Besides temperature, ionic strength, and common ion effect, the pH of a solution can also have a large impact on solubility whenever one (or both) of the dissociated ions from a solid can act as a weak acid/base. Consider the series of simultaneous equilibria shown below (you can assume all species are aqueous unless otherwise noted): CaF2(s) ⇌ Ca2++ 2F-
Ca2++ F-⇌ CaF+
CaF2(s) ⇌ CaF2(aq)
Ca2++ H2O ⇌ CaOH++ H+
F -+ H+ ⇌ HF
HF + F- ⇌ HF2-
H2O ⇌ H+ + OH-
(a) Write the charge-balance expression for this system.
(b) Write the mass-balance expressions for this system.

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