HANDOUT ON PLANNING AND DESIGNING
(With special reference to CXC Chemistry)
WHAT IS PLANNING AND DESIGNING
According to the CXC syllabus, it is the ability to develop hypotheses to test them; plan and execute experimental
procedures and operations in appropriate sequence; use controls where appropriate; modify original plan or sequence of
operations as a result of difficulties encountered in carrying out experiments or obtaining unexpected results.
It is an experimental skill assessed in the fourth and fifth forms of the two year CSEC course and for Cape Units 1 and 2.
(The other experimental skills that are assessed are Observation/Recording/Reporting and Manipulation/Measurement.)
HERE IS HOW IT HAPPENS
A.
BACKGROUND
1.
The person doing Planning and Designing (P&D) will have some background knowledge, some
experience, or would have made some observations.
2.
B.
From this, there is a desire to determine whether there is/are any relationship/s existing in the situation
under focus.
HYPOTHESIS
1.
A hypothesis is developed/formulated. Now, what is a hypothesis? It is a supposition made as a basis for
reasoning, without assumption of its truth. It forms the basis for investigating the relationship/s in the
situation under focus. It is the starting point for investigation.
2.
Within the hypothesis the following should be clearly identifiable.
(a)
INDEPENDENT VARIABLE same as MANIPULATED VARIABLE
(b)
DEPENDENT VARIABLE same as RESPONDING VARIABLE.
NOW FOR AN EXAMPLE CLARIFYING POINTS A. AND B.
BACKGROUND KNOWLEDGE/EXPERIENCE; A Health visitor visited a poor community where some
families only used canned orange juice while some other families only used fresh oranges.
OBSERVATION The children of the families who used only canned orange juice appeared to show a higher
incidence of scurvy (a disease caused by lack of vitamin C) than children of families who used only fresh orange
oranges.
HYPOTHESIS Fresh orange juice has a higher concentration of vitamin C than canned orange juice.
Independent variable – fresh orange juice or canned orange juice
Dependent variable – concentration in vitamin C in Juice
C.
WHERE DO WE GO FROM HERE? IT IS NOW TIME TO TEST THE HYPOTHESIS
THE FOLLOWING MUST BE DONE.
1.
Identify variables
2. Select apparatus and
materials / reagents
Independent/manipulated variable – fresh or canned orange juice
Dependent variable – concentration of vitamin C in juice
Controlled variable/s – temperature of juice; volume of juice tested
Burette, retort stand,
2 – 25 cm3 pipettes, 50 cm3 measuring cylinder, 6 – 250 cm3 conical flasks
2 – 250 cm3 beakers, white tile, 200 cm3 fresh orange juice, 200 cm3 canned orange juice
0.05 mol dm-3 iodine solution, 20 cm3 starch solution, 2 mol dm3 sulphuric acid.
Prepared by S. Elinor Jordan B. Sc. Dip. Ed. M.Ed.
A labelled diagram showing the apparatus and reagents in the titrations is drawn.
Burette containing
iodine solution
Conical flask with orange
juice
3.
(a)
Devise method
Method to be used
should be written in
steps that can be
clearly followed.
(b)
Limitations to the
method/investigation
(c)
Precautions to be taken
(d)
Sources of error
4.
(i)
(ii)
(iii)
(iv)
(v)
Using a pipette, 50 cm3 fresh orange juice is transferred to a conical flask.
20 cm3 sulphuric acid is then added to the flask.
Starch is then added to the conical flask.
The contents of the flask are then titrated against iodine solution, until there is
the first permanent blue – black colour.
The titration is repeated twice. The entire method is repeated using canned
orange juice.
(i)
(ii)
(iii)
Only one brand of canned orange juice is used.
Fresh oranges from only one source are used.
Lack of information regarding other possible vitamin C inputs in the diets of the
families.
(i)
Fresh orange juice should be squeezed and the canned juice should opened just
before the titration is done, since vitamin C deteriorates with exposure.
(i)
For this investigation ONLY EXPERIMENTAL ERROR IS POSSIBLE. This
may be as a result of improper use of measuring instruments like the pipette, or
carelessness when recording results.
Clearly identify DATA that
should be collected, showing how
this data is to be recorded – tables
etc. Do not use actual figures (use
letters) etc. that show a
predetermined result. Remember
that you have not yet done the
experiment.
Titration number
Trial
1
2
Final reading / cm3
b
c
d
Initial reading/cm3
a
b
c
b- a
c- b
d- c
Volume of I2
Prepared by S. Elinor Jordan B. Sc. Dip. Ed. M.Ed.
5.
State how results will be treated –
calculations, graphs etc.
Volume of I2 used in calculation is ½ {(c-b) + (d-c)} cm3
(let this f cm3.)
Eqn:
C6H8O6 (aq) + I2 (aq) → C6H6O6 (aq) + 2HI (aq)
Vitamin C + Iodine
1 mole
1 mole
No. of moles I2 in f cm3 is 0.05 (f/1000) mole
0.05 (f/1000) mole I2 reacts with 0.5 (f/1000) mol C6H8O6
(see eqn. 1:1 ratio)
50 cm3 orange juice contains 0.05 (f/1000) mol C6H8O6
Therefore 1000 cm3 orange juice contains 1000 /50 {0.05(f/1000)} mole (let this
be p mol) C6H8O6
Concentration of vitamin C is p mol dm-3
This calculation is done with the results from both fresh and canned
orange juice.
6.
State what conclusions will be
reached if results show trends in one
direction, in the other/opposite
direction or if no trend is observed?
If the concentration of vitamin C in the fresh orange juice is higher than that of
the canned orange juice, then the hypothesis is proven true, and it is very
possible that the lower incidence of scurvy among the families that use the fresh
orange juice, may be due to the use of fresh juice.
If the concentration of Vitamin C in the canned orange juice is higher then the
hypothesis is proven false and the use of orange juice, fresh or canned, cannot
be related to the incidence of scurvy.
Prepared by S. Elinor Jordan B. Sc. Dip. Ed. M.Ed.
BACKGROUND KNOWLEDGE
EXPERIENCE/ OBSERVATION
HYPOTHESIS
FORMULATED
TESTING HYPOTHESIS
IDENTIFY
VARIABLES
SELECT APPARATUS
(Draw diagrams)
DEVISE METHOD
(a)
Write it out -Passive Voice
(b)
Indicate limitations,
assumptions, sources of
errors and precautions
IDENTIFY DATA TO BE
COLLECTED SHOWING HOW
RECORDED
TREATMENT OF RESULTS
STATEMENTS OF POSSIBLE
CONCLUSIONS
EXECUTE
INTERPRET
IF UNRELIABLE RESULTS
MODIFY PLAN
COLLECT RESULTS
REPORT
ANALYSE AND
IF RELIABLE RESULTS, HYPOTHESIS IS
PROVEN OR DISPROVEN
CARRY OUT NEW PLAN
Diagram summarizing the operations involved in Planning and Designing (shaded boxes).
Prepared by S. Elinor Jordan B. Sc. Dip. Ed. M.Ed.