Level 3 Chemistry internal assessment resource



Timaru Girls High School

2015 Assessment

Chemistry Level 3

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Internal Assessment Resource

Achievement Standard Chemistry 91387 v 1: Carry out an investigation in chemistry involving quantitative analysis

Resource reference: Chemistry 3.1A

Resource title: How much Vitamin C?

Credits: 4

|Achievement |Achievement with Merit |Achievement with Excellence |

|Carry out an investigation in chemistry involving |Carry out an in-depth investigation in chemistry |Carry out a comprehensive investigation in chemistry|

|quantitative analysis. |involving quantitative analysis. |involving quantitative analysis. |

Authenticity statement:

The work that I am submitting is genuinely my own work and I have completed this investigation without communication with others or the use of notes to support my investigation.

I understand that cheating of any form may result in exclusion from the assessment or a Not Achieved grade being given.

Student Signature and Date

Final Grade : _____________

Student signature: ____________________ Date: __________________

Teacher Signature:_______________________

Student instructions

Introduction

This activity requires you to investigate the concentration of Vitamin C in fruit juices under different conditions (exposure to UV, effect of temperature, exposure to air, addition of stabilisers etc).

You can plan and carry out the investigation as a group. However, you need to keep your own logbook throughout the investigation, and you must process the data on your own and write an individual report for submission.

You will be assessed on the quality of your investigation, which involves:

• keeping a logbook

• developing and carrying out a procedure to collect data about the concentration of Vitamin C in fruit juice.

• processing the data to reach a conclusion

• discussing the investigation in terms of the procedure used and the reliability of the data

• comprehensively reporting your investigation in a written report.

You have the first 7 weeks of Term Two to plan and research your investigation including carrying out trials. The investigation will be carried out on ____________ June. Please ensure you are available on this date.

Task

In your group, define the purpose of your investigation, conduct background research, and identify how you will ensure safety. The purpose should include exploring a possible trend or pattern in the quantity of Vitamin C in fruit juice. Then plan your practical work and conduct some trials to refine your method. Each member of the group should collect and record data for at least one of the independent variables. All data should then be collected together and shared with the group. Finally, you must individually process the group data and write your report.

Please note the following milestone dates:

Milestone 1: Aim. Research, hypothesis and sampling plan due: 5th June

Milestone 2: Sample calculations due: __________

Report due: 24th July (end of Week 1 Term 3) – may be emailed or hand written.

Your report should include the following sections:

• purpose

• description of procedure – include a description of how significant variables are controlled, the preparation of samples, and any modifications made to the method during the course of the investigation

• results

• conclusion

• discussion – an evaluation of the whole investigation that considers:

– an evaluation of the reliability of data by considering the procedure used and possible sources of error

– reasons for any modifications made to the original method

– the accuracy and reliability of the data collected

– comments on the significance and validity of the conclusion

– links between conclusion(s) and chemical principles and/or real life applications

• bibliography – an acknowledgement and identification of sources of information.

A method used to measure the concentration of Vitamin C in solution is given in Resource A.

Resource A

(from )

Determination of Vitamin C by Redox Titration with Iodate

Introduction

This method determines the vitamin C concentration in a solution by a redox titration with potassium iodate in the presence of potassium iodide. Vitamin C, more properly called ascorbic acid, is an essential antioxidant needed by the human body (see additional notes).

When iodate ions (IO3-) are added to an acidic solution containing iodide ions (I-), an oxidation-reduction reaction occurs;

- the iodate ions are reduced to form iodine

IO3- + 6 H+ + 5 e- --> ½ I2 + 3 H2O

- while the iodide ions are oxidised to form iodine.

2 I- --> I2 + 2 e-

Combining these half-equations demonstrates the reaction between iodate and iodide

IO3- + 5 I- + 6 H+ --> 3 I2 + 3 H2O

It is the iodine formed by this reaction that oxidises the ascorbic acid to dehydroascorbic acid as the iodine is reduced to iodide ions.

ascorbic acid + I2 --> 2 I- + dehydroascorbic acid

Due to this reaction the iodine formed is immediately reduced to iodide as long as there is any ascorbic acid present. Once all the ascorbic acid has been oxidised, the excess iodine is free to react with the starch indicator, forming the blue-black starch-iodine complex. This is the endpoint of the titration.

The method is suitable for use with Vitamin C tablets, fresh or packaged fruit juices and solid fruits and vegetables.

NB: This method is really the same as titrating ascorbic acid directly with iodine solution (see Vitamin C Method using Iodine). However, this method is more reliable as the potassium iodate solution is more stable than iodine as a primary standard.

Method

To download a printable version of the senior school experiment (in pdf format) use the link below.

Vitamin C Titration with Iodate (PDF 189Kb)

Assessment schedule: Chemistry 91387: Is your pool sterile?

|Evidence/Judgements for Achievement |Evidence/Judgements for Achievement with Merit |Evidence/Judgements for Achievement with Excellence |

|The student carries out an investigation in chemistry involving |The student carries out an in-depth investigation in chemistry |The student carries out a comprehensive investigation in chemistry |

|quantitative analysis. They do this by: |involving quantitative analysis. They do this by: |involving quantitative analysis. They do this by: |

|carrying out an investigation into the concentration of sodium |carry out a quality investigation into the concentration of sodium |carry out and comprehensively evaluate an investigation into the |

|hypochlorite leading to a conclusion |hypochlorite leading to a conclusion |concentration of sodium hypochlorite leading to a conclusion. |

|keeping a logbook and producing a report |keeping a logbook and produce a report |keeping a logbook and produce a report |

|The student: |The student: |The student: |

|develops a purpose |carries out trials |accurately processes the data and uses appropriate significant |

|includes a description of the procedure that includes preparation of |controls significant variables |figures |

|samples and the analytical technique used |has five values for the independent variable |elaborates on reasons for any modifications to procedure |

|has four values for the independent variable |describes their method in sufficient detail to enable it to be |justifies how the processed data supports the conclusion(s) |

|includes a summary of the collected and processed data |duplicated |evaluates the reliability of the data by considering the procedure |

|makes a conclusion based on processed data. |standardises standard solution(s) |used and sources of error |

| |shows the mathematical steps used to process the data |links the conclusion(s) to chemical principles and/or real life |

| |makes a valid conclusion relevant to the purpose of the investigation|applications. |

| |explains how the procedure used contributed to the collection of | |

| |quality data. | |

Final grades will be decided using professional judgement based on a holistic examination of the evidence provided against the criteria in the Achievement Standard.

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