I know what is relative density and how to find it, but what I can't understand is how do I find relative density of something soluble in water like salt?
Since, relative density is with respect to density of water, if I replace the water with some other liquid in which it is insoluble, then how do I get the relative density of the solid(since I replaced water itself)?
A worked out derivation of something would be helpful.
The 'trick' here is to assume the dissolution of solute into solvent brings about no changes to the solvent's volume $V_S$ and no changes to the solute's volume $V_t$. For the most part this a very reasonable assumption.
Assume the relative densities (to water) to be $d_s^1$:
$$d_s^1=\frac{m_s}{V_s}$$
And $d_t^1$:
$$d_t^1=\frac{m_t}{V_t}$$
For a mixture containing $m_s$ of $1$ and $m_t$ of $2$:
$$m_s=d_s^2\times V_s$$ $$m_t=d_t^2\times V_t$$
The final density $d_{solution}^1$ is:
$$\boxed{d_{solution}^1=\frac{d_s^1\times V_s+d_s^1\times V_t}{V_s+V_t}}$$
