Experiment 9 Prelaboratory Assignment A Volumetric Analysis Desk No._ lab Sec. N

Question

Experiment 9 Prelaboratory Assignment A Volumetric Analysis Desk No._ lab Sec. Name is the tiarant for this experiment? What 1. a is the indicalox generally aded to the titrant or the analyte in a titrnation? standard used in this experiment (name and formula)? Define z a What is the primary standare a primary standard. b. What is the secondary standard used in this experiment (name and formula)? Define a secondary standard. Distinguish between a stoichiometric point and an endpoint in an acid-base titration 16e When rinsing a buret after When rinsing a buret after cleaning it with soap and water, should the rinse be dispensed through the 4. buret tip or the top opening of the buret? Explain. b. Experimental Procedure, Part A.4. In preparing the buret for titration, the final rinse is with the NaOH titrant rather than with deionized water. Explain 5 Part A.3. Calculate the mass of KHC, H,O, (molar mass 204.23 g/mol) that reacts with 15 mL of the 0.15 M NaOH solution prepared in Part A.2. Express this mass KHC,H,O, to the correct number of significant figures and record the calculation on the Report Sheet Experiment 9 1

Explanation / Answer

1. a) The titrant is the solution which is taken in the burette. So, in this experiment, NaOH solution is the titrant.

b) Indicator is generally used in the analyte, i.e. in volumetric flask in a titration.

2. a) The primary standard used in the experiment is potassium hydrogen phthalate (C8H5KO4). The primary standard is a substance which has high purity, large molar mass and is non-hygroscopic. They are used to calibrate other standards.

b) Secondary standard used in the experiment is sodium hydroxide (NaOH). The secondary standard is the solution which is to be analysed and it standardised using primary standard.

3. Stoichiometric point in an acid-base titration is the number of moles of base required to neutralise number of moles of acid. When the moles of both of them are same, then that is the stoichiometric point. But end point is little bit more than the stoichiometric point. It is the point in the titration when the indicator just gives its colour and it gives the colour when the pH of the solution changes. The pH changes just above neutralisation. Thus end point is bit more than stoichiometric point.

4. a) When rinsing the buret with soap and water, the rinse should be dispensed from the tip and not the top opening. Because we need to clean the tip of the buret also. It is also done to remove the air droplets in the tip. The rinsing will help to know if there is any air bubble in it.

b) The final rinse is done with NaOH, titrant, so that whole of the buret is coated with NaOH solution. If the final rinse is with water, then it leads to dilution of the titrant. And the reading would be incorrect. So, final rinse is done with titrant.

5. In the reaction of (C8H5KO4) with NaOH, 1 mol of C8H5KO4 reacts with 1 mol of NaOH.

For NaOH, Molarity = 0.15 M

Volume = 15 ml = 0.015 L

Moles of NaOH = molarity*volume = 0.15*0.015 = 0.00225 mol

Mole of (C8H5KO4) = mole of NaOH = 0.00225 mol

molar mass of (C8H5KO4) = 204.23 g/mol

Mass of (C8H5KO4) = molar mass*number of moles = 204.23*0.00225 = 0.459 mol = 0.46 mol

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