practical techniques

Question 1

how is gas-liquid chromatography used to identify compounds?

Answer 1

• the solubility determines the retention time (time taken to reach detector)
• each peak represents a substance with a particular retention time
• the area under each peak is proportional to the relative amount of each substance

Question 2

why is Gas-liquid chromatography often combined with mass spectrometry?

Answer 2

GLC is very good at separating a mixture into individual compounds, but not so good at identifying them

Question 3

describe the events which occur during GLC

Answer 3

• sample injected into stream of inert carrier gas, which carries it through the tube over the stationary phase
• the components of the mixture constantly dissolve in the stationary phase, evaporate in the mobile phase, and redissolve in the tube

Question 4

describe the procedure for finding the concentration of an ion with visible spectroscopy

Answer 4

• use a filter to separate light into monochromatic light
• pass a beam of monochromatic light through a solution of the complex
• detector measures the intensity of light before and after its passed through the solution

Question 5

how do you set up an electrochemical cell?

Answer 5

• get a strip of metal, clean with emery board and propanone
• place each electrode into a beaker containing ions of that metal
• create a salt bridge
• connect to voltmeter

Question 6

describe an experiment to measure enthalpy change of solution

Answer 6

-put reactants in a container, stick a thermometer and measure temperature change

Question 7

list the ways you can measure the rate of a reaction

Answer 7

gas syringe
mass balance
titration
colorimetry

Question 8

how do you hydrolyse a protein?

Answer 8

heat with hot 6 molar HCl under reflux for 24 hours, neutralise ammonium salts using a base

Question 9

how do you remove soluble impurities?

Answer 9

by adding water to an organic mixture in a separating funnel

Question 10

how do you make a salt in a precipitation reaction? PFWD

Answer 10

pick two solutions containing the ions you need, allow the salt to precipitate out, filter, wash, dry

Question 11

how do you make soluble salts using an insoluble base? DFEE

Answer 11

pick an acid, metal/insoluble base and dissolve
filter out the excess metal
evaporate some of solution off before leaving the rest to evaporate slowly

Question 12

how do you make soluble salts using an alkali?

Answer 12

titrate an alkali against an acid using indicator

evaporate

Question 13

in which order should you test for ions?

Answer 13

carbonates -> sulfates -> halides

Question 14

describe procedure for the electrolysis of an aqueous solution

Answer 14

use wires and clips to connect electrodes to power supply

insert inert electrodes into electrolyte

Question 15

name 2 ways in which the concentration of ions in solution can be measured

Answer 15

• colorimetry

- titration (if solution is acidic or alkaline)

Question 16

how do you determine the concentration of a component of an equilibrium mixture without disrupting the system?

Answer 16

titration (after quenching)
colorimetry
pH

Question 17

what do you need for cracking?

Answer 17

collection trough with boiling tube
delivery tube
porcelain chips
mineral wool soaked with liquid parrafin 
bunsen