A100 watt bulb emits monochromatic light of wavelength 400 nm. calculate the number of photons emitted per second by the bulb.

f = 7.5 E14 s-1

Explanation:

energy emitted by photon:

∴ λ = (400nm)(m/1 E9 nm) = 4.00 E-7 m

∴ h ( Planck's constant) = 6.626070150 E-34 J.s

∴ c (velocity of light) = 3.00 E8 m/s

∴ f (frequency): photon/s

If (1) = (2):

⇒ f = c / λ = E / h

⇒ f = (3.0 E8 m/s) / ( 4.00 E-7 m) = 7.5 E14 s-1

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%