After the large eruption of Mount St. Helens in 1980, gas samplesfrom the volcan

Question

After the large eruption of Mount St. Helens in 1980, gas samplesfrom the volcano were taken by sampling the downwind gas plume. Theunfiltered gas samples were passed over a gold-coated wire coil toabsorb Hg present in the gas. The mercury was recovered from thecoil by heating it, and then analyzed. In one particular set ofexperiments scientists found a mercury vapor level of 1800ng of Hgper cubic meter in the plume, at a gas temperature of 11 degCelsius.

Calculate the partial pressure of Hg vapor in the plume.

Calculate the number of atoms per cubic meter in the gas.

Explanation / Answer

1. Partial Pressure P = nRT/V P(Pressure) = atm, n = moles, R(Constant) = 0.082, T(Temp) = K, V(volume) = L n: moles = g / molar mass; 1.8x10^-6 / 201= 8.96X10^-9moles g = 1800ng = 1.8x10^-6g mm = 201 R: 0.082 T: 11C + 273 = 284K V: cm^3 = 1000L Partial Pressure P = 8.96X10^-9 x 0.082 x 284 / 1000 P = 2.1x10^-10atm 2. Number of atoms = moles x Avogadro's# moles = moles of Hg Avogadro's# = 6.22x10^23 Moles Hg: 8.96x10^-9 A# = 6.22x10^23 # of atoms = 8.96x10^-9 x 6.22x10^23 = 5.4x10^15

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