pag 2 measurement of an enthalpy change

What are the substances used in this method

Anhydrous copper sulfate

And hydrated copper sulfate

How much anhydrous copper sulfate is needed

Around 4g

What’s the amount of distilled water used

25cm³ and use a volumetric pipette

What is the basic method

Weigh around 4g of anyhdrous copper sulfate in a measuring boat

25cm³ of distilled water in polystyrene cup

Record temp at t=0 and at evry minute whilst stirring

At t=4 add the powdered a.c.s and continue o stir and dont record temp

Reweigh the measuring boat and using weighing by difference calculate the exact mass used

Stir and record every minute until 15 minutes

What happens after the 15 minutes is over

What are the calculations used

What do u do after

Plot a graph and extrapolate

Use graph to calculate temp change at t=4

Use Q=mc change in T to wok out energy change

Calc the enthalpy of solution by doing Q/N (moles of anhydrous c.sulfate)

Then repeat experiment using hydrated copper sulfate - the 2 enthalpy of solution calc can be used to calc the enthalpy h age of forming a hydrated salt

What happens if reaction is slow what should u do and what do we do to counteract and why

If reaction is slow - exact temp rise can be difficult to obtain as cooling occurs simultaneously with the solution

To counteract this the temp at regular intervals is taken and extrapolated back t o the time the reactants were added together

The temp before addition of other reactants to get a better average temperature.

What are possible errors of the practical

Heat transfers to or from surroundings

Neglecting s.h.c of calorimeter - any heat absorbed by apparatus is ignored

Reaction or dissolving may have been incomplete or slow

Method assumes all substances have heat capacity of water

What should u do to improve accuracy (4)

Use a beaker to place a polystyrene cup in - increase insulation

Clamp thermometer in place ensuring bulb is immersed in liquid

Make sure to add powdered anhydrous copper sulfate rapidly

Use a lid on p. Cup - minimise heat loss

What other method could be used to calculate enthalpy change

Flame calorimeter