Core Practicals Flashcards
How measure the molar volume of a gas
Collection of gas method (upturned measuring cylinder in water)
Gas syringe
Potential errors with gas syringe
Gas escaped before insertion
Strung sticks
Gas being insoluble in water
Method for measuring molar volume of gas
Measure acid and transfer to conical flask
Attach syringe/use gas collection method
Measure the mass of bottle with CaCO3
Add CaCO3
Quickly add bung before gas escapes
Read result
Reweigh empty bottle
Heating in a crucible method
Weigh empty dry crucible and lid
Add 2g of hydrated calcium sulphate
Reweigh
Heat strongly with a Bunsen
Allow to call
Reweigh
Continue until a constant mass is reached- shows end of reaction
Use of heating in a crucible
Water of crystallisation can be removed from calcium sulphate crystals
How to make a standard solution
Weigh the sample bottle with required mass of solid on balance
Transfer to beaker- use washings
Reweigh empty bottle and record mass difference
Add distilled water and dissolve usinh glass rod
Pour into volumetric flask
Add all washings
Make up to mark using distilled water
Invert flask several times
Phenophalein colour change
Pink/purple to colourless
Methyl orange colour change
Acid: red to orange
Alkali: yellow to orange
How to calculate uncertainty
Uncertainty =(uncertainty/measure made on apparatus) x 100
How to reduce uncertainty in titration
Make the titre a larger volume
Increase volume or concentration of solution being titrated
Means error is a Lower percentage
How to test rate of hydrolysis of halogenoalkanes
Arrange three test tubes in a row
Add three drops of Halogenoalkane- 1-chlorobutane , 1-bromobutane and 1-iodobutane
Add silver nitrate to each Halogenoalkane
Put all three simultaneously in water bath
Note order of precipitates forming
What is the ppt in test of hydrolysis of Halogenoalkane and why is it’s formation important
Halide combines with silver ion to form a silver halide ppt
Precipitate only formed when halide ion has left the haloalkane and thus rate of formation can be used to compare reactivity
What is the formation speed of silver halogen ppt showing
Quicker the ppt formed, faster the reaction and more reactive the haloalkane
Rate of reaction depends on strength of C-X bond. Weaker the bond, faster the reaction
Rate of silver halide ppt formation fastest to slowest and colour formed
AgCl-Yellow
AgBr-Cream
AgI-White
Differences between partial and full oxidisation of primary alcohol
Partial uses limited amount of potassium dichromate, full uses in excess
Partial distills of aldehyde as formed
Full heats under reflux
Reaction for partial oxidation of propan-1-ol
CH3CH2CHOH + [O] becomes CH3CH2CHO + H2O
Method for partial oxidation of propan-1-ol
Place dilute Sulfuric acid in a flask
Add 3G of potassium dichromate and add anti-bumping granules
Shake until solution complete
Add propan-1-ol in drops
Shake flask to mix contents
Gently heat and distil liquid into test tube
Distillation equipment
Round bottom flask being heated
Thermometer in top
Heated flask attached to Liebig condenser
Eventually runs to another flask
KEY: water in at bottom to go against gravity and ensure more efficient cooling
Observation on full oxidation of alcohol
Orange dichromate ion reduces to green Cr3+ ion
Equation for full oxidation of propan-1-ol
CH3CH2CH2OH + [O] becomes CH3CH2COOH + H2O
Method for full oxidation of alcohol
Place water and sodium dichromate in boiling tube, then shake
Place Propan-1-ol, water and anti-bumping granules into round bottom flask
Set up for reflux
Add conc H2SO4 down condenser in drops and add sodium dichromate in drops
When all sodium dichromate added, use low Bunsen flame for 10 mins
At the end of that time set up for distillation
Equipment for reflux
Round bottom flask heated from bottom
Condenser
Water in at bottom
What is the use of anti-bumping granules
Prevents vigorous boiling by making small bubbles form
Detailed method for preparing and purifying an ester
Propan-1-ol and Ethanolic acid mixed in round bottomed flask
Conc H2SO4 added drop by drop
Keep contents of flask well-shaken and cooled in ice-water bath
When all acid added, a reflux condenser is fitted and mixture boiled for 30 mins
Mixture cooled and prepared for distillation
Distillate placed in seperating funnel and shaken
30% sodium carbonate solution makes up roughly half of volume
Aqueous layer discarded
Crude ester shaken in seperating funnel with half its volume of Calcium chloride solution
Lower layer discarded
Ester ran into clean dry flash with anhydrous calcium chloride
Ester filtered into clean dry flask with anti bumping granules and is distilled
Collect 100-103degrees C fraction
Flame test method
Use a nichrome wire
Clean the wire by dipping in conc HCl and heat in Bunsen
Dip wire in powdered solid
Place at edge of flame and record colour
Method for dilute NaOH test
Place drops of Metal ion solution in a test tube
Add drops of NaOH and mix well
Continue to add NaOH, by drops with shaking, until in excess
Result of Magnesium hydroxide and sodium hydroxide
Insoluble min water
White ppt
Result of calcium hydroxide and sodium hydroxide
Partially soluble in water
White pot
Will strontium and barium produce a result in sodium hydroxide test
No
Due to high solubility
How to test for ammonium ions
Place drops of ammonium chloride
Add drops of NaOH
Shake mixture well
Warm mixture in test tube using water bath
Test fumes released by using damp red litmus paper
Results of ammonium test
Alkaline ammonium is released tuning red litmus paper blue
Test for an Alkene and result
Add bromine water
Alkene will decolourise bromine water
Reaction of 2-4 DNP (aka Brady’s reagent)
Tracts with both aldehydes and ketones
Yellow ppt
Tollens reagent test
Test for an aldehyde
Heat gently
Aldehydes are oxidised by tollens leading to a silver mirror formed
Fehlings solution test
Heat gently
Aldehydes only oxidised by Fehlings solution
Blue copper ions change to red ppt
PCl5 test for alcohol and carboxylic acid
Add PCl5
Positive result- misty white fumes
What functional groups does sodium metal test for and what is a positive result
Alcohols, phenols and carboxylic acids
Effervescence due to H2 gas
What does sodium carbonate test for and what is a positive result
Carboxylic acid
Effervescence of CO2
What does sodium dichromate and sulphuric acid test for
Primary/secondary alcohol and aldehyde
Orange to green
Methods to measure enthalpy change experimentally
Calorimetric method- one substance mixed with another in insulated container. Temp rise measured
Flame calorimetry- used for enthalpy of combustion. Spirit burner used and the change in mass Is measured
Errors with calorimetric method of enthalpy change
Energy loss to surroundings
Approximation in SHC of solution
Neglecting SHC of calorimeter
Reaction may be incomplete or slow
What is the use of a salt bridge
Used to connect circuit- free moving ions conduct charge
Made from filter paper soaked in salt solution, normally Potassium nitrate
Should be in reactive with electrodes and electrolyte
When and why is a platinum electrode used
If one or both of the half cells do not contain a conducting metal
Platinum used as unreactive and can conduct electricity
Different ways to measure rate of reaction and when used
Change in vol of gas- used when moles of gas changes
Measurement of change of mass- used when gas formed which can escape
Titrating samples of reaction mixture- used for suitable products
Colorimity- used if change in colour
Change in conductivity- used if Change in number of ions
What is continuous monitoring and how is it fine
Following one experiment by recording change in concentration
How to calculate activation energy using Arrhenius equation
Draw graph of 1/T against ln(rate)
Gradient of line = -Ea/R
Ea = -gradient x R
What does barium chloride test for
Sulfate and phosphorous ions
