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Chemical dilution and solution makeup

Choose product, strengths and volume to see how much concentrate and water to use, how much heat the mix releases and the safe order of mixing.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

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Product and strengths
Quantity

Densities at 68 °F from published tables (CRC Handbook, Perry). Hypochlorite uses a typical relation for industrial bleach with residual salt; check the lot density on the supplier certificate.

—Concentrate and water for the dilution
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Final temperature versus target strength

Adiabatic estimate, with no heat loss to the tank or air, starting from the entered temperature.

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Product density versus strength

Table at 68 °F used in the calculation, with concentrate and final solution marked.

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Method, assumptions and references

Equations used

Mass balance: m₁ · w₁ = m₂ · w₂; m = V · ρ(w); water = m₂ − m₁; V₂ ≠ V₁ + V_water
Heat: Q = n_solute · (ΔH_soln(n₁) − ΔH_soln(n₂)), with n = mol of water per mol of solute before and after
Adiabatic final temperature: T = T₀ + Q ÷ (m₂ · cp(w₂))
Hypochlorite: SG ≈ 0.998 + 0.017 · % available chlorine (industrial bleach with residual salt)

Assumptions and limits

  • Densities at 68 °F interpolated from tables; product and water at the same starting temperature. Enthalpies of solution at 77 °F (NBS); tabulated specific heat of the final solution.
  • Final temperature is adiabatic, an upper bound: tank, air and addition time shed some heat. Local hot spots can far exceed the average if mixing is fast or unstirred.
  • Hypochlorite heat of dilution taken as negligible; for other products, enter densities and check the SDS.

Standards and technical documents

  • CRC Handbook of Chemistry and Physics: Concentrative properties of aqueous solutions (H₂SO₄, NaOH)
  • Perry's Chemical Engineers' Handbook, 9th ed., McGraw-Hill: densities, heat capacities and heats of solution
  • Wagman, D. D. et al. The NBS tables of chemical thermodynamic properties. J. Phys. Chem. Ref. Data 11, Suppl. 2, 1982
  • Dow / OxyChem: Caustic Soda Handbook (dilution and heat of dilution)
  • The Chlorine Institute: Pamphlet 96, Sodium Hypochlorite Manual
  • NACE / AMPP: Corrosion Data Survey (materiais para ácido sulfúrico e soda)

U.S. regulations

  • OSHA 29 CFR 1910.1200: Hazard Communication (SDS and labels)
  • OSHA 29 CFR 1910.132 and 1910.151(c): PPE and quick drenching facilities for corrosives; ANSI/ISEA Z358.1 emergency eyewash and shower
  • EPA 40 CFR 355 and 370 (EPCRA): emergency planning and Tier II reporting (sulfuric acid is an extremely hazardous substance)
  • DOT 49 CFR 171–180: hazardous materials transport

Frequently asked questions

How do I dilute 98% sulfuric acid to 10%?

For 250 gal of 10% solution (SG 1.066, about 2,224 lb), you need about 227 lb of 98% acid, or 14.8 gal, and about 240 gal of water. Put the water in first and add acid slowly with stirring: temperature rises about 34 °F.

Why always add acid to water?

Diluting sulfuric acid releases a lot of heat. If water falls on acid, the small amount of water boils instantly and spatters acid. With acid going into water, the large mass of water absorbs the heat.

Why is the final volume not the sum of the volumes?

Water and acid molecules pack more tightly together. Diluting 98% sulfuric acid to 10%, the solution has about 2% less volume than the sum of the parts.

How do I dilute 50% caustic soda?

For 250 gal at 20% (SG 1.219), use about 1,017 lb of 50% caustic, or about 80 gal, and about 183 gal of water. The mix warms by about 49 °F; add caustic to water slowly with stirring.