Question

16 grams of NaOH is dissolved in 100 grams of water at 25$^0C$ to form a saturated solution. Find the solubility and weight percentage of the solution.

Answer 1

Hint: In this question, by applying the formulas of solubility and concentration by weight percentage, we can get the answer. The temperature given is the standard temperature on which all the calculations were made so there should not be any problem.

Complete Solution :
You might be thinking what a saturated solution is. Let's find it out.
- A saturated solution is a type of solution that contains the maximum amount of solute that can be dissolved under the given conditions. After studying solutions and properties of the solution, one can understand that a solution can reach a state of saturation. This state is when the solution has reached a point in which no more solute can be added in it. Addition of solute after this point would result in formation of solid precipitate. Such a mixture is called a saturated solution.

Now, we have to find solubility and weight percentage. Let's check out what it means.
- Solubility: Solubility is the property of solid, liquid or gaseous substance called solute to dissolve in a solid, liquid or gaseous solvent. The solubility of a substance is fundamentally depending on the physical and chemical properties of the solute and solvent as well as on temperature, pressure and presence of other chemicals of the solution. Solubility is measured either in grams of solute per 100 g of solvent i.e. number of moles of solute per 1 L of the solution.

- Weight percentage: Solutions are sometimes represented in terms of relative percentage of concentration of solute in a solution. To determine the weight percent of a solution, divide the mass of solute by mass of the solution (solute + solvent) and multiply by 100 to obtain the value in percent. The percent by weight formula can be expressed as the ratio of grams of solute per 100g of solution.

- With reference to the above discussion, let's find out the answers of the given questions.
Given mass of NaOH = 16 grams (Solute).
Given mass of water = 100 grams (Solvent)
Solubility (in $\dfrac{g}{{100g}}$) = $\dfrac{{mass{\text{ of solute}}}}{{mass{\text{ of solvent}}}} \times 100$ = $\dfrac{{16}}{{100}} \times 100$ = 16%
Solubility of the solution is 16($\dfrac{g}{{100g}}$)

Weight Percentage = $\dfrac{{mass{\text{ of solute}}}}{{mass{\text{ of solution}}}} \times 100$ = $\dfrac{{16g}}{{(100 + 16)g}} \times 100$$$
Therefore, Weight percentage = 13.79%

Note: You should not get confused between solubility and solubility products. Solubility is the property of a solid, liquid or gaseous substance which is called solute to dissolve in a solid, liquid or gaseous solvent whereas solubility product is a kind of equilibrium constant and its value depends on temperature. ${K_{sp}}$ (equilibrium constant) usually increases with an increase in temperature due to increased solubility of the given solution.