Indicators For Acids & Alkalis D. Crowley, 2008

Indicators For Acids & Alkalis Thursday, April 27, 2017 Indicators For Acids & Alkalis To know that indicators can be used to show acids and alkalis

Acids What do you know about acids? Brainstorm in pairs, then in small groups any information you know… Acids are common in both the home, and within the science laboratory Some acids found in the home are safe to handle and even taste (acids have a sour taste), e.g. vinegar; lemons; grapes etc…

Acids In The Laboratory Some acids, like those found in the laboratory or in a car battery are very dangerous (too dangerous to touch) Dilute laboratory acids are irritants, which causes your skin to become red or blistered Strong acids are corrosive as they can damage other materials by wearing them away (destroying skin)!

Alkalis What do you know about alkalis? Brainstorm in pairs, then in small groups any information you know… Alkalis are common in both the home, and within the science laboratory Some alkalis found in the home are safe to handle and even taste e.g. tooth paste; soap; washing-up liquid etc…

Alkalis In The Laboratory Some alkalis, like those found in the laboratory or in cleaning materials are too dangerous to touch Dilute laboratory alkalis are irritants, which causes your skin to become red or blistered – they feel soapy when you touch them Strong alkalis are corrosive as they can damage other materials by wearing them away (destroying skin)! They are just as dangerous as concentrated acids!

Alkali & Bases Bases are substances that react with acids and neutralise them Many bases are insoluble - they do not dissolve in water If a base is soluble and does dissolve in water it is called an alkali All alkalis are bases, but only soluble bases are alkalis!

Litmus is blue in alkali Acid Or Alkali How can we test a liquid to find out if it is an acid or alkali? An indicator is a special chemical that changes to a different colour in an acid or alkali Litmus paper and litmus solution is a good indicator… Litmus is red in acid Litmus is blue in alkali

Acid Or Alkali? stronger acid stronger alkali strongacid weakacid Litmus only shows if an solution is an acid or alkali – it does not tell us how strong the acid or alkali is For this we can use universal indicator which has a range of colours… stronger acid stronger alkali strongacid weakacid weak alkali strongalkali neutral

Acid Or Alkali? 1 2 3 4 5 6 7 8 9 1011 1213 14 stronger acid The strength of an acid or alkali is measured by the pH scale – universal indicator can tell you the pH of a solution as each colour has a separate pH value stronger acid stronger alkali 1 2 3 4 5 6 7 8 9 1011 1213 14 strongacid weakacid weak alkali strongalkali neutral

pH Complete the pH worksheet, cutting out the examples and sticking them in. Make sure you colour your pH scale the appropriate colour

pH pH 1 – car battery acid pH 4 – lemon juice; vinegar pH 6 – rain water; coke; citric acid pH 7 – water; salt pH 8 – washing up liquid pH 12 – oven cleaner pH 13 – sodium hydroxide; ammonium hydroxide

pH

Acid Or Alkali? very weak acid very strong acid very weak alkali Are the following substance acid or alkali? Are they weak or strong (pH number) Substance pH Description of acid/alkali soda water 6 car battery acid 1 soap 8 washing soda 10 stomach acid 2 oven cleaner 14 vinegar 4 very weak acid very strong acid very weak alkali weak alkali strong acid very strong alkali weak acid