BISHOPS
Grade :11PHYSICAL SCIENCE
PRACTICAL:Standard solution and titration
Date :…………………………..
Name :…………………………………………………Set:……………………
MARK ACHIEVED:……………… [out of 25]
SKILLS:In this practical, you will be evaluated on your ability to :
- measure out solutions accurately.
- record and process readings from the experiment.
- understand the scientific concepts utilised.
AIM:Making a standard solution and using it to find the concentration of an unknown solution by titration and calculation.
1.Making a standard solution of sodium carbonate (Na2CO3).
n = m/Mc = n/Vc = m/(M.V)1dm3 = 1000 cm3
Using an electronic balance, weigh out about 2,0 g of anhydrous sodium carbonate on a watch glass. Record mass below.
Mass of sodium carbonate = …………………………..
Place your weighed sodium carbonate into a 100 ml beaker which contains about 50 ml of warmed distilled water. Stir to dissolve and rinse the stirring rod with distilled water ensuring you do not lose any. Carefully pour the solutioninto a 100 cm3 volumetric flask. Make sure every last drop of solution is washed out of the 100 ml beaker, using distilled water. Now add distilled water to the volumetric flask until the bottom of the meniscus is on the graduation. Stopper and shake so that the concentration of the solution is even throughout the flask. This is now your standard solution.
Calculate the concentration of your standard solution inmol.dm-3, showing all your working.
Concentration of sodium carbonate = ………………………..
2.Titration: using the standard solution of sodium carbonate to find the concentration of a solution of hydrochloric acid.
ca.Va = a
cb.Vb b
Pipette 25 cm3 of the sodium carbonate solution into a conical flask. Addtwelve to twenty drops of methyl red indicator. It should turn yellow.
Fill a burette with the hydrochloric acid provided. Run some out to fill the portion below the tap. Record the initial reading (titre) in the table below.
Now run the acid from the burette into the sodium carbonate solution in the conical flask until one drop changes its colour from yellow to red. Record the final titre in the table below.
If you felt this first one was inaccurate, then record it as a rough and do two more titrations, using only the second and third titrations to record the average titre. If you felt it was accurate then do one more titration only.
1 / 2 / 3Final titre (cm3)
Initial titre (cm3)
Titre (cm3)
Average titre = ………………….cm3
Calculate the concentration of the hydrochloric acid, showing all your working:
Na2CO3 + 2HCl 2NaCl + H2O + CO2
Concentration of hydrochloric acid = ……………………………
ASSESSMENT:
0 / 1 / 2 / 3 / 4Recording of mass / Not attempted. / Done, but not close to 2 g (more than
0,5 g out). / Near 2 g but recorded to no decimal places. / Near 2 g, recorded to at least 1 decimal place. No units. / Near 2 g, recorded to at least 1 decimal place. Correct units.
Calculation of [Na2CO3]. / Not attempted. / Attempted. / One error in calculation. / All correct but no units and/or no use of initial equation(s). / All correct, with units and use of initial equation(s).
Recording of titres. / Not attempted. / Two quantities are more than 0,5 cm3 apart and values recorded to differing numbers of decimal places / Two quantities are more than
0,5 cm3 apart but all to one decimal place. / Two quantities are less than 0,5 cm3 apart but values recorded to differing numbers of decimal places. / Two quantities are less than
0,5 cm3 apart and all to one decimal place.
Average titre / Not attempted. / Incorrectly calculated. / Correctly calculated.
Calculation of [HCl] / Not attempted / Attempted / One or two errors in calculation. / All correct but no final units and/or no use of initial equation. / All correct, with final units and use of initial equation.
Accuracy of final answer. / Below 30% / Within 30% / Within 20% / Within 10% / Within 5%
Responsible use of apparatus/clearing up/following instructions etc / Completely uncooperative / Too many instructions or requests not followed / Some requests or instructions not followed. / No problems encountered
Total………./25