Do now! Can you spell the following words correctly in the back of your book? Nuetralisasion, indicater, litmas, alkcali, burete.

Stick it in!

Acids and alkalis What have you remembered?

Acids and alkalis What have you remembered from year 7?

Acid tastes

Acid comes from the latin word acer, which means sharp. Acids are sharp tasting! (“Tangy”)

Indicators Indicators are chemicals (coloured dyes) which change colour in acids and alkalis.

Litmus Turns red in acid Turns blue in alkali

Litmus Turns red in acid Turns blue in alkali Litmus can tell us if something is an acid or an alkali, but it cannot tell us how strong the acid or alkali is

Other indicators Red cabbage and beetroot make excellent indicators

The pH scale The strength of an acid is measured on the pH scale pH stands for the “potential of hydrogen”

Universal Indicator To measure pH, we need an indicator that has a different colour for each value of pH Universal Indicator

It comes in the form of a paper

Universal Indicator It also comes in the form of a liquid

Mission impossible?

Your task is to produce the colours of the rainbow in 6 test tubes using only Universal Indicator liquid and the acids and alkalis provided.

Mission impossible?

The first group to succeed will receive 3 house marks each

Mission impossible? Use SMALL amounts – it’s easier! Don’t forget safety glasses!

Mission impossible?

Formulae of acids Hydrochloric acidHCl Sulphuric acidH 2 SO 4 Nitric acidHNO 3

Neutralisation

What happens when we add an acid to an alkali?

Neutralisation Acid + alkalisalt + water Both neutral

Acid + base Acid + basesalt + water Hydrochloric acid + sodium hydroxidesodium chloride + water HCl+NaOHNaCl+ H 2 O Sulphuric acid + magnesium hydroxidemagnesium sulphate + water H 2 SO 4 +Mg(OH) 2 MgSO 4 + 2H 2 O

Examples of neutralisation

Acid + Metals Hydrochloric acid + magnesiummagnesium chloride + hydrogen Nitric acid + ironiron nitrate + hydrogen Sulphuric acid + zinc zinc sulphate + hydrogen In general, hydrochloric acid makes a chloride, nitric acid makes a nitrate, and sulphuric acid makes a sulphate. “salts”

Acid + carbonate Acid + carbonate“salt” + carbon dioxide + water Hydrochloric acid + sodium carbonatesodium chloride + carbon dioxide + water Sulphuric acid + calcium carbonatecalcium sulphate + carbon dioxide + water Nitric acid + copper carbonatecopper nitrate + carbon dioxide + water a “salt”

Let’s play a game!

Can you stick the summary sheets in please?

Acids need water!

HCl (g) H + (aq) + Cl - (aq) H + (aq) is the ion that makes an acid acidic! (Remember pH is the potential of hydrogen)

Neutralisation H + (aq) are removed from the solution when an acid is neutralised. Alkaline solutions contain hydroxide ions OH - (aq) H + (aq) + OH - (aq) H 2 O (l)

Proton (H + ) transfer A hydrogen ion is just a proton! Acids react therefore by giving protons (H + ) They are proton donors. Alkalis are proton acceptors.

Titrations

HCl + NaOHNaCl + H 2 O

So one mole of HCl reacts with one mole of NaOH

HCl + NaOHNaCl + H 2 O How many moles of HCl were needed?

HCl + NaOHNaCl + H 2 O How many moles of HCl were needed? # of moles = concentration x volume (cm 3 )/1000

HCl + NaOHNaCl + H 2 O How many moles of HCl were needed? # of moles = concentration x volume (cm 3 )/1000 This must also be equal to the number of moles of NaOH

HCl + NaOHNaCl + H 2 O How many moles of HCl were needed? # of moles = concentration x volume (cm 3 )/1000 This must also be equal to the number of moles of NaOH Concentration of NaOH = # of moles/(volume (cm 3 )/1000)

Your task Mrs Issacs forgot to label the molarity of the sodium hydroxide. Your job is to use titration to find out (using 1M HCl solution)

Weak and strong acids - dissociation

Strong acids split up (dissociate) almost completely in water HCl (g) H + (aq) + Cl - (aq) Low pH (1)

Weak and strong acids - dissociation Weak acids reach a dynamic equilibrium. The ions recombine to form a balance between unsplit molecules and ions. CH 3 COOH (aq) H + (aq) + CH 3 COO - (aq) Higher pH (5)