Question

ammonia + magnesium sulfate yields ammonium sulfate + magnesium hydroxide



What happens when you mix ammonia (windex) and magnesium sulfate (epsom salt)?

Analyze Reaction 1

Identify observations that you think could be used to identify that the change was a chemical change and not a physical one.

Answer 1

Short answer
- If you mix aqueous ammonia (the ammonia in Windex is basically NH3 in water) with a solution of magnesium sulfate (Epsom salt dissolved in water), you will often see a white cloudy solid form. That solid is (or is mostly) magnesium hydroxide, Mg(OH)2, formed when NH3 produces OH− in water and the OH− reacts with Mg2+. Ammonium sulfate remains in the solution.

Balanced molecular equation
2 NH3(aq) + MgSO4(aq) + 2 H2O(l) → (NH4)2SO4(aq) + Mg(OH)2(s)

Net ionic form (shows the chemical change)
Mg2+(aq) + 2 OH−(aq) → Mg(OH)2(s)
(with OH− supplied by NH3 + H2O ⇌ NH4+ + OH−)

Why this happens (brief chemical explanation)
- Ammonia in water is a weak base: NH3 + H2O ⇌ NH4+ + OH−. If enough OH− is generated, Mg2+ from MgSO4 reacts with OH− to produce insoluble Mg(OH)2 (Ksp ≈ 1.5×10−11), which precipitates as a white solid. The sulfate stays in solution paired with ammonium as (NH4)2SO4.

Observations that indicate a chemical change (not just a physical mixing)
- Formation of a new solid (white cloudy precipitate) that was not present before mixing.
- The precipitate remains after you let the mixture settle and can be separated by filtration — showing a new substance was made.
- pH change: the solution becomes more basic (testable with pH paper). The production of OH− is part of the chemical reaction.
- Chemical tests showing new species:
- Add dilute acid (e.g., HCl) to the collected solid: Mg(OH)2 will dissolve, consistent with it being a hydroxide (Mg(OH)2 + 2 HCl → MgCl2 + 2 H2O).
- To the filtered supernatant, add BaCl2 solution: formation of a white BaSO4 precipitate confirms sulfate is present in solution (as ammonium sulfate).
- Heat the supernatant with NaOH (or add Nessler’s reagent) to detect NH4+: warming with strong base will release NH3 (ammonia smell) from NH4+, or Nessler’s reagent gives a color change with ammonium.
- (Possible) slight temperature change — weakly exothermic if noticeable — also indicates a chemical process, though this may be too small to feel.

Things that can rule out a purely physical change
- If the white material is a precipitate that can be separated and identified (dissolves in acid, does not redissolve simply by stirring), that supports a chemical reaction rather than simple insoluble impurity.
- If specific chemical tests on the liquid and solid (BaCl2 for SO4^2−, acid dissolution of the solid, NH3 liberation from the liquid) show new chemical species consistent with ammonium sulfate in solution and Mg(OH)2 solid, that confirms a chemical change.

Caveats and practical notes
- Whether you see precipitation depends on concentrations and pH. Mg(OH)2 only precipitates when [OH−] is high enough (roughly pH ≳ 9–10, depending on [Mg2+]). Very dilute ammonia or magnesium concentrations might not give a visible precipitate.
- Windex is not just ammonia and water; other ingredients (surfactants, solvents, dyes) can change the appearance or mask/test-interference.
- Safety: do this in a well-ventilated area or fume hood; ammonia vapors are irritating. Wear eye protection and gloves.

If you want, I can suggest a simple safe experimental sequence (quantities, step-by-step tests) you can do at home or in a lab to confirm the identities of the products.