3) ***Any chemical which neutralizes an acid can be considered a base

Indicators An indicator is a compound that will change color in the presence of an acid or base Red Litmus-Turns blue in base Blue Litmus-Turns red in acid Universal indicator (pH paper) Used for the full pH range Phenolphthalein-Turns pink in base

pH pH stands for “potential of Hydrogen” and is a measure of how many H+ ions there are in solution. The MORE H+ there are, the LOWER the pH will be.

Shows the range of H+ concentrations pH Scale Shows the range of H+ concentrations High H+ concentration Low H+ concentration

Reactions between acids and bases When an acid and a base react with each other , the characteristic properties of both are destroyed. This is called neutralisation. This happens because equal amounts of the two substances cancel each others properties and produce two neutral substances (water and a salt).

Reactions between acids and bases General formula for acid base reaction: → + + Base Water Salt Acid “Salt” means any ionic compound formed from an acid/base reaction NOT JUST NaCl !!

Neutralisation HCl + NaOH → H2O + NaCl acid base water salt

Neutralisation H Cl K OH Another Example HCl + KOH → H2O + KCl acid base water salt

Complete and incomplete neutralisation Any time an acid and base react neutralisation will occur. However, whether the solutions are fully neutralised depends on several factors: The pH of both reactants The concentration of both reactants The quantity of both reactants If any of these factors occur then neutralisation will be incomplete. This means in the solution there will be a metal salt, water and an acid or base.

Name the following compounds CaO NaOH Na2S PbCO3 CuHCO3 Ag2O PbCl2 CuSO4

General equations These are all extensions of the acid + base equations Acid + metal oxide metal salt + water Acid + metal hydroxide Metal salt + water Acid + Metal carbonate metal salt+ water + carbon dioxide Acid + metal hydrogen carbonate metal salt + water+ carbon dioxide

WHAT SALT IS FORMED DEPENDS ON WHAT ACID IS USED Hydrochloric acid makes a chloride salt Sulfuric acid makes a sulfate salt Nitric acid makes a nitrate salt

Predict what acid these salts were made from NaNO3 CaSO4 PbCl2 CuCl2 Fe2(SO4)3 Fe(NO3)2

Complete the following as word equations only Hydrochloric acid + Calcium hydroxide Sulphuric acid + Lead oxide Nitric acid + sodium bi-carbonate Silver oxide + sulphuric acid Copper carbonate + nitric acid

2. Balancing word equations Calcium oxide + Hydrochloric acid Calcium chloride + water Nitric acid + copper carbonate copper nitrate + water + carbon dioxide Hydrochloric acid + lead hydroxide lead chloride + water Copper oxide + sulphuric acid copper sulphate + water Sodium hydrogen carbonate + nitric acid sodium nitrate + water + carbon dioxide

NCEA 2009 A student carried out an experiment to neutralise sulfuric acid by adding sodium hydroxide to it. Discuss how the student could have determined when the sulfuric acid had been neutralised and what effect adding the sodium hydroxide has on the pH of the solution. In your answer include: • an explanation of neutralisation in terms of an acid-base reaction • the name of the indicator used • observations that the student would make as the sodium hydroxide is added to the acid • a word and balanced chemical equation for the reaction.

NCEA 2006 The pH values of three substances are given below: Hydrochloric acid pH = 1 Potassium carbonate solution pH = 9 Sodium hydroxide solution pH = 14 (a) When Universal Indicator solution is added to each of these substances, what colour would result? (i) Hydrochloric acid __________________ (ii) Potassium carbonate solution __________________ (iii) Sodium hydroxide solution __________________ Potassium carbonate solution is added slowly to the hydrochloric acid (without indicator) in a beaker until no further change is seen. (b) (i) Describe what you would see happening when potassium carbonate is added to the acid. (ii) Write a balanced chemical equation for the reaction between potassium carbonate and hydrochloric acid.

NCEA QUESTION HCl is added to a solution of sodium hydroxide. The reaction takes place but complete neutralisation did not occur. Discuss three things that could have lead to this.

TRY THESE – IN WORDS AND THEN BALANCED CHEMICAL EQUATIONS Hydrochloric acid + potassium hydroxide Sulfuric acid + calcium oxide Sulfuric acid + sodium hydroxide