Titration And Standard Solution Practical 2 Flashcards
What is the purpose of a titration?
To find the concentration/volume of an unknown acid or alkali
Purpose of a burette?
Delivers the variable volume of a liquid and contains the standard solution
Read at 2DP where the last digit is a 0 or a 5
What is a pipette?
Accurately delivers a stated volume of a liquid
What is a standard solution?
A solution whose concentration can be precisely determined and used in later titrations
What’s the function of a conical flask?
Contains solution of unknown concentration
What is a titre?
Difference between initial and final readings from burette
What are concordant results?
2 values within 0.2cm³ away from each other
Titration-Preparing a standard solution
1.Weigh boat and requires mass of solid
2.Tip solid into beaker and add small volume of distilled water
3.reweigh boat
4.Stir to homogenise solution and solute is dissolved
5.Transfer solution to a volumetric flask
6.Wash beaker,funnel and Rod with distilled water
7.Use a dropper pipette to add volume up until mark
8.Stop the flask and mix by inversion
What would happen if conical flask was washed with reagent solution rather than distilled water?
More moles of solution will be present which leads to an overestimate
What would happen and explain the effect if droplets of solution from burette was left on the side of the walls?
Droplets didn’t react with solution so less actual volume in volumetric pipette than expected so this will cause an overestimate so more moles of solution calculated
What are concordant results?
Results that are within 0.2 away from each other
What is accuracy?
How close your results are to the original value
What is precision?
How close all your results are in comparison to each other
More varied results means lower precision
What is Dilution?
Process by which solvent is added to a solution to increase its volume and decrease solute conc
Only the volume changes
What would happen if you did not reweight the weighing boat during titration?
Some mass may be left on the boat so actual mass in burette is lower leading to an overestimate
As you think you’ve put a higher amount
What would happen if volume was not added to the mark?
Inaccuracy as adding too much volume means the concentration changes which means no standard solution
What colour does methyl orange go from?
Red to yellow in alkali
Yellow to red in acid
What are random errors and how to improve accuracy?
Random errors are caused by unpredictable changes in conditions such as temp or pressure
Improve accuracy by: repeating experiment and removing anomalies
What is a systematic error and how to improve?
Error caused by the apparatus and leads to recorded value being to high
Recalibrate or replace the apparatus
What would happen if there was a bubble in the pipette containing NAOH and what error would it be?
Random error
Will affect volume of NAOH as there is less volume than you think so underestimate as there is less moles of NAOH
What would happen of funnel was left on top of the burette and what error would this be?
Random error,this would increase the vol of acid so the titre is smaller as initial vol of greater so its an underestimate
What would happen if the tap of the burette was not filled?
Random error as greater volume of NAOH was actually used so more moles of naoh leading to an overestimate
What is the measurement uncertainty of a burette?
±0.05vm³ and for a measuring cylinder as well
What is the calculation of percentage uncertainty?
Total error(uncertainty of apparatus)/quantity measured
Than times by a 100 for a percentage
Why should the total error sometimes be multiplied by 2 in percentage uncertainty?
As some apparatus require it to be read twice like a burette or a ruler or a mass balance
How to minimise error and uncertainty?
Use best type of uncertainty,calibrate
Measure out a greater quantity of susbstance
Explain the steps of a back titration?
Weigh a precise amount of the sample
Add a known excess of a standard reagent that fully reacts with the analyte(unknown reagent)(This is a neutralisation reaction)
Mix thoroughly and allow reaction to complete
Titrate the remaining unreached reagent(the one in excess)with a second solution
Calculate amount of reagent that reacted with the analyte by subtracting the excess
Determine the concentration or quantity of the analyte by using stochiometry
Why are back titrations necessary instead of normal titrations
Slow reactions
No clear endpoint
Some substances are volatile
Some substances are insoluble
