AS 1012.20.2:2016 pdf free

AS 1012.20.2:2016 pdf free.Methods of testing concrete
If a potentiometric titration by ion selective electrode is used, the procedure shall be as follows:
(a) Add three drops of methyl orange indicator to the test solution, then add nitric acid dropwise until a permanent pink to red colour is obtained. Make up the volume to 200 mL with water.
(b) For instruments equipped with dial readout, establish an approximate ‘equivalent point’by immersing the electrodes in a beaker of water and adjusting the instrument to read about 20 mV lower than midscale. Record the approximate millivoltmeter reading. Remove the beaker and wipe the electrodes with absorbent paper.
(c) Carefully pipette 2 mL of standard 0.05 mol/L NaCl solution into the test solution in the beaker. Place the beaker on a magnetic stirrer and add a TFE fluorocarbon-coated magnetic stirring bar. Immerse the electrodes in the solution, taking care that the stirring bar does not strike the electrodes, and begin stirring gently. Place the delivery tip to the 10 mL burette, filled to the mark with a standard 0.05 mol/L silver nitrate solution, in or above the solution.
NOTES:
1 It is advisable to maintain a constant temperature during measurement, for the solubility relationship of silver chloride varies markedly with temperature at low concentrations.
2 If the tip of the burette is out of the solution, any adhering droplet should be rinsed onto the beaker with a few millilitres of water following each titration increment.
(d) Gradually titrate, and record the amount of standard 0.05 mol/L silver nitrate solution required to bring the millivoltmeter reading to -60.0 mV of the  quivalent point determined in the water.
(e) Continue the titration at 0.20 mL increments. Record the burette reading and the corresponding millivoltmeter reading in columns 1 and 2 of a four-column recording form. Allow sufficient time between each addition for the electrodes to reach equilibrium with the test solution.
NOTES:
1 An example recording form is shown in Appendix A.
2 Experience has shown that aceptable readings are obtained when the minimum scale reading does not change within a 5 s period (this usually happens within 2 min).AS 1012.20.2 pdf free download.