SS1 Chemistry Lesson Note on Titration Precautions

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TITRATION PRECAUTIONS

1. The burette must be clamped vertically or not tilted.
2. Wash the burette and pipette with water andrinse with distiled water.
3. Rinse the burette with acid,the pipette with base (alkali)before putting these solutions into them.
4. Ensure no air bubbles in the burette or pipette.
5. Remove the funnel after putting the acid into the burette(if a funnel is used).
6. The content of the pipette should be allowed to run into the conical flask without blowing air into it.
7. Use a drop or two (small amount)of indicators.
8. Read the lower meniscus.
9. Ensure the tap of the burette is not leaking.

NOTE: Most examination bodies have different ways of assessing students practical skills and report writing procedures. For instance, the following are some of the penalities.

i)use of pencil;   -2marks

ii)Alteration (cancillation) on table of titrevalues; -2marks foreach,maximum of  -4marks.

iii)No unit or wrong unit on table;  -1mark.

iv)Non concordant values(i.e.difference greater than pluse or minus 0.2)for average titre value;  -1mark.

STEPS IN RECORDING OBSERVATIONS MADE DURING ACID- BASE TITRATION EXPERIMENT

1. Construct the specimen table:Example

Burette Readings in cm3	Trial or Rough	1st	2nd
Final Burette reading	24.80	24.00	24.00
Initial Burette reading	0.00	0.00	0.00
Volume of Acid used	24.80	24.00	24.00

 

1. Determine the average volume of acid used (i.e. average titer value).

Thus:Average Titre:- 24.00 + 24.00  = 24.00cm³

                                              2

Depending on the differences in readings of the titre values. All your readings must have their units, i.e.cm³.

NOTE:This value and that of the table should be recorded to two places of decimal.

    iii. SIGNIFICANT FIGURES

Sudent should learn to round  off their calculation numbers to three significant figures,since they are using foure figure table for their calculations.

Significant figures start from non-zero digit and all other digits that follow including zero are considered Significant. As usual the digits, 5,6,7,8,9 are rounded up while 1,2,3,4,are round off.

Examples:

                          Numbers                                    Rounded  off

                          299.30                                         299 to 3 S.f

0.0128                                          0.0128 to  3 S.f

6.0246                                          6.02   to    3  S.f

NOTE : for the sake of the examination,prepere your table on a sheet of paper and then neatly transfer it in INK to the answer sheet.

EXAMPLE 1

A is a solution of tetraoxosulphate {vi} acid.

B is a solution containing 0.0500 mole of anhydrous Na₂CO₃ per dm3.

(a)Put A in the burette and titrate 20.00 or 25.00 cm3 portions of B using methyl orange as the indicator. Record the size of your pipette. Tabulate the burette readings, and calculate the average volume of the acid used.                                                                                                                                                                                       (b) From your result and data provided, calculate the

I   amount of Na2CO3 IN 25.00 CM3 OF B used

Ii    concentration of A in moldm^-3                                                                                                                                                                                                                                      

Iii    concentration of A in gdm^-3

Iv   number of hydrogen ions in 1.00dm3 of A. {Avogadro number = 6.02×1023 mol1}

The equation of reaction is: H₂SO₄{aq} +Na₂CO₃{aq]                      Na₂SO₄ {aq} + H₂O +CO₂

{H =1,O=16, S=32}

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