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How can a clear liquid be the source of a mineral deposit?
Transparency does not establish the absence of dissolved constituents.
Sources for this view
Calcium and magnesium contribute to water hardness. Hard water can leave scale in pipes and heating equipment. Before identifying a particular deposit, separate the dissolved-water composition from evidence about the solid.
Sources for this view
Explore the model (optional)
EXPLORE THE MODEL
Carbonate species at 25 °C
α₀ : α₁ : α₂ = [H⁺]² : K₁[H⁺] : K₁K₂
Read sampled numerical values
| pH | CO₂* | HCO₃⁻ | CO₃²⁻ |
|---|---|---|---|
| 5 | 0.957 | 0.043 | 2.000e-7 |
| 5.7 | 0.817 | 0.183 | 4.288e-6 |
| 6.4 | 0.471 | 0.529 | 6.212e-5 |
| 7.1 | 0.151 | 0.849 | 4.997e-4 |
| 7.8 | 0.034 | 0.963 | 0.003 |
| 8.5 | 0.007 | 0.979 | 0.014 |
| 9.2 | 0.001 | 0.93 | 0.069 |
| 9.9 | 2.054e-4 | 0.729 | 0.271 |
| 10.6 | 1.965e-5 | 0.349 | 0.651 |
| 11.3 | 1.086e-6 | 0.097 | 0.903 |
| 12 | 4.686e-8 | 0.021 | 0.979 |
The three carbon forms sum to the prescribed total. A positive saturation index permits a thermodynamic drive toward calcite precipitation; it gives no rate. The authored starting account is CaCl₂ plus NaHCO₃. NaOH or HCl bookkeeping closes the charge balance at the prescribed pH; added volume is neglected. This is not a measured water sample.
What this model can establish
Fixed 25 °C, concentration used as activity, prescribed pH and free calcium. CO₂* groups dissolved CO₂ and carbonic acid. No gas exchange, precipitation kinetics or mineral depletion is calculated.
Optional: check your understanding
MAKE THE CONNECTION
A white deposit appears after using clear water. What is justified?