Chloride Content by Weight of Concrete. Q.: For corrosion protection, ACI 318-95, Building Code Requirements for Structural Concrete, specifies maximum water-soluble chloride ion in concrete as percent by weight of cement. What are acceptable levels when measuring chloride-ion content in existing concreteâspecifically, by weight of the concrete sample?
Plasma membranes are selectively permeable, regulating the cellâs molecular traffic. Hydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and. pass through the membrane rapidly. Polar molecules, such as sugars, do not cross the membrane easily. Transport Membranes Transport proteins allow passage of hydrophilic substances across the membrane.
They are semi-permeable, which means that some molecules can diffuse across the lipid bilayer but others cannot. Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly. Small polar molecules, such as water and ethanol, can also pass through membranes, but they do so more slowly.A) The plasma membrane of a cell is a bilayer of glycerophospholipid molecules. (B) A single glycerophospholipid molecule is composed of two major regions: a hydrophilic head (green) and hydrophobic tails (purple). (C) The subregions of a glycerophospholipid molecule; phosphatidylcholine is shown as an example.