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1988 WAEC Biology Practical In the following experiments wash the test tube and the measuring cylinder before each use....

Biology
WAEC 1988

In the following experiments wash the test tube and the measuring cylinder before each use. You are provided with Solution A (a) Place three drops of solution A on a white tile and add one drop of iodine solution. Record your observation (b) Put 10cm³ of solution A in a beaker and add a few drops of dilute tetraoxosulphate (vi) acid (H\(_2\)SO\(_4\),) in a test tube and boil fora few minutes. Then add a few drops of sodium hydroxide solution and allów the mixture to cool. Divide the mixture into two equal portions

 

 

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Explanation

(a) solution A is a corn starch solution

TEST PERFORMED

(a) Solution A, placed on a white tile + 1 drop of iodine solution

(b) Solution A + a few drops of dilute acidH\(_2/)SO/(_4/) and boiled + a few drops of sodium hydroxide and allowed to cool. Mixture is divided into two equal parts

(i) One portion of the mixture + iodine solution 

(ii) Another portion of mixture + equal amount of Fehling's

(c) A fresh portion of solution A + enzyme left in a hot water bath for five minutes

(i) A small portion of it + a few drops of iodine solution

(ii) Another portion of the mixture t equal portions of solutionA and B and warmed Fehling's solution A and B and warmed

 

OBSERVATION

(a)Blue - black colour is observed

(b)(i)Brown colour is observed (iodine colour)

(ii)Brick red or reddish-brown or orange colour is observed

(c) (i)Brown colour or colour of iodine is observed

(ii) Brick red precipitate is observed

 


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