10 Acids and alkalis (cont.)

b) Which of these indicators cannotbe used to detec t an acid? Explain your answer c) Doany ofthese indicator sprovideinformationabout the s trengthofanacid? Explain your ans wer. b) Name the acid formed by this gas in solution. c) State threeprocesses which result in theproduc tion of this gas. d) Name the reagent used to detec t this gas. e) Describeapositive test for this gas.

3 a) Which gas isneeded by plant s for photosynthesis?

10.3 Strength of anacid

1 a) What does thepH scalemeasure?

b) On this scalewhat range of values indicatesasolutionisacidic?

2 c) Which indicator gives information about thepH value of asolution? d) Explain why using this indicator maybe more useful than usingblue litmus paper. e) Complete the followingtable. a) Predic ta likelypH value for each of the followingacids by consideringwhether they are strong acids or weak acids. i) Sulfuric acid ii) Carbonic acid iii) Lactic acid(in milk) iv) Nitric acid b) Leaves of theplant Aloe vera are used to treatburnson theskin.The juice they contain hasapH value of 6.1. i) Is Aloe vera juice best describedas:a strongacid,a weak acid orneutral? ii) Predic t the colour produced when a few drops of univer sal indicator are added to this juice.

10 Acids and alkalis (cont.)

2 a) Predic ta likelypH value for each of the following alkalis by considering whether they are strong alkalis or weak alkalis.

i) Sodium hydroxide ii) Aqueous ammonia iii) Toothpas te iv) Antacid tablet s b) Sodium hydrogencarbonateis used to treatbee stings .It hasapH value of 8.3. i) Is sodium hydrogencarbonate best describedas:a strong alkali, a weak alkali or neutral? ii) Predic t the colour produced when a few drops of univer sal indicator are added to sodium hydrogencarbonatesolution.

10.6Makinganacid– alkali indicator

1 a) Fromwhat is litmus indicatorobtained?

b) Give one example of each of the following that might provide an acid –alkali indicator.

i) A flower ii) A vegetable c) What essential proper ty must an acid –alkali indicator have? b) i) Why is ethanoladded to theplantmaterial? ii) Why isethanol preferred towater? c) i) How is the plant ex trac t separated from the plantmaterial? ii) Describe an alternativemethod of separation that could be used. iii) Comparethe twomethods of separation interms of speed and effectiveness .

2 a) Name the piece of apparatus picturedwhichis used in preparing an acid –alkali indicator and describe it s func tion.

10.7 Acid –alkali reactions

1 a) What type of reaction takes place when an acid react s with an alkali?