Practical-related Flashcards
if we see effervescence and heat, we must….
test for gas
for cation, anion and gas tests, we must…
copy observations from the QA table directly
for gas tests, we must…
state the name of the gas
what does it mean to write clearly what an observation refers to?
note whether it is a gas/precipitate/solid/solution
an example of soluble ppt and stating what solution forms
blue ppt soluble in excess aqueous ammonia to form dark blue solution
what is the evidence for conclusion?
state step/question number, test and observation
what is the chemistry involved?
concept behind reaction, what kind of reaction and explain
e.g displacement, neutralisation, combustion
if need to reuse apparatus, we must…
wash with tap water and distilled water
how to identify precipitates?
cloudiness and cannot see through
how to identify solutions?
can see through and has no cloudiness
when heating solid and see water droplets at the sides of the tube?
water droplets observed at the side of the test tube; water of crystallisation is lost.
when heating solid and see the solid appear at the top of the test tube?
solid turned into gas and condensed at the top of the tube; solid sublimed
when solid changes colour upon being heated?
the colour of the solide changed from ____ to ____
when solid turns into liquid upon heating?
the solid melts to form a ____ liquid
during QA experiment, three things we must observe is:
- formation of ppt
- production of gases
- changes in colour of soln/ppt/solid
magnesium ribbon in acid eg
upon adding magnesium strips into acid, solid magnesium dissolves in acid and effervescence produced.
gas evolved ‘pops’ a lighted splint. gas is hydrogen.
when —- is added to solution
upon adding —–, —- is seen.
soln becomes cloudy and does not change when excess was added when solns mixed?
a —- ppt was observed, the ppt won’t dissolve in excess
soln becomes cloudy and becomes clear after adding excess when mixing solns?
a — ppt was observed; the ppt dissolves in excess giving a — soln
no change when mixing solns
no visible change was observed
when writing observations, turns into (some colour)
(some colour) ppt is formed
when writing observations, solid is formed, soln turns into white ppt.
white ppt is formed
when writing observations, the solution is clear, becomes transparent, is white
solution remained colourless
when writing observations, limewater became cloudy
a white ppt was observed in the limewater
when writing observations, carbon dioxide is fomed
effervescence observed, the gas gave a white ppt in limewater
when writing observations, the ppt dissolves
the ppt dissolves in excess to give a colourless soln.
recording temperature
to nearest 0.5 degrees Celsius
recording mass
to nearest 0.01g
recording time
to nearest second
recording volume in measuring cylinder
0 to 1 d.p.
recording volume in pipette
1 d.p.
recording volume in burette
to nearest 0.05 cm cube
when drawing graph, y-axis is
the dependent variable (measured quantities such as time, temp., vol. of gas produced)
when drawing graph, x-axis is
the independent variable (changed quantity asked by question such as conc.)
graph requirements
- Title
- Axis titles
- X data points
- Larger triangle to minimise error
- Marked big squares
- Start labelled
key source of error for salt preparation
salt may not be completely dry, loss of some salts during filtration/transfer
key source of error for energy changes
heat loss to the surroundings
key source of error for speed of reaction
human reaction time (with respect to use of stopwatch for e.g.)
inconsistent swirling/ stirring of solution mixture
how does salt not being completely dry affect the results and how to improve?
mass of salt obtained will be greater than expected. we should dry salt between filter paper.
how does loss of some salt during filtration/transfer affect the results and how to improve?
mass of salt obtained will be lower than expected. we should rinse with deionised water during filtration/transfer.
how does heat loss to the surroundings affect the results and how to improve?
temp. change is less/smaller than expected; use a lid or insulate the apparatus
how does human reaction time affect the results and how to improve?
inaccurate time measurements; take average of readings
how does inconsistent swirling/stirring of solution mixture affect the results and how to improve?
inaccurate time measurements; use magnetic stirrer
