Homework 1. Q1a). Describe how you could test the ph of a solution and obtain its ph value.

Transcription

1 Homework 1 Q1a). Describe how you could test the ph of a solution and obtain its ph value. b) What colours do acids turn universal indicator? c) What range of ph values can be shown by acids? d) What colours do alkalis turn universal indicator? e) What range of values can be shown by alkalis? f) What colour do neutral solutions turn universal indicator? g) What is the ph value of a neutral solution? Q2a) As a homework exercise, pupils were asked to find the ph values of a number of substances. Present this information as a bar graph. HOUSEHOLD SUBSTANCE ph VALUE drain cleaner 14 coca-cola 3 milk 8 window cleaner 12 washing up liquid 7 b) Which of these substances is the least alkaline? c) Which of these substances is the most acidic?

2 Homework 2 Q1. Each statement is false. Rewrite each one as a true statement. a) A neutral solution has a ph of about 6. b) A liquid with a ph of above 7 is an acid. c) Universal indicator goes red in pure water. d) Alkalis make universal indicator turn green. e) Acids make universal indicator turn purple. f) Strong acids have a ph value equal to ph 7. g) As ph increases the strength of the alkali decreases. Q2. Copy and complete the table: HOME LAB ACIDS ALKALIS

3 Homework 3 Q1. The table below shows the ph of some foodstuffs. Food Approximate ph number Jelly 3.1 Ketchup 3.6 Mayonnaise 3.7 Canned tomatoes 4.0 Meats Soya bean milk 7.0 Crackers 8.2 Milk of magnesia 10.5 a) Which food has a neutral ph value? b) Name a food to avoid if you already have too much acid in your stomach. c) Which food is the least alkaline? d) Which food is the most acidic? Q2. Read the passage below and answer the questions which follow. All additives used in foodstuffs must be safe. Many foods go off quickly without the use of preservatives. It is now known that preservatives prevent the growth of micro-organisms, some of which are extremely dangerous. Most preservatives are simple chemicals and are closely related to natural substances. For example, benzoic acid occurs in several fruits and is widely used in fruit preservation. Sorbic acid, another preservative, is an unsaturated acid found in some plants. Some preservatives have been used for hundreds of years. For example wood smoke contains a large number of hydrocarbons, some of which can cause cancer. Dangerous or threatening additives may include the colourings, preservatives, flavours, flavour enhancers, sweeteners, texture agents and processing agents. As you can see the list is endless. Details of these must be included on the labelling (shown as E numbers). Ideally, food that has no additives at all is to be preferred and especially if it is to be used to feed children. Additives can lead to certain health complications.

4 a) Why are preservatives added to food? b) Name the unsaturated acid found in some plants. c) Which type of compounds present in wood smoke may cause cancer? d) Another widely used preservative is sulphur dioxide. Try to find out examples of foods containing this preservative. e) Try to find out some examples of health problems which may arise from eating foods containing too many E numbers.

5 Homework 4 Q1. Class 2C made some statements about the effect of adding water to an alkaline solution. A The ph of the solution will rise. B The ph of the solution will fall towards 7. C The solution will become more dilute. D Adding water will have no effect on the solution. a) Identify the 2 correct statements. b) Copy and complete the following sentences by choosing the correct words: i) When an acidic solution is diluted with water, the ph falls/rises and the acidity increases/decreases. ii) When an alkaline solution is diluted with water, the ph falls/rises and the alkalinity increases/decreases. Q2a) Apart from water, what is formed when an acid reacts with an alkali? b) Name the type of reaction when an acid reacts with an alkali. c) What happens to the ph of an acid when an alkali is added? d) What happens to the ph of an alkali when an acid is added? Q3a) Explain why vinegar is added to wasp stings to soothe the pain. b) Explain why farmers add lime to soil which is too acidic.

6 Homework 5 Q1. Shampoos contain different types of chemicals. The three main types of chemicals, and their uses, are shown in the key below. SHAMPOO cleaning chemicals (usually laureth sulphates) conditioning chemicals (silicon containing compounds) shining chemicals (usually acids) dissolve grease stick to hair making it feel smooth makes hair surface smooth and reflects light a) Why do cleaning chemicals in shampoo remove grease from hair? b) Shampoos contain chemicals to make the hair shine. Suggest a ph value for these chemicals. c) What type of compounds in shampoo would be useful for someone with frizzy hair? d) The label shows the ingredients in shampoo: 3 in 1 Shampoo & Conditioner FOR ALL HAIR TYPES INGREDIENTS: Aqua, sodium laureth sulphate, hydrogenated glyceryl palmate, magnesium laureth sulphate, methylparben, parfume. 75ml e e) Identify an ingredient which could be a cleaning chemical.