administration student task rubric student work technical quality
Acid-Base Titration

Grade 9-12 Performance Task
Developed by: New York State Education Department (NYSED)
University of Buffalo and NORC (1991, revised 1993)

Task-Specific Scoring Criteria for Chemistry Task #1: Acid Base Titration


1. Statement of hypothesis Not required for this task
- Effect linked to variable  
- Directionality of effect  
- Expected effect/change  
- Independent variable  
- Dependent variable  
2. Procedures for investigation  
- Detailed procedure/experimentally feasible Method includes details which will clearly result in accurate determination of concentration of unknown, including steps below and repeated trials.
- Sequence to plan Suggests method to determine molarity of unknown solution
- General strategy First identifies unknown solution as an acid or base using appropriate indicator, then suggests titration using neutralizing solution.
- Safety procedures Safety goggles should be worn; care in handling acids and bases.
- Use of equipment/diagram Appropriate equipment and materials are suggested, especially use of burette and indicator.
3. Plan for recording and organizing observations/data  
- Space for manipulation of data or qualitative description Could include space for averaging data; stipulation of indicator used.
- Matched to plan Plan is comprehensive so that all observations and data generated by plan may be recorded; e.g., space for repeated trials is included.
- Organized sequentially Organized so that recording follows data as generated.
- Labelled fully (units included) All columns and rows are identified; correct units of measurement are used.
- Variables identified Solution used to titrate unknown is indicated as acid or base.



4. Quality of observations/data  
- Consistent data At least two trials are consistent with expectations.
- Accurate measurements, observations Measurements are +/- 3.0 mL
- Completed data table All trials performed and data recorded.
- Correct units Volumes labelled as mL or L.
- Qualitative description Indicator is identified.
5. Graph Not required for this task.
- Curve is appropriate to data trend  
- Points plotted accurately  
- Appropriate scale  
- Axes labelled with variabls  
- Variables placed on correct axes  
6. Calculations  
- Calculated accruately Calculations are complete and mathematically correct.
- Substituted correctly into relationship Moles of neutralizing solution are used to find molarity unknown solution.
- Relationship stated or implied Volume of neutralizing solution is converted to moles.
- Units used correctly mL correctly converted to L.
- Use all data available Calculations are performed on all generated data; reason stated if data is excluded.
7. Conclusion  
- Consistent with scientific principle Conclusion based on student's data is consistent with identity and concentration of unknown solution.
- Sources of error *
- Consistent with data Unknown solution is identified as an acid or a base and concentration is determined, based on student's data.(1)
- Relationship among variables stated Unknown solution is neutralized by acid or base used as titrating solution.
- Variables stated in conclusion Unknown and acid or base (neutralizing solution) are mentioned here.

* These elements were not scored in this task; a "holistic" scoring approach was utilized so that the other four elements had a total value of 5 points.

(1) Conclusion may not accurately reflect identity or concentration of unknown solution, but if conclusion is a reasonable reflection of student's work, a point should be given.


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