Practicals Flashcards
Standard Solution
- accurately weight out a dry sample of solid using a high precision balance
- transfer to a beaker and freeing the weighing boat to determine mass transferred
- dissolve acid in a small volume of distilled water, stirring with a glass rod
- transfer to volumetric flask
- add deionised water up to calibration line
- ensure meniscus rests on calibration line
- stopper bottle and invert 10 times to homogenise the solution
Acid-Base Titration
_____ = any substance
- rinse the burette with whatever is going in the burette to remove any contamination (can’t use water because there will be water left behind which will dilute whatever is in burette)
- overfill burette with _____ and run through so jet space is filled/ remove air
- use volumetric pipette to transfer 25cm3 of (other thing tittering) to a conical flask (we use conical flask to avoid any splashing during titration)
- add 2 drops of suitable indicator e.g. phenolphthalein
- slowly add contents inside burette
- swirl between additions
- rinse burette and sides of conical flask with wash bottle
- stop at first permanent colour change and record volume of contents inside burette
- repeat titrations until concordant data achieved and use concordant data to calculate mean titre
- use n=cv to calculate moles of whatever added
Measuring Enthalpy change of a reaction
_____ = any substance
- measure _cm^3 of water using a burette/pipette (not measuring cylinder because that adds error)
- transfer to polystyrene cup with lid
- measure 4g of ____ using an accurate balance
- use a thermometer to take the temperature of the water each minute for 2-3 minutes to establish an accurate initial temperature
- pour the solid (i.e copper sulfate) into the water at minute 4
- reweigh the weighing boat again to find the correct mass of _____ transferred
- stir solution
- continue to record the temperature at minute intervals up to 15 minutes
- plot a temperature against time graph
- extrapolate back to point of addition and determine temperature change
Distillation
_____ = any substance
- transfer reaction to a round-bottomed flask
- add anti bumping granules (to create smaller bubbles)
- clamp round-bottomed flask over electric heater (safer than naked flame cuz alcohol flammable )
- add bung with integrated thermometer, which sits at height of side-arm
- ensure bung fully seals flask to allow collection of ____
- attach condenser - water should enter at the bottom and leave through top
- apply heat
- collect the distillate from beaker within ice bath when thermometer shows boiling point of ____
Iodine Clock (initial rate of reaction)
- perform a series of experiments in which only the concentration of solution A varies
- add 5cm^3 of solution B and 1cm^3 of starch to a beaker
- simultaneously add 5cm^3 of solution A and start timer
- record time taken for blue colour change to appear
- dilute solution A so concentration is half original
- repeat experiment and record time taken
- use 1/time taken for blue to appear
- if rate x2 when [A] x2, 1st order if rate does not change then zero order or x4 then 2nd order etc
Continuous monitoring of rate of reaction (gas syringe one)
_____ = any substance
- Use a burette to measure 50cm^3 of ____ (likely hydrogen peroxide) into a conical flask
- use a high precision balance to measure 1g of manganese dioxide (aka the catalyst, this is significantly in excess so concentration is effectively unchanging)
- prepare bung with delivery tube attached to gas syringe
- add catalyst to flask, insert bung and start stop watch
- record volume of gas released every 10 seconds until syringe is full
- calculate concentration remaining for each time point
- plot concentration against time
- draw tangents at each time point to establish rate for each concentration
- plot a rate-concentration graph and identity the order
REFLUX DIAGRAM
Why is a water bath used during heating of a reaction mixture rather than a bunsen burner flame?
Water Bath is needed because a reaction mixture is composed of reactants that are flammable.
When preparing an organic liquid/solid why must you continue to keep the mixture cool as reactants are being added?
- Many reactions are vigorous at the beginning and can react violently
- By keeping the mixture cool at the beginning it reduces the mixtures ability to be violent
- once the initial reaction is underway it can be heated.
How are solutions heated when preparing an organic liquid or solid?
- Reflux
- If reactants, catalysts or solvent is
volatile
- If reactants, catalysts or solvent is
- Distillation
- Volatile and has possibility of
further reaction (e.g. primary
alcohols - aldehydes )
- Volatile and has possibility of
Best method of separating products of a reaction mixture when preparing an organic solid/liquid?
- Filtration
- w/ a Buchner Funnel with a
vacuum pump
- w/ a Buchner Funnel with a
- Separating Funnel
- use if the liquid is immiscible with
the reaction mixture
- use if the liquid is immiscible with
- Distillation
- use if the liquid is miscible with
the reaction mixture
- use if the liquid is miscible with
Process of Recrystallisation of an organic product?
Solid dissolved in a minimum amount of hot solvent
- Organic compound will be very soluble in HOT solvent but not when cold
- insoluble impurities will not dissolve and thus can be removed by filtration
Hot solution can be cooled to room temp
- to allow for crystals to form
Filtered under reduced pressure
and washed in cold solvent
- soluble impurities will be separated from products and dissolved impurities will have been washed away
Product is dried between two pieces of filter paper
- ( do not use an oven as this
may melt/decompose the
product, which decreases
yield further)
Why do we recrystallise organic products?
- A procedure for purifying an impure compound in a solvent
- It is done based on the principle that the solubility of most solids increases with increased temperature
Why must a pre-heated funnel be used for filtration when doing recrystallisation?
- A hot filtration is used for filtering solutions that will crystallize when allowed to cool
- therefore it is important that the funnel is kept hot during filtration to prevent crystals prematurely form on the filter paper/stem of funnel
Method of testing the purity of an organic product?
- melt a solid in melting point apparatus slow down the heating close to the melting point.
- should melt exactly at that temp over a small range, which corresponds to data booklet values for that product.
Why would a filtration with hot glassware be used during the recrystallisation. Why should the glassware be hot?
- to remove any impurities that are not soluble in water
- glassware is hot so that the hot aspirin solution does not cool down leading to the aspirin crystallising out on the apparatus.
Why are anti-bumping granules used during a reflux or distillation?
- To reduce the size of bubbles/ make smaller bubbles when the reactants are heated
