Is gravity an obstacle for homogenous solvation due to diffusion? If you have a glas with a spoon of salt ($\ce{NaCl}$) in it and you carefully add the water($15^\circ\mathrm{C}$). A lot of the salt will not be dissolved immediatelly, it will take a while for full dissolution.

When the salt dissolves, it is said that the salt is mixed equally in the water. But $\ce{NaCl}$ is split in two ions $\ce{Na+}$ and $\ce{Cl-}$. $\ce{Cl}$ has a mass of $35$ and Na $23$. But due to gravity (or is really curved space in the glass a better word) you should expect that the $\ce{Cl}$ atom will be more at the bottom then the $\ce{Na}$ ion. Is that right or is there someting I'm missing?

So can you say that after an hour the salt is evenly diffused through the water and that there are probably more more $\ce{Na+}$ ions at the top of the glass, so that the top of the salt water will taste more salty due to presence of sodium, which has more power of giving salty tast?
At normal Earth gravity, for all practical purposes homogeneous solvation is not hindered by gravitational force.
However: For some solutes such as sucrose and $\ce{CsCl}$, though, the &quot;artificial large gravity&quot; of centrifugation is capable of establishing concentration gradients in their solutions. One example in common laboratory use is buoyant density centrifugation:

One of the most common methods of fractionating DNA is to exploit differences in density between different types of DNA in concentrated salt solutions. Caesium chloride is the most commonly used. The method involves prolonged high speed centrifugation of purified DNA in concentrated caesium chloride. The centrifugation produces a gradient of salt concentration in the centrifuge tube and the DNA migrates to occupy a position in the gradient which corresponds to its own buoyant density.