Neutralisation Noadswood Science, 2012

Neutralisation To understand neutralisation reactions Friday, April 21, 2017 Neutralisation To understand neutralisation reactions

Acid Or Alkali Are the following acids or alkalis? Hydrochloric (HCl) Sodium hydroxide (NaOH) Sulphuric (H2SO4) Nitric (HNO3) Ammonium hydroxide (NH4OH) Toothpaste Lemon juice Oven cleaner Stomach fluid Indigestion tablets Acid (Hydrochloric acid) Alkali Acid (Sulphuric acid) Acid (Nitric acid) Alkali Alkali Acid Alkali Acid (Stomach acid) Alkali

Acids & Alkalis Strong acid Weak acid Neutral Weak alkali Strong alkali Stomach acid Vinegar Skin Pure water Indigestion tablets Washing powder Oven cleaner Lemon juice Fizzy drinks Milk Blood Toothpaste

Acid + Alkali What happens when we mix and acid and alkali? Mixing an acid and alkali results in a chemical reaction, forming new products…

Neutralisation The chemical reaction between an acid and alkali is called neutralisation Acid Alkali Salt + Water If you add just the right amount of acid and alkali together a neutral solution is formed (the pH value gets close to pH 7 - neutral)

Experiment Your task is to see if you can undertake a neutralisation reaction In a boiling tube add a small amount of acid Using a pipette add one drop of alkali at a time, until you produce a neutral solution

Chemical Reaction Acid Alkali Salt Water The chemical reaction between an acid and alkali is: - Acid Alkali Salt Water

Acids Substances with a pH of less than 7 are acids The stronger the acid, the lower the pH number Acids turn blue litmus paper red and turn universal indicator red if they are strong, and orange or yellow if they are weak Acid Formula Strength Sulphuric H2SO4 Strong Hydrochloric HCl Nitric HNO3 Ethanoic (vinegar) CH3COOH Weak

HCl(aq) → H+(aq) + Cl-(aq) Acids When acids dissolve in water they produce hydrogen ions, H+ For example, looking at hydrochloric acid: - HCl(aq) → H+(aq) + Cl-(aq)

Acids & Bases When acids react with bases, a salt and water are made – neutralisation Acid + Metal Oxide → Salt + Water Acid + Metal Hydroxide → Salt + Water

Acid + Metal Carbonate → Salt + Water + Carbon Dioxide Acids & Carbonates When acids react with carbonates a salt, water and carbon dioxide are made Acid + Metal Carbonate → Salt + Water + Carbon Dioxide * Carbon dioxide causes bubbling during the reaction, and can be detected using limewater

Acid + Metal → Salt + Hydrogen Acids & Metals Acids will react with reactive metals to make a salt and hydrogen Acid + Metal → Salt + Hydrogen *Hydrogen causes bubbling during the reaction, and can be detected using a lighted splint

Bases Substances that can react with acids and neutralise them to make a salt and water are called bases Bases are usually metal oxides or metal hydroxides, e.g. copper oxide and sodium hydroxide are bases Type Of Compound Formula Strength Metal Hydroxides OH- Water + Salt Metal Oxides O2- Metal Carbonates CO32- Water + Salt + CO2

Alkalis Bases that dissolve in water are called alkalis Alkaline solutions have a pH of more than 7 (the stronger the alkali, the higher the pH number) – alkalis turn red litmus paper blue and they turn universal indicator dark blue or purple if they are strong, and blue-green if they are weak Alkalis Formula Strength Sodium Hydroxide NaOH Strong Potassium Hydroxide KOH Calcium Hydroxide Ca(OH)2 Ammonium Hydroxide NH4OH Weak

NaOH(aq) → Na+(aq) + OH-(aq) Alkalis When alkalis dissolve in water they produce hydroxide ions, OH- For example, looking at sodium hydroxide: - NaOH(aq) → Na+(aq) + OH-(aq)

H+(aq) + OH-(aq) → H2O(l) Neutral Neutral solutions have a pH of 7 They do not change the colour of litmus paper, but they turn universal indicator green (e.g. water is neutral) When the H+ ions from an acid react with the OH- ions from an alkali, a neutralisation reaction occurs to form water: - H+(aq) + OH-(aq) → H2O(l) In the reaction between sodium hydroxide and hydrochloric acid Na+ ions and Cl- ions left over – these form sodium chloride, NaCl

Stings A bee sting is acidic A wasp sting is alkaline Why can bicarbonate of soda (pH 9) be used to treat a bee sting? Why can vinegar (pH 3) be used to treat a wasp sting? Adding just the right amount of acid or alkali to the sting causes it to neutralise!

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