Interactive: concentration and dilution. Copper(II) and sulfate ions sit in a container of solution. Set the final volume of solution: the ion count stays fixed while the liquid rises, the ions spread out and the colour fades. A graph of concentration against volume shows a rectangle of area c times V that never changes. A toggle switches between making a standard solution from a weighed solid and diluting a stock solution with a pipette.
Dilute it ten times and not one ion leaves
Concentration is an amount of solute shared out through a volume of solution: c = n ÷ V. Add water and the count of solute particles stays exactly the same; only the volume they share grows. Make the solution up to a new volume and watch the ions spread out, then switch between making a standard solution and diluting a stock.
Same moles, more waterLive · 250 mL
0.0500 mol CuSO₄ = 25 Cu²⁺ + 25 SO₄²⁻ dots, 2 mmol each · change the final volume and watch the colour fade
0.0500 mol in 0.250 L → 0.200 mol L⁻¹
Final volume of solution250 mL
100 mL550 mL1000 mL
Concentration
0.200mol L⁻¹
c = n ÷ V = 0.0500 ÷ 0.250 L
Same, by mass
31.9g L⁻¹
3.19 %(m/v) · ≈ 31 900 ppm
Know This
Adding water changes the volume but never the moles of solute, so the concentration falls in proportion and c₁V₁ = c₂V₂.