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Analytical Chemistry Lab Exam Questions and Answers 2023
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Analytical Chemistry Lab Exam Questions and Answers 2023
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Analytical Chemistry Lab Exam Questions and Answers 2023What is meant by "Class A Glassware" and "Class B Glassware"? Which type of glassware is referred for analytical volume measurements? Ans- Class A glassware is preferred for analytical volume measurement because it provides the highest accuracy and compiles with Class A volumetric tolerances. Class B glassware has volumetric tolerances greater than Class A and they comply with Class B glassware.
What do the symbols "TD" and "TC" mean on volumetric glassware? Which devices are associated with each using a volumetric device? Ans- TD stands for "to deliver" and which is on graduated cylinders, burets, and pipets. TC stands for "to contain" which is on volumetric flasks.
What is parallax error? What steps can be taken to minimize this type of error when you
are using a volumetric device? Ans- A parallax error is when you look at the miniscus incorrectly. To avoid this measure the water level at the bottom of the meniscus when the water level is at eye level.
Explain why it is important to calibrate volumetric devices. How does temperature affect this calibration? Ans- It is important to calibrate volumetric devices in order to obtain the most accurate measurement possible. Glassware can expand or contract with different temperatures.
A 50.00 mL volumetric flask is filled at 30C with deionized water. The mass of the water in the flask at this temperature (as read directly from the balance) is 47.7380g. a)What is the true internal volume of the flask at 30C? You may assume a density of 0.0012 g/mL for the surrounding air and that the balance has been calibrated with an 8.0g/ml reference weight.
b)What is the true volume of the volumetruc flask at 20C? Ans- a) 50.01 mL
b) 50.00 mL
Show how you would prepare 250mL of a 0.10M NaCl solution in the lab. Ans- 1.47g NaCl dissolved in 250 mL water
You pipetted 25mL of 0.10M NaCl into 250 mL Erlenmeyer flask to which 5 drops of indicator and 0.05g of dextrin have been added. Then you carried out the titration in diffuse light to the equivalence point.
a) What is the titrant in this titration?
b) Write the molecular, complete ionic and net ionic equations for the titration reaction
c) Why is the titration carried out in diffuse light?
d) What is the function of dextrin? e) What volume of 0.12M AgNO3 is required to reach the equivalence point? Ans- a)AgNO3
b)NaCl + AgNO3 --> NaNO3 + AgCl Cl- + Ag --> AgCl
c) Diffuse light is used to minimize the possible error of photocomposition of AgCl which
is when there is a purple-black hue on top of the white AgCl.
d)Dextrin is used to prevent colloidal particles from coagulating and the reduction of precipitates surface area.
e) 0.021L AgNO3
A 0.2334g quantity of primary standard NaCl is dissolved in 250.00mL. A 10.00mL aliquot of this solution consumes 14.32mL of a silver nitrate solution before reaching the
end point in a Fajans titration. A chloride solution, prepared by dissolving 0.2789g of an unknown sample in 250.00mL taking a 10mL aliquot of the resulting solution, requires 11.21mL of the same silver nitrate solution to reach the end point. What percentage chloride (w/w) does the unknown contain Ans- 39.79%
What is meant by argentometric titration? Ans- Argentometric titrations are titrations that involve silver (1) ion
Explain the principles of absorption indicators. Use the Fajans method as example. Ans- When Ag is added to Cl excess Cl is absorbed onto the AgCl surface creating a negative charge prior to the equivalence point. After the equivalence point excess Ag is absorbed onto the AgCl surface creating a positive charge. The negativily charged dye partiles are absorbed onto the positively charged surface, signaling the end point of the titration by the color change..
Why we need to standardize NaOH and HCl? Ans- So that we know the exact concentration resulting in increasing reproducibility of an experiment
Why are KHP and Na2CO3 used as primary standards? Ans- Primary standards should be 100% pure, they must be easy to obtain, purity, dry and preserve, they should
not change in air during weighing, they should be of high relative molar mass, they should be readily soluble under the conditions in which it is used, and they should posses the properties required for a titration. KHP and Na2CO3 meet these requirements.
Standardization of NaOH with KHP
a) Calculate the volume of 50 wt% NaOH needed to prepare 1.0L of 0.10M NaOH (density is 1.50g/mL)
b) Calculate the mass of solid potassium hydrogen phthalate you will titrate. Each sample should contain enough solid to react with 25mL of 0.10M NaOH Ans- a) 0.0053L NaOH
b) 0.51g KHP
Standardization of HCl with Na2CO3
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