Detection inorganic compounds. Sodium phosphate, ammonium nitrate and sodium nitrate

Detection of sodium phosphate, ammonium nitrate and sodium nitrate


Распознавание растворов фосфата натрия и др

by ФизматФильм


Be careful with the different chemical reagents. Perform experiments in fume hood. Use protective gloves and googles when you work with sulphuric 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

NH4NO3 + H2O → NH4OH + HNO3

Na3PO4 + 3AgNO3 → Ag3PO4 + 3NaNO3

2NaNO3 + H2SO4 → 2HNO3 + Na2SO4

Cu + 4HNO3 → Cu(NO3)2 + 2NO2 + 2H2O

Step-by-step instruction

  1. Take 3 flasks. Place 5 g of sodium phosphate into flask #1, 5 g of ammonium nitrate into flask #2 and 5 g of sodium nitrate into flask #3. Dissolve the salts in 50 ml of water. Mark the flasks and play detective.
  2. Take 3 test-tubes. Pour into them 3 ml of the solutions #1, #2 and #3. Mark the test-tubes with the number of their flask.
  3. Lower a strip of universal indicator paper into each test-tube. You have a red strip in tube #2.
  4. Repeat point 2.
  5. Add 5 ml of silver nitrate solution into each test-tube. A yellow precipitate forms in tube #1.
  6. Repeat point 2.
  7. Add 5 ml of concentrated sulphuric acid to the remaining test-tube and add a small amount of copper wire. Take the tube with tongs and heat it over an alcoholic lamp. You have a blue solution and red gas.

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 ammonium nitrate NH4NO3 we used universal indicator paper. When we dissolved solid ammonium nitrate in the water, hydrolysis process occurred. Hydrolysis process is the exchange reaction between salt and water. A salt can be formed by a strong or weak base and a strong or weak acid. Different combinations of acids and bases define how the hydrolysis takes place. Ammonium nitrate is formed by a weak base and a strong acid. So when it reacts with water, a strong acid is formed:

NH4NO3 + H2O → NH4OH + HNO3.

And when we lower the strip of universal indicator paper into this solution, the indicator paper becomes red.

We can detect phosphate PO43- ions in the solution by adding silver ions. Yellow precipitate forms as a result of this reaction:

Na3PO4 + 3AgNO3 → Ag3PO4 + 3NaNO3.

We can detect nitrate NO3- ions in the solution using copper and concentrated sulphuric acid. Adding sulphuric acid to the sodium nitrate solution causes nitric acid formation:

2NaNO3 + H2SO4 → 2HNO3 + Na2SO4.

And now we have nitric acid in the solution. So when we add copper wire and heat the mixture, the RedOx reaction starts:

Cu + 4HNO3 → Cu(NO3)2 + 2NO2 + 2H2O.

Copper nitrate Cu(NO3)2 makes the solution green. Nitrogen dioxide NO2 is a dark-red gas.


Published on 11 October 2015

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