Salviya AntonySenior Executive - Content
Solubility refers to the ability of a substance (the solute) to dissolve in another substance (the solvent) to form a homogeneous mixture. This process typically occurs when the attractive forces between the solute particles and the solvent particles are strong enough to overcome the attractive forces between the solute particles themselves.
The topic solubility comes in the chapter Solutions in NCERT Class 12 Chemistry. Students can expect questions from Solubility for board exams as well as entrance exams like JEE, NEET etc. They are advised to learn this topic thoroughly so that they can score well in the exams.
Solubility: Key points
- Solute and Solvent: Solubility involves a solute (the substance being dissolved) and a solvent (the substance in which the solute is dissolved). For example, when sugar (solute) dissolves in water (solvent), it forms a sugar solution.
- Factors Affecting Solubility: Several factors influence the solubility of a substance, including temperature, pressure (in the case of gases), and the nature of the solute and solvent. Different substances have different solubilities in various solvents.
- Saturation: A solution is considered saturated when it contains the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature and pressure. Further addition of solute will not dissolve; instead, it will accumulate as a solid at the bottom of the container.
- Unsaturated and Supersaturated Solutions: An unsaturated solution contains less solute than the maximum amount it can hold at a given temperature and pressure. A supersaturated solution contains more solute than is normally possible at a particular temperature and pressure; these solutions are usually unstable and can precipitate out solute when disturbed.
- Solubility Curves: Solubility can be graphically represented by solubility curves, which show how the solubility of a substance changes with temperature. In some cases, solubility increases with temperature, while in others, it decreases.
- Concentration: Solubility is often expressed as the concentration of solute in a saturated solution. Common units include grams per liter (g/L), moles per liter (mol/L), or other appropriate measurements depending on the nature of the solute.
Solubility Product
Solubility Product is the maximum product of the molar concentration of the ions which are produced due to dissociation of the compound. The term solubility product is applicable for salts which are sparingly soluble. The solubility product is constant at a given temperature. Lower the value of solubility product denotes lower solubility. High value of solubility product denotes higher solubility.
FAQs on Solubility
Q: Calculate the mass percentage of benzene (C6H6) and carbon tetrachloride (CCl4) if 22 g of benzene is dissolved in 122 g of carbon tetrachloride.
A: Mass of Solution = Mass of Benzene + Mass of Carbon Tetrachloride
= 22 g + 122 g = 144 g
Mass percentage of Benzene = Mass of Benzene / Mass of Solution X 100 = 22/144 X 100 = 15.28%
Mass percentage of CCl4 = Mass of CCl4 / Mass of Solution X 100 = 122/144 X 100 = 84.72%
Q: Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.
A: Let the total mass of the solution be 100 g and the mass of benzene be 30 g.
∴ Mass of carbon tetrachloride = (100 - 30) g = 70 g
Molar mass of benzene (C6H6) = (6 × 12 + 6 × 1) g mol -1
= 78 g mol -1
∴ Number of moles of C6H6 =30/78 mol
= 0.3846 mol
Molar mass of carbon tetrachloride (CCl4) = 1 × 12 + 4 × 35.5
= 154 g mol -1
∴ Number of moles of CCl4 = 70/154 mol
= 0.4545 mol
Thus, the mole fraction of C6H6 is given as:
Number of moles of C6H6 / Number of moles of C6H6 + Number of moles of CCl4
= 0.3846 / (0.3846 + 0.4545)
Q: Based on solute-solvent interactions, arrange the following in order of increasing solubility in n-octane and explain. Cyclohexane, KCl, CH3OH, CH3CN.
A: Now n-octane is non-polar solvent due to long chain saturated structure. We know that “like dissolves like” so a non-polar compound will be more soluble in non-polar solvent as compared to polar compound.
So cyclohexane is non-polar due to symmetric structure. KCl is ionic in nature as it will dissociate into K + and Cl- ions. CH3CN is polar as mentioned above and CH3OH is also polar in nature.
The order of increasing polarity is:
Cyclohexane < CH3CN < CH3OH < KCl (O is more electronegative than N)
Therefore, the order of increasing solubility is:
KCl < CH3OH < CH3CN < Cyclohexane
Q: Amongst the following compounds, identify which are insoluble, partially soluble and highly soluble in water? (i) phenol (ii) toluene (iii) formic acid (iv) ethylene glycol (v) chloroform (vi) pentanol.
A:
- A 2.25 Water is a polar compound (due to electronegativity difference between O and H) . We know that “like dissolves like”. So, a non-polar compound will be more soluble in non-polar solvent as compared to polar compound.
- Phenol has the polar group -OH and non-polar group –C6H5 and it can not form H bonding with water(presence of bulky non-polar group) . Thus, phenol is partially soluble in water
- Toluene has no polar Thus, toluene is insoluble in water.
- Formic acid (HCOOH) has the polar group -OH and can form H-bond with water. Thus, formic acid is highly soluble in water
- Ethylene glycol(OH-CH2-CH2-OH) has polar -OH group and can form H-bond with Thus, it is highly soluble in water.
- Chloroform is partly soluble as CHCl3 is polar in nature due to high electronegativity of Cl atoms, there will be production of partial + charge on H atom so it can form H bonding with water but it is also surrounded by 3 Cl atoms, so partly soluble
- Pentanol(C5H11OH) has polar -OH group, but it also contains a very bulky non- polar group –C5H11. Thus, pentanol is partially soluble in water
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