Q1.
(Step 7) What do you observe?
Answer
A milky white precipitate appears at once when the barium chloride solution is poured into the sodium sulfate solution. The clear liquid turns cloudy white.
Sodium sulfate + Barium chloride → Barium sulfate + Sodium chloride
Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2 NaCl
Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2 NaCl
The white solid is barium sulfate, which is insoluble in water and so settles out. The sodium chloride formed alongside it stays dissolved and is invisible.
Why it happens: both starting solutions contain free ions — Na⁺ and SO₄²⁻ in one flask, Ba²⁺ and Cl⁻ in the other. When they meet, Ba²⁺ and SO₄²⁻ attract each other so strongly that they lock together into a solid lattice instead of staying in solution. Na⁺ and Cl⁻ have no such tendency, so they remain free. A new insoluble solid formed in this way is called a precipitate, and its appearance is proof that a chemical change has occurred.