Calculate the frequency, in s-1, of ultraviolet radiation that has a wavelength

ID: 831715 • Letter: C

Question

Calculate the frequency, in s-1, of ultraviolet radiation that has a wavelength of 248nm.

I know the answer is 1.21x10^15. Will someone please explain and show me the steps.

Calculate the energy change, in joules, that occurs when an electron falls from the n=4 to the n=2 energy level in a hydrogen atom.

I know the answer is -4.09x10^-19. Once again, will some please explain and show me the steps?

Calcukate the molarity of a soultion containing 40.0g glucose (C6H12O6) in enough ethanol (C2H5OH) to make 40.0 mL of solution,

I know the answer is 5.56. Please help me to understand!! Appreciate it:)

(1) Wavelength = 248 nm = 248 x 10^(-9) m

Frequency = speed of light/wavelength

= 2.998 x 10^8/248 x 10^(-9)

= 1.21 x 10^15 Hz

(2) Rydberg equation:

Energy = hcR(1/n1^2 - 1/n2^2)

where h is Planck constant, c is speed of light, R is Rydberg constant, n1 and n2 are quantum numbers

For n1 = 4 and n2 = 2

Energy = 6.626 x 10^(-34) x 2.998 x 10^8 x 1.097 x 10^7 x (1/4^2 - 1/2^2)

= -4.09 x 10^(-19) J

(3) Moles of glucose = mass/molar mass of glucose

= 40.0/180 = 0.2222 mol

Molarity = moles of glucose/volume of soluton in L

= 0.2222/0.0400

= 5.56 M

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