U2 AOS2 Chapter 15

Question 1

analyte

Answer 1

substance which is quantified/indentified

Question 2

anhydrous

Answer 2

without water

Question 3

gravimetric analysis

Answer 3

chemical analysis involving the weighing of a precipitate formed from an analyte

Question 4

hydrated salt

Answer 4

contains water of crystallisation molecules

Question 5

hygroscopic

Answer 5

able to absorb or adsorb water from its surroundings

Question 6

water of crytsallisation

Answer 6

molecules of water bonded into a crystal structure of salts

Question 7

salinity testing

Answer 7

determining the concentration of dissolved ions in a sample through measuring the electrical conductivity of a sample of water

Question 8

impact of water and soil with high concentration of salt

Answer 8

toxic to plants, animals, humans

Question 9

application of salinity testing

Answer 9

can provide researchers with an indication of the salt concentration, enables researchers to determine whether soil/water is safe for usage eg. drinking, growing crops

Question 10

gravimetric analysis process

Answer 10

1. prepare analyte solution
2. add an excess of reactants,
3. wash precipitate (to ensure all soluble ions are removed),
4. filter sample,
5. wash sample,
6. dry sample thoroughly,
7. calculate mass of analyte

Question 11

calibration curve

Answer 11

graph depicting relationship between concentration and light absorbance

Question 12

colorimeter

Answer 12

instrument used to undertake colorimetric analysis

Question 13

monochromator

Answer 13

device used to select a particular wavelength of light (in UV spectroscopy - similar to filter in colorimetry)

Question 14

UV - visible spectroscopy

Answer 14

spectroscopy which uses ultraviolet or visible light

Question 15

UV - visible spectrophotometer

Answer 15

instrument used in UV visible spectroscopy, scans for different wavelengths of light

Question 16

colorimetry

Answer 16

allows for the analysis of coloured substances which correspond to wavelengths of visible light

Question 17

opaque substance

Answer 17

complementary colour strongly absorbed

= high concentration

Question 18

transparent substance

Answer 18

complementary colour transmitted

lower concentration?

Question 19

process of colorimetry

Answer 19

1.prepare set of standard solutions at known concentrations,
2. measure absorbance of standard solutions at a particular wavelength,
3. measure absorbance of solution of unknown concentration,
4. determine concentration of calibration curve

Question 20

metal complex

Answer 20

some metal ions are not coloured, solution needs to be made into metal complex which is coloured

Question 21

applications of colorimetry and UV spectroscopy

Answer 21

analysing contents of blood, assessing contents for toxixity, quality assurance of milk etc, testing air, assessing phosphate concentration to prevent eutrophication

Question 22

megametre to metre

Answer 22

M = mM/1000

Question 23

what could cause a higher concentration of ions in river water?

Answer 23

industrial/agricultural runoff, mining operations, sewerage

Question 24

possible sources of error in gravimetric analysis leading to overestimation

Answer 24

sample not rinsed = soluble components may be trapped in precipitate, precipitate not fully dried

Question 25

differences between UV spectroscopy and colorimetry

Answer 25

colorimetry = pass light through coloured sample, UV spectroscopy = pass UV and visible light into compounds that may not have a visible colour

Question 26

Explain how colorimetry and UV-visible spectroscopy make use of the interactions between ions in solution and light to provide information about a sample. (2 marks)

Answer 26

colorimetry and UV-visible spectroscopy are both qualitative (wavelength used to determine substance) and quantitative (absorbance of wavelength = concentration)
due to specific ions strongly absorbing particular wavelengths

Question 27

why does UV spectroscopy not work for solid samples?

Answer 27

solution must be transparent, solid precipitate may settle and not homogenise with solution

Question 28

effect of faulty equipment ONLY on calibration curve

Answer 28

calibration lower than expected, unknown true value of absorbance, unknown higher than expected

Question 29

steps of creating a calibration curve with UV vis spectrometry

Answer 29

1. UV-vis measures absorbance so opposite colour to colour transmitted/appears should
   be used,
2. Prepare standard solutions of target substance
3. Measure absorbance of each standard in UV-Visible spectrophotometer
4. Chart absorbance against concentration to create the calibration curve