Unit 1-Electromagnetic Radiation And Atomic Spectra

Question 1

What is the relationship between frequency and wavelength?

Answer 1

c = f x λ

c represents the speed of light (3 × 10⁸ m s^-1)

f represents the frequency of the wave (Hz or s^-1 )

λ represents the wavelength in metres or nanometres

(1 nm = 10^-9 m)

Question 2

State the order of the electromagnetic spectrum in increasing wavelength.

Answer 2

Gamma rays, X-rays, Ultraviolet, Visible, Infrared, Microwaves, Radiowaves.

Question 3

What is the formula to calculate:

(a) the energy lost or gained by electrons associated with a single photon
(b) the energy lost or gained by electrons associated with a mole of photons

Answer 3

(a) E = h x f or E = h x c / λ
(b) E = L x h x f or E = L x h x c / λ

h is Planck’s constant = 6.63 × 10^-34 J s

L is Avogadro’s constant = 6.02 x 10²³ mol^-1

Question 4

When using E = L x h x c / λ,

i) what 2 things must be done to calculate E?
ii) what 2 things must be done to calculate λ?

Answer 4

i) λ must be converted from nm to m e.g. 550nm becomes 550 x 10^-9

and

final answer must be converted to kJ by dividing by 1000

ii) energy must be converted to J/mol by multiplying by 1000

and

wavelength must be converted back to nm

Question 5

What is meant by Atomic emission?

Answer 5

When energy is transferred to atoms, electrons may be promoted to higher energy levels. When the electron returns to its original lower level that energy is released in the form of a photon.

Question 6

State the uses of atomic emission and atomic absorption spectroscopy.

Answer 6

Atomic emission and atomic absorption spectroscopy are used to identify and quantify the elements present in a sample.

Question 7

Describe how absorption spectroscopy is carried out.

Answer 7

EM radiation is directed at an atomised sample. Radiation is absorbed as electrons are promoted to higher energy levels. An absorption spectrum can be produced by detecting the light that has been taken in by the sample.

Question 8

Explain why purple solutions appear purple and green solution appear green when white light is shone on them?

Answer 8

Purple solutions appear purple because they absorb green light, allowing blue and red light to pass through.
Green solutions appear green because they absorb blue and red light, allowing green light to pass through.