Distinguish Between Mixture and Compound

Materials Required: 

Real Lab Procedure: 

Preparation of mixture using iron filings and sulphur powder:

Take about 14g of fine iron filings and 8g of sulphur powder in a big petridish or a beaker. Mix them well to prepare a mixture of iron filings and sulphur powder. Label the mixture A.

Preparation of compound using iron filings and sulphur powder:

Take about 14g of fine iron fillings and 8g sulphur powder in a china dish. Mix them well and heat the contents of the china dish, first gently, then strongly. Stir it constantly till a black mass, i.e., compound of sulphur and iron is formed. When a black mass is formed, cool it and powder the black mass. Label the compound powder as B.

To distinguish between the iron filings and sulphur powder mixture and compound on the basis of:

  • Appearance: Homogeneity and Heterogeneity:Take some powder A (iron filings and sulphur powder mixture) in one watch glass and mixture B black mass (compound) powder in another watch glass. Observe both of them carefully. Record your observations in a table.
     
  • Behaviour towards magnet: Place a small quantity of mixture: A in a watch glass and move a magnet over it.
    Place a small quantity of B (black powder) in another watch glass and move the same magnet over it. Examine the movement of the magnet and record your observations.
  • Action of Carbon Disulphide:Take a small quantity of A in a watch glass and add 1ml of carbon disulphide (CS2) to it. Observe the mixture for some time and then record your observations.
    Take a small quantity of compound B in another watch glass and add 1ml of CS2 to it. Observe the compound for some time and record your observations.  
  • Effect of Heat: Take a small quantity of mixture A in a test tube and heat it. Observe the change in the mixture after some time.
    Take a small quantity of compound powder B in a test tube and heat it for the same period as powder A was heated. Observe the change
  • Effect of heating with dil. HCl:Take a small quantity of mixture A in a test tube and add few drops of dil. HCl into it. Then heat the contents of the test tube gently and collect the gas formed in another test tube. Then bring a glowing match stick near the mouth of the test tube in which gas is collected and record your observations.
    Now take a small quantity of compound B in a test tube and add few drops of dil. HCl into it. Then heat the contents of the test tube gently and pass the gas evolved through copper sulphate solution taken in another test tube and record your observations.

Simulator Procedure (as performed through the Online Labs)

You can select the test from ‘Select the test’ dropdown list.

Basis of appearance

  • You can select the Mixture/Compound by clicking on the respective icon.
  • Stir the sample by clicking on the glass rod.
  • Click on the inference icon to see the inference.

Behavior towards magnet

  • You can select the Mixture/Compound by clicking on the respective icon.
  • To test the magnetic property of the sample, drag the magnet towards it.
  • Click on the inference icon to see the inference.

Action with Carbon disulphide

You can select the Mixture/Compound by clicking on the respective icon.

Mixture

  • To pour carbon disulphide into the test tube, drag the dropper towards it.
  • Click on the test tube to shake its contents.
  • Drag the test tube towards the petridish to pour the upper solution into it.
  • Wait for two minutes for the carbon disulphide to evaporate from the petridish.
  • Click on the inference icon to see the inference.

Compound

  • To pour carbon disulphide into the test tube, drag the dropper towards it.
  • Click on the test tube to shake its contents.
  • Click on the inference icon to see the inference.

Action of heat

  • You can select the Mixture/Compound by clicking on the respective icon.
  • Click on the knob of the burner to turn it on.
  • Click on the inference icon to see the inference.

Action with dil. HCl

You can select the Mixture/Compound by clicking on the respective icon.

Mixture

  • Click on the knob of the burner to turn it on.
  • Gas bubbles are produced in the test tube that then pases through the bent tube into the empty test tube on the test tube rack.
  • To remove the bent tube from both the test tubes, click on it.
  • Drag the match stick towards the mouth of the test tube on the test tube rack. 
  • It extinguishes the burining matchstick with a mild explosion while producing a popping sound.
  • Click on the inference icon to see the inference.

Compound

  • Click on the knob of the burner to turn it on.
  • Gas bubbles are produced in the test tube that then passes through the bent tube into the test tube on the rack thus forming a black precipitate.
  • Click on the inference icon to see the inference.

You can click on the ‘Reset’ button to redo the experiment.

Note: Click on the ‘HELP’ button to see the instructions

Observations and Inference: 

SI.No Experiment Observations Inference
A B
1. Observation with naked eye, i.e., appearance Yellow powder in which some iron filing is visible, i.e., heterogeneous. On heating A, B is obtained which is black in colour. No iron filings visible, i.e., homogeneous. 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 a 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 (CS2 - 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. Mixture of iron filings and sulphur powder forms compound FeS on heating.

Compound FeS does not show any reaction on heating.
 5. Effect of heating with dil.HCl On heating, a gas is formed. On bringing the glowing match stick near the mouth of the test tube, the flame dips out producing a popping sound and with a mild explosion. On heating, a gas is evolved. On passing the gas through copper sulphate solution, a black precipitate is formed. In A iron reacts with dil. HCl to form hydrogen gas which extinguishes the burning match stick with a mild explosion and producing a popping sound. In B, the compound FeS react with dil. HCl to produce H2S gas which reacts with copper sulphate solution to form a black precipitate of copper sulphide.
FeS (s) + 2HCl (aq) --> FeCl2 (aq) + H2S (g)
CuSO4 (aq) + H2S (g) --> CuS (s) + H2SO4 (aq)

Result:

  1. When iron filings and sulphur powder are mixed, both retain their properties. It means they have not undergone any chemical reaction. Therefore, mixing of iron and sulphur is a physical change.
  2. When iron filings and sulphur powder are mixed and heated they undergo a chemical reaction  and form ferrous sulphide (FeS). It is a new substance which has properties entirely different from Fe and S.Therefore, heating of mixture of iron and sulphur powder is a chemical change.

Precautions:

  1. Care should be taken while heating iron and sulphur mixture.
  2. Do not brong carbon disulphide near the burner (carbon disulphide is volatile and its vapours catch fire).
  3. Do not inhale gases evolved directly, for example, hydrogen sulphide. 

 

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