Homework Acids and Alkalis

Transcription

1 S2 Homework Acids and Alkalis

2 This booklet is split into the main areas of the topic. Each main area has three different spice levels which tell you about the difficulty of the homework. Each week your teacher will tell you what main area to complete and you will have the choice of level of difficulty. You need make sure that you are trying a new spice every week! *A bonus Extra Hot homework may be found for some areas if you are feeling adventurous or in need of extra revision*

3 The main areas of this topic are: 1. The ph Scale 2. ph of food and drink 3. Effect of Dilution 4. Solubility of Oxides 5. Neutralisation Reactions 6. Acid Rain

4 1. The ph Scale 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?

5 1. The ph Scale 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?

6 1. The ph Scale 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

7 2.The ph of Food and Drink Read the passage below and answer the questions which follow. 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.

8 2.The ph of Food and Drink 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? e) If you tested Milk of Magnesia with indicator, what colour would it go?

9 2.The ph of Food and Drink 2. Using the table you have just made, create a bar graph. 3. In a paragraph, summarise the results, analysing the data.( Highest, lowest, any trends)

10 3. The Effect of Dilution Using no more than 140 characters(including letters, spaces and symbols) explain what dilution is and how it effects the ph of acids and alkalis.

11 3. The Effect of Dilution. 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: 2.i) When an acidic solution is diluted with water, the ph falls/rises and the acidity increases/decreases. 2.ii) When an alkaline solution is diluted with water, the ph falls/rises and the alkalinity increases/decreases.

12 3. The Effect of Dilution Test Tube Instructions ph number 1 10mL of alkali mL from test tube 1 +9mL of water 3 1mL from test tube 1 +9mL of water 4 1mL from test tube 1 +9mL of water 5 1mL from test tube 1 +9mL of water a) If test tube 1 contains 100% alkali, what % alkali is present in test tube 2? b) What is the % alkali in test tube 3 shown as a fraction? c) What is the trend between the % of alkali present and the ph number d) What colour would the solution in test tube 5 be once universal indicator is added?

13 4. The Solubility of Oxides 1. Copy and complete the following table: Name of Oxide Appearance of oxide Effect on Universal Indicator Carbon dioxide gas Acid Nitrogen dioxide gas Sodium oxide Solid Alkali Calcium oxide Solid Copper oxide solid 2. What main conclusions can you draw from this table of results?

14 4. The Solubility of Oxides 1. Which of the following oxides would dissolve in water to produce an acidic solution? A. sulphur dioxide B. iron (III) oxide C. copper (II) oxide D. sodium oxide 2. Which of the following oxides would dissolve in water to produce an alkaline solution? A. sulphur dioxide B. iron (III) oxide C. copper (II) oxide D. sodium oxide 3. What do the following terms mean? a. Soluble b. Insoluble 4. a) How are acids formed? b) How are alkaline solutions formed? 5.Use the solutions in Q1 as an example- Draw a diagram showing how you would test their ph

15 4. The Solubility of Oxides Using your knowledge of Science, comment on the solubility of oxides and the effect they can have on the environment. You may wish to include the terms: Non- metal oxide, Metal oxide, Insoluble oxides and acid rain.

16 5. Neutralisation Reactions 1. a)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? 2. a) Explain why vinegar is added to wasp stings to soothe the pain. b) Explain why farmers add lime to soil which is too acidic.

17 5. Neutralisation Reactions 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 6. 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

18 Identify an ingredient which could be a cleaning chemical. 5. Neutralisation Reactions The following is a report given by SEPA to a fish farmer. Sample Date ph 1 5 th of January th of March th of May th of July 7 1. Describe how you would use Universal Indicator to measure the ph of the water. 2. Give a name of a substance which could be used to neutralise the water. 3. Explain what is meant by neutralisation 4. What are the two products formed in a neutralisation reaction between an acid and an alkali? 5. What water sample had a ph suitable for drinking? 6. What could have contaminated the water to make it unsafe for drinking? 7. What happened do you think could have happened after 13 th of May? 8. Who are SEPA and why is their job important?

19 6. Everyday Examples of Neutralisation Create a cartoon strip about one of the following neutralisation reactions: a)acid rain b) Indigestion c) bee sting d)wasp sting Make sure you label the cartoon strip with the scientific terms.

20 6. Everyday Examples of Neutralisation Read this information about acid rain and answer the questions which follow: As rain falls through the air, it can dissolve gases. The carbon dioxide which we breathe out is dissolved by the rain. Carbon dioxide is acidic. This means that normal rain has a ph of 5 or 6. Animals and plants are used to this weakly acidic rain. However, there are other acids in the atmosphere. These can make rain water much more acidic and more harmful. The ph can fall to 4 or even lower. These other acids are oxides of sulphur and oxides or nitrogen. Sulphur dioxide is made when some fuels, containing sulphur, burn in air. It can be made at power stations. Nitrogen dioxide comes from the exhaust fumes of cars. This acid rain is a serious problem. It can attack building materials, such as metals and limestone. It can be washed into rivers and lakes. This can lower the ph so much that all the plants and fish die. The acid rain can also destroy trees. Acid rain can be blown to other countries too, by the wind. Forests in Norway and Sweden are being affected by acid rain. This may be from pollution in Britain. 1.Why is normal, unpolluted rain water acidic? 2. Which acidic gases cause polluted rain? 3.. How do cars contribute to acid rain problems? 4. How could the acid rain problem in Scotland affect people in Norway? 5. Suggest a way of preventing acid rain.

21 6. Everyday Examples of Neutralisation Create a revision poster about three everyday examples of neutralisation reactions of your choice. Make sure your posters are detailed and include diagrams and facts you have researched yourself. Include your references at the bottom of your poster.