Credit will be given for strict adherence to instructions, for observations precisely recorded, and for accurate inferences. All tests, observations, and inferences must be clearly entered in your answer book, in ink, at the time they are made.
C is one of the following substances; starch or sucrose or glucose D is a simple salt. Carry out the following exercises on C and D. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test.
(a)(i) Add about 5 cm\(^3\) of distilled water to a portion of C in a test tube. Stir thoroughly and test with litmus
(ii) Add about 2cm\(^2\) of Fehling’s solution to the resulting mixture from (a)(i) above the heat.
(b)(i) Heat a portion of D strongly in a test tube
(ii) Put the rest of D in a boiling tube and add about 10 cm\(^3\) of distilled water. Shake the mixture
(iii) Put about 2 cm\(^3\) of the mixture from (b)(ii)) in a test tube. Add aqueous ammonia in drops and then in excess
Explanation
|
Test |
Observation |
Inference |
| (a) (i) C + water and tested with litmus | C is soluble in water, no action on litmus | Soluble, carbohydrate(Sugar) |
| (ii) C + water + Fehling's solution | Brick red precipitate was observed |
Reducing sugar glucose is suspected |
| (b)(i) D + strong heat | A black residue was obtained and a reddish-brown gas evolved |
NO\(_2\) from NO\(_3^-\) CUO is suspected (as residue) |
| (ii) D + water | A light blue solution was obtained. D is a soluble in water | Cu\(^{2+}\) is suspected |
| (iii) D + NH\(_4\)OH | A blue precipitate was observed which dissolved in excess alkali to give a blue solution | Cu\(^{2+}\) is present |
Conclusion - C is a reducing sugar (glucose) and is a salt which is Cu(NO\(_3\))\(_2\)