12Chemistry – Forensic Exam revision

  1. Forensic science – processes – definition
  2. Define the following terms
  3. Forensic
  4. Contamination (what things can contaminate samples?)
  5. Chain of custody
  6. Accuracy
  7. thoroughness
  8. Writeionic equations for reactions between the following pairs of solutions
  9. Sodium sulfate and lead chloride
  10. Calcium hydroxide and ammonium carbonate
  11. Iron (III) nitrate and potassium hydroxide
  12. Magnesium bromide and sodium phosphate
  13. Knowledge of solubility rules carbonates, hydroxides etc…
  14. An unknown solution formed a precipitate when sodium hydroxide was added to it. How useful is this information in identifying the cation in the unknown solution?
  15. What further tests could be used to positively identify the cation?
  16. Repeat a and b above for sodium carbonate’s addition to an unknown solution
  17. Specific tests that distinguish cations; show equations that explain the chemistry
  18. How can you distinguish between a solution containing Fe2+ and one containing Fe3+?
  19. A solution was known to contain Ba2+, Ca2+, or Zn2+ ions. How could you positively identify each?
  20. Provide specific tests that would allow you to distinguish between solutions containing the following anions. Show equations that explain the chemistry
  21. Sodium chloride and sodium fluoride.
  22. Ammonium carbonate and potassium sulfate.
  23. Potassium hydroxide and potassium thiocyanate. (KSCN)
  24. This question is about amino acids
  25. For what naturally occurring biomolecules are amino acids the structural unit?
  26. for these substances how many amino acids are typically linked?
  27. Show the structure of the amino acid glycine as it exists in neutral solution (pH = 7)
  28. Explain why its structure will change when placed into a solution of high pH
  29. Draw the structure of glycine at low pH
  30. A sample of water in the Derwent estuary, near Hobart, was taken after it had passed through an industrial area. Lead, zinc and copper were suspected as contaminants. Explain how you could identify these metal ions using chemical tests.
  31. A student was given four solutions (A – D) and told that each contained one of the following cations: Pb2+, Cu2+, Ba2+, Ca2+, Fe2+, Fe3+. Results of tests are as shown

Reagent / A / B / C / D
Na2CO3 / ppt / ppt / ppt / Ppt
HCl / ppt
NaOH / brown
K2SO4 / ppt / ppt

Use the given results to identify possible cations for A to D.

Provide a complete justification of your decision.

If there is not enough information to reach a definitive conclusion regarding the identity of any unknown, suggest other possible tests, and their expected results, which could be used to identify it.

  1. Use table 9.2 p 414 in your text to assist with answering this question

A mixture of amino acids containing phenylalanine, cysteine and aspartic acid was separated using both chromatography and electrophoresis. The results of the two processes were compared.

  1. Compare the two separation processes. How does each process achieve separation of the molecules?
  2. Predict the results of each process by drawing a chromatogram and an electrophoresis gel.
  3. Explain, using the structures of the amino acids, why the results are as you have predicted.

/ The results electrophoresis of proteins in blood of several individuals of one family are shown in the photograph. The columns M, C, C and F are drawn from Mum, dad and two children. The two right hand columns is a second woman’s blood and her child’s as the far right. She claims that the man is the father to her child. Systematically analyse the evidence to reach a conclusion and fully justify your response.
  1. A grazier found that animals were dying after being placed in one of his paddocks. Nearby there had been a garbage dump. He reasoned that organic substances and other toxic materials may have leached into the ground water and flowed into his property. Animals eating plants using this water might be the cause. Laboratory analysis of water and soil sample revealed the results below the flow chart. One set of tests was used to identify possible organic contaminants.
RESULTS / Bubbles formed on reaction with sodium
Green on addition of acidified dichromate solution
Brick-red on heating added Benedict’s solution
Reaction to bromine

Which organic group or groups is/are present? Clearly explain your reasoning.(IP)

  1. Contamination from toxic metals was also a possibility, so testing was done to detect the presence of the following ions

Pb2+, Ba2+, Hg2+, Ni2+, Cr3+, Ag+, Cs+, Ra2+, Zn2+, Rb+, Be2+ or Sr2+

They again conducted a series of tests on the sample and obtained the following results:

  • Addition of sodium hydroxide produced a white precipitate.
  • No precipitate was formed with the addition of either HCl or H2SO4.
  • A precipitate formed with alkaline H2S.
  • Addition of excess hydroxide does not dissolve precipitate formed

What cation was found to be present? Justify how you came to your answer.

  1. a. Draw a dichotomous flowchart that permits the identification of chloride, fluoride, hydroxide, carbonate and sulfides,

b. The chemists then proceeded to test the water sample to determine the anions present (chloride, fluoride, hydroxide, carbonate and sulfides). They suspected there might be several. The following tests results were obtained:

  • Addition of Mg(NO3)2 to the water sample produced a milky white precipitate

Which anion/s may be present as indicated by these results?

Suggest other tests that would give greater confidence in the identification