Practical Skills Flashcards
How do u make a volumetric solution
- Weigh out using a weighing boat the mass of solid needed
- Dissolve solid in a beaker using distilled water. Include washings
- Use funnel to transfer solution to a volumetric flask
- make up to mark using distilled water
- then invert to mix
How do you carry out a titration
- Rinse burette and pipettes with correct solutions
- fill burette using a plastic funnel make sure there are no bubbles
- when using pipette allow to drain and touch tip to surface. Put into conical flask
- add 2 drops of indicators
- swirl solution and add from burette
- read burette to 0.5 cm3
- repeat process to get concordant results
What are some of the sources of error in an enthalpy change experiment
Heat loss
Not taking into account the specific heat capacity of cup
5 things to consider when assessing uncertainty
- Resolution of instrument - manufactures tolerance on instrument
- judgements made
- procedure adopted
- size of increments
How to calculate percentage uncertainty
Uncertainty
————- X100
Value
How to calculate overall apparatus uncertainty
Add all the percentage errors together
What are 3 uncertainties in titre
Reading the burette at start of titration
Reading the burette at end of titration
Judging the end point to within one drop
7 improvements that can be made to an investigation
- Repeating to get more results increases reliability
- change concentration of solution to reduce error
- change the size of pipette to reduce error
- weighing a larger mass to reduce error
- use more accurate apparatus
- improve lagging in calorimetry experiment
- control temperature
Why repeat experiments
Repeating improves reliability and identifies anomalies
Why test more than one sample
Samples can have a different composition and consistency
What should you do if a substance is corrosive
Handle with care wash spillages off skin or wear gloves and eye protection should be worn
What should you do if a substance is an irritant
Gloves and eye protection
What should you do if a substance is flammable
Keep well away from flame
What should you do if a substance is toxic
Wash hands after use.
Toxicity depends on dosage if possible use fum cupboard
Define accuracy
A measurement result is considered accurate if judged to be close to true value
Define calibration
Marking a scale on a measuring instrument
Define data
Information that has been collected
Define measurement error
The difference between a measured value and the true value.
Define anomalies
Values in a set of results which are judged not to be part of the variation cause by random uncertainty
Define random error
These cause readings to be spread about the true value due to results varying. Cannot be corrected
Define systematic error
Cause reading to differ from the true value by a consistent amount each time
Define zero error
Any indication the measuring systems is giving a false reading
Define categoric variables
Values that are labelled
How to test for carbonate ions
Add HCl
Get effervescence
CO3 2- + 2 H+ = CO2 + H2O
Test for sulphate ions
Add HCl then barium chloride
White precipitate
SO42- + Ba2+= BaSO4
Test for hydroxide ions
Add NH4 +
Ammonia gas produced
OH- + NH4 + = NH3 +H2O
Halide ion tests
Add dilute nitric acid then silver nitrate Cl- white Br- cream I - yellow Then add NH3 Cl - dissolve Br - dissolve in concentrated I- turns white in concentrated
Equations for Halide ions tests
Cl-(aq) + Ag +(aq) —-AgCl(s)
Carbon dioxide test
- Gives very weak acid
2. Bubbling through limewater gives a white precipitate
Sulphur dioxide gas test
- Chocking smell give weakly acidic solution
2. When gas passed through paper soaked in potassium dichromate so reduced to green blue chromium (III) ions
Test for hydrogen sulphide ions
Smell of bad eggs
Passed over paper soaked in less nitrate solution to give a silvery precipitate
Hydrogen halide gas tests
colourless gas produce misty fumes in moist surface
Gas passed over gaseous ammonia and white fumes observed
Test for ammonia gas
Pungent smell
Comes into contact with gaseous hydrogen chloride white fumes are observed
Test for chlorine gas
A pale green gas
Turns moist litmus paper first red and then white
Test for Mg 2+ ions
Add dilute sodium hydroxide
Will give white precipitate because is much more insoluble
Mg2+ + 2OH- – Mg(OH)2
Testing for Ba2+ ions
add dilute sodium sulphate Na2SO4
Give white precipitate because more insoluble
Ba2+ + SO4 2- — BaSO4
Test for alkene
Add bromine water and it will decolourise
Test for OH alcohols
Warm with acidified potassium dichromate
K2Cr2O7
Turns from orange to green
Test for aldehyde
CHO
- Warm with tollens reagent = a sliver mirror
- Add fehlings solution = blue to brick red precipitate
- Acidified K2Cr2O7 turns orange to greens
Test for halogenalkane
Add HNO3
Add AgNO3
Cl = white Br = cream I = yellow
Test for carboxylic acid
Add Na2CO3 give effervescence
Then litmus paper turn red
