TEST OF PRACTICAL KNOWLEDGE QUESTION Credit will... | WAEC SSCE - Chemistry - 2001

Question 1 Report

TEST OF PRACTICAL KNOWLEDGE QUESTION

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

Answer

Test	Observation	Inference
(a)(i) Add distilled water to C, stir and test with litmus paper.	C dissolves to give a colourless solution. There is no change in either red or blue litmus paper.	C is soluble in water and is neutral. It is a carbohydrate (sugar).
(a)(ii) Add Fehling's solution to the mixture and heat.	A brick-red precipitate is formed.	C is a reducing sugar. Therefore, C is glucose.
(b)(i) Heat D strongly in a dry test tube.	A reddish-brown gas is evolved and a black residue remains.	The gas is nitrogen(IV) oxide, \(\mathrm{NO_2}\), showing the presence of nitrate ions, \(\mathrm{NO_3^-}\). The black residue is copper(II) oxide, \(\mathrm{CuO}\).
(b)(ii) Add distilled water to the remaining D and shake.	D dissolves to give a light-blue solution.	D is soluble and copper(II) ions, \(\mathrm{Cu^{2+}}\), are suspected.
(b)(iii) Add aqueous ammonia dropwise to the solution of D, then add it in excess.	A pale-blue precipitate is formed. The precipitate dissolves in excess aqueous ammonia to give a deep-blue solution.	Copper(II) ions, \(\mathrm{Cu^{2+}}\), are confirmed.

Test	Observation	Inference
(a)(i) Add distilled water to C, stir and test with litmus paper.	C dissolves to give a colourless solution. There is no change in either red or blue litmus paper.	C is soluble in water and is neutral. It is a carbohydrate (sugar).
(a)(ii) Add Fehling's solution to the mixture and heat.	A brick-red precipitate is formed.	C is a reducing sugar. Therefore, C is glucose.
(b)(i) Heat D strongly in a dry test tube.	A reddish-brown gas is evolved and a black residue remains.	The gas is nitrogen(IV) oxide, \(\mathrm{NO_2}\), showing the presence of nitrate ions, \(\mathrm{NO_3^-}\). The black residue is copper(II) oxide, \(\mathrm{CuO}\).
(b)(ii) Add distilled water to the remaining D and shake.	D dissolves to give a light-blue solution.	D is soluble and copper(II) ions, \(\mathrm{Cu^{2+}}\), are suspected.
(b)(iii) Add aqueous ammonia dropwise to the solution of D, then add it in excess.	A pale-blue precipitate is formed. The precipitate dissolves in excess aqueous ammonia to give a deep-blue solution.	Copper(II) ions, \(\mathrm{Cu^{2+}}\), are confirmed.

Solubility

Acids, Bases And Salts

View Answer

TEST OF PRACTICAL KNOWLEDGE QUESTION Credit will be given for strict adherence to instructions, for observations precisely recorded, and for accurate infere...

Tests on C and D

Tests on C and D

Download The App On Google Playstore

TEST OF PRACTICAL KNOWLEDGE QUESTION Credit will be given for strict adherence to instructions, for observations precisely recorded, and for accurate infere...

Tests on C and D

Tests on C and D

Related Questions

Download The App On Google Playstore