post lab discussion: exp. 6

Question 1

Sweet, sticky, yellowish food made by bees from nectar collected from flowers

Answer 1

honey
- good source of carbs which gives our bodies strength and energy
- 69% glucose _ fructose; substitute for sugar

Question 2

what are the enzyme content of honey

Answer 2

diastase
catalases
B-glucosidase

Question 3

what type of sugar that fructose is belonged to

Answer 3

ketohexoses
- fructose in a 6C sugar w a ketone grp

Question 4

test in distinguishing ketoses and aldoses

Answer 4

seliwanoff’s test

positive result: cherry-red colored complex formed - fr ketoses
(fr aldoses - faint pink color)

Question 5

reagent of seliwanoff’s test

Answer 5

resorcinol and conc. HCI

Question 6

deals with the production, measurement, and interpretation of spectra arising from the interaction of electromagnetic radiation (light) with matter.

Answer 6

spectroscopy
- there are diff spectroscopic methods

Question 7

spectroscopy utilizing radiation in the UV–Vis range

Answer 7

UV-Vis spectroscopy

Question 8

what is the ranges in wavelength of the elecromagnetic radiation in the UV-Vis portion of the spectrum

Answer 8

~200 nm to ~700nm
(Note: In other literature, the wavelength range for UV-Vis may be somewhat higher or lower, hence the symbol ~)

Question 9

what is the
UV range:
Vis range:

Answer 9

UV range:
200 to 350 nm

Vis range:
350 to 700 nm

• UV range is colorless to the human eye
• diff wavelengths in the visible range each have a characteristics color (ROYGBIV)

Question 10

instrument used for this experiment

Answer 10

UV-Vis Spectrophotometers
Sample models of UV-Vis spectrophotometer

Question 11

it shld be chosen after the general spectral region to be used in a spectrophotometric measurement has been determined.

Answer 11

sample holding cell or cuvettes

Question 12

what shld the composed material for sample holding cell shld be

Answer 12

a material that does not absorn radiation in the spectral region being used

Question 13

the cells meeting this requirement for measurements is composed of what in the
UV range:
Vis range:

Answer 13

UV range:
quartz or fused silica

Vis range:
silicate glass are appropriate
plastic cells - inexpensive and available for some applications

Question 14

why shld we not touch the clear/ transparent sides of the cuvette

Answer 14

to not interfere and not cause unnecessary absorption

contaminating the clear sides of the cuvette with fingerprints
particles from wiping tissues
other contaminant that can affect the reading

Question 15

what happens if the cuvette gets wet outside during filling

Answer 15

wipe the cuvette clean and dry with soft facial tissue to avoid scratching the surface

Question 16

how much do u fill the cuvettes

Answer 16

3/4 full with your prepared standard soln and sample will be done in the lab

Question 17

what us the r/s bten absorbance and conc

Answer 17

Under appropriate conditions, absorbance is directly proportional to the concentration of the absorbing species in the solution. In general, this relationship is applicable only to dilute solutions, up to approximately 10mM for most analytes.

why? cos u had to diltue the honey sample

Note: Since the concentration of fructose in your honey sample is unknown, you had to find the appropriate dilution by preparing a series of 10-fold dilution (1:10, 1:100, 1:1000) to determine which one falls within the range of the standard curve.

In principle, the concentration range covered by the standard solutions must include that expected for the unknown – very important for accurate measurement.

Question 18

standard -
sample -

Answer 18

standard - fructose
sample - honey

Question 19

A calibration curve can be used to determine the?

Answer 19

concentration of unknown sample solution by measuring its absorbance.

Question 20

The calibration curve is used to establish

Answer 20

the relationship between analyte concentration and absorbance.

• This relationship is established experimentally by analyzing a series of samples of known analyte concentration (standards).

Question 21

y axis -
x axis -

Answer 21

y axis - absorbance
x axis - corresponding conc
- under appropriate conditions, it shld be linear

Question 22

how to find the conc of fructose from the calibration curve

Answer 22

use the eqn of the line
x = y - b / m

x is the conc.
y is the absorbance