1.1 Practical Skills Flashcards
Define variable.
A quantity that has the potential to change and can affect the outcome of an experiment
Define independent variable.
The thing you change to see the effect t has on one other factor
Define dependant variable.
The thin that you observe in the experiment.
What are the three different types of data?
Discrete, continuous and categoric.
How do you obtain continuous data?
Any value on a scale - can never measure the exact value.
How do you obtain categoric data?
Values that can be sorted into categories - eg blue green and red.
Where do you read the volume of a liquid from?
The bottom of the meniscus.
How do you make it easier to measure colour change?
White background.
How do you make it easier to see a precipitate?
Mark and x on a piece of paper and put in under the reaction contained - it is cloudy when you can no longer see the x.
What are valid results?
Results that answer the original question - if you haven’t controlled all variables BC not testing what you wanted.
What are accurate results?
Results that are really close to the true value.
What are precise results?
Results that can be independently reproduced in independent experiment s.
Define valid
A valid expediency provides information to test the aim of the experiment
What is a hypothesis?
A prediction and explanation of the chemistry behind the prediction
What’s an experiment?
An ordered see of practical steps used to test the hypothesis
What is resolution
The smallest change in the quantity being measured that can be observed
What is accuracy?
How close to the true value a measurement is
What is the control variable?
The actor theta you must keep contacts between experimental runs so you can compare results
What is an extraneous variable?
A factor that is not controlled or measure in the experiment but may introduce error into the results
What is a plan?
A summary of an experiment that you wish to complete
What is a method?
A step by step detailed explanation of how to complete an experiment
How to measure mass
weigh full and empty
How to measure solutions
volumetric pipette from bottom of meniscus
How to measure gas
- gas syringe
- over water - fill measuring cylinder and measure water displaced
Preparing standard solution
- dissolve solid in beaker (approx 100ml water)
- pour into volumetric flask using funnel
- rinse beaker
- pour into volumetric flask
- fill so bottom of meniscus is on the line
Titration
- measure 25cm3 of standard solution using volumetric pipette
- add to conical flask with 2-3 drops of indicator
- fill burette with unknown conc
- add this to conical flask
- while over white tile until permanent colour change
- record volume added to 2dp (either 0.00 or 0.05)
- repeat adding drop by drop until end poinit
- repeat until concordant results
What are concordant results?
within 0.1
Test for carbonate
add strong dilute acid
collect gas and pass through limewater
positive = fizzing and limewater cloudy
Test for sulphate
dilute hydrochloric acid and then barium chloride
white precipitate of barium sulfate produced
Test for halide
- dissolve halide in water
- silver nitrate and dilute nitric acid
- ppt colour
- dilute then conc ammonia
- note solubility
Test for ammonium ions
- add sodium hydroxide and warm gently
- test gas with red litmus
- turns blue
What happens when metal ions react with ammonia or hydroxide ions?
insoluble coloured compounds
Method for testing for metal ions
- fill half a test tube with sample
- add aqueous ammonia or NaOH dropwise
- note colour of ppt
What transition metal is it if a blue ppt is formed?
Cu2+
What transition metal is it if a brown ppt is formed?
Mn2+or Fe2+
What transition metal is it if a green ppt is formed?
Fe2+ ot Cr3+ (green-grey)
Testing enthalpy change of combustion
weigh fuel, burn it to heat a know amount of water, measure temp change, reweigh fuel
use q=mc delta t
and change in H =-q/n where q=energy change
Determining enthalpy change of neutralisation
measure out known conc of acid and alkali
measure temp change
use q=mc delta t for TOTAL volume
use delta H = -q/n for limiting reactant
Determining enthalpy change of reaction
- dissolve salt in water
- measure enthalpy change
- dissolve hydrated salt in water
- measure enthalpy change
- q= mcdeltat
- find enthalpy change of forming hydrated salt from salt and water
How can you measure rate of reaction?
-loss in mass
-volume of gas produced
-amount of light passing through over time
plot graph and find gradient
How do you determine initial rate?
- make solution of known concentration
- react and measure initial rate
- change conc but keep volume same
- react and measure initial rate
- compare difference
Quickfit for reflux
- vertical condenser attached to flask
- water goes in bottom of condenser
- often use water bath or heating element to heat flask rather than bunsen burner as chemicals may be flammable
Quickfit for distillation
- condenser at angle (higher end at flask and sloping away)
- water attached at lower end
- -thermometer level with entrance to condenser
Purification of organic liquid
separating funnel to remove organic layer from aqueous layer
drain off bottom
Example of anhydrous salt used for drying
MgSO4
CaCl2
How to dry with anhydrous salt
add and will absorb water
filter to remove hydrated salt
How to purify an organic solid
- filter under pressure, buchner funnel attached to tap with filter paper dampened with solvent, wash product with solvent
- recyrstallize by adding min amount of hot solvent until crystals dissolve, cool and recrystallize, filter under pressure, wash with cold solvent, dry, check melting point with melting point apparatus
