How to Find pH from a Titration Curve

Updated 6 November 2026 · Standard formula, shown below

This guide explains how to read a pH titration curve to determine the pH at any point during a titration, including the equivalence point and buffer regions. You will learn to identify key features on the graph and calculate or estimate pH values accurately. No prior knowledge beyond basic acid-base chemistry is required.

What You’ll Need

A titration curve (graph of pH vs. volume of titrant added)
A ruler or straight edge
A pencil (for drawing tangent lines)
Access to the original data (optional, for precise calculations)

Step-by-Step

Identify the axes. The x-axis is the volume of titrant (usually in mL) added from the burette. The y-axis is the pH of the solution. Each point on the curve represents the pH after a specific volume of titrant has been added.
Locate the equivalence point. This is the steepest part of the curve—where the pH changes most rapidly per drop of titrant. It appears as a nearly vertical section. For a strong acid-strong base titration, this point is at pH 7. For weak acid-strong base, it is above 7; for strong acid-weak base, it is below 7. Mark this point on the curve.
Find the half-equivalence point (if applicable). For a weak acid or weak base, the half-equivalence point is at half the volume of titrant needed to reach the equivalence point. Locate this volume on the x-axis, then read the corresponding pH on the y-axis. At this point, pH = pKa (for an acid) or pOH = pKb (for a base). This gives you the acid dissociation constant.
Read the initial pH. The pH at volume = 0 mL is the pH of the original solution before any titrant is added. This is the starting point of the curve.
Determine pH at any specific volume. Choose a volume on the x-axis (e.g., 15 mL). Draw a vertical line up to the curve, then a horizontal line to the y-axis. The value where it hits the y-axis is the pH at that volume. This is the most direct method for any point on the curve.
For points before the equivalence point (buffer region). If the solution contains a weak acid and its conjugate base, use the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]). You can find pKa from the half-equivalence point (step 3). The concentrations can be calculated from the initial moles and the volume of titrant added.
For the equivalence point itself. The pH is the pH of the salt solution formed. For a strong acid-strong base, it is 7. For a weak acid-strong base, the salt is basic, so pH > 7. Calculate it using the Kb of the conjugate base and the concentration of the salt.
For points after the equivalence point. The pH is determined by the excess strong acid or strong base added. Calculate the moles of excess titrant, divide by the total volume, and find pH (for strong base) or pOH (for strong acid) directly.
Use the first derivative (if you have data). If you have a table of pH vs. volume, calculate the change in pH divided by the change in volume (ΔpH/ΔV). The maximum of this derivative corresponds to the equivalence point. This is more precise than eyeballing the steepest part.
For a polyprotic acid. There will be multiple equivalence points and multiple half-equivalence points. Each half-equivalence point gives a different pKa. The pH at any point is found using the same methods, but you must consider which acid species is dominant.

Common Mistakes

Confusing equivalence point with endpoint. The equivalence point is where moles of acid = moles of base (theoretical). The endpoint is where the indicator changes color (practical). They are not always exactly the same.
Misreading the half-equivalence point. Make sure you use half the volume of the equivalence point, not half the pH. For example, if the equivalence point is at 40 mL, the half-equivalence point is at 20 mL, not at pH 7.
Forgetting to account for dilution. When calculating concentrations from the curve, remember that the total volume increases as titrant is added. Use the total volume (initial + added) in your calculations.
Assuming pH is linear. The titration curve is not a straight line except in the steep region. Do not interpolate linearly between points; use the curve’s shape.
Ignoring temperature. pH is temperature-dependent. The curve is valid only at the temperature at which it was recorded. If you need pH at a different temperature, you must correct for it.

Tips

Use a large, clear graph. If you are working from a printed curve, use a ruler to draw precise lines. If using software, zoom in on the equivalence point for accuracy.
Draw tangent lines. To find the equivalence point precisely, draw two tangent lines along the relatively flat parts of the curve before and after the steep rise. Then draw a line that bisects the angle between them. The point where this bisector crosses the curve is the equivalence point.
Check the shape. A strong acid-strong base curve has a very sharp, vertical jump. A weak acid-strong base curve has a less steep jump and a buffer region (a flatter section) before the jump. This helps you identify the type of titration.
Use the data table. If you have the raw data, use it to calculate pH more accurately than reading from a graph. The graph is a visual aid; the data is the source of truth.
Remember the pH scale. pH ranges from 0 to 14, but the curve may not span the entire range. Always check that your readings are within the plotted range.

Troubleshooting

The curve does not have a clear vertical section. This may indicate a very weak acid or base, or a very dilute solution. In such cases, the equivalence point is less distinct. Use the first derivative method (step 9) to find the inflection point.
The pH you read seems off. Double-check that you are reading the correct axis. Also, ensure you are using the correct scale (e.g., pH vs. mL, not pH vs. drops). If using drops, convert to mL using the drop factor (e.g., 20 drops/mL).
You have multiple equivalence points. For polyprotic acids, you will see multiple jumps. Label each one and treat them separately. The first jump corresponds to the first proton, the second to the second proton, etc.
Your calculated pKa does not match the literature. This could be due to temperature differences, ionic strength effects, or a misread half-equivalence point. Re-check your volume reading. Also, ensure you are using the correct pKa for the specific acid (e.g., acetic acid has pKa ≈ 4.76 at 25°C).
The curve is not smooth. This may be due to poor mixing or slow pH electrode response. If you are generating the curve, allow sufficient time for the pH to stabilize after each addition. If you are analyzing a given curve, use the overall trend rather than individual noisy points.

Frequently Asked Questions

How do I find the pH at the equivalence point?

Read the pH value on the y-axis that corresponds to the volume of the equivalence point on the x-axis. For a strong acid-strong base, it is 7. For a weak acid-strong base, it is above 7 (e.g., around 8-9 for acetic acid). For a strong acid-weak base, it is below 7.

What is the half-equivalence point and why is it important?

It is the point where half of the acid (or base) has been neutralized. At this point, the concentrations of the acid and its conjugate base are equal, so pH = pKa. This allows you to determine the acid dissociation constant (Ka) from the curve.

Can I find pH without a calculator?

Yes, for reading from the graph, you can estimate the pH by eye. For calculations, you may need a calculator for logarithms. However, the graph itself provides a direct visual answer for any volume.

What if the titration curve is for a diprotic acid?

You will see two equivalence points and two half-equivalence points. Each half-equivalence point gives a different pKa. To find pH at any point, determine which region you are in (first buffer, first equivalence, second buffer, second equivalence, excess base) and apply the appropriate formula.

How does temperature affect the pH on the curve?

pH is temperature-dependent because the dissociation constants (Ka, Kw) change with temperature. A curve recorded at 25°C is not valid at 50°C. If you need pH at a different temperature, you must either record the curve at that temperature or correct the pH values using known temperature coefficients.

Is the pH at the equivalence point always 7?

No. Only for a strong acid titrated with a strong base (or vice versa) is the equivalence point pH exactly 7. For weak acids or bases, the salt formed hydrolyzes, making the solution slightly acidic or basic.

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.