How do I rank ion concentrations in a salt solution?

Ions that do not hydrolyse (such as Na⁺) come first. Hydrolysis is slight, so the hydrolysing ion remains much more abundant than its products, and the acid/base character decides between H⁺ and OH⁻. For 0.1 M sodium acetate: c(Na⁺) = 0.1 > c(CH₃COO⁻) ≈ 0.09999 > c(OH⁻) = 7.5×10⁻⁶ > c(H⁺) = 1.3×10⁻⁹. In Na₂CO₃ the order is c(Na⁺) > c(CO₃²⁻) > c(OH⁻) > c(HCO₃⁻) > c(H⁺), because OH⁻ also comes from the second step and from water.

How are the mass balance and proton condition written?

The mass balance conserves each element in the ratio of the formula: in Na₂CO₃, Na : C = 2 : 1, so c(Na⁺) = 2[c(CO₃²⁻) + c(HCO₃⁻) + c(H₂CO₃)]. The proton condition takes the dissolved species and water as the reference: the products that gained protons balance those that lost protons, weighting H₂CO₃ by 2 because it gained two, so c(OH⁻) = c(H⁺) + c(HCO₃⁻) + 2c(H₂CO₃). For mixtures it follows from subtracting the mass balance from the charge balance.

Why is NaHCO₃ solution basic but NaHSO₃ solution acidic?

An acid anion both ionises and hydrolyses, so compare the two constants. For HCO₃⁻, Ka₂ = 4.7×10⁻¹¹ but Kh = Kw/Ka₁ = 2.2×10⁻⁸: hydrolysis wins and 0.1 M NaHCO₃ has pH ≈ 8.3. For HSO₃⁻, Ka₂ = 6.3×10⁻⁸ while Kh = Kw/Ka₁ = 7.1×10⁻¹³: ionisation wins and the pH is about 4.6. Likewise H₂PO₄⁻ is acidic and HPO₄²⁻ is basic.

How do temperature and dilution affect hydrolysis?

Hydrolysis is the reverse of neutralisation and is endothermic, so heating shifts it forward, increases Kh and the degree of hydrolysis — hot soda solution cleans grease better. Dilution also shifts it forward and raises the degree of hydrolysis, but c(OH⁻) or c(H⁺) still decreases and the pH moves towards 7; Kh depends only on temperature. Adding a hydrolysis product, such as HCl to FeCl₃ solution, suppresses hydrolysis.

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💦Salt Hydrolysis Calculator - pH of Salt Solutions, Ion Concentrations, Charge, Mass & Proton Balance

When a salt dissolves, the ion of a weak acid or weak base reacts with water (hydrolysis) and shifts the pH. This tool first explains the chemistry of each solute: it writes the hydrolysis or ionisation equations, computes Kh = Kw/Ka, shows the stepwise hydrolysis of polyprotic anions (for CO₃²⁻, Kh₁ = 2.1×10⁻⁴ is far larger than Kh₂ = 2.2×10⁻⁸, so the first step dominates) and, for acid salts, compares Ka with Kh — HCO₃⁻ and HPO₄²⁻ hydrolyse more than they ionise and give basic solutions, while HSO₃⁻ and H₂PO₄⁻ give acidic ones. It then solves the charge balance, mass balances and all dissociation equilibria exactly to give the pH and the equilibrium concentration of every ion and molecule: 0.1 M sodium acetate has pH 8.88 with c(Na⁺) > c(CH₃COO⁻) > c(OH⁻) > c(H⁺); 0.1 M Na₂CO₃ has pH 11.65; 0.1 M NaHCO₃ has pH 8.34; an equimolar acetic acid/acetate mixture has pH 4.75 with c(CH₃COO⁻) > c(Na⁺) > c(H⁺) > c(OH⁻). The charge balance, mass balance and proton condition are written automatically and checked numerically — for Na₂CO₃, c(Na⁺) = 2[c(CO₃²⁻) + c(HCO₃⁻) + c(H₂CO₃)] and c(OH⁻) = c(H⁺) + c(HCO₃⁻) + 2c(H₂CO₃); for mixtures the proton condition is derived by eliminating the spectator ion. A mixing mode handles problems such as 0.2 M acetic acid plus 0.1 M NaOH in equal volumes and shows the equivalent composition after neutralisation. Finally, exam-style true/false statements are generated from the computed data, and reference cards cover temperature, dilution and common-ion effects and applications such as soda cleaning, alum water treatment, preparing FeCl₃ solution and foam fire extinguishers.

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How to use Salt hydrolysis & solution balances

1Choose a salt (or add several solutes to make a mixture) and enter concentrations, or use Mix two solutions with concentrations and volumes; examples are one tap away
2Read the pH, hydrolysis analysis, species concentrations and their order, and the automatically written and verified charge, mass and proton balances
3Test yourself with the generated true/false statements (New set gives fresh ones), and review the factors and applications tab

FAQ

How do I rank ion concentrations in a salt solution?: Ions that do not hydrolyse (such as Na⁺) come first. Hydrolysis is slight, so the hydrolysing ion remains much more abundant than its products, and the acid/base character decides between H⁺ and OH⁻. For 0.1 M sodium acetate: c(Na⁺) = 0.1 > c(CH₃COO⁻) ≈ 0.09999 > c(OH⁻) = 7.5×10⁻⁶ > c(H⁺) = 1.3×10⁻⁹. In Na₂CO₃ the order is c(Na⁺) > c(CO₃²⁻) > c(OH⁻) > c(HCO₃⁻) > c(H⁺), because OH⁻ also comes from the second step and from water.
How are the mass balance and proton condition written?: The mass balance conserves each element in the ratio of the formula: in Na₂CO₃, Na : C = 2 : 1, so c(Na⁺) = 2[c(CO₃²⁻) + c(HCO₃⁻) + c(H₂CO₃)]. The proton condition takes the dissolved species and water as the reference: the products that gained protons balance those that lost protons, weighting H₂CO₃ by 2 because it gained two, so c(OH⁻) = c(H⁺) + c(HCO₃⁻) + 2c(H₂CO₃). For mixtures it follows from subtracting the mass balance from the charge balance.
Why is NaHCO₃ solution basic but NaHSO₃ solution acidic?: An acid anion both ionises and hydrolyses, so compare the two constants. For HCO₃⁻, Ka₂ = 4.7×10⁻¹¹ but Kh = Kw/Ka₁ = 2.2×10⁻⁸: hydrolysis wins and 0.1 M NaHCO₃ has pH ≈ 8.3. For HSO₃⁻, Ka₂ = 6.3×10⁻⁸ while Kh = Kw/Ka₁ = 7.1×10⁻¹³: ionisation wins and the pH is about 4.6. Likewise H₂PO₄⁻ is acidic and HPO₄²⁻ is basic.
How do temperature and dilution affect hydrolysis?: Hydrolysis is the reverse of neutralisation and is endothermic, so heating shifts it forward, increases Kh and the degree of hydrolysis — hot soda solution cleans grease better. Dilution also shifts it forward and raises the degree of hydrolysis, but c(OH⁻) or c(H⁺) still decreases and the pH moves towards 7; Kh depends only on temperature. Adding a hydrolysis product, such as HCl to FeCl₃ solution, suppresses hydrolysis.

Features

60+ salts, acids and bases: normal salts, acid salts, ammonium salts, weak acid–weak base salts, and mixtures
Mix two solutions by concentration and volume, with the equivalent composition after reaction
Hydrolysis and ionisation equations, Kh = Kw/Ka, stepwise hydrolysis of polyprotic anions
Acid salts: Ka vs Kh; weak acid–weak base salts: Ka vs Kb, to predict acidic or basic
Exact charge-balance solution for pH and every species' equilibrium concentration
Ion concentration ranking (ions only or including molecules) with copy
Charge balance, mass balance and proton condition written automatically and verified with numbers
Exam-style true/false quiz built from the results, plus factor and application cards

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