Practical work 3.1. Identification of mineral fertilizers

General notes

When performing this work, use the information given in Table 30.2.

In your report, present the reaction equations in molecular, full ionic, and net ionic forms.

Table 30.2. Mineral fertilizers

Fertilizer		Appearance	Solubility
Ammonium nitrate Ammonium nitrate (ammonium (ammonia) saltpeter) NH4NO3		White crystals or granules	Good
Ammonium sulfate (ammonium sulfate, Lat. ammonii sulfas), (NH4)2SO4		Colorless or gray-green crystals (due to impurities)	Good
Ammonium chloride (ammonium chloride; technical name — sal ammoniac, NH4Cl		White crystals	Good
Calcium saltpeter Calcium nitrate, calcium saltpeter, calcium nitrate Са(NО3)2		White crystals or flakes	Good
Potassium saltpeter Potassium nitrate (potassium nitrate, potassium saltpeter, potash saltpeter, Indian saltpeter, etc.) KNO3		White crystals	Good
Potash Рotassium carbonate (carbonate of potash, calcined potash) K2CO3		White crystals	Good
Potassium salt Sylvite (КCl) 52% of the substance. carnallite (35%), kainite (14%), polyhalite (12%), langbeinite (18%); others — leonite (21%), schoenite (19%); syngenite (23%).		Heterogeneous white and pink crystals	Good
Potassium chloride KCl		White crystals	Good
Simple superphosphate a mixture of Ca(H2PO4)2*H2O and CaSO4		Light-gray granules or powder	Low

1. The numbered bags contain the following fertilizers:

• a) ammonium nitrate and superphosphate;
• b) superphosphate and potash.

Check the solubility of each sample provided, describe their appearance. Based on the investigation carried out, state the contents of each bag.

1. Appearance of the fertilizers

1. Ammonium nitrate (NH₄NO₃):

• white or slightly grayish granules

• odorless

• uniform structure

2. Superphosphate:

• gray or grayish-brown powder

• may contain lumps

• sometimes slightly damp

3. Potash (potassium carbonate, K₂CO₃):

• white powder or fine crystals

• resembles salt

• dry and free-flowing

2. Solubility in water

Let us carry out a simple test — adding water:

• Ammonium nitrate → dissolves very well (the solution is clear)

• Superphosphate → dissolves poorly (a cloudy residue remains)

• Potash → dissolves well (clear solution)

3. How to distinguish the substances in the bags

Case (a): ammonium nitrate and superphosphate

1. Add water to both samples:

   • one dissolved completely → this is ammonium nitrate

   • the other produced a precipitate → this is superphosphate

Conclusion:

• clear solution → ammonium nitrate

• cloudy/precipitate → superphosphate

Case (b): superphosphate and potash

1. Check solubility:

   • dissolved completely → potash

   • precipitate remained → superphosphate

2. Additionally, one can check:

   • the potash solution has an alkaline medium (can be checked with an indicator)

Conclusion:

• dissolves well → potash

• dissolves poorly → superphosphate

Final identification

Reaction equations in molecular, full ionic, and net ionic forms.

1. Ammonium nitrate (NH₄NO₃)

This is a highly soluble fertilizer → it dissociates in water:

Molecular equation:

NH₄NO₃ → NH₄⁺ + NO₃⁻

Full ionic form:

(the same, since the substance is completely soluble)
NH₄NO₃ → NH₄⁺ + NO₃⁻

Net ionic:

coincides:
NH₄⁺ + NO₃⁻

2. Potash (K₂CO₃)

Also dissolves well and dissociates:

Molecular equation:

K₂CO₃ → 2K⁺ + CO₃²⁻

Full ionic form:

K₂CO₃ → 2K⁺ + CO₃²⁻

Net ionic:

2K⁺ + CO₃²⁻

3. Superphosphate

Superphosphate mainly contains:

• Ca(H₂PO₄)₂ (the soluble part)

• CaSO₄ (the poorly soluble part)

Therefore a precipitate is observed.

Reaction of the soluble part:

Molecular:

Ca(H₂PO₄)₂ → Ca²⁺ + 2H₂PO₄⁻

Full ionic:

Ca(H₂PO₄)₂ → Ca²⁺ + 2H₂PO₄⁻

Net ionic:

Ca²⁺ + 2H₂PO₄⁻

Insoluble part:

CaSO₄ ↓ (precipitate)

4. (Additionally, to confirm potash — reaction with an acid)

The reaction with an acid (for example, HCl) can be written:

Molecular:

K₂CO₃ + 2HCl → 2KCl + H₂O + CO₂↑

Full ionic:

2K⁺ + CO₃²⁻ + 2H⁺ + 2Cl⁻ → 2K⁺ + 2Cl⁻ + H₂O + CO₂↑

Net ionic:

CO₃²⁻ + 2H⁺ → H₂O + CO₂↑

General conclusion

• Ammonium nitrate and potash → dissolve completely (electrolytes)

• Superphosphate → produces a precipitate (insoluble Ca salts)

• A qualitative indicator of potash → the evolution of CO₂ upon reaction with an acid

The main distinguishing feature — solubility:

• if the substance does not dissolve → it is superphosphate

• if it dissolves:

  • within pair (a) → saltpeter

  • within pair (b) → potash

2. Two numbered test tubes contain fertilizers:

• a) ammonium nitrate and potash;
• b) ammonium sulfate and potassium chloride.

Prepare solutions of these fertilizers and test them using a universal indicator. State the contents of each test tube.

Identifying fertilizers using a universal indicator

1. Preparing the solutions

Dissolve small amounts of the substance from each test tube in water.

2. Testing with a universal indicator

Observations:

a) Ammonium nitrate and potash

• Ammonium nitrate (NH₄NO₃)
  → the solution is weakly acidic (indicator: yellow-green)

• Potash (K₂CO₃)
  → the solution is alkaline (indicator: blue/violet)

Therefore:

• acidic medium → NH₄NO₃

• alkaline medium → K₂CO₃

b) Ammonium sulfate and potassium chloride

• Ammonium sulfate ((NH₄)₂SO₄)
  → the solution is acidic

• Potassium chloride (KCl)
  → the solution is neutral (indicator green)

Therefore:

• acidic → (NH₄)₂SO₄

• neutral → KCl

Explanation (salt hydrolysis)

1. Ammonium nitrate

Molecular:

NH₄NO₃ + H₂O ⇄ NH₄OH + HNO₃

Full ionic:

NH₄⁺ + NO₃⁻ + H₂O ⇄ NH₄OH + H⁺ + NO₃⁻

Net ionic:

NH₄⁺ + H₂O ⇄ NH₃ + H₃O⁺

Acidic medium due to NH₄⁺

2. Potash (potassium carbonate)

Molecular:

K₂CO₃ + H₂O ⇄ KHCO₃ + KOH

Full ionic:

2K⁺ + CO₃²⁻ + H₂O ⇄ K⁺ + HCO₃⁻ + K⁺ + OH⁻

Net ionic:

CO₃²⁻ + H₂O ⇄ HCO₃⁻ + OH⁻

Alkaline medium

3. Ammonium sulfate

Molecular:

(NH₄)₂SO₄ + H₂O ⇄ NH₄OH + H₂SO₄

Full ionic:

2NH₄⁺ + SO₄²⁻ + H₂O ⇄ NH₄OH + NH₄⁺ + H⁺ + SO₄²⁻

Net ionic:

NH₄⁺ + H₂O ⇄ NH₃ + H₃O⁺

Acidic medium

4. Potassium chloride

Molecular:

KCl → K⁺ + Cl⁻

Full ionic:

K⁺ + Cl⁻

Net ionic:

(no reaction)

Neutral medium (no hydrolysis occurs)

Summary

Conclusion:

• All ammonium salts produce an acidic medium

• Carbonates → an alkaline medium

• Salts of a strong acid and a strong base → a neutral medium

3. The numbered test tubes contain fertilizers:

• a) ammonium sulfate and ammonium chloride;
• b) potassium chloride and potash.

Prepare solutions of these fertilizers and determine the contents of each test tube using the reagents provided.

Identifying fertilizers in the test tubes

a) Ammonium sulfate and ammonium chloride

Formulas:

• ammonium sulfate → (NH₄)₂SO₄

• ammonium chloride → NH₄Cl

How to distinguish

Use a solution of BaCl₂ (barium chloride)

Indication:

• if a white precipitate appears → this is the sulfate (SO₄²⁻)

• if there is no precipitate → this is the chloride

Reactions

1. Ammonium sulfate + barium chloride

Molecular equation:

$(N{H}_4{)}_{2}S{O}_4+BaC{l}_2\to BaS{O}_4\downarrow +2N{H}_{4}Cl$

Full ionic:

$2N{H}_4^{+}+S{O}_4^{2-}+B{a}^{2+}+2C{l}^{-}\to BaS{O}_4\downarrow +2N{H}_4^{+}+2C{l}^{-}$

Net ionic:

$B{a}^{2+}+S{O}_4^{2-}\to BaS{O}_4\downarrow$

2. Ammonium chloride + barium chloride

No reaction (no precipitate forms)

b) Potassium chloride and potash

Formulas:

• potassium chloride → KCl

• potash (potassium carbonate) → K₂CO₃

How to distinguish

Use hydrochloric acid (HCl)

Indication:

• if gas evolution (CO₂) occurs → this is the carbonate (potash)

• if there is no reaction → this is KCl

Reactions

1. Potash + hydrochloric acid

Molecular equation:

$K_{2}C{O}_3+2HCl\to 2KCl+H_{2}O+C{O}_2\uparrow$

Full ionic:

$2K^{+}+C{O}_3^{2-}+2H^{+}+2C{l}^{-}\to 2K^{+}+2C{l}^{-}+H_{2}O+C{O}_2\uparrow$

Net ionic:

$C{O}_3^{2-}+2H^{+}\to H_{2}O+C{O}_2\uparrow$

2. Potassium chloride + hydrochloric acid

No reaction

Summary (what is in which test tube)

4. Determine which of the numbered test tubes contains each of the four given fertilizers:

• a) superphosphate, potash, ammonium chloride, potassium chloride;

• b) calcium saltpeter, superphosphate, ammonium sulfate, ammonium nitrate.

a) Superphosphate, potash, NH₄Cl, KCl

1. Solubility in water

• Superphosphate → dissolves partially, the solution may be cloudy (contains CaSO₄ impurities)

• The others (K₂CO₃, NH₄Cl, KCl) → highly soluble

Cloudy solution = superphosphate

2. Identifying potash (K₂CO₃)

Add an acid (for example, HCl):

Indication: CO₂ is evolved (fizzing)

Molecular:

$K_{2}C{O}_3+2HCl\to 2KCl+H_{2}O+C{O}_2\uparrow$

Full ionic:

$2K^{+}+C{O}_3^{2-}+2H^{+}+2C{l}^{-}\to 2K^{+}+2C{l}^{-}+H_{2}O+C{O}_2$ ​

Net:

$C{O}_3^{2-}+2H^{+}\to H_{2}O+C{O}_2\uparrow$

Fizzes = potash

3. Identifying NH₄Cl

Add alkali (NaOH), heat:

Indication: smell of ammonia (NH₃)

Molecular:

$N{H}_{4}Cl+NaOH\to N{H}_3\uparrow +NaCl+H_{2}O$

Full ionic:

$N{H}_4^{+}+C{l}^{-}+N{a}^{+}+O{H}^{-}\to N{H}_3+N{a}^{+}+C{l}^{-}+H_{2}O$

Net:

$N{H}_4^{+}+O{H}^{-}\to N{H}_3\uparrow +H_{2}O$

Smell of ammonia = ammonium chloride

4. Remaining substance

Potassium chloride (KCl) — gives no characteristic reactions

b) Ca(NO₃)₂, superphosphate, (NH₄)₂SO₄, NH₄NO₃

1. Superphosphate

Again identified by poor solubility / cloudiness

2. Ammonium sulfate ((NH₄)₂SO₄)

Add BaCl₂:

Indication: white precipitate BaSO₄

Molecular:

$(N{H}_4{)}_{2}S{O}_4+BaC{l}_2\to BaS{O}_4\downarrow +2N{H}_{4}Cl$

Full ionic:

$2N{H}_4^{+}+S{O}_4^{2-}+B{a}^{2+}+2C{l}^{-}\to BaS{O}_4\downarrow +2N{H}_4^{+}+2C{l}^{-}$

Net:

$B{a}^{2+}+S{O}_4^{2-}\to BaS{O}_4\downarrow$

Precipitate = ammonium sulfate

3. Ammonium salts (NH₄NO₃ and (NH₄)₂SO₄)

Checked with alkali → release NH₃ (as above)

4. Calcium saltpeter Ca(NO₃)₂

Add Na₂CO₃:

Indication: white precipitate CaCO₃

Molecular:

$Ca(N{O}_3{)}_2+N{a}_{2}C{O}_3\to CaC{O}_3\downarrow +2NaN{O}_3$ ​

Full ionic:

$C{a}^{2+}+2N{O}_3^{-}+2N{a}^{+}+C{O}_3^{2-}\to CaC{O}_3\downarrow +2N{a}^{+}+2N{O}_3^{-}$ ​

Net:

$C{a}^{2+}+C{O}_3^{2-}\to CaC{O}_3\downarrow$

Precipitate = calcium saltpeter

5. Ammonium nitrate NH₄NO₃

Remains:

• highly soluble

• gives NH₃ with alkali

• does NOT give a precipitate with BaCl₂

Summary (brief)

a)

• cloudy → superphosphate

• fizzes with acid → potash

• NH₃ with alkali → NH₄Cl

• remainder → KCl

b)

• cloudy → superphosphate

• BaSO₄↓ → (NH₄)₂SO₄

• CaCO₃↓ → Ca(NO₃)₂

• remainder → NH₄NO₃

See also

• [[b13083]]
• [[b13084]]