Detection inorganic anions - chloride, carbonate and sulphate

Getting multicolored precipitations

Scientific name: Getting multicolored precipitations by ion exchange reactions

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Calcium Carbonate and Hydrochloric Acid Demo

Lab Protocol - Chloride Ion Detection (Unit 7 Diffusion)

by Mark Garcia

Распознавание растворов натрия

Reaction of BARIUM CHLORIDE & SODIUM SULFATE solutions

by Basco36

Lab Protocol - Sulfate Ion Detection Assay (Unit 7 Diffusion)

by Mark Garcia

Safety

Be careful with the different chemical reagents. Use protective gloves and googles when you work with hydrochloric acid.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

Na2CO3 + 2HCl → CO2 + H2O + 2NaCl

NaCl + AgNO3 → AgCl + NaNO3 Na2SO4 + BaNO3 → BaSO4 + 2NaNO3

Step-by-step instruction

  1. Take 3 flasks. Pour sodium carbonate into flask #1, sodium chloride into flask #2 and sodium sulphate into flask #3. Mark the flasks and play detective.
  2. Take 3 test-tubes. Pour 3 ml of the solutions #1, #2 and #3 into them. Mark the test-tubes with the number of the flask.
  3. Add 3 ml of hydrochloric acid into each test-tube. The gas is released in the tube #1.
  4. Repeat point 2.
  5. Add 3 ml of silver nitrate solution into each test-tube. The white precipitate forms in the tube #2.
  6. Repeat point 2.
  7. Add 3 ml of barium nitrate solution into each test-tube. The white precipitate forms in the tube #3.Take a test-tube, pour 3 ml of iron (III) chloride solution into it. Add dropwise 1-3 ml of potassium thiocyanate and shake the mixture. You have a red or dark-red solution of K3[Fe(SCN)6].

Scientific background

In this experiment the ability of substances to react with specific reagents is used for detection of inorganic ions in the solutions. These reactions are called qualitative reactions. A Qualitative reaction is a reaction that allows us to say whether there is a substance in the solution or not, but does not allow say how much of it there is.

For the detection of carbonate CO32- ions we should add a small amount of acid to the solution. An Ion exchange reaction occurs forming carbonic acid. But carbonic acid is unstable; it decomposes forming carbon dioxide and water:

Na2CO3 + 2HCl → CO2 + H2O + 2NaCl.

We can detect chloride Cl- ions in the solution by adding silver ions. A White precipitate forms as a result of this reaction:

NaCl + AgNO3 → AgCl + NaNO3. Also, the silver nitrate solution can be used to detect bromine Br- and iodine I- ions.

Adding barium chloride to the solution with sulphate SO42-ions can show presence of these ions in the solution:

Na2SO4 + BaNO3 → BaSO4 + 2NaNO3.

This is a qualitative reaction for detection of barium Ba2+ and sulphate SO42- ions.

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Published on 11 October 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst