KS3 Chemistry 7E Acids and Alkalis 7E Acids and Alkalis What are acids and alkalis? Hazard symbols
Contents 7E Acids and Alkalis What are acids and alkalis? Hazard symbols Indicators and the pH scale Neutralization Summary activities What is an acid? Acids are a group of chemicals.
What do you know about acids? Are all acids dangerous? everyday acids laboratory acids
What is an acid? Acids are a group of chemicals. Which of these items contains an acid? everyday acids laboratory acids Can you think of other examples of acids? What is a weak acid? Acids are found in household items such as food, drink and beauty/skincare products. It is safe to handle these acids and even taste them, if they are for eating! These acids are known weak acids. What is a strong acid? Some acids, like those found in the laboratory or a car battery, are very dangerous (too dangerous to taste or touch). These acids are said to be corrosive as they can damage other materials by wearing them away! They are strong acids. Why must strong acids always be handled very carefully? everyday alkalis laboratory alkalis
What is an alkali? Alkalis are another group of chemicals, the opposite of acids. Which of these items contains an alkali? everyday alkalis laboratory alkalis Can you think of other examples of alkalis? What is a weak alkali? Alkalis are found in soaps and other materials used forcleaning. It is safe to handle these alkalis, which can feel soapy. These alkalis are known as weak alkalis. What is a strong alkali? Some alkalis, like those in the laboratory or in cleaning materials such as toilet cleaner, are too dangerous to touch. These alkalis are said to be caustic because they can burn skin and damage other materials! They are strong alkalis. Why must strong alkalis always be handled very carefully? 7E Acids and Alkalis What are acids and alkalis? Hazard symbols
Contents 7E Acids and Alkalis What are acids and alkalis? Hazard symbols Indicators and the pH scale Neutralization Summary activities What are hazard symbols?
How can you tell which chemicals are safe and which are dangerous? Special symbols are used on bottles and vehicles that contain dangerous chemicals. toxic irritant harmful corrosive highly flammable These hazard symbols show why the chemical is dangerous. Why is it important that these symbols can be recognised by people from other countries? What do hazard symbols mean? 7E Acids and Alkalis What are acids and alkalis? Hazard symbols
Contents 7E Acids and Alkalis What are acids and alkalis? Hazard symbols Indicators and the pH scale Neutralization Summary activities Litmus is red in acid. Litmus is blue in alkali.
What is an indicator? How can you test a liquid to find if it is an acid or an alkali? An indicator is a special chemical that changes to a different colour in an acid or an alkali. Litmus paper and litmus solution are examples of indicators. Litmus is red in acid. Litmus is blue in alkali. Litmus test experiment
The results for the litmus tests are: Tube 1. The solution is an alkali which turns blue when red litmus is added to it and remains blue when blue litmus is added to it. Tube 2.The solution is an acid which remains red when red litmus is added to it and turns blue when red litmus is added to it. Tube 3.The solution is water which remains red when red litmus is added to it and remains blue when blue litmus is added to it. What is universal indicator?
Litmus is used to show if a solution is acid or alkali. Litmus does not show if the acid or alkali is weak or strong. Universal indicator has a range of colours that show how weak or strong the acid or alkali is. stronger acid stronger alkali strongacid weakacid weak alkali strongalkali neutral What is the colour for a weak acid? What is the colour for a strong alkali? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 What is the pH scale? stronger acid
The strength of an acid or alkali is measured by the pH scale. Each universal indicator colour is given a number called the pH value. Universal indicator can tell you the pH of a solution. stronger acid stronger alkali strongacid weakacid weak alkali strongalkali neutral What is the pH of a weak acid? What is the pH of strong alkali? What is the pH? What type of substance? 7 Are these substances acidic or alkaline?
Are they weak or strong? 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 alkali acid 1 2 14 13 12 11 10 9 8 7 6 5 4 3 7E Acids and Alkalis What are acids and alkalis? Hazard symbols
Contents 7E Acids and Alkalis What are acids and alkalis? Hazard symbols Indicators and the pH scale Neutralization Summary activities Mixing an acid and an alkali
What happens when an acid and an alkali are mixed? ? Mixing an acid and an alkali causes a chemical change. This chemical change is called a chemical reaction. How do you know this chemical reaction has taken place? What is neutralization?
The chemical reaction between an acid and an alkali is called neutralization. acid alkali a salt water What happens to the pH value of the reaction mixture during neutralization? The pH value of the reaction mixture becomes closer to 7. What is neutralization?
The chemical reaction between an an acid and an alkali can be written as: acid alkali a salt water What are the two new substances produced by a neutralization reaction? Neutralization and indigestion Why can bicarbonate of soda (pH 9) be used to treat a bee sting?
Neutralizing 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? Neutralizing soil Soils in different places can be acidic, alkaline or neutral. Many plants do not grow well in acidic soil. Why do farmers test soil to check the pH? Farmers often add an alkali to acidic soil to make their plants grow better. How does the alkali help to treat the acidic soil? Neutralizing acid rain
Gases emitted by cars, power stations and factories mix with rainwater in the atmosphere. This rainwater has a pH