Basics of Chemical Calculations · Chemical Calculator

Don't just calculate it. Prepare it.

Type the chemical, the strength you need and the volume. You get the weight or volume to take and how to make it at the bench. The method behind every answer is in the book.

Chemical

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Strength required

Volume to prepare

Assay / purity on label (%)

Use the figure on your bottle or its certificate of analysis.

Commercial acids and bases

Typical AR-grade values; the label overrides. Molarity = % × SG × 10 / Mol. wt.

n-factor (equivalents per mole)

Normality = Molarity × n. Eq. weight = Mol. weight / n.

Primary standards

Standard	Mol. wt	Eq. wt	Dry at	Standardises
Potassium hydrogen phthalate (KHP)	204.22	204.22	110–120 °C, 2 h	NaOH, KOH
Sodium carbonate, anhydrous	105.99	53.00	270–300 °C, 1 h	HCl, H₂SO₄
Borax (Na₂B₄O₇·10H₂O)	381.37	190.69	do not dry	HCl, H₂SO₄
Sulphamic acid	97.09	97.09	desiccator	NaOH
Sodium oxalate	134.00	67.00	105–110 °C	KMnO₄, Ce⁴⁺
Oxalic acid dihydrate	126.07	63.04	do not dry	KMnO₄, NaOH
Potassium dichromate	294.18	49.03	150 °C, 1–2 h	Na₂S₂O₃ (iodometry), Fe²⁺
Potassium iodate	214.00	35.67	110 °C	Na₂S₂O₃ (iodometry)
Sodium chloride	58.44	58.44	110 °C, 2 h	AgNO₃
Calcium carbonate	100.09	50.04	110 °C	EDTA
Zinc metal / ZnSO₄·7H₂O	65.38 / 287.54	—	—	EDTA

Indicators

Indicator	pH range	Acid colour → base colour	Used for
Methyl orange	3.1 – 4.4	red → yellow	strong acid vs weak base (Na₂CO₃, NH₃)
Methyl red	4.4 – 6.2	red → yellow	strong acid vs weak base
Bromothymol blue	6.0 – 7.6	yellow → blue	strong acid vs strong base
Phenol red	6.8 – 8.4	yellow → red	near-neutral end points
Phenolphthalein	8.3 – 10.0	colourless → pink	weak acid vs strong base (KHP, oxalic, acetic)
Thymolphthalein	9.3 – 10.5	colourless → blue	strong base titrations
Starch	—	blue with I₂ → colourless	iodometry; add near the end point
Eriochrome Black T	pH 10	wine red → blue	EDTA (Ca, Mg hardness)
Murexide	pH 12	pink → violet	EDTA (Ca only)
Potassium chromate	6.5 – 10	yellow → brick red (Ag₂CrO₄)	Mohr chloride titration
Ferric ammonium sulphate	acidic	colourless → red-brown	Volhard (thiocyanate)
Diphenylamine / ferroin	redox	colourless → violet / red → pale blue	dichromate, cerate titrations

Volumetric glassware: tolerances (Class A, 20 °C)

Item	Tolerance	Note
Volumetric flask 100 mL	± 0.10 mL	TC (to contain). Read the bottom of the meniscus at eye level.
Volumetric flask 250 mL	± 0.15 mL	Never heat a volumetric flask.
Volumetric flask 1000 mL	± 0.40 mL	Cool hot solutions before making up.
Bulb pipette 10 mL	± 0.02 mL	TD (to deliver). Do not blow out the last drop.
Bulb pipette 25 mL	± 0.03 mL	Rinse with the solution first.
Burette 50 mL	± 0.05 mL	Read to 0.02 mL. No air in the tip.
Measuring cylinder 100 mL	± 0.5 mL	Not for standard solutions.

Water for solutions

Grade	Conductivity	Use
Distilled / RO	1 – 5 µS/cm	General reagents, cleaning
Deionised (Type II)	< 1 µS/cm	Standard solutions, titrants
Ultrapure (Type I, Milli-Q)	0.055 µS/cm	Trace analysis, HPLC, ppm standards
CO₂-free (boiled and cooled)	—	NaOH, KOH, Ba(OH)₂, thiosulphate

Don't just calculate it. Prepare it.

Dilute a stock solution

Dilution factor

Serial dilution

Mixing two solutions

Molecular weight of any formula

Find an element

Periodic table

What strength did I make?

Convert concentration units

Titration: strength of the unknown

Titration factor

pH of a strong acid or base

Buffer pH

Practice at the bench

Commercial acids and bases

n-factor (equivalents per mole)

Primary standards

Indicators

Volumetric glassware: tolerances (Class A, 20 °C)

Water for solutions

Preparation record