BASE ADDED0.0 mL
PROBE READING—
Begin with the support stand.
Identify the unknown acid.
Add a known base. Find the neutral point. Use your evidence to identify the concentration.
Lab options
Your next action
YOUR MISSION
How concentrated is this acid sample?
Your sample is 20.0 mL of an unknown strong, monoprotic acid. The base is 0.100 M sodium hydroxide. At the neutral point, equal amounts of acid and base have reacted.
Build the apparatus, add base, and use the pH probe to find where the solution changes from acidic to basic. Repeat with three fresh samples from the same unknown.
Acidic: pH < 7Neutral: pH 7Basic: pH > 7
This is a virtual strong-acid/strong-base titration at 25°C. Universal-indicator color is illustrative. A real lab needs appropriate supervision, protective equipment, and its own chemical safety procedure.
What does the neutral point tell us?
In this 1:1 reaction, acid concentration × acid volume = base concentration × base volume at equivalence. The pH changes sharply near this point. You may pass from below pH 7 to above pH 7 without measuring exactly 7.
We estimate the endpoint halfway between the last acidic reading and first basic reading. That interval is your evidence, not an exact reading of neutrality. After 10.0 mL, the dose decreases from 5.0 mL to 0.2 mL to narrow the interval.
Each repeat uses a fresh nominal 20.0 mL sample. Tiny modeled sample-volume and delivery variation, plus pH measurement noise, may shift the estimated endpoint. Repeated results may still agree at the displayed resolution.
Current trial · pH observations
| Base added (mL) | Measured pH | Observation |
|---|
Your repeated trials
| Trial | Lower endpoint bound | Upper endpoint bound | Endpoint estimate |
|---|
3 / EXPLAIN YOUR EVIDENCE
What does the repeated evidence tell you?
Use the average endpoint volume to identify the acid concentration. Then explain why smaller doses helped.
AVERAGE ENDPOINT
ESTIMATED ACID CONCENTRATION
ENDPOINT RANGE
| Trial | Endpoint estimate | Estimated concentration |
|---|
Optional calculation: work it out yourself
Cacid = Cbase × Vbase ÷ Vacid.
Use 0.100 M base, your average endpoint volume, and 20.0 mL acid. Both volumes use mL, so their units cancel. Report concentration to 0.001 M.
Help me explain my results
Measurements from your investigation
These are your recorded model results. Choose the evidence that supports your own conclusion.
- Make a claim.
- Use evidence.
- Explain the science.
- Set a limit.
Before downloading: Does your explanation answer the question, use a number with units, explain why, and state a limit? Revise it above if needed.
This guide does not write or grade your explanation. A teacher reviews your scientific reasoning.
Numerical and multiple-choice checks are automatic. A teacher reviews the scientific quality of your explanation.