UMD CHEM 425 - midterm_I_sample_1 (7 pages)

Name Section CHEM 425 INSTRUMENTAL METHODS OF ANALYSIS MID TERM EXAM I XXX 140 Points Instructor XXX Calculations Multiple choice 5 pts each Short Answers 5 pts each Total Pts Possible 40 pts Question 60 pts 1 12 40 pts 1 Grade 1 2 3 4 5 6 7 8 EXAM GRADE 140 Honor Pledge Copy the following and sign below I pledge on my honor that I have not given or received any unauthorized assistance on this examination Signature Calculations 40 pts total 1 The following data apply to apply to a column for liquid chromatography Length of column 25 7 cm Flow rate 0 313 mL min VM 1 37 mL VS 0 164 mL A chromatogram of species A and B provided the following data Non retained A B Retention Time min 3 1 13 3 14 1 Calculate A the number of plates and plate height from each peak B the capacity factor for each peak C the selectivity factor D the resolution Type text Width of Peak Base W min 1 07 1 16 E the expected resolution if the column length was doubled F the expected capacity factors if the column length was doubled G the length of column necessary to give a resolution of 1 5 H the time required to separate A and B with a resolution of 1 5 Type text Multiple Choice 5 points each right or wrong no partial credit Total 60 points 1 How will increasing the column length by a factor of 4 affect resolution A No change B Increase by a factor of 4 C Increase by a factor of 2 D Decrease by a factor of 2 E Increase by 21 2 2 How will increasing column length by a factor of 4 affect separation time A B C D E No change Increase by a factor of 4 Increase by a factor of 2 Increase by 21 2 Decrease by a factor of 4 3 By what factor will resolution be improved when k B the capacity factor is increased from 1 to 2 A B C D E 2 1 5 4 1 33 1 75 4 By what factor will the resolution be improved when the selectivity factor is increased from 1 5 to 2 A B C D E 1 5 1 33 2 1 75 3 For questions 5 9 indicate which terms i e A B C in the van Deemter equation will be affected and how 5 A smaller particle size of the stationary phase packing A B C D E Type text Decrease A only Decrease C only Increase A but decrease C Decrease both A and C Increase B 6 A larger film thickness on the stationary phase packing A B C D E Decrease B only Increase A only Increase C only Decrease C only Decrease both A and C 7 A distribution of particle sizes in the stationary phase packing A B C D E Decrease A only Increase A only Increase both A and C Decrease C but increase B Decrease A but increase C 8 Small diffusion coefficient of the analyte A B C D E Decrease B but increase C Increase C but decrease B Increase C only Increase B only Decrease A only 9 Lower solvent viscosity LC A B C D E Decrease B but increase C Increase C but decrease B Increase B but decrease C Increase B only Decrease C only 10 How is H plate height affected by a very high linear flow velocity A Increased B Decreased C Unchanged 11 How is H plate height affected by increasing the column length A Increased B Decreased C Unchanged 12 How is k capacity factor affected by increasing the column length A Increased Type text B Decrease C Unchanged Short Answers 5 points each 40 pts total 1 What carrier gas mobile phase do we employ for GC separations in the CHEM 425 lab 2 What other gases are employed in the GC 425 lab and for what purpose 3 What stationary phase do we employ for LC separations in the CHEM 425 laboratory 4 How would you change the mobile phase to increase retention of analytes on the LC in the 425 lab Should this increase or decrease resolution 5 What would you change to decrease the retention of analytes on the GC Would this increase or decrease resolution 6 What two detectors are employed on the LC in the 425 lab 7 What two detectors are employed on the GC s in the 425 lab 8 Why is smaller better for high efficiency separations e g small particle sizes small column diameters GC thin stationary phase film thicknesses Type text Type text