Practicals

• All apparatus rinsed with distilled water and then with the relevant solution. • Using a pipette and pipette filler, pipette 25cm3 of NaOH into a conical flask. Touch surface of solution with tip of pipette to ensure correct quantity is transferred. • Using a funnel, fill burette with acid and then remove funnel • otherwise, some drops may fall through the titration after the initial reading has been taken => lower volume recorded than used. • Allow a small quantity of the acid to flow through the burette to ensure jet space is filled. Note initial reading on burette. • If jet space not filled, titre value higher than volume actually added. • Add 2-3 drops of phenolphthalein (or another suitable indicator) to the conical flask and place it on a white tile - can see colour change better. • Add acid from burette into conical flask, swirling mixture during addition, until indicator changes colour (pink —> colourless). • During titration, rinse sides of conical flask with water —> ensures all acid is in solution. • Note the burette reading. • Repeat experiment but add acid dropwise (drop by drop) towards the end point. • Continue repeating until at least two concordant results obtained (within 0.10cm3).

• Formulae determination. • Water of crystallisation. • Decomposition.

Crucible weighed on a balance and its mass is recorded (mass 1). • Some sample placed in the crucible. • Crucible and contents reweighed on a balance and its mass recorded (mass 2). • Sample heated strongly in Bunsen. • Crucible and contents reweighed on a balance and its mass recorded. • The sample heated and reweighed until mass no longer changed —> ensures reaction completed.

Water does not react —> doesn’t affect number of moles present.

Can be swirled without losing any solution.

To ensure that solutions mix and so react completely

To see indicator colour change better.

Heat until constant mass.

Fuel is burnt and the energy released is used to heat a set volume of water. • Fuel continues to burn until the temperature of water rises by a set change (20C etc.). • Mass of fuel used then measured using a balance. • Calculation.

Heat loss to surroundings (air/flask) • Incomplete combustion. • High temperature changes lead to evaporation of water. => Heat loss can be reduced by adding lagging to the flask.

Lagging in polystyrene cup. • Add a lid to the polystyrene cup. Main source of apparatus error = thermometer —> can reduce this by increasing the temperature change. —> can increase temperature change by using a lower volume but higher concentration of solution.

Plot a graph of temperature (y) against time (x). • Before the addition of reagent to solution (0-4 mins): • Join points for first 3 minutes with a straight line. • Extrapolate (extend) line to 4th minute. • After addition of reagent to solution (4-12 mins): • Draw a line of best fit through the points between the 5th and 12th minutes and extrapolate (extend) this line to 4th minute. => Temperature change can be measured - distance between 2 lines. Show it clearly on graph.

Solution is measured out and placed in a polystyrene cup. • Initial temperature of solution recorded for a few minutes before second reagent is added (allows temperature to equilibrate). • Set, known quantity (mass/volume) of second reagent is added into the solution at fourth time. • Temperature recorded every minute until some cooling observed. NB=> Polystyrene cup used to reduce heat loss.

Rate can be determined by measuring amount (volume/mass) of gas produced at regular time intervals (every 10/20s etc.). • Plot graph of volume/mass against time. • Rate calculated by determining gradient of a tangent to graph. => rate would have units based on the units of the axes on the graph.

Rate determined by measuring time taken for a set amount of product to be formed. (in this method Rate = 1/T —> units s-1.) • Equal volumes of reactants used in each experiment to ensure time recorded is for same amount of product each time. • If ppt formed: • Reaction can be timed until enough ppt formed to obscure a cross on paper. If coloured product is formed: • Another reagent often added to reaction mixture which reacts with product as it is formed to produce a colourless substance. • When this additional reagent runs out, a colour change is observed => reaction then timed until the colour change is observed. => When investigating effect of temperature, the reaction mixture is heated to required temperature - could be using a water/sand bath.

• Total volume • Concentration. • Surface area of any solid reactants.

Enthalpy change of reaction will affect temperature at which reaction is completed. • At high temperatures, difficult to measure rate as water will begin to evaporate. • At high temperatures, time for reaction is very short —> increases degree of uncertainty in the timer. • Human reaction times will affect the number of decimal places that can be recorded accurately if the times are measured manually

Reacts with other anions (and so removes them from the solution) —> may also produce a ppt such as CO3 2- /O 2- / OH-. • Many carbonates, hydroxides and oxides are insoluble so would also form a ppt (except those of group 1 metal ions).

Can distil a product from a reaction if it has a lower boiling point than the reactants.

To prevent vaporisation of aldehyde product from the test-tube/boiling tube.

=> Can apply constant heat to a mixture without losing any of the liquid to evaporation - way of getting reaction to go to completion. => Many organic reactions need to be heated as this supplies the activation energy to break bonds and allow the reaction to occur. ^ Using a condenser allows this to happen whilst preventing the reagents from leaving the reaction vessel (they would otherwise evaporate).

Reactants (and products) can be heated together constantly, over a period of time. • Components of reaction mixture don’t escape from the reaction vessel (as heating causes them to evaporate/boil). • Vapour formed is cooled by the condenser —> condenses then falls back into the flask.

Include: • Liebig condenser. • COLD water in (bottom right). • COLD water out (top left) • Pear-shaped flask. • Anti-bumping granules. • Open top. • HEAT.