A tank contains 480.0 g of oxygen and 80.00 g of helium at a total pressure of 7.00 atm. Calculate the following: a) Moles of O2 in the tank. e) Mole fraction of He. b) Moles of He in the tank. f) Partial pressure of oxygen. c) Total moles in the tank. g) Partial pressure of He. d) Mole fraction of O2.

The allotropes of carbon include a variety of structures that include three-dimensional tetrahedral lattices, planes of hexagonal rings, cylindrical tubes of hexagonal rings, and spheres of five- and six-membered rings. similar shapes of network covalent atomic solids are possible with carbon nitride, boron, and pure silicon (e.g., silicene is a graphene-like allotrope of pure silicon). in contrast, silicates exist as either highly ordered or amorphous (more random) three-dimensional lattices. what could explain why there are there no naturally occurring sheets, stacked sheets, cylindrical tubes, or spheres of network covalent atomic solids composed of silicon and oxygen (sio2)? would pure silicate structures make good lubricants or good electrical conductors?