Module 8 - Applying Chemical Ideas

Question 1

Purpose of AAS

Answer 1

Atomic Absorption Spectroscopy is used to determine the concentration of metal ions in a substance at very low concentrations

Question 2

Set up of AAS

Answer 2

A hollow cathode lamp with the metal to be analysed emits electrons at a certain wave length, a flame containing the vaporised sample absorbs some of the light, the monochromator selecting the wave length and the detector records the intensity

Question 3

Using an AAS curve

Answer 3

Requires a calibration curve, using the absorbance to find the concentration

Question 4

Units of concentration in AAS

Answer 4

ppm or mg/L

Question 5

Purpose of mass spectrometry

Answer 5

Used to determine molar mass of element and the isotopes

Question 6

Set up of mass spectrometry

Answer 6

Sample is vaporised and ionised, molecular ion breaks apart into smaller fragments, ions are accelerated through an electric field and deflected by the magnetic field with the amount depending on their mass-to-charge ratio (m/z), then detected

Question 7

What is the base peak in mass spectrometry?

Answer 7

The highest peak is the most abundant peak (the highest)

Question 8

What is the parent peak in mass spectrometry?

Answer 8

The peak with the highest m/z (furtherest to the right), usually the molar mass

Question 9

Purpose of infrared spectroscopy

Answer 9

To determine the bonds/functional groups

Question 10

How IR spectroscopy works

Answer 10

IR radiation causes molecules to stretch, bend and vibrate, each bond vibrating at a characteristic frequency

Question 11

Set up of IR spectroscopy

Answer 11

IR is split into two beams so it is shot at sample and reference, the splitter and detector recording the results

Question 12

The region below 1500cm in IR Spectroscopy

Answer 12

The fingerprint print - Can be compared with spectra of known compounds, but not as useful for functional groups

Question 13

Purpose of NMR

Answer 13

To map the atomic structure - the presence and position of molecules

Question 14

Set up of NMR

Answer 14

Matter is placed in a magnetic field, nuclei must have an odd number of nucleons, moving from low to high energy state allowing them to absorb energy (radiofrequency radiation)

Question 15

Standardising chemical in NMR

Answer 15

TMS (very shielded)

Question 16

Name of peaks in NMR and their number of peaks

Answer 16

Singlet - no split
Doublet - Two peaks
Triplet - Three peaks
Quartet - our peaks

Question 17

Number of peaks in H1 NMR

Answer 17

How many different chemical environments

Question 18

Location of the peaks in H1 NMR

Answer 18

The closer to the right is more shielded, left is less shielded

Question 19

Splitting in H1 NMR

Answer 19

n+1 peaks shows how n*H1 nuclei on neighbouring carbons

Question 20

Area under the curve in H1 NMR

Answer 20

Corresponds to the relative number of hydrogens present in the environment

Question 21

Differences in C13 vs H1 NMR

Answer 21

Height and splitting is not important

Question 22

Reading 13C NMR graphs

Answer 22

Use data sheet to determine functional groups

Question 23

What is colourimetry?

Answer 23

To determine the concentration of a coloured analyte in solution by absorption of a specific wavelength of visible light

Question 24

The Beer-Lambert Law

Answer 24

Concentration is proportional to the amount of light absorbed. A = e[molar absorptivity, depends on substance]l[path length]c[concentration] or A = log(Io[incident light]/I[transmitted light])

Question 25

Set up of colourimetry

Answer 25

Light source -> coloured filter -> sample solution -> detector -> recorder

Question 26

Colours absorbed in colourimetry

Answer 26

Solutions absorbs the complementary colour of the visible colour (e.g. a blue solution absorbs red) which must be chosen

Question 27

How to use colourimetry

Answer 27

Create a calibration curve using a series of standard solutions

Question 28

What is UV-Visible spectrophotometry?

Answer 28

Use of the absorption of UV, visible electromagnetic radiation (EMR) to deduce molecular structure. The substance must absorb UV and EMR to be useful. It is qualitative

Question 29

Set up of spectrophotometry

Answer 29

Light source -> monochromator -> sample solution -> detector -> recorder

Question 30

How to use spectrophotometry graph

Answer 30

Monochromator allows for the selection of specific wavelengths. Maximum absorbance (highest point on graph) + minimal interference with other substances

Question 31

How spectrophotometry operates

Answer 31

Measures absorbance at a range of wavelengths to plot absorbance vs wavelength, creating a spectrum

Question 32

Availability of reagents in chemical synthesis + design (example)

Answer 32

Haber process - take Nitrogen from the air and Hydrogen from natural gas (CH4)

Question 33

Reaction conditions in chemical synthesis + design (example)

Answer 33

Haber process - 500oC (exothermic but compromise which increases rate); 200atm (moderate as high risk + cost); magnetite (iron) catalyst; set up to remove ammonia so it favours the forward reaction

Question 34

Yield and purity in chemical synthesis + design (example)

Answer 34

Haber Process - Yield is maximised by using a moderate temperature (500oC which slows down yield but increases rate) & moderate pressure (200atm to increase yield but balance cost + risk); condenser used to liquefy NH3 while pumping back in N2 + H2 purifying the product; must also monitor the incoming gas so it’s pure as O2 at high temps can explode

Question 35

Industrial uses of chemical synthesis + design (example)

Answer 35

Ammonia from the Haber process used in fertilisers (ammonium nitrate), explosives, household cleaners/detergents, refrigerant gas

Question 36

Environmental, social and economic issues of chemical synthesis + design (example)

Answer 36

Solvay process for Na2CO3 (used in glass making)
Environmental - Mining CaCO3 can disrupt ecosystems; waste product of CaCl2 is discharged into the ocean (as already a lot of ions, but not in rivers)
Social - Site must not be too close to people due to noise and dust pollution, but close enough for workers
Economic - Site must be close to supply of raw materials and market to sell; accessible by transport

Question 37

What a precipitation titration involves + how to find equivalence point

Answer 37

Involves using Ag+ to detect halide ions (Group VII); Equivalence point determined by formation of a second coloured ppt, formation of a coloured complex ion, conductivity measurements