Template · Chemistry

Acid-base titration curve calculator

pH at every titrant volume for a strong or weak acid titrated with NaOH, with equivalence, half-equivalence and an indicator check.

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	A	B	C	D	E
1	Acid-base titration curve calculator
2	Example data — replace the blue input cells with your own.
3	Titration type: Weak acid. Analyte: Acetic acid (example). Titrant: sodium hydroxide, NaOH.
4	EQUIVALENCE VOLUME (ML)	PH AT EQUIVALENCE		PH AT HALF-EQUIVALENCE	SUGGESTED INDICATOR
5	25.00	8.72		4.74	Phenolphthalein
6	Moles of acid divided by titrant molarity	Calculated on the Setup tab		Equals pKa for a weak acid	Range nearest the equivalence pH
7
8	Titration curve, sampled at the Setup interval
9	Titrant added (mL)	pH	Region	pH bar (0 to 14)
10	0.0	2.88	Initial	██████
11	2.0	3.68	Buffer	███████
12	4.0	4.02	Buffer	████████
13	6.0	4.24	Buffer	████████
14	8.0	4.42	Buffer	█████████
15	10.0	4.57	Buffer	█████████
16	12.0	4.71	Buffer	█████████

Showing the first 16 of 59 rows and 6 of 6 columns. Cells with formulas show the formula on hover.

	A	B	C
1	Setup: titration inputs and derived values
2	Blue cells are inputs. Everything else follows from them.
3
4	Titration inputs
5	Titration type	Weak acid	Strong acid or Weak acid. The titrant is always a strong base, sodium hydroxide (NaOH).
6	Analyte name	Acetic acid (example)	Label only. Shown on the Dashboard.
7	Ka of the weak acid	1.80E-05	Weak acid only. Acetic acid at 25 °C is about 1.8E-5. Ignored for a strong acid.
8	Analyte concentration (mol/L)	0.100	Concentration of the acid in the flask.
9	Analyte volume (mL)	25.00	Volume of acid solution in the flask.
10	Titrant concentration, NaOH (mol/L)	0.100	Strong base in the burette.
11	Volume step (mL)	0.50	Spacing of the curve rows. The curve runs from 0 to 2 times the equivalence volume, up to 120 rows.
12	Kw, ion product of water at 25 °C	1.00E-14	Keep 1.0E-14 unless you work at another temperature.
13	Dashboard sample interval (mL)	2.00	Spacing of the sampled pH bars on the Dashboard. Must be a multiple of the volume step.
14
15	Derived values
16	Moles of acid (mmol)	2.50	Concentration (mol/L) times volume (mL) gives millimoles.

Showing the first 16 of 31 rows and 4 of 4 columns. Cells with formulas show the formula on hover.

	A	B	C	D	E	F	G	H	I	J	K	L
1	Titration curve table
2	One row per titrant volume: moles added, region, pH, slope and the steepest step.
3
4	Curve table: rows past 2 times the equivalence volume stay blank
5	Point	Titrant added (mL)	OH- added (mmol)	Total volume (mL)	Region	Acid left (mmol)	Base in excess (mmol)	Net excess (M)	pH	pH bar (0 to 14)	Marker	Slope (pH per mL)
6	0	0.00	0.00	25.00	Initial	2.50	0.00	0.00E+00	2.88	██████
7	1	0.50	0.05	25.50	Buffer	2.45	0.00	0.00E+00	3.05	██████		0.36
8	2	1.00	0.10	26.00	Buffer	2.40	0.00	0.00E+00	3.36	███████		0.62
9	3	1.50	0.15	26.50	Buffer	2.35	0.00	0.00E+00	3.55	███████		0.37
10	4	2.00	0.20	27.00	Buffer	2.30	0.00	0.00E+00	3.68	███████		0.27
11	5	2.50	0.25	27.50	Buffer	2.25	0.00	0.00E+00	3.79	████████		0.21
12	6	3.00	0.30	28.00	Buffer	2.20	0.00	0.00E+00	3.88	████████		0.18
13	7	3.50	0.35	28.50	Buffer	2.15	0.00	0.00E+00	3.96	████████		0.15
14	8	4.00	0.40	29.00	Buffer	2.10	0.00	0.00E+00	4.02	████████		0.14
15	9	4.50	0.45	29.50	Buffer	2.05	0.00	0.00E+00	4.09	████████		0.12
16	10	5.00	0.50	30.00	Buffer	2.00	0.00	0.00E+00	4.14	████████		0.11

Showing the first 16 of 125 rows and 12 of 13 columns. Cells with formulas show the formula on hover.

	A	B	C	D	E	F	G	H
1	Indicator transition ranges
2	Standard pH transition intervals, tested against the equivalence pH of the titration.
3
4	Transition ranges and suitability at the equivalence pH
5	Indicator	Color change	Low pH	High pH	Midpoint (pH)	Suitable at equivalence	Distance from equivalence (pH)	Range on a 0 to 14 pH scale
6	Methyl orange	Red to yellow	3.1	4.4	3.75	Not suitable		░░░░░░███
7	Methyl red	Red to yellow	4.4	6.2	5.30	Not suitable		░░░░░░░░░███
8	Bromothymol blue	Yellow to blue	6.0	7.6	6.80	Not suitable		░░░░░░░░░░░░███
9	Phenol red	Yellow to red	6.8	8.4	7.60	Not suitable		░░░░░░░░░░░░░░███
10	Phenolphthalein	Colorless to pink	8.2	10.0	9.10	Suitable	0.38	░░░░░░░░░░░░░░░░████
11	Thymolphthalein	Colorless to blue	9.3	10.5	9.90	Not suitable		░░░░░░░░░░░░░░░░░░░██
12
13	Equivalence pH	8.72						◆
14
15	Suggested indicator	Phenolphthalein	The suitable range whose midpoint is closest to the equivalence pH.
16	Check	OK: at least one indicator is suitable

Showing the first 16 of 18 rows and 8 of 8 columns. Cells with formulas show the formula on hover.

	A
1	Acid-base titration curve calculator
2	Notes: what this workbook does, how to use it and the method behind it.
3
4	What it does
5	Calculates the pH curve of an acid-base titration: a strong or weak acid in the flask, sodium hydroxide in the burette.
6	Gives the equivalence volume, the pH at equivalence and at half-equivalence, and a 120-row curve table with regions, pH bars, slopes and the steepest step.
7	Tests six indicators against the equivalence pH and suggests the one whose transition range is closest to it.
8
9	How to use it
10	1. On the Setup tab, choose Strong acid or Weak acid in B5, then enter the analyte name, concentration (B8) and volume (B9).
11	2. Enter the NaOH concentration (B10), the volume step (B11), Kw (B12) and, for a weak acid, the Ka (B7).
12	3. Read the input check in B28. Fix any message before you use the results.
13	4. Read the tiles and the sampled curve on the Dashboard. The region summary is on the same tab.
14	5. Use the Curve tab for every volume and the Indicators tab to compare the ranges with the equivalence pH.
15
16	Formulas and method

Showing the first 16 of 38 rows and 1 of 1 columns. Cells with formulas show the formula on hover.

What does this template do?

This workbook calculates the pH curve of an acid-base titration. Choose a strong acid or a weak acid, then enter the analyte concentration and volume, the concentration of the sodium hydroxide titrant, the volume step and, for a weak acid, the Ka. The Curve tab gives the pH at each titrant volume from zero to twice the equivalence volume, with the region of the curve, the slope between neighboring points and the steepest step.

The pH formulas follow standard textbook treatments. A strong acid is solved from the net excess of hydrogen or hydroxide ions, including water through the ion product Kw. A weak acid starts from the quadratic for a weak acid, moves through the Henderson-Hasselbalch buffer region, reaches equivalence through hydrolysis of its conjugate base and finishes with the excess hydroxide. The Indicators tab tests six common indicators against the equivalence pH and suggests the one whose transition range is closest to it.

The example is 0.100 M acetic acid with a Ka of 1.8E-5, 25.00 mL, titrated with 0.100 M sodium hydroxide. The Dashboard shows the equivalence volume, the pH at equivalence and at half-equivalence, sampled pH bars and a summary of the regions.

What’s inside

pH at every titrant volume for a strong acid or a weak acid, computed from the moles of base added
Equivalence volume, pH at equivalence and pH at half-equivalence, with pKa calculated from Ka
Each curve row labeled as buffer, equivalence, excess base or acid excess, with a pH bar
Slope between points and a flag on the steepest step of the curve
Six indicators with transition ranges, a suitability check and a range bar on a 0 to 14 scale

Which tabs does the workbook have?

Tab	What it holds
Dashboard	Headline tiles, the sampled pH curve, the indicator ranges on a 0 to 14 scale and a summary of the regions.
Setup	Titration type, concentrations, volumes, Ka, Kw and the derived equivalence values, with an input check.
Curve	One row per titrant volume: moles added, region, pH, pH bar, marker, slope and the steepest step.
Indicators	Six indicators with their transition ranges, a suitability check against the equivalence pH and a range bar.
Notes	What the workbook does, the method, assumptions and limits.

What formulas does this template use?

This template holds 1,775 formulas in 1,965 cells across 5 tabs, so 90% of its cells calculate. They use 16 distinct functions; the longest formula is 557 characters and 1,349 of them read from another tab.

Function	Uses	What it does
`IF`	3,307	one result when a test is true, another when false
`MAX`	530	largest value
`ABS`	488	absolute value
`LOG10`	484	base-10 logarithm
`SQRT`	363	square root
`ROUND`	259	rounds to a number of digits
`REPT`	184	repeats text
`MIN`	160	smallest value
`OR`	125	true when any test is true
`INDEX`	66	value at a position in a range
`AND`	8	true when every test is true
`MATCH`	6	position of a value in a range

The 12 most used of 16 functions. Counted from the workbook itself. Only functions that Excel, LibreOffice Calc, Google Sheets and Apple Numbers evaluate the same way are used, so the formulas survive every download format.

How do you use it?

On the Setup tab, choose Strong acid or Weak acid and enter the analyte name, concentration and volume.
Enter the NaOH concentration, the volume step, Kw at 25 °C and, for a weak acid, the Ka.
Read the equivalence volume and the pH values in the tiles at the top of the Dashboard.
Check the input check on the Setup tab. It names the first problem it finds, or shows OK.
Use the Curve tab for every volume, and the Indicators tab to compare ranges with the equivalence pH.

What is it good for?

Estimating the equivalence volume and the endpoint pH before a titration
Teaching how the pH curve of a strong acid differs from that of a weak acid
Choosing an indicator whose transition range contains the equivalence pH
Checking a hand calculation of pH at a chosen titrant volume

Questions about this sheet

Why is the pH at half-equivalence equal to the pKa?

At half-equivalence the concentrations of the weak acid and its conjugate base are equal, so the Henderson-Hasselbalch equation gives a pH equal to the pKa. The Setup tab calculates it from Ka.

Does the workbook handle polyprotic acids?

No. It treats the analyte as a mono-protic acid, so one mole of NaOH reacts with one mole of acid. Diprotic and triprotic acids need their own equilibrium calculation.

Why does a strong acid curve show Acid excess before equivalence?

A buffer exists only for a weak acid. Before equivalence a strong acid solution holds unreacted strong acid, so those rows are labeled Acid excess.

What if the equivalence volume is not on a curve row?

The equivalence KPIs stay exact. The curve has no row at equivalence, so the Equivalence region and the markers do not appear, and the input check says so.