Core Practicals Flashcards by Bay Gorrod

How measure the molar volume of a gas

Collection of gas method (upturned measuring cylinder in water)
Gas syringe

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Potential errors with gas syringe

Gas escaped before insertion
Strung sticks
Gas being insoluble in water

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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

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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

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Use of heating in a crucible

Water of crystallisation can be removed from calcium sulphate crystals

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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

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Phenophalein colour change

Pink/purple to colourless

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Methyl orange colour change

Acid: red to orange
Alkali: yellow to orange

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How to calculate uncertainty

Uncertainty =(uncertainty/measure made on apparatus) x 100

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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

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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

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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

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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

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Rate of silver halide ppt formation fastest to slowest and colour formed

AgCl-Yellow
AgBr-Cream
AgI-White

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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

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Reaction for partial oxidation of propan-1-ol

CH3CH2CHOH + [O] becomes CH3CH2CHO + H2O

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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

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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

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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