IB CHEMISTRY PRACTICAL GUIDE (from UWCSEA Chemistry Dept)

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IB CHEMISTRY PRACTICAL GUIDE (from UWCSEA Chemistry Dept) Powered By Docstoc
					  IB CHEMISTRY
Internal Assessment
 STUDENT GUIDE
                                                          INTERNAL ASSESSMENT (IA)

Introduction

The Internal Assessment (IA) consists of an interdisciplinary project, a mixture of short- and long-term investigations (such as practicals and
subject-specific projects). Student work is internally assessed by the teacher and externally moderated by the IBO. The performance in IA at both
higher level and standard level is judged against assessment criteria each consisting of achievement levels 0–3.

IA Time Allocation

Higher level students are required to spend 60 hours, and SL students 40 hours, on practical activities (excluding time spent writing up work). These
times include 10 to 15 hours for the group 4 project. Only 2–3 hours of investigative work can be carried out after the deadline for submission of
work to the moderator and still be counted in the total hours for the practical scheme of work.

Criteria and Aspects

There are eight assessment criteria which are used to assess the work of both higher level and standard level candidates.
    planning (a)—Pl (a)
    planning (b)—Pl (b)
    data collection—DC
    data processing and presentation—DPP
    conclusion and evaluation—CE
    manipulative skills—MS
    personal skills (a)—PS (a)
    personal skills (b)—PS (b)


Each candidate must be assessed at least twice on each of the eight criteria. The two marks for each of the criteria are added together to determine
the final mark out of 48 for the IA component. This will then be scaled at IBCA to give a total out of 24%.

Each of the assessment criteria can be separated into two or three aspects. Descriptions are provided to indicate what is expected in order to meet
the requirements of a given aspect completely (c) and partially (p). A description is also given for circumstances in which the requirements are not
satisfied, not at all (n)
                                                                  IB Chemistry Internal Assessment

Name:_________________________________________________________                                 Date(s):_____________________     Number of Hours:___________
Title of Experiment: _______________________________________________                           Topic:_____________________________________________________

        Criteria                                                                   Aspect                                                                           Matrix   Level
Planning A            Identifies a focused problem or           Relates the hypothesis or prediction directly to     Selects the relevant independent and     ccc 3 cpn 1
                      research question                         the research question and explains it                controlled variables                     ccp 2 cnn 1
                                                                                                                                                              ccn 2 ppn 1
                                                                                                                                                              cpp 2 pnn 0
                                   C P N                                         C P N                                              C P N                     ppp 1 nnn 0
Planning B            Selects appropriate materials             Describes a method that allows for the control       Describes a method that allows           ccc 3 cpn 1
                                                                of the variables                                     collection of sufficient relevant data   ccp 2 cnn 1
                                                                                                                                                              ccn 2 ppn 1
                                                                                                                                                              cpp 2 pnn 0
                                    C P N                                         C     P      N                                   C P N                      ppp 1 nnn 0
Data Collection       Records appropriate raw data (qualitative and/or quantitative),       Presents raw data clearly, allowing for easy interpretation       cc 3 pp 1
                      including units and uncertainties where necessary                                                                                       cp 2 pn 0
                                                C P N                                                             C P N                                       cn 1 nn 0
Data Processing and   Processes the data correctly                                      Presents processed data appropriately, helping interpretation         cc 3 pp 1
Presentation                                                                            and, where relevant, takes into account errors and uncertainties      cp 2 pn 0
                                                  C P N                                                           C P N                                       cn 1 nn 0
Conclusion and        Gives a valid conclusion based on the     Evaluates procedure(s) and results including     Identifies weaknesses and states             ccc 3 cpn 1
Evaluation            correct interpretation of the results,    limitations and errors                           realistic suggestions to improve the         ccp 2 cnn 1
                      with an explanation where appropriate,                                                     investigation                                ccn 2 ppn 1
                      compares results with literature values                                                                                                 cpp 2 pnn 0
                                    C P N                                         C P N                                          C P N                        ppp 1 nnn 0
Manipulative Skills   Is competent and methodical in the use of techniques and           Follows the instructions accurately, adapting to new                 cc 3 pp 1
                      equipment, and pays attention to safety issues                     circumstances (seeking assistance when required)                     cp 2 pn 0
                                                  C P N                                                             C P N                                     cn 1 nn 0
Personal Skills (A)   Collaborates with others, recognizing     Expects, actively seeks and acknowledges the Exchanges ideas with others,                     ccc 3 cpn 1
                      their needs, in order to complete the     views of others                                    integrating them into the task             ccp 2 cnn 1
                      task                                                                                                                                    ccn 2 ppn 1
                                                                                                                                                              cpp 2 pnn 0
                                   C P N                                           C P N                                           C P N                      ppp 1 nnn 0
Personal Skills (B)   Approaches the investigation with self-   Pays considerable attention to the authenticity      Pays attention to the environmental      ccc 3 cpn 1
                      motivation and follows it through to      of the data and information, and the approach        impact of the investigation              ccp 2 cnn 1
                      completion                                to materials (living or non living)                                                           ccn 2 ppn 1
                                                                                                                                                              cpp 2 pnn 0
                                   C     P    N                                   C     P      N                                   C     P     N              ppp 1 nnn 0
                                                                                                                               IB Chemistry IA Student Guide


                                                            Laboratory Report Format

Typed Report essentials
   (Top-left)                                           (Top-right)                                              (Center)
    Name                                                Date( month/ day/ year)                                 Title of Experiment
    Topic                                               Number of Hours

Planning (A)
     Research Question
     Hypothesis                                                                    Samantha Smith                                       February 2, 2005
     Variables                                                                     Stoichiometry                                        2 hours

                                                                                                                 HYDRATES
Planning (B)                                                                        Problem:
     Materials/ Apparatus                                                          Hypothesis:
     Procedure                                                                     Variables:
                                                                                    Materials/ Apparatus:
     Diagram of set-up                                                             Procedure:
                                                                                    Data and Observations:
Data Collection                                                                     Calculations:
    Observations                                                                   Graphs:
                                                                                    Diagrams:
    Data Table                                                                     Conclusion and Evaluation:

Data Processing and Presentation
    Calculations
    Graphs
    Diagrams

Conclusion and Evaluation
    Conclusion
    Evaluation of procedure
    Weaknesses and realistic suggestion to improve experiment



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PLANNING A
                  Aspects                                                             Comments
Identifies a focused problem or research      Expect an open-ended problem from the teacher
question.                                     Use the title "research question”
                                              Do not just repeat the teacher’s title
                                              Indicate what specific aspect of the general problem you will be investigating

Relates the hypothesis or prediction          Hypothesis is a testable statement that predicts the relationship of the independent and
directly to the research question and          dependent variables.
explains it, quantitatively where             It should be specific and detailed using scientific knowledge.
appropriate.                                  This should be quantitative if you're hypothesis calls for it. ( For higher level, you may be
                                               expected to go into quantitative details)
                                              Usually in the form “if y is done, then z will occur”
                                              It should be as long as is needed.

Selects the relevant independent and          Independent variable- is the variable that you change
controlled variables.                         Dependent variable- is the variable that responds to what you have already changed
                                              Controlled variables- are the variables that remain the same, the things that you fix in order
                                               to maintain a fair test.




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SAMPLE- Planning A

     The requirements for all aspects of this criterion are fully satisfied. The level of achievement for all aspects is complete.




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PLANNING B
                 Aspects                                                                 Comments
Selects appropriate apparatus or materials.      Include a comprehensive list of everything that you use- apparatus, chemicals, reagents etc.
                                                 Your list must include units, uncertainty, sizes and accurate concentrations
                                                 Draw a detailed diagram of any setup

Describes a method that allows for the           Write the details of a procedure in chronological order – number list or paragraph form.
control of the variables.                        State precisely how you will vary the independent variable
                                                 State how you are going to measure or observe the dependent variable
                                                 Indicate how many replicates will be made.
                                                 It is also important to outline why one approach is taken versus another, if appropriate

Describes a method that allows for the           State clearly and exactly what you will do so that any other student could follow your plan
collection of sufficient relevant data           State what number and range of measurements you will use
                                                 Include how many different and suitable readings you need
                                                 Take into account the fact that you are trying to collect precise and reliable data




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SAMPLE- Planning B

        There is no apparatus listed, but the diagram is well labeled. The level of achievement for aspect 1 is complete. The volume and
concentration of the acid, the volume of water, and the size of the plates are not mentioned. The level of achievement for aspect 2 is partial.
Concentration values should be calculated, and the changes should be carried out so that the volume (and hence the surface exposed to the
electrolyte) does not increase. There is no mention of the number of different concentrations to be
used, or the number of repeat readings. The level of achievement for aspect 3 is partial.




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DATA COLLECTION
               Aspects                                                              Comments
Records appropriate raw data             Record ALL relevant data and observations
(qualitative and/or quantitative),       Include quantitative data (e.g, measurements of temperature, mass, volume, absorbance, pressure
including units and uncertainties         – all with the appropriate units)
where necessary.                         Include qualitative observations (e.g. “the final color at the endpoint was a faint pink”, “during the
                                          reaction, the bromine water changed from being a bright yellow to solution of no color”).
                                         Report any changes in procedure or unusual conditions.
                                         All data recorded should be to the greatest possible number of significant figures that the accuracy
                                          of the equipment allows.
                                         Consider uncertainties and errors in your measurements and deal with it properly ( See Appendix A)

Presents raw data clearly, allowing      Make sure that someone else could understand exactly what your data means.
for easy interpretation                  Do not include deductions/ interpretations/inferences, although you may find it easier to present
                                          deductions and interpretations alongside the observations. If you do this, you must clearly label the
                                          deductions.
                                         Your presentation should be methodical and logical.
                                         All tables, and graphs should be clearly identified and labeled.




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SAMPLE- Data Collection (Qualitative)

       Appropriate qualitative raw data is recorded, but the candidate should also record the colour of the “crusty deposit”, and the colour of the
alcohols. The data is clearly presented and it is easily interpreted. The requirements for all aspects of this criterion are fully satisfied. The level of
achievement is complete.




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SAMPLE- Data Collection (Quantitative)

        Appropriate qualitative and quantitative raw data is recorded, including units and uncertainties. Presentation is well organized and easy to
interpret. The requirements for all aspects of this criterion are fully satisfied. The level of achievement is complete.




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DATA PROCESSING AND PRESENTATION
             Aspects                                                                 Comments
Processes the data correctly               Always process and show your results mathematically in some way (eg. use averages or
                                            calculations with appropriate formula to process your results)
                                           Include analysis of any errors (See Notes on Appendix A) which have been stated in your data
                                            collection.
                                           Convert tabulated data into a graphical form.
                                           Convert drawings into diagrams

Presents processed data                    Quality of layout should be orderly and easy to follow
appropriately, helping interpretation      Use of proper scientific conventions in tables, graphs, etc
and, where relevant, takes into            Label appropriate bar charts, histograms, pie charts or line graphs (using lines of best fit whenever
account errors and uncertainties            relevant).




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SAMPLE- Data Processing and Presentation (Qualitative)

        This DPP is clear, concise, and correct. Uncertainties are indicated. Raw data has been reduced to an easily-interpreted form. Unnecessary
and irrelevant items have been omitted. The choice of format is highly appropriate because it makes it easy to spot patterns (eg the Rate pattern
and the pH pattern).



                                                         Reaction of Metals with Water




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SAMPLE- Data Processing and Presentation (Quantitative)

      The requirements for all aspects of this criterion are fully satisfied. The average volume of the titrant in the second titration should be 0.0406
dm3, and not 0.0405 dm3. Also, exclusion of the first trial should be stated and justified. The level of achievement is complete.




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CONCLUSION and EVALUATION
                Aspects                                                               Comments
Gives a valid conclusion based on         This is where you draw conclusions about the experiment as it relates to your aim and hypothesis
the correct interpretation of the         Use detailed scientific knowledge to explain a valid conclusion given the evidence available from
results, with an explanation where         your results.
appropriate, compares results with        Compare your results with information from books or other sources and indicate the reference
literature values                         Try to identify trends or patterns in the results to backup your conclusion.
                                          Explain how your results support or don’t support your original hypothesis if appropriate.
                                          Calculate percentage error ( See Appendix A)

Evaluates procedure(s) and results        Explain how the equipment might you used and/or the school environments have limited the
including limitations and errors           accuracy of your results.
                                          State how the weaknesses in your method might have contributed to incorrect results.
                                          Clearly state if the systematic errors are larger or smaller than the random errors and if the
                                           experimental result is within the random errors range. ( See Appendix A)
                                          Identify all the main systematic errors and if possible give some evidence for them. (Do not give
                                           trivial errors as this indicates that you are not evaluating the procedure).

Identifies weaknesses and states          Include improvements could you make to your plan to overcome the weaknesses you have
realistic suggestions to improve the       identified
investigation                             State what further investigations would you suggest to test your conclusions or even extend the
                                           inquiry




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SAMPLE 1- Conclusion and Evaluation

        The level of achievement for aspects 1 and 2 of conclusion and evaluation is complete.

                                                  Melting/freezing point of para-dichlorobenzene

Melting point = boiling point = 55.0 ± 0.5°C




Literature value of melting point of para-dichlorobenzene = 53.1°C (Handbook of Chemistry and Physics).




The fact that % difference > % uncertainty means random errors alone cannot explain the difference and some systematic error(s) must be present.

Melting point (or freezing point) is the temperature at which the solid and the liquid are in equilibrium with each other:   . This is the
temperature at which there is no change in kinetic energy (no change in temperature), but a change in potential energy. The value suggests a small
degree of systematic error in comparison with the literature value as random errors alone are unable to explain the percentage difference.

Evaluation of procedure and modifications:

  i.    Duplicate readings were not taken. Other groups of students had % uncertainty > % difference, ie in their case random errors could explain
        the % difference, so repeating the investigation is important.
  ii.   The thermometer—how accurate was it? It should have been calibration. In order to eliminate any systematic errors due to the use of a
        particular thermometer, calibration against the boiling point of water (at 1 atmosphere) or better still against a solid of known melting point
        (close to the sample) should be done.
 iii.   The sample in the test tube was not as large as in other groups. Thus the temperature rises/falls were much faster than for other groups. A
        greater quantity of solid, plus use of a more accurate thermometer (not 0.5°C divisions, but the longer one used by some groups), would
        have provided more accurate results.




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SAMPLE 2- Conclusion and Evaluation


        Sources of accepted values should be indicated. Percentage errors could be calculated, and the similarity of values considered. An
explanation of exothermicity is not needed unless required by the aim. There should be a more specific explanation of errors, including the direction
of systematic errors. The relevance of the high rate could be explained, along with how to obtain better measurements of the maximum
temperatures. The level of achievement for aspect 1 is partial. The level of achievement for spects 2 and 3 is complete.


                                                             Heats of Neutralization




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                                                                     APPENDIX A

                                              ERRORS/ UNCERTAINTIES OF MEASUREMENTS

      It is impossible to perform a chemical analysis that is error free or without uncertainty.
      In everyday usage “error” means a mistake, but in science an “error” is anything that contributes to a measured value being different than
       the “true” value.

Significant Figures/Digits

      digits in a measurement that are certain, plus one digit that is an estimate
      follows certain rules:
            o Non-zero digits are always significant.
            o Any zeros between two significant digits are significant.
            o A final zero or trailing zeros in the decimal portion ONLY are significant.


Web Exercises on Determining Uncertainties: http://antoine.frostburg.edu/cgi-bin/senese/tutorials/sigfig/index.cgi




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TYPES OF ERRORS:
   1. Random errors
         related in taking measurements on imperfect tools (balances, cylinders, etc)
         can be estimated and the degree of error can be calculated.
         are related to insufficiently controlled variations in experimental
           conditions
         Affect precision, but not accuracy
         Cannot be eliminated


   2.    Systematic error
         Usually are related to improper experimental design or adjustment
           of experimental apparatus.
         Sometime related to a particular method.
         These errors systematically distort the observations.
         do not affect precision, and can, in theory, be eliminated.

   Examples :
    Sticking or leaking gas syringes.
    Calibration errors in pH meters.
    Stop clock running low.
    Changes in external influences such as temperature and atmospheric pressure affect the measurement of gas volumes, etc.
    Personal errors such as reading scales incorrectly.
    Unaccounted heat loss.
    Liquids evaporating.

Accuracy
Accuracy can be expressed as a percent error, if the true value is known.




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DEALING WITH UNCERTAINTIES (use of simple calculator or online calculator)

Absolute and Relative Uncertainty

A. Absolute uncertainty is an expression of the uncertainty of a measurement. Usually, it is plus-or-minus the last digit = absolute uncertainty. For
example, 10.20 g ==> implies that the measurement is +/- 0.01 g so, Absolute uncertainty = +/- 0.01 g

B. Relative uncertainty = (absolute uncertainty)/measurement. For example, 10.20 g ==> absolute uncertainty = +/- 0.01 g
relative uncertainty = (0.01 g)/10.20) x 100 = 0.09803 % = 0.001%


Multiple Readings
     If more than one reading of a measurement is made, then the uncertainty increases with each reading. For example:

                                                          Trial           Volume of acid
                                                           1              10.0 +/- 0.1 cm3
                                                           2              10.0 +/- 0.1 cm3
                                                           3              10.0 +/- 0.1 cm3
                                                          Total           30.0 +/- 0.3 cm3

                       So the rule is :
                                           WHEN ADDING OR SUBTRACTING UNCERTAIN VALUES,
                                                 ADD THE ABSOLUTE UNCERTAINTIES


       If a set of data is multiplied or divided, convert the absolute uncertainties to percentage uncertainties and add them together. When finished,
convert the total uncertainty back to an absolute uncertainty:
                                                eg. number of moles = concentration x volume
                                                                        = (0.53 +/- 0.05 mol.dm-3) x (0.50 + 0.01 dm3)
                                                                        = (0.53 +/- 9% mol.dm-3) x (0.50 +/- 2% dm3)
                                                                        = 0.265 +/- 11% mol.
                                                                        = 0.265 +/- 0.029 mol = 0.27 +/- 0.02 mol


                                     WHEN MULTIPLY OR DIVIDING, ADD THE PERCENTAGE UNCERTAINTIES,
                                        CONVERT THE TOTAL % UNCERTAINTY BACK TO AN ABSOLUTE
                                                             UNCERTAINTY

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UNCERTAINTY CALCULATOR

Assume that you wish to use the ideal gas law to calculate the pressure of a gas:




Start up the applet (http://www.colby.edu/chemistry/PChem/scripts/error.html)
and then type the formula into the Equation box, without the equal sign as follows:




After pressing [calculate], the Variables window will be displayed:




Then type in the values for the various parameters and their uncertainties.
For example, you would type in 0.53 for n and 0.02 for the Uncertainty for n.
The program also has available a table of constants and their uncertainties.
Click the mouse in the R Value box, then click on the [Constants] button.
The constants window will be displayed, as shown.




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Clicking on the check box for the line that reads "R =0.08205783" will
automatically enter the value and its uncertainty in the Variables window.
After you type in the values for T and V the Variables window should appear.




Now if you click on the [Calculate] button the final result and its uncertainty will be displayed:




Your final pressure would be 1.282 atm with an uncertainty of ±0.057.


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RESOURCES

http://occ.ibo.org Chemistry Guide, Internal Assessment
http://occ.ibo.org Chemistry Resource by Ruth Sanderson
http://occ.ibo.org Chemistry Resource by Julie Sykes
http://antoine.frostburg.edu/chem/senese/101/measurement/index.shtml
http://www.sbuniv.edu/~ggray/CHE3345/chp5.html
http://home.comcast.net/~christylthomas/aplaberrors.pdf#search='types%20of%20errors%20chemistry'
http://www2.truman.edu/~jmccormi/LabManual/StatisticsFundamentals_files/StatisticsInChemistry.pdf#search='types%20of%20errors%2
0chemistry'
http://www.sciencegeek.net/Chemistry/chempdfs/ch02sigs.pdf#search='RULES%20chemistry%20significant%20figures'
http://dbhs.wvusd.k12.ca.us/webdocs/SigFigs/SigFigRules.html
http://www.colby.edu/chemistry/PChem/scripts/error.html




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