Question

Solute potential of a solution is always
A. $= 0$
B. $< 0$
C. $> 0$
D. Between $0.1{\text{ }} - {\text{ }}1.0$

Answer 1

Solute potential is defined as the lowering of water potential when some amount of solute particles get dissolved in the water. It has a direct relation with the number of solute molecules. More will be the number of solute molecules added the lower will be the solute potential.

Complete answer:
By standard conditions the water potential of pure water at standard temperatures, which is not under any pressure, is taken to be zero.
When some amount of solute is dissolved in pure water, the solution now becomes deficient of free water and the concentration of water decreases, reducing its water potential.
Hence, all solutions have a water potential lower than that of a pure water; the magnitude of lowering of water potential due to dissolution of a solute is called solute potential.
All living organisms, including plants, require free energy to grow and reproduce. In thermodynamics, free energy represents the potential to do work.
The free energy of water is referred to as water potential. It is represented by the symbol $\mathop \varphi \nolimits_S$.
$\mathop \varphi \nolimits_S$ is always negative. The presence of more number of solute molecules means , the lower is the solute potential (more negative) is the $\mathop \varphi \nolimits_S$ .
Now let us match this given options :-
$= 0$ :- solute potential can never be zero. The 0 potential is defined as the water potential of pure water. In a flaccid cell the same amount of solute goes in and outside so its pressure potential becomes potential.
$< 0$ :- Solute potential is always negative because it is a measure of lowering of the water potential when solute molecules get added in water. The more the number of solute molecules added the more negative will be the solute potential.
$> 0$ :- solute potential can never be positive as it gives the measure of lowering of water potential and not increase of water potential. So it can only be negative so that it can provide magnitude of relative lowering.
Between $0.1{\text{ }} - {\text{ }}1.0$ :- solute potential can never be positive as it gives the measure of lowering of water potential and not increase of water potential. So it can only be negative so that it can provide magnitude of relative lowering so it is always less than zero.

**Our required answer is B that is $< 0$. **

Note:
For a solution at atmospheric pressure (water potential) $\mathop \varphi \nolimits_W$ = (solute potential) $\mathop \varphi \nolimits_S$, If the pressure greater than atmospheric pressure is applied to pure water or a solution, its water potential increases. The Absolute potential of a solution is always measured as negative that is less than zero.