tests

Question 1

how to test for reducing sugars

Answer 1

-sample of food into solution
-add benedict’s reagent (contains CU2+ ions)
-if turn red, showing reducing sugars as CU2+ goes into CU+

Question 2

how to test for non reducing sugars

Answer 2

hydrolase bonds to free up reducing sugars

Question 3

steps for testing for non reducing sugars

Answer 3

-test sample for reducing sugars
-separate sample + boil with hydrochloric acid to hydrolase the sucrose into glucose and fructose
-cool solution and use sodium hydro carbonate solution to neutralise it
-test for reducing sugars again

Question 4

steps for testing for protein

Answer 4

-test solution must be alkaline so add a few drops of sodium hydroxide
-add copper (II) sulphate solution(biuret solution)
(the peptide bonds that react with copper sulphate ions in biuret solution)

Question 5

emulsion test for lipids

Answer 5

-Take a small sample of the substance you want to test
-Add a few drops (or enough to cover the sample) of ethanol (dissolves lipids present)
-Shake the test tube so the lipids (if present) dissolve in the ethanol.
- After shaking, add an equal volume of distilled water
-After adding water, shake the test tube again
-present = milky white or form a cloudy emulsion.

Question 6

iodine test for startch

Answer 6

-the solution added is iodine dissolved in potassium iodide so u must say iodine solution
-turns blue black
-add to spotting tile with food

Question 7

how to determine dilution factors

Answer 7

• if its 1:20, use 1ml stock solution and 19ml diluent so that you get 20 parts in total
  -transfer one part of previous solution to another 19 part solution and continue
  -will be a 20th of the beginning solution

Question 8

what are biosensers

Answer 8

use detector and light source shone through a solution to determine concentration

Question 9

example of biosensors in a weak glucose concentration

Answer 9

-light source –> less absorption in solution—> receives more light

Question 10

example of biosensors in a strong concentration

Answer 10

-light source–> more absorption–> detector receives less light

Question 11

what’s a colorimeter

Answer 11

-biosensor that measures the strength of a coloured solution by how much light passes through it

Question 12

what colour does a colorimeter detect in benedict’s

Answer 12

-blue as not directing light through precipitate, rather the solution

Question 13

what does it mean if there’s a higher concentration of glucose molecules at the start

Answer 13

-less light absorbed at end as more available glucose molecules to react with benedict’s so more orange solution

Question 14

why would a lot of light pass through if theres less benedicts

Answer 14

benedict’s contains CU2+ ions which are blue, so more blue light passes through when theres less benedicts as light isnt absorbed by blue solution

Question 15

comparison of biosensers at beginning and end of glucose reaction with a lot of glucose

Answer 15

• beginning detector recieves less light as copper ions havent reacted
  -end, receives more light as low conc of CU2+ ions as its all reacted

Question 16

what does lower glucose molecules mean

Answer 16

-means less reaction with CU2+ ions, lower transmission of light read by detector

Question 17

whats the curved called that has glucose copnc on x axis and transmission of y

Answer 17

calibration curve

Question 18

whats it called when when testing for glucose, u need to make up several glucose solutions of different known concentrations, way to do this

Answer 18

serial dilution

Question 19

describe chemical reaction that causes colour change in startch test

Answer 19

the iodine (I2) forms a triiodide (I3-) which slips into the middle of the amylose helix causing colour change

Question 20

alternate method to test for reducing sugars

Answer 20

-commercially manufactured test strips, dip into solution and compare colour with calibration card supplied

Question 21

why is important to check there are no reducing sugars in the solution before carrying out non reduce test

Answer 21

interferance in results, reliability and validity

Question 22

why is sucrose a non reducing

Answer 22

-no free aldehyde groups or ketone groups

Question 23

chemical reaction that causes colour change to occur

Answer 23

reaction between nitrogen atoms in peptide chain and CU2+ ions, detects presence of peptide bonds

Question 24

what is emulsion

Answer 24

a mixture of two immiscible (liquids that dont combine to form same solution) liquids, where one liquid is dispersed in the other in the form of small droplets.

Question 25

why do lipids form emulsion in water

Answer 25

hydrophobic, seperate in water causing layers or small droplets (micelles)

Question 26

chromatography for amino acids

Answer 26

-draw pencil line
-concentrate spot of solution using capillary tube on surface
-add prepared solvent
-into fume cupboard with lid
-allow paper to dip into solvent
-paper sprayed with ninhydrin solution, amino acid turns purple

Question 27

what solvent is normally used for amino acids

Answer 27

-mix of butan-1-ol, glacial ethanoic acid and water

Question 28

stationary phase

Answer 28

chromatography paper or solid layer coated on a glass, plastic, or aluminum plate. (e.g. silica gel on glass/ plastic plate)

Question 29

mobile phase

Answer 29

solvent

Question 30

rf value calculation

Answer 30

dividing distance from pencil line to centre of spot over distance of pencil line to solvent front

Question 31

how to view amino acids in TLC and paper chromatography

Answer 31

-ninhydrin spray(after dry)
-iodine(place in enclosed counter with iodine crystals after dry)
-both bind with molecules to allow visibility

Question 32

what can u use to view amino aicds in TLC

Answer 32

-use ultraviolet light, plates have chemical with fluoresces, most will glow except places where spots have travelled to

Question 33

how do both chromatographys work

Answer 33

-speed which molecules move is determined by solubility and polarity (in PC depend on size)
-exposed OH groups make surface of paper or plate very polar, allowing hydrogen bonds with molecules

Question 34

how does polarity effect chromatography

Answer 34

high polarity= stick to surface
low polarity=travel v quickly