Chemistry-only Required Practical 2: measure reacting volumes
| English | 中文 | Pinyin |
|---|---|---|
| titration/taɪˈtreɪʃn/ | 滴定 | dī dìng |
| concordant titres | 相符滴定体积 | xiāng fú dī dìng tǐ jī |
What would explain this observation?
- A burette lets you add acid in small measured steps to a known alkali volume. A suitable indicator shows when to stop; it does not calculate the concentration by itself.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Required Practical 2 determines reacting acid and alkali volumes. A volumetric pipette and filler transfer a known alkali volume into a conical flask. A burette holds the chosen dilute strong acid: hydrochloric, nitric or sulfuric acid in the source scope. Use a suitable indicator, a white tile and swirling. Add dropwise near the end-point and record the delivered volume.
- titration 滴定: A method measuring the volume of one solution needed to react with a measured amount of another; concordant titres 相符滴定体积: Titre results agreeing within the stated practical tolerance.
Which reading gives a titre?
Titre equals final burette reading minus initial reading. Read the appropriate meniscus at eye level, with the burette vertical and the filling funnel removed. A rough trial locates the endpoint; subsequent careful trials supply an accurate mean under the school’s stated concordance rule. Phenolphthalein is pink in alkali and becomes permanently colourless at the handbook’s acid-into-alkali endpoint. Universal indicator is unsuitable for a sharply defined accurate endpoint.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Titre equals final burette reading minus initial reading. Read the appropriate meniscus at eye level, with the burette vertical and the filling funnel removed. A rough trial locates the endpoint; subsequent careful trials supply an accurate mean under the school’s stated concordance rule. Phenolphthalein is pink in alkali and becomes permanently colourless at the handbook’s acid-into-alkali endpoint. Universal indicator is unsuitable for a sharply defined accurate endpoint.
- Perform the actual school-supervised task with approved dilute solutions and eye protection. Rinse apparatus as instructed to avoid unwanted dilution, fill the burette tip and use the pipette’s specified draining method. Never pipette by mouth. Retain initial/final readings, trials, selected mean and exclusion reason. Foundation students measure reacting volumes; concentration determination is the separate Higher extension.
Which two habits make the investigation or model in this case more defensible?
Perform the actual school-supervised task with approved dilute solutions and eye protection. Rinse apparatus as instructed to avoid unwanted dilution, fill the burette tip and use the pipette’s specified draining method. Never pipette by mouth. Retain initial/final readings, trials, selected mean and exclusion reason. Foundation students measure reacting volumes; concentration determination is the separate Higher extension.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: an accurate trial begins at 1.20 cm³ and ends at 19.55 cm³, so titre=18.35 cm³. A second accepted titre is 18.25 cm³; mean=(18.35+18.25)/2=18.30 cm³. The school supplies its acceptable concordance tolerance; this example does not impose a qualification-wide 0.10 cm³ rule.
A trial starts at 2.35 cm³ and finishes at 22.70 cm³. Find the titre. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A trial starts at 2.35 cm³ and finishes at 22.70 cm³. Find the titre.
The result is 20.35 cm³. Known: an accurate trial begins at 1.20 cm³ and ends at 19.55 cm³, so titre=18.35 cm³. A second accepted titre is 18.25 cm³; mean=(18.35+18.25)/2=18.30 cm³. The school supplies its acceptable concordance tolerance; this example does not impose a qualification-wide 0.10 cm³ rule.
Check the conclusion and its limits
- Do not average the rough trial automatically or read only the final burette value. Adding water to the flask does not change the amount of pipetted solute if nothing is lost. Written methods are preparation/review; they do not replace the student’s actual titration performance.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
RP2 reacting-volume technique is Higher-only because some concentration calculations are Higher-only. This claim is false: Do not average the rough trial automatically or read only the final burette value. Adding water to the flask does not change the amount of pipetted solute if nothing is lost. Written methods are preparation/review; they do not replace the student’s actual titration performance.
Chemistry-only Required Practical 2: measure reacting volumes: Titre equals final burette reading minus initial reading. Read the appropriate meniscus at eye level, with the burette vertical and the filling funnel removed. A rough trial locates the endpoint; subsequent careful trials supply an accurate mean under the school’s stated concordance rule. Phenolphthalein is pink in alkali and becomes permanently colourless at the handbook’s acid-into-alkali endpoint. Universal indicator is unsuitable for a sharply defined accurate endpoint.
RP2 reacting-volume technique is Higher-only because some concentration calculations are Higher-only.
Do not average the rough trial automatically or read only the final burette value. Adding water to the flask does not change the amount of pipetted solute if nothing is lost. Written methods are preparation/review; they do not replace the student’s actual titration performance.
A method measuring the volume of one solution needed to react with a measured amount of another: write the technical term.
titration means A method measuring the volume of one solution needed to react with a measured amount of another.