The average adult human male has a total blood volume of 5.0 l. if the concentration of sodium ion in this average individual is 0.135 m, what is the mass of sodium ion circulating in the blood?

Molarity is a way of expressing concentration that is equal to the ratio of the moles of the solute to the liters of solution. The amount of substance in moles can be calculated through,
                         moles = (molarity) x (volume in liters)
Substituting the values,
                         moles = (0.135 M) x (5.0 L) = 0.675 moles
Multiply this value with the molar mass of sodium ion,
                         mass = (0.675 moles) x (23 g/ mole) = 15.525 grams
Therefore, the mass of sodium ion in the blood is 15.525 grams.  

For cyclohexane compounds drawn in a chair conformation:   -axial bonds are vertical  -equatorial bonds are parallel to two bonds within the ring.  thus, as i assume the chair conformation is drawn:   -the x group is in an axial position, as are the five other vertical bonds.  -three axial bonds are on the top face of the ring  -the other three axial bonds are on the bottom face  the position of the second substituent on each ring carbon is equatorial.  gauche groups must be on an adjacent carbon such as carbon 6 and carbon 2, and also gauche groups are rotated by 60 degrees relative to each other.  drawing the newman projections for c1–c2 and c1–c6 aids in visualizing the groups that are gauche to the y group on c1.  click this link and watch some academic videos that may you more understand the topic