the standard deviation ind Discuss the relative standard deviation briefly a com
ID: 1030760 • Letter: T
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the standard deviation ind Discuss the relative standard deviation briefly a comparison of the two vinegars or for an analysis of a single vinegar, calcu . Data Analysis C and D Laboratory Questions Circle the questions that have been assigned. 1. Part A2 A 20-mL volume of previously boiled, deionized waier is added to the Erlenmey er flask to prepare the sample for titration. Explain why this volume is not critical to the analysis 2 Pat A.2 Previously boiled, deionized water is unavailable. in a uzy to pursue the analysis, deionized water (oe orted percent a etic acid in vinegar. to en te re biled) s added. Howdoes this attempt to expedite the analysis a high, too low, or unaffected? Explain. Part A.2 and B.1. The 20 mL of water added to the Erlenmeyer flast is to be previously boiled, deionized water.Since water does absorb CO, from the atmosphere and since CO, dissolved in water causes it to be slightly acidic, will he use of deionized water that has not been previously boiled cause the mass of acetic acid in the vinegar to be calculated as too high or too low? Explain. 4. Part A.2 a. In determining the percent acetic acid in vinegar, the mass of each vinegar sample is measured rather than the vol- ume. Explairn h. If the vinegar were measured volumetrically (e.g., a pipet), what additional piece of data would be needed to com plete the calculations for the experiment? 5. Part A.3. The buret is filled with the NaOH titrant and the initial volume reading is immediately recorded withou waiting the recommended 10-15 seconds. However in Part B.1, the 10-15 second time lapse does occur before the reading is made. Does this technique error result in an increase, a decrease, or have no effect on the reported percest 6. Part B.1. The endpoint of the titration is overshot! Does this technique 7. Part B.1. The wall of the flask is periodically rinsed with the previous 8. Part B.1. A drop of NaOH titrant, dispensed from the buret, adheres to the wall of the Erlenmeyer flask acetic acid in the vinegar? Explain. no effect on the reported percent acetic acid in the vinegar? Explain. Does this titrimetric technique result in an increase, a decrease, or have no effect on the reported percert error result in an increase, a decrease, or have ly boiled, deionized water from the wash botle acid a the vinegar? Explain. but is not washed into the vinegar with the wash bottle. Does this error in technique result in the reported percent being too high, too low, or unaffected? Explain 148 Vinegar AnalysisExplanation / Answer
1. Vinegar is a solution of acetic acid in water. Here we are estimating the amount of acid present in the solution by reacting it with the solution of base of known concentration. This method is called Volumetric analysis or Titration.
Concentration = _ grams of vinegar _________
Volume of solution in 1000 mL
So finally the volume terms get cancelled and we end up comparing mass of sodium hydroxide reacting with given mass of acetic acid.
Hence volume is not critical in this analysis. We can dilute the vinegar in any volume of previously boiled deionised water based on the strength of given sodium hydroxide solution.
CH3COOH + NaOH ----------> CH3COONa + H2O
1 mole of acetic acid (gram molecular mass) reacts with one mole of sodium hydroxide (gram molecular mass).
Hence 60g (gram molecular mass) of acetic acid gets completely neutralised by 40g (gram molecular mass) of NaOH.
According to the volumetric analysis
(Concentration x Volume )acetic acid = (concentration x Volume )sodium hydroxide
(Molarity X Volume ) acetic acid = (Molarity X Volume ) sodium hydroxide
[(Grams of acetic acid / gram molecular mass of acetic acid)/1000m L] X Volume of sample =
[(Grams of sodium hydroxide/gram molecular mass of sodium hydroxide)/1000m L]X Volume of titrant added in m L.
2. Percentage acetic acid present in the Vinegar is calculated based on the mass of Vinegar present in the given volume of solution by making it react with known amount of NaOH.
Water is called an universal solvent. It can contain several dissolved salts as well as gases in it. So we have to take deionised water so that all dissolved salts are removed. Not only that, we have to make sure that the deionised water taken for this activity is pre boiled to remove dissolved gases from it. Most importantly carbon dioxide gas dissolved in water.
Carbon dioxide is acidic in nature. So when vinegar sample is prepared in an unboiled deionised water, it reacts with a small amount of excess NaOH. This creates a false impression that the vinegar solution contains a little excess acid and the percentage mass of the acetic acid will be more than what is expected. The error is because of presence of dissolved CO2.
3. Carbon dioxide is acidic in nature, hence it will consume a small amount of additional NaOH along with the volume required for neutralising acetic acid present in Vinegar. Hence this shows that the solution of vinegar contains excess acetic acid than what was expected. Hence it shows excess mass of acetic acid in Vinegar.
4. Volume of liquids change with change in temperature. Hence concentration of the solution may vary and we end up getting wrong results if we consider volume percentage of acetic acid. Hence we consider mass of acetic acid present in given volume of vinegar solution to determine the concentration. Hence amount of substance and concentration is directly proportional to mass.
5. In B after filling the burette with NaOH solution and waited for few seconds. Then initial burette reading is noted and titration is started. In this method some amount of sodium hydroxide present in the burette will be neutralised by carbon dioxide present in atmosphere. Concentration of NaOH will now decrease. Vinegar solution now consumes more NaOH solution than expected and hence the vinegar solution will show an increased acid content.
6. Overshooting the end point by not observing the colour change carefully results in addition of excess amount of sodium hydroxide than required to neutralise the acetic acid in vinegar. Hence the vinegar solution shows increased vinegar content in the solution.
7. Periodic rinsing of inner walls of the conical flask used for titration will remove unreacted NaOH droplets sticking on to the walls which can react with the next sample. Now this trial consumes less NaOH solution indicating less amount of acid is present in the vinegar solution.
If the flask is not drained completely then the water present initially will dilute the vinegar sample taken for next trial. Hence less amount of NaOH is consumed and the acetic acid content shown here will be less than expected.
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