Titration

Questions: 1- When preparing a standard solution why is it important to completely dissolve the chemical (i.e. sodium carbonate) you are using before making the solution up to the meniscus mark in the volumetric flask?2- Why do you not rinse your conical flask with your solution before you add in your 20mL of solution using the volumetric pipette?3- In the step 6 of the titration procedure; why does it not matter if you add water?4- Name two other indicators( besides Methy| Orange that was used for this titration) that can be used for an acid-base titration and detail their respective colour changes at a particular HP. Answers: 1- When preparing a standard solution why is it important to completely dissolve the chemical (i.e. sodium carbonate) you are using before making the solution up to the meniscus mark in the volumetric flask? The sodium carbonate works as a primary standard solution while performing a titration. This primary standard solution is one whose concentration is known in the experiment that is used further to calculate the concentration of an unknown solution. The standard solution of sodium carbonate is 1.2 g in 250 ml deionized water for this experiment. The volumetric flask meniscus mark is the final level of solution that is complete 250 ml standard solution above which no further water could be added. Therefore, it is important to dissolve complete sodium carbonate before reaching the meniscus of flask because no further water can be added after this point where the solution will be 250ml (Wenclawiak, Koch Hadjicostas, 2010). 2- Why do you not rinse your conical flask with your solution before you add in your 20mL of solution using the volumetric pipette? The conical flask is not rinsed with the standard solution because rinsing the flask with sample solution can lead to the potential small increase in solution volume that can lead to error in getting an accurate reading. As the standard solution volume is taken as 20ml, if the flask in rinsed with the solution there can be an increase in this volume that can lead to error in the experiment (Wenclawiak, Koch Hadjicostas, 2010). 3- In step 6 of the titration procedure; why does it not matter if you add water? The experiment involves volume and concentration of base equals the number of moles in the base that is used to determine the acid number of moles. The addition of deionized water (containing no acid or base) can never affect the number of moles of acid. Hence, adding water does not affect the neutralisation reaction (Wenclawiak, Koch Hadjicostas, 2010). 4- Name two other indicators (besides Methyl Orange that was used for this titration) that can be used for an acid-base titration and detail their respective colour changes at a particular HP? The indicators used for acid-base titration except Methyl Orange are: - Indicator Colour (Acid) Colour (Base) pH range pKln Phenol Red Yellow Red 6.8-8.4 7.9 Phenolphthalein Colourless Pink 8.2-10.0 9.4 Source: (ACID_BASE INDICATORS. 2016) References ACID_BASE INDICATORS. (2016).Ch.ic.ac.uk. Retrieved 20 June 2016. Wenclawiak, B. W., Koch, M., Hadjicostas, E. (2010).Quality assurance in analytical chemistry: training and teaching. Springer Science Business Media.