Title: Lesson 2 Properties of Acids and Bases Learning Objectives: Understand the reactions of acids with: Metals Bases Carbonates Understand the effect of acids/alkalis on indicators Conduct experiments to confirm the above properties

Refresh Define the terms acid and base according to the Brønsted-Lowry theory. Give one example of each. Which statement explains why ammonia can act as a Lewis base? Ammonia can donate a lone pair of electrons. Ammonia can accept a lone pair of electrons. Ammonia can donate a proton. Ammonia can accept a proton.

Neutralisation ACID + ALKALI  SALT + WATER hydrochloric acid + sodium hydroxide  sodium chloride + water net ionic equation = H+(aq) + OH-(aq) H2O(l) sulfuric acid + ammonia  ammonium sulfate + water This is always an exothermic reaction. It is called neutralisation but won’t always lead to a perfectly neutral solution Summary of acid reactions that form salts: Acid + Metal  Salt + Hydrogen Acid + Base  Salt and Water Acid + Carbonate  Salt + Water + Carbon dioxide

What is a salt? What is the difference between a base and alkali? A salt is an ionic compound formed when the hydrogen of an acid is replaced by a metal or another positive ion. What is the difference between a base and alkali?

ACID + METAL  SALT + HYDROGEN Net ionic equation for 1st equation: Rules for writing ionic equations: Separate all aqueous species into their ions and leave all solids, liquids and gases in their molecular form. Cancel all species common to both sides of the equation. The cancelled species are known as spectator ions as they do not change during the reaction. Gas given off with visible bubbles is known as EFFERVESCENCE.

Writing ionic equations for neutralisation reactions Consider the reaction between hydrochloric acid and sodium hydroxide; HCl(aq) + NaOH(aq) ---> To write the products we combine the anion of the acid with the cation of the base and write the correct formula following the principle of electroneutrality. The other product is water. Molecular equation: HCl(aq) + NaOH(aq) ---> NaCl(aq) + H2O(l) To write the ionic equation we must separate all aqueous species into their ions and leave any solid, liquid or gaseous substance in its molecular form. So in this case HCl(aq), NaOH(aq), and NaCl(aq) must be written as aqueous ions and H2O(l)remains in its molecualr form. ionic equation: H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) ---> Na+(aq) + Cl-(aq) + H2O(l) Finally to write the net ionic equation we must cancel all species common to both sides of the equation ionic equation: H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) ---> Na+(aq) + Cl-(aq) + H2O(l) net ionic equation: H+(aq) + OH-(aq) ---> H2O(l)

ACID + BASE  SALT + WATER Net ionic equation for 1st equation: Acid Base reactions are neutralisation reactions. Exothermic Enthalpy change of neutralisation is the enthalpy change when an acid and a base react to form one mole of water. For reactions between all strong acids and strong bases, the enthalpy change is similar because the net reaction is the same, involving formation of water from its ions.

ACID + CARBONATE  SALT + CARBON DIOXIDE + WATER Net ionic equation for 1st equation: Gas given off with visible bubbles is known as EFFERVESCENCE.

Indicators Can be used to identify pH. Common Indicators Universal (actually a mixture of indicators): Litmus: Acid is Red / Base is Blue Phenolpthalein: Acid is Colourless / Alkali is Pink

Acid-Base Indicators Acid-Base indicators change colour reversibly according to the concentration of H+ ions in the solution. This is because they are weak acids and bases whose conjugates have different colours. HIn(aq)  H+(aq) + In-(aq) Information on different indicators are given in section 22 of the data booklet.

Acid-Base titrations are based on neutralisation reactions Find an unknown concentration of acid or alkali if the other is known concentration. Solution that is of known concentration is the standard solution. Equivalence point is where neutralisation occurs. Indicator is required to tell us when the equivalence point is reached.

Solutions

Key Points Acids react in similar ways to each other Bases react in similar ways to each other Reactions tend to neutralise acid/base properties