Techniques For Analyzing Inorganic Chemical Compounds

Task 1: Analyzing Inorganic Chemical Compounds

Solution Task 1

1. Flame test  

Procedure

• Dip a platinum or nichrome wire in a concentrated hydrochloric acid and then hold it into a hot Bunsen flame
• When the nichrome wire is clean up, then dip it into the amount of solid you are testing
• Place the wire back to the flame again 

Observation and presence of ions

Flame colour

Metals presences in the solution

Red

Lithium

Strong persisted orange

Sodium

Lilac

Potassium

Reddish-violet

Rubidium

Blue – violet

Caesium

Orange –red

Calcium

Blue-green

Copper

Greyish- white

Lead

Pale-green

Barium 

1. Sulphate test and sulphite

Procedure

• To 2.0 cm³ of sodium sulphate in a test tube, add 2.0 cm³ of barium chloride or nitrate solution
• To the mixture add 2 cm³ of dilute hydrochloric acid or dilute nitric (V) acid
• Repeat the above two procedure using a solution of sodium sulphite

Observation and conclusion

A white precipitate, insoluble in the dilute acid was observed, this indicate the presence of sulphate ions A white precipitate which dissolves in dilute acid with production of a colourless gas which turns filter paper soaked in acidified orange potassium chromate (VI) from orange to green indicate the presence of sulphite ions  

• Carbonate test

Procedure

• Place a spatulaful of sodium carbonate in a clean test tube
• Add 2 cm³ of hydrochloric acid
• Add 2 cm³ of lime water
• Place a burning split at the open end of the test-tube

Observation and conclusion

Carbonates react with hydrochloric acid evolving carbon dioxide gas that forms a white precipitate with lime water.

The gas also extinguishes a burning wooden split  

1. Nitrate test  

Procedure

• Place one spatulaful of sodium nitrate into a clean test tube
• Add 2 cm³ of distilled water and shake the mixture
• Add 1 cm³ of freshly prepared iron (II) sulphate and shake
• Add concentrated sulphuric acid slowly and carefully along the wall of the test tube  Observation

When concentrated sulphuric acid is added to the mixture of sodium nitrate and iron (II) sulphate solution, the aciod sinks to the bottom, this because the acid is denser than the solution.The reaction produces heat

A brown ring is due to the formation of iron (II) sulphate-nitrogen (II) oxide complex ( FeSO₄ .NO)

Conclusion

All nitrates gives the same result and the reaction is reffered to as the brown ring test for nitrates 

1. Halide test  

Apparatus

Test-tubes rack, test-tube, solutions that will be used for testing that include KCl, KBr and KI, together with acidified silver nitrate solution reagent and dilute ammonia solution.

Procedure

• Put 2 cm³ of KCl solution into a test tube.
• Add 2 cm³ of silver nitrate solution.
• Note the observation and record all the changes that will take place in the test tube.
• Put 2 cm³ of KBr solution into another clean test tube and repeat procedure (ii) and (ii).
• Put 2 cm³ of KI solution into a clean third test tube and repeat procedure (ii) and (iii).

Observation

Table 1 Precipitates obtained with silver nitrate solution

Ions

Observation

chloride

Presence of white precipitate

bromide

Presence of cream precipitate

iodide

Presence of pale yellow precipitate 

Task 2

You have been given six solutions. You need to classify according to their pH. You need to use Litmus paper and universal indicator to figure out whether they are acidic or basic in nature.  Once you finished, then you need to use pH meter to find their pH values.

Apparatus

• Litmus paper / universal indicator
• Six different solution
• 6 test-tube
• Test –tube rack

Procedure:

• Using six red litmus paper and six blue litmus paper, dip one red and one blue litmus paper to each test tube.
• Drop a drop of universal indicator onto each solution and note the colour change.se the pH scale to write up results

Result:

Using litmus paper: acids turn a blue litmus from blue to red, bases turn a red litmus from red to blue 

Task 3

Carry out Experiments to show how chromatography is used to analyse materials.  You need to write the steps you have taken to demonstrate your technique and understanding.  

Thin Layer Chromatography

Procedure

1. Take a piece of thin layer chromatography paper.
2. Cut a portion of the chromatography paper using a piece of ruler with the dimensions 10 centimeter by 8 centimeter.

• Draw a straight line across the sheet of paper at about 1.5 cm from the bottom using a pencil.

1. Get and clean a piece of the glass plate. Place one drop of a samples of solutions at various parts on the glass plate. 
2. Mark about five small circles across the line draw in procedure (III) using a pencil.
3. The solutions containing the unknown ions, mixture and known ions will be spotted on the circles drawn in procedure (V).

• Dip the broken end of the capillary tubes into one of the solutions and the tube is taped inside the dot.
• The solution is allowed to dry a re-dotting is done too. The circle is dotted for five times, and it is allowed to dry between each marking.

1. To the beaker add about 5 ml of chromatography solvent (acetone) and cover it with a watch glass.
2. The beaker is placed in a position to avoid it being disturbed.
3. The plate/paper is placed into the undisturbed beaker and allowed to rest at the beakers bottom. 

• The chromatogram is allowed to develop uninterrupted until the solvent front forms at about 1 cm of the top of the plate/paper.
• When the solvent spreads to an appropriate level, the paper is removed from the beaker and the position of the solvent front is marked using a pencil.
• The visibilities of the spots shown on the chromatogram are made possible through it being exposed on gaseous ammonia.

1. Once the spots have been circled after being made visible, a ruler is used to measure the distance between the base line to the line marked as the solvent front line.The distances are then recorded.

The measures of the amount of separation of solutes in a chromatogram are expressed in terms of R_f value of each solute. The_, retardation factor of R_f value is calculated by dividing the distance moved by the mobile phase into the distance traveled by the solute:

R_f =

R_f =                      

You have been given two unknown amino acids i.e. Lucine    and Tyrosine and one unknown amino acid. You need to first find the Rf values for Lucine and T Tyrosie and the Rf value of unknown amino acid. You need to find the name of the unknown amino acids with the   help of Rf data Using 3 different pipette place a drop of each amino acid and mixture X, at the appropriate position of the line

Rf  for Lucine =

Rf for Tyrosine  = 

Rf for unknown amino acid =

The unknown amino acid is known as Phenylalanine 

Task 4

Carry out experiments to identify chemicals in unknown compounds  Procedure

• Mix the two unknown compounds
• Add 6M hydrochloric acid
• Filter the precipitate out
• Warm the precipitate
• To the filtrate pass over hydrogen sulphide gas
• Add a solution of ammonium (II) sulphide to the residue formed after filtering the above results

Observation and conclusion

Addition of 6M hydrochloric acid and warming the precipitate, the precipitate dissolved confirming presence of Lead (II) chloride ( PbCl₂)Addition of ammonium sulphate to the residue formed when hydrogen sulphide was passed over the filtrate (procedure 5), a red-brown precipitate was formed.The blue precipitated confirmed presence of iron (III) hydroxide (FeOH₃)