To prepare a mixture and a compound using iron filings and sulphur powder - Lab Work

To prepare a mixture and a compound using iron filings and sulphur powder and distinguish between appearance, behaviour towards magnet, behaviour towards carbon disulphide and effect of heat

Aim
To prepare a) a mixture b) a compound
using iron filings and sulphur powder and distinguish between these on the basis of:
(i) appearance, i.e., homogeneity and heterogeneity
(ii) behaviour towards a magnet
(iii) behaviour towards carbon disulphide as a solvent
(iv) effect of heat

Theory
Physical Change: These changes can be observed and take place without changing the composition of substances. There are no changes in chemical nature of substance. The changes which can be observed are like change in colour, boiling point, melting point, hardness, density, fluidity, rigidity etc. The interconversion of states of matter is also a physical change.

Chemical change: In this change, chemical reaction takes place and completely a new substance with different properties is formed. There are changes in chemical properties and composition of substance.
ex: Mg(s) + O2(g) → 2MgO(s)
Here, the chemical composition and properties of product MgO is totally different from its reactants Mg and O.

Mixture. A mixture is obtained when two or more substances are mixed in any proportion which are physically separable. Each constituent substance keeps its characteristics. It is physical change, no new substance is formed e.g., mixing of sulphur powder with iron Sling.

Compound. It is a pure substance which is composed of two or more elements combined chemically in a fixed ratio such that they can be broken into elements only by chemical means. 

Chemicals Required
Sulphur powder, Carbon disulphide, Dilute Hydrochloric acid, Iron filings

Apparatus Required
Magnet, Watch glass, China dish, Test tube, Burner, Tripod stand, Glass rod, Wire Gauze, Match Box 

Procedure 
Preparation of mixture using iron filings and sulphur powder:
Step 1: About 14 g of fine iron filings and 8 g of sulphur powder in a big petridish or a beaker is taken.
Step 2: They were mixed well to prepare iron filings and sulphur powder. This mixture is labelled as A.

Preparation of compound using iron filings and sulphur powder:
Step 1: About 14 g of fine iron filings and 8 g of sulphur powder in a china dish is taken.
Step 2: They were mixed well and the content of the china dish is heated, first gently then strongly. Step 3: Content is stirred constantly till a black mass i.e., compound of sulphur and iron is formed. Step 4: After black mass is formed, it is cooled and powdered. This compound is labelled as B.

To distinguish the iron filings and sulphur powder mixture and compound on the basis of:
(i) Appearance i.e., Homogeneity and Heterogeneity: Some powder A (iron filings and sulphur powder mixture) is taken in one watch glass and B black mass (compound) powder is taken in another watch glass. Both of them observed carefully observations are recorded.

(ii) Behaviour towards Magnet:  A small quantity of mixture A in a watch glass is placed and a magnet is moved over it. A small quantity of B (black powder) is taken in another watch glass and the same magnet is moved over it. The magnet is examined and observations are recorded.

(iii) Action of Carbon Disulphide: A small quantity of A in a watch glass is taken and 1 ml of carbon disulphide (CS2) is added to it. The mixture is observed for sometime and observations are recorded. Now, a small quantity of B is taken in a watch glass and 1 ml of CS2 is added to it. Observations are recorded.

(iv) Effect of Heat: A small quantity of mixture A in a test tube is taken and heated. Change in mixture after sometime is observed. A small quantity of compound powder B in a test tube is taken and heated for the same period as powder A was heated. Changes are bserved.

Observation Table
S. No. Experiment Observation of A Observation of B Inference
1. Appearance: Observation through naked eyes Heterogeneous because yellow powder in which some iron filing is visible. B is obtained on heating A, which is black in colour. Homogeneus because no iron filings are visible. Iron and sulphur powder retain their properties in A.
In B, iron and sulphur both loose their properties due to the reaction
Fe + S → FeS
Iron +Sulphur → Ferrous sulphide.
2. Behaviour towards magnet Iron filings cling to magnet. No particle attaches to magnet. In A, iron retains its properties. In B, iron has lost its properties.
3. Behaviour towards carbon disulphide as a solvent Sulphur dissolves first and reappears after some time.  No change is observed. In A, sulphur retains its properties. In B, sulphur has lost its original properties after reaction with Fe.
4. Effect of heat A black mass is obtained which is homogeneous.  No change is observed.  Mixture of iron filings and sulphur powder forms compound FeS on heating.

Compound FeS does not show any reaction on heating.

Results
1. When iron filings and sulphur powder are mixed, both retain their properties. Hence, mixing of iron and sulphur is a physical change.
2. When iron filings and sulphur powder are mixed and heated they undergo chemical reaction and ferrous sulphide (FeS) is formed which is a new substance with entirely different properties from Fe and S. Therefore, heating of mixture of iron and sulphur powder is a chemical change.

Precautions
1. Heat the mixture of iron and sulphur in the hard glass test tubes only.
2. Care should be taken while heating iron and sulphur.
3. Do not inhale gases evolved directly, for example, hydrogen sulphide.
4. Do not bring carbon disulphide near the burner (carbon disulphide is volatile and its vapour catch fire).

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