chemistry paper 3 Flashcards
pieces of equipment used when making a volumetric solution
Beaker
glass rod
Volumetric Flask
making a volumetric solution
1.weigh out precise amount of solid- using weighing boat or weigh by difference technique
2. add to small volume of water and pre dissolve the solid
3. then add the dissolved solid to a volumetric flask and making up the volume with washings
4. bottom of meniscus should be at the scratch mark
solute
the substance dissolved in solvent to form solution
steps of titration
1.Measuring a known volume (usually 20 or 25 cm3) of one of the solutions with a volumetric pipette and placing it into a conical flask
2.The other solution is placed in the burette.To start with, the burette will usually be filled to 0.00 cm3
3.A few drops of the indicator are added to the solution in the conical flask
4.The tap on the burette is carefully opened and the solution added, portion by portion, to the conical flask until the indicator starts to change colour
5.As you start getting near to the end point, the flow of the burette should be slowed right down so that the solution is added dropwise. You should be able to close the tap on the burette after one drop has caused the colour change
concordant results
with 0.1cm3 2d.p
uncertainty when doing titration
initial and final burette reading is recorder to 0.05 uncertainty so the final reading is that uncertainty double. percentage uncertainty multiplies by how much you use it.
percentage uncertainty equation
uncertainty/ measured value x 100
shows how precise the measurement it
percentage error
experimental - true/ true x100%
Percentage error measures the accuracy of a measurement by comparing the experimental value to a known or accepted true value. It indicates how close the measured value is to the true value.
two types of calorimetry
-Enthalpy changes of reactions in solution
-Enthalpy changes of combustion
calorimetry experiment
(enthalpy changes in reaction)
-used to measure enthalpy changes in experiments
-calorimeter can be made up of a polystyrene drinking cup, a vacuum flask or metal can
steps:
1.Using a measuring cylinder place 25 cm3 of the 1.0 mol dm-3 copper(II) sulphate solution into the polystyrene cup
2.Weigh about 6 g of zinc powder- as this is an excess there is no need to be very accurate
3.Draw a table to record the initial temperature and then the temperature and time every half minute up to 9.5 minutes
4.Put a thermometer or temperature probe in the cup, stir, and record the temperature every half minute for 2½minutes
5.At precisely 3 minutes, add the zinc powder to the cup (DO NOT RECORD THE TEMPERATURE AT 3MIN)
Continue stirring and record the temperature for an additional 6 minutes
6. plot results draw graph
how do we get maximum temperature in calorimetry
-for reactions that are not instantaneous there is a delay before maximum temperature is reached
-when maximum temperature is actually reached heat has already been lost to. the surroundings. so ween need to plot a graph and extrapolate to where the reactant was added too get maximum temperature.
calorimetry combustion experiment
The principle here is to use the heat released by a combustion reaction to increase the heat content of water
steps
1. fill copper can with water
2.weigh empty spirit burner and a the one you are using and minus to get grams of fuel
3. light wick and record tempreature of water going up, find mass of fuel burnt
is all heat transferred to water
no some water is lost to surroundings and some is absorbed by calorimeter
what should you do to minimise heat losses
-place a lid over the calorimeter
-make sure the calorimeter is not to far from the flame
-sheilidng can be used to reduce draughts
main sources of error in calorimetry
-incomplete combustion
-heat losses
