Chemistry Answers

A CAPE Chemistry student sought to determine the solubility product, Ksp of calcium hydroxide by titrating saturated solution of Ca(OH)2 against standardized hydrochloric acid solution, HCl. The saturated Ca(OH)2 solution was filtered, to remove excess solute, and 25mL aliquots were titrated against 0.10M HCl solution using bromothymol blue indicator.

State the colour change the student observed as the end-point was reached. 

Calculate the concentration of Calcium Hydroxide.

Write the Ksp expression for Ca(OH)2.

Use the equilibrium expression for the dissolution of Ca(OH)2 to determine the concentration of Ca2+ and OH–.

Calculate the Ksp for calcium hydroxide (state the units).

The value the student calculated deviated significantly from the accepted value. The reason given was 

‘some of the excess solute got into the filtrate during filtration of the saturated calcium hydroxide’.

State how this could have affected the Ksp value.

State one other factor that could have affected the Ksp value.

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9. Shore has developed systematic procedures for making boron hydrides in good yield taking advantage of ;

A. Pyrolysis of diborane. B. Acidity of -H.

C. Hydrogen abstraction. D. Abstraction of H- .

E. Thermal decomposition.

Application limitations and strength of Mossbauer spectroscopy

Working principle of Mossbauer spectroscopy

Methanol is manufactured industrially by the reaction CO(g) + 2H2(g) <-> CH3OH(g). A gaseous mixture at 500K is 0.020 M CH3OH; 0.10M CO; and 0.10M H2. Calculate the equilibrium constant for the reation if the temperature is 300K. At what side will the equilibrium lie?

Any remaining solid impurities are removed by filtration before continuing with the analysis. In a typical total analysis method, the procedure might read

After digesting the sample in a beaker, remove any solid impurities by passing the solution containing the analyte through filter paper, collecting the filtrate in a clean Erlenmeyer flask. Rinse the beaker with several small portions of solvent, passing these rinsings through the filter paper and collecting them in the same Erlenmeyer flask. Finally, rinse the filter paper with several portions of solvent, collecting the rinsings in the same Erlenmeyer flask.

For a typical concentration method, however, the procedure might state

After digesting the sample in a beaker, remove any solid impurities by filtering a portion of the solution containing the analyte. Collect and discard the first several mL of filtrate before collecting a sample of approximately 5 mL for further analysis.

Explain why these two procedures are different.

A method for the analysis of Ca2+ in water suffers from an interference in the presence of Zn2+. When the concentration of a Ca2+ is 50 times greater than that Zn2+, an analysis for Ca2+ gives a relative error of 2.0%. What is the value of the selectivity coefficient for this method?

A sample is analyzed to determine the concentration of an analyte. Under the conditions of the analysis the sensitivity is 17.2 ppm-1. What is the analyte’s concentration if S total is 35.2 and S reag is 0.6?

A certain concentration works best when the analyte’s concentration is approximately 10ppb.

a. If the method requires sample of 0.5mL, about what mass of analyte is being measured?

c. Repeat for the case where the analyte is present at 10% w/w. 59

d. Based on your answer to parts (a) - (c) comment on the method’s suitability for the determination of a major analyte.