Teach lesson
Titration: endpoint, stoichiometry, and uncertainty
Students use the Acid-Base Titration remote lab to estimate an endpoint, calculate titratable/equivalent acidity with the guide's 1:1 model, and justify uncertainty from real pH-volume data.
Sign in with an educator account to prepare a class session. Students join with a class code.
New to LabsLand? Create your teacher account
Learning Outcomes
Identify titrant, analyte, indicator, endpoint, and equivalence-point evidence in a titration.
Use the remote lab to collect or cite pH-volume rows around the endpoint.
Choose an endpoint volume from indicator and pH-curve evidence.
Calculate the titratable/equivalent acidity of an unknown citric-acid solution using the high-school guide's 1:1 model.
Explain uncertainty in the endpoint choice and final titratable/equivalent-acidity result.
Write a claim that includes method, evidence, calculation, units, and limitations.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
Frame the titration model
8 min
In this remote lab, a known sodium hydroxide solution is added drop by drop to an unknown citric-acid solution. Phenolphthalein is the indicator: it is colorless in acidic solution and turns pink in the basic range. The pH sensor and volume readout give a second way to judge where the endpoint occurs.
The goal is not just to calculate a number. Your job is to decide which endpoint volume is justified by the evidence, then use that volume carefully.
Acid-base titration remote lab
This capture illustrates the apparatus and type of readout. The example values shown literally on the display, pH 8,35 and volume (Volumen) 13.750 mL, belong to a different run and are not data for this activity; use only its evidence rows.
In this lab, what is the titrant?
What does phenolphthalein help you detect in this titration?
Before opening the lab, predict the shape of the pH curve as NaOH is added. Include what should happen before, near, and after the endpoint.
Reference pH curve
This source-backed figure is the teacher-checked fallback graph used with the nine supplied rows when the runtime is unavailable. The curve changes rapidly near 5.16–5.20 mL; when you collect live data, focus on rows around that jump.
Plan an endpoint decision
8 min
The lab does not simply announce the correct endpoint. You must decide it from the color endpoint, the pH curve, and the rows around the rapid change. A defensible endpoint is better than a falsely precise one.
Remote lab workflow
Use the exact verified configuration citrico#1 with 0.065M_NaOH throughout the run.
Which endpoint decision is most defensible?
Write a 3–5 sentence plan. Include the solution and titrant you will use, which rows you will record near the jump, the exact fallback if the runtime is unavailable, and how you will decide the endpoint volume.
Collect and organize evidence
24 min
If the experiment has been confirmed to work, open it with the verified citric-acid sample and sodium hydroxide titrant and add drops until the endpoint region is visible. Record rows before, during, and after the rapid pH change. If it is unavailable or time is short, use exactly the nine supplied rows without adding, replacing, or altering data, together with the displayed Reference pH curve (fig_curve), and label their source clearly.
For the compact 45-minute option, use exactly the nine supplied starter rows and the displayed Reference pH curve (fig_curve) as the teacher-checked graph. Do not add, replace, or alter rows, and do not create a new graph. For the 60-minute option, collect or download your own rows and create or attach your own graph only after the experiment has been confirmed to work. If it does not load or run, do not invent data: use exactly the nine supplied rows and fig_curve, then continue the analysis.
Open the Acid-Base Titration lab
Choose the only verified configuration for this activity:
citrico#1and0.065M_NaOH.If the experiment does not load or run, do not invent data. Use exactly the nine supplied reference rows without adding, replacing, or altering data and use
fig_curveas the teacher-checked graph, then continue with the analysis.If the experiment is working, start the run and observe the initial acidic pH.
Add drops and wait for each stabilized reading.
Record NaOH volume and pH, especially near the color change and rapid pH jump.
If a download button is available, download the spreadsheet and check the rows near the jump.
If the raw table shows the incorrect Spanish headings
Tiempo,Temperatura, andConductividad, do not interpret them literally: after#, the first numeric value in each row is volume in mL and the second is pH. Check this mapping against the pH-versus-volume graph axes and the equipment display.Mark whether each row comes from your own run, a classmate, or a teacher-provided reference row.
Titration pH-volume evidence
When live collection works, record at least nine genuine rows before and after the rapid pH change. Otherwise, use exactly the nine supplied rows without adding, replacing, or altering data. Use mL for NaOH volume and mark the source of each row.
| NaOH volume mL | pH | Color / signal | Run/source | Endpoint note |
|---|---|---|---|---|
pH curve or graph evidence
In the compact option, reference the displayed Reference pH curve (fig_curve) as the teacher-checked graph; do not create a new one. In the 60-minute option, attach or reference your own pH-versus-volume graph or spreadsheet only when the experiment is working; otherwise, reference fig_curve. If your evidence is a screenshot, attach it as an image reference rather than as a file upload.
Estimate endpoint and titratable/equivalent acidity
12 min
The reference endpoint is around 5.16-5.20 mL for citric acid #1 with 0.065 M NaOH. You may choose a value in that region if your evidence supports it. Your explanation matters as much as the number.
Endpoint calculation model
The published high-school guide uses a simplified 1:1 model that yields titratable/equivalent acidity, not molecular citric-acid concentration. Your teacher may adapt the stoichiometry for an advanced course.
High-school guide model
[\text{equivalent acid}]\,V_{\text{aliquot}}=[\text{NaOH}]\,V_{\text{NaOH}}
Which row region best supports the endpoint choice for the demo-supported run?
Estimate the endpoint volume in mL from the pH/color evidence. Enter a value in mL, then explain which rows or graph feature support it.
Use [equivalent acid] * V_aliquot = [NaOH] * V_NaOH with V_aliquot = 10.00 mL, [NaOH] = 0.065 mol/L, and your endpoint volume. Enter the titratable/equivalent acidity from the guide's 1:1 model in mol/L, then show the substitution.
Make and qualify the claim
8 min
Your final answer should sound like a careful chemist: clear method, measured endpoint, calculation, units, and uncertainty.
Name two sources of uncertainty in this titration and explain how each could affect the endpoint volume or calculated titratable/equivalent acidity.
Write your final claim. Include: (1) the endpoint volume you chose, (2) the titratable/equivalent acidity calculated with the guide's 1:1 model, with units, (3) at least two pieces of evidence from the table or graph, and (4) one limitation or uncertainty.
Optional extension
15 min
Use this only if your teacher assigns the longer version.
The activity guide describes using the first derivative, ΔpH/ΔV, to estimate the equivalence point. How would this method use your table, and why might it be more precise than only watching the color change?
Turn this preview into a live class session
Continue to LabsLand Teach to use this lesson with your students and review the access available to your account.
New to LabsLand? Create your teacher account