1.1 EM radition and atomic spectra

Question 1

EM radiation dual nature

Answer 1

can act as both a particle and as a wave

Question 2

EM radiation in increasing wavelength/decreasing frequency

Answer 2

gamma rays → x rays → ultraviolet → visible light → infrared → microwaves → radiowaves

Question 3

gamma rays → x rays → ultraviolet → visible light → infrared → microwaves → radiowaves

Answer 3

EM radiation in increasing wavelength/decreasing frequency

Question 4

frequency and wavelength calculations

Answer 4

• c = f × λ
  
  • c is speed of light (3 x 10^8 m s^-1)
  • f is frequency (Hz or m^-1)
  • λ is wavelength (m/nm)
• wavenumber = 1 / λ
  
  • λ is wavelength (m/nm)
• f = 1 / T
  
  • T is time (seconds)

Question 5

what is the frequency of light with a wavelength of 690nm?

Answer 5

f = c / λ

= 3 x 10^8 / 690 x 10^-9

= 4.35 x 10^14 Hz

Question 6

when do we multiply wavelength and what do we multiply by

Answer 6

multiply wavelength by 10^-9 if wavelength is given in nm

Question 7

what is the wavelength and frequency of alkyne (wavenumber = 3300 cm^-1)?

Answer 7

wavenumber = 1 / λ

= 1/3300

= 0.000003m

f = c / λ

= 3 x 10^8 / 3.03 x 10^-6 

= 9.9 x 10^13 s^-1

Question 8

energy, frequency, and wavelength calculations

Answer 8

• E = L x h x f
  
  • E is energy (kJ/mol^-1)
  • L is Avogadro’s constant (6.023 x 10^23 mol^-1)
  • h is Plancks constant (6.63 x 10^-34 J/s)
  • f is frequency (Hz)
• E = L x h x c / λ
  
  • E is energy (kJ/mol^-1)
  • L is Avogadro’s constant (6.023 x 10^23 mol^-1)
  • h is Plancks constant (6.63 x 10^-34 J/s)
  • c is the speed of light (3 x 10^8)
  • λ is wavelength (m/nm)

Question 9

what provides evidence for energy levels of atoms

Answer 9

spectrum that is made up of a series of lines at discrete energy levels when light energy is emitted by an atom

Question 10

relationship between energy of a photon and frequency

Answer 10

it is proportional

• high frequency photon = high energy
• low frequency photon = low energy

Question 11

two types of atomic spectra

Answer 11

atomic emission spectra
atomic absorption spectra

Question 12

the concentration of an element within a sample is related to what in electroscopy

Answer 12

the intensity of light emitted or absorbed

Question 13

atomic absorption spectra and ions

Answer 13

the higher the concentration of metal ions in a solution, the higher the intensity of radiation absorbed

Question 14

colour of a highly ionic solution that absorbs light only in the UV region

Answer 14

colourless

Question 15

how can the quantity of an element be determined with electroscopy

Answer 15

from the intensity of the radiation emitted

Question 16

emission spectroscopy steps

Answer 16

1. high temperatures used to excite the electrons
2. excited electrons are promoted from their ground state to a higher energy levels
3. electrons drop to lower energy levels and emit photons of light
4. each photons is equal in energy to the difference between energy levels
5. these photons of light can be gathered through a slit and pasted through a prism, which splits the wavelength

Question 17

what does atomic emission spectroscopy measure

Answer 17

wavelength of emitted radiation by measuring the intensity of light at different wavelengths

Question 18

what measures wavelength of emitted radiation by measuring the intensity of light at different wavelengths

Answer 18

atomic emission spectroscopy

Question 19

what does atomic emission spectroscopy produce

Answer 19

a black backdrop with coloured lines, each representing one transition of an electron from a higher energy level back down to ground state

Question 20

what produces a black backdrop with coloured lines, each representing one transition of an electron from a higher energy level back down to ground state

Answer 20

atomic emission spectroscopy

Question 21

why does an atomic emission spectra have multiple lines

Answer 21

due to many different energy levels or many different electron transitions

Question 22

atomic emission spectra and ions

Answer 22

as the concentration of an ionic solution decreases, radiation transmitted increases in intensity

Question 23

atomic absorption spectra steps

Answer 23

1. sample is atomised and EM radiation is directed at the sample
2. radiation is absorbed as electrons are promoted to higher energy levels by absorption of specific photons
3. each photons is equal in energy to the difference between energy levels
4. the light can be passed through a slit, then a prism

Question 24

what does atomic absorption measure

Answer 24

wavelength of absorbed radiation is measured by measuring how the intensity of absorbed light varies with wavelength

Question 25

what does atomic absorption spectra produce

Answer 25

ainbow backdrop with missing lines. each line represents an electron being excited from ground state to a higher energy level

Question 26

calculate the wavelength of a photon of light with the frequency 5 x10^14 s^-1

Answer 26

6 x 10^-7

Question 27

calculate the wavelength of a photon of light with the frequency 3.2 x 10^14 s^-1

Answer 27

9.4 x 10^-7 m

Question 28

calculate the frequency of a photon of light with the wavelength 4.26 x 10^-7m

Answer 28

7 x 10^14 s^-1

Question 29

calculate the energy of one mole of photons in kJ mol for photons with a wavelength of 400nm

Answer 29

300 kJ mol

Question 30

how is a line produced on an emission spectra

Answer 30

an electron is excited and promoted to a higher energy level when it falls back down to ground state, energy is emitted

Question 31

calculate the energy of one mole of photons in kJ mol for photons with a wavelength of 650nm

Answer 31

184 kJ mol

Question 32

what causes electrons to become excited in atomic emission spectra

Answer 32

heat

Question 33

A sample of strontium was exposed to electromagnetic radiation with a frequency of 3·08 × 1017 s−1 Calculate the energy, in J, of this electromagnetic radiation

Answer 33

2.04x10-16 J

Question 34

when do you use L in frequency calculations

Answer 34

if the answer is asking for a mole/in mol units

Question 35

The concentration of ethanol in vodka can be determined by reacting the ethanol with excess acidified potassium dichromate solution. 20·0 cm3 of vodka was transferred to a 1 litre volumetric flask and made up to the mark with deionised water. 1·0 cm3 of the diluted vodka was pipetted into a conical flask. 25·0cm3 of 0·010moll−1 acidified potassium dichromate was added to the conical flask. The conical flask was then stoppered and warmed until the reaction was complete. 3C2H5OH(aq) + 2Cr2O72−(aq) + 16H+(aq) ↓ 3CH3COOH(aq) + 4Cr3+(aq) + 11H2O(l) It was found that 1·65 × 10−4 moles of dichromate ions were left unreacted Calculate the concentration of ethanol, in mol l−1, in the undiluted vodka

Answer 35

Total Dichromate in flask: no. of mol = volume x concentration = 0.025litres x 0.010 mol l-1 = 2.5x10-4mol Dichromate left at end of reaction: no. of mol = 1.65x10-4mol (in question) Dichromate which reacted with ethanol: no. of mol = 2.5x10-4 mol – 1.65x10-4mol = 8.5x10-5mol 6.4 mol l-1

Question 36

why do you make a reactant be in excess

Answer 36

to ensure all of it is reacted

Question 37

back titration

Answer 37

A known quantity of either an acid or base is reacted with an unknown quantity of some chemical. How much leftover acid or base remaining can be determined via titration and so how much of it reacted with the other chemical can be worked out to determine the chemical’s concentration.