Title: CHE2MOC Pre-lab quizzes

CHE2MOC Pre-lab quizzes

Q: In the hydrolysis of sucrose in experiment Ins3, what is the role of the hydrochloric acid?
- it is a pH buffer
- it is a catalyst
- it is a reagent
- it is both reagent and catalyst
A: it is a catalyst

Q: The TLC in experiment B5 is run with an eluent containing acetic acid.  The R_f value for aspirin under these conditions is approximately 0.8.  How would the R_f value change if the acid were omitted from the eluent?
- Rf would increase
- Rf would decrease
- Rf would remain unchanged
A: Rf would decrease

Q: What is the molar concentration (in mol/L) of a 100 mL^ solution containing 20 g of sucrose (molecular formula C_12H_22O_11)?
A: 0.58 (± 0.1)

Q: What rotation angle would you expect to observe for a sucrose solution of concentration 0.2 g/cm3 in a polarimeter tube of 20 centimetres pathlength (specific rotation of sucrose: 66 cm3/dm g)
A: 26.4 (± 2)

Q: A solution containing 1 mmol/L each of compounds 1 and 2 is analysed by UV/vis spectroscopy at a wavelength of 510 nm.  The absorbances of the individual compounds at 1 mmol/L are A1 and A2 (at 510 nm).  What is the absorbance of the mixture?
- A1 x A2
- A1 + A2
- A1 - A2
- A1 or A2, whichever is greater
A: A1 + A2

Q: Methanol is a classed as dangerous good and hazardous substance. What hazards are associated with it?
- highly flammable
- toxic
- teratogenic
- corrosive
A: highly flammable; toxic

Three of the techniques you will be using in this lab exercise are recrystallisation, thin-layer chromatography (TLC) and solvent extraction. You can remind yourself of the procedure and principles of these techniques at the Interactive Lab Primers web page (Royal Society of Chemistry, UK):

Recrystallisation (http://www.chem-ilp.net/labTechniques/Recrystallisation.htm)

TLC (http://www.chem-ilp.net/labTechniques/TLC.htm)

Solvent extraction (http://www.chem-ilp.net/labTechniques/SolventExtraction.htm)

Each of these links includes an animation and video, as well as other resources. Use these materials to answer the questions in this quiz.

Q: The suitability of a TLC solvent to separate spotted samples mainly depends on which property?
- Polarity
- Molecular weight
- Viscosity
- Colour
- Boiling point
A: Polarity

Q: In a solvent extraction using water and an organic solvent, which property will determine whether the organic phase will be the top layer or the bottom layer?
- Density
- Molecular weight
- Polarity
- Colour
- Boiling point
A: Density

Q: What would you expect for the melting point of your recrystallised benzoic acid compared to the benzoic acid-fructose mixture?
- The recrystallised benzoic acid has a higher melting point than the mixture.
- The recrystallised benzoic acid has a lower melting point than the mixture.
- The recrystallised benzoic acid has the same melting point as the mixture.
A: The recrystallised benzoic acid has a higher melting point than the mixture.

Q: What symmetry element(s) are there in trans-1,2-diaminocyclohexane?
- inversion centre
- C2 rotational axis
- mirror plane
A: C2 rotational axis

Q: Under what pH conditions is 1,2-diaminocyclohexane soluble in organic solvents, such as dichloromethane?
- In alkaline solution.
- In acidic solution
- At neutral pH.
- 1,2-Diaminocyclohexane is soluble in organic solvents at any pH.
A: In alkaline solution.

Q: Which molecule is depicted in the Newman projection below?

[Image: Newman projection]
- chloropropane
- 2-chloropropane
- chlorobutane
- chloroethane
- 2-chlorobutane
A: chloropropane

Q: Besides flavanone, what other product is formed in the base-catalysed reaction of 2-hydroxyacetophenone and benzaldehyde?
- water
- hydrogen peroxide
- carbon dioxide
- HCl
- carbon monoxide
A: water

Q: What happens to a sample of bromine when its temperature increases from 50 to 60 degrees Celsius?
- it sublimes
- it boils
- it melts
- nothing
A: it boils

Q: What is the concentration of sodium hydroxide (in mol/L) in the reaction in part A?
A: 2.5 (± 0.25)

Q: Which of the following solvent combinations (for thin-layer chromatography) is the most polar one?
- acetone:hexane 50:50
- chloroform:hexane 50:50
- acetone:hexane 75:25
A: acetone:hexane 75:25