Zusammenfassung der Ressource
Practical &
Investigative
Skills
- Apparatus
- Burette
- Glass Pippette
- Condenser
- Gas Syringe
- Funnel
- Beaker
- Round-bottomed Flask
- Conical Flask
- Dropping Funnel
- Hazard Symbols
- Highly Flammable
- Toxic
- Corrosive
- Harmful
- Irritant
- Oxidising Agent
- Separation Techniques
- Filtration
- - Separates
insoluble solid
from a solid/liquid
- - Residue remains
on filter paper
- - Filtrate runs
through the filter
paper
- Distillation
- - Separates the
solvent from a
solution
- - Can be used to
determine the BP
- - Pure water can be
obtained from
seawater
- Fractional Distillation
- - Separates
immiscible
liquids
- - Substance with
lowest boiling
point is collected
first
- Separating Funnel
- - Separates
immiscible
liquids
- - The liquid with
the greatest
density separates
out as the lower
layer
- Magnetism
- - Iron, Nickel and
Cobalt are
attracted to
magnets
- Crystallisation
- - Used to
remove small
quantities of
an impurity
from a solid
- 1. The impure
sample is dissolved
in a minimum
volume of hot
solvent
- 2. As the solution slowly
cools, the saturated
substance crystallises out
- 3. The mixture is then
filtered and the
crystals washed with a
small amount of cold
solvent
- 4. The crystals
can be dried out
between two filter
papers or placed
in a warm oven
- Paper Chromatography
- - Separates
mixes of
different
substances e.g.
dyes
- METHOD
- 1. Small spots of
coloured
substances are
placed in a line
near the base of
the paper
- 2. The paper is
placed vertically into
a beaker or tank
contaning a small
volume of a suitable
solvent
- 3. The solvent is
absorbed and
rises up the paper
- 4. The coloured
chemicals in the
spots dissolve in the
solvent and are
carried up the
paper
- 5. The resulting
chromatogram is
dried and
analysed
- - The greater the
solubility of a
compound in the
solvent, the greater
the distance it will
travel up the paper
- This technique can
be used to...
- - Detect whether a
coloured dye is a
pure compound or a
mixture of pigments
- A pure compound will
produce a single spot on
the chromatogram
- Indentify a
compound/substance by
comparison to a known
sample
- The unknown and
known compound will
produce the same
coloured spot at the
same height on the
chromatogram
- An Investigation
- Planning
- Aim
- What is the
investigation trying
to find out?
- Safety
- A lab coat and
safety glasses
must be worn for
all practical work
- You need to
consider specific
hazards such as...
- Toxic gases -
work in a fume
cupboard
- Corrosive
chemicals -
wear gloves
- Flammable
organic
compounds - do
not heat with a
Bunsen burner,
use a water bath
- Preliminary work
- Trial and error is
used to find out
which practical
method and
apparatus will work
- One of the
reagents must be
in EXCESS
- One of the
reagents LIMITS
the reaction
- Prediction
- A prediction is made
using you knowledge
and the preliminary
work
- Your prediction
should include...
- - a simple statement
of the expected
results
- - the predicted shape of
any graph which you
will draw
- - a quantitative prediction
based on the reaction
equation, mole ratios or other
scientific knowledge
- Always
support and
explain your
prediction
with scientific
knowledge
- Fair test
- Variables
make and
experiment
Valid
- Only one
variable can be
changed
- Independent Variable
- This is the condition
that you decide to
change
- Dependent Variable
- This is the variable
that you measure as a
consequence of the
changes in the
independent variable
- Controlled Variable
- These are the
conditions that
need to be kept
constant to make
the experiment a
fair test
- keep the
temperature the
same
- keep the
volume the
same
- keep the
same
atmosphere
- Method
- Give a detailed
step-by-step method
of the experiment,
such that another
person could carry
out the investigation
without further help
- Obtaining
sufficient,
reliable and
accurate
- Five is the
minimum number
of variations of the
factor under
investigation
- Reliability of data
- If the repeated results
for an experiment are
the same or very similar,
they are said to be
reliable
- Anomalous results
- - A result which is
significantly different
from the rest, in a set
of results from an
experiment repeated
several times
- - Results that do not
follow the pattern
formed by the other
results/points on a
graph or in a table
- Anomalous results must
be clearly identified and
not used when
calculating averages or
drawing lines of best fit
on graphs
- Accuracy : Is the
result obtained
correct?
- Accuracy is
increased by using
the correct
measuring
Apparatus for the
task
- All apparatus
possess
inherent errors
- Obtaining (and
recording) the
evidence
- Results should
be displayed in
a table
- The
independent
variable must
be in the left
column
- Use clear, accurate
headings, which
include units
- Use SI
units
- Record all the
readings to the
appropriate level
of accuracy
- Record all the
readings to the
same number of
decimal places
- Calculations
- An average
value is usually
calculated - DO
NOT include
anomalous
- In rate investigations use -
rate of reaction = 1/time
- Analysis
- Graphs
- - Use a sensible
scale which uses
as much of the
graph paper as
possible
- - The independent
variable goes on
the x-axis and the
dependent
variable goes
y-axis
- - Use small
crosses to mark
the points
- - Label the
axes carefully
and give the
units
- - Always add a
title, indicating
what the graph
shows
- - Circle (and
label) any
anomalous
results
- - Draw a line or
curve of best fit
(do not join up
the points)
- Conclusion
- - State simply what
the table of results
and graph show
- - Use scientific
knowledge to
explain what you
have found out
- - Refer to
your
prediction
- Evaluation
- An evaluation should
comment on how well
the investigation went
and address...
- Reliability of the
procedure and
evidence
- - How close together
are your results? Are
your results reliable?
- - Identify and try
to explain what
caused any
anomalous results
- - Were there
any problems
with the
procedure?
- - Do you have
sufficient evidence
to support or
disprove your
prediction?
- Accuracy
- How close to the
real figure are
your results? (not
always possible to
answer)
- Inprovements
- Reliability
- Can be improved by
doing more repeats
and only using
results which are
very similar
- Accuracy
- Can be improved
by changing the
method or
equipment used
- Limitations
- What are the flaws
in the practical
method and how
could it be
improved?
- Always give a
reason with your
suggestion
- Validity
- Assess the above
factors and decide
how they have
affected your results
and hence your
conclusion. Is your
conclusion valid?
- Further work
- Further work is carried
out to obtain more
evidence to support the
conclusion made in your
investigation
- It could involve
- - Changing one or
more reactants and
using same method
- - Using different
method/apparatus
- - Obtaining a
wider range of
results