Marking guidelines Dilution Marks Correctly states appropriate use of glassware and that dilution is made with deionized or distilled water 2 States that pipette must be rinsed with vinegar prior to use States appropriate use of glassware and dilution made with deionized or distilled water OR 1 States that pipette must be rinsed with vinegar prior to use Titration - method States correct outlining the indicator used. Includes the rinsing of the burette with standard solution, the correct volumes and terms for glassware. Explains that the experiment is repeated 3 until consistent titres are achieved. Ensures steps are in logical sequence. 2 One of the above is omitted. Two of the above are omitted. 1 Titration - indicator States that the titration is between strong base and weak acid therefore end point is in basic region. 2 ID phenolphthalein as an indicator that changes in Basic solution pH >8. States that the titration is between strong base and weak acid therefore end point is in basic region. 1 OR ID phenolphthalein as an indicator that changes in Basic solution pH >8. Results has appropriate headings, all data in the table, units are in the headings of each column, 3- 4 more than two titres, two concordant titres, average of concordant titres shown, organised and well set out allowing easy access of data. Some data in table, data organised with some missing, at least two sets of results shown. 1-2 Calculations a) – Answer shows correct calculations, consistent use of significant figures, uses the average of the 2 concordant titres and has consistent and correct units. 1 One of the above is omitted. Calculations b) – Answer shows correct calculations, consistent use of significant figures, uses the average of the 2 concordant titres and has consistent and correct units. One of the above is omitted. 1 Analysis - errors Identifies two appropriate errors such as inaccuracy in transferring aliquots, parallax error in 2 reading burette, not rinsing burette with NaOH solution before filling, not washing drops of NaOH solution off side of conical flask or end of burette, not rinsing conical flask with distilled water.
Marking guidelines Dilution Marks Correctly states appropriate use of glassware and that dilution is made with deionized or distilled water States that pipette must be rinsed with vinegar prior to use 2 States appropriate use of glassware and dilution made with deionized or distilled water OR States that pipette must be rinsed with vinegar prior to use 1 Titration - method States correct outlining the indicator used. Includes the rinsing of the burette with standard solution, the correct volumes and terms for glassware. Explains that the experiment is repeated until consistent titres are achieved. Ensures steps are in logical sequence. 3 One of the above is omitted. 2 Two of the above are omitted. 1 Titration - indicator States that the titration is between strong base and weak acid therefore end point is in basic region. ID phenolphthalein as an indicator that changes in Basic solution pH >8. 2 States that the titration is between strong base and weak acid therefore end point is in basic region. OR ID phenolphthalein as an indicator that changes in Basic solution pH >8. 1 Results has appropriate headings, all data in the table, units are in the headings of each column, more than two titres, two concordant titres, average of concordant titres shown, organised and well set out allowing easy access of data. 3- 4 Some data in table, data organised with some missing, at least two sets of results shown. 1-2 Calculations – a) Answer shows correct calculations, consistent use of significant figures, uses the average of the concordant titres and has consistent and correct units. 2 One of the above is omitted. 1 Calculations – b) Answer shows correct calculations, consistent use of significant figures, uses the average of the concordant titres and has consistent and correct units. 2 One of the above is omitted. 1 Analysis - errors Identifies two appropriate errors such as inaccuracy in transferring aliquots, parallax error in reading burette, not rinsing burette with NaOH solution before filling, not washing drops of NaOH solution off side of conical flask or end of burette, not rinsing conical flask with distilled water. 2
chemistry-stage-6-year-12-assessment-task-and-marking-guidelines-titration-prac-exam.docx