Solubility – the “how much” of dissolving 😊

Important concepts for NEET 🔑

• Dynamic equilibrium: the forward (dissolution) and reverse (crystallisation) processes balance each other – that’s when a solution is saturated. :contentReference[oaicite:0]{index=0}
• “Like dissolves like”: polar solutes prefer polar solvents, non-polar solutes prefer non-polar ones. :contentReference[oaicite:1]{index=1}
• Temperature trends: for most solids, ⬆️ temperature ⬆️ solubility if the process is endothermic, and ⬇️ solubility if exothermic; for gases, solubility always drops as temperature rises.
• Henry’s law: \(p = K_H x\) links gas pressure with its mole fraction in solution – a must-know relation.
• Real-life links: soda fizz 🥤, scuba “bends” 🤿, and high-altitude anoxia 🏔️ are all explained through gas solubility principles.

1 • What is solubility? 🧪

Solubility is the maximum amount of a substance that dissolves in a given amount of solvent at a specified temperature. It varies with the nature of solute and solvent, temperature, and (for gases) pressure. :contentReference[oaicite:2]{index=2}

2 • Solids in liquids 🌡️

2.1 Like dissolves like

Sodium chloride and sugar disappear easily in water, but naphthalene prefers benzene. Why? Because similar intermolecular forces attract – polar loves polar, non-polar loves non-polar. :contentReference[oaicite:3]{index=3}

2.2 Dynamic equilibrium

When a solid meets a solvent, two opposite processes start:

\( \text{Solute} + \text{Solvent} \; \rightleftharpoons \; \text{Solution} \)   (1.10) :contentReference[oaicite:4]{index=4}

• Dissolution adds particles to the liquid.
• Crystallisation removes particles back to the solid.
• At equilibrium the rates match and concentration stays constant – that’s your saturated solution.

2.3 Temperature effect 🔥

If dissolving absorbs heat (\(\Delta_{\text{sol}} H > 0\)), higher temperature increases solubility. If it releases heat (\(\Delta_{\text{sol}} H < 0\)), raising the temperature decreases solubility. :contentReference[oaicite:5]{index=5}

2.4 Pressure effect 🏋️

Solids and liquids barely compress, so changing pressure has almost no impact on how much solid dissolves. :contentReference[oaicite:6]{index=6}

3 • Gases in liquids 💧

3.1 General behaviour

• Dissolved oxygen keeps fish alive, but its solubility is low. HCl, by contrast, is highly soluble. :contentReference[oaicite:7]{index=7}
• Gas solubility increases sharply with pressure but falls as temperature rises.

3.2 Henry’s law 📈

At constant temperature, the partial pressure of a gas above the solution is directly proportional to its mole fraction in the liquid:

\( p = K_H x \)   (1.11)

• \(K_H\) depends on the gas; a larger \(K_H\) means poorer solubility.
• \(K_H\) rises with temperature for most gases, confirming that cold water holds more dissolved gas. :contentReference[oaicite:8]{index=8}

3.3 Quick data peek

For water at 293 K: \(K_H\,(\text{kbar})\) – He 145, H₂ 69, N₂ 76, O₂ 35, CO₂ 1.7 (very soluble!). :contentReference[oaicite:9]{index=9}

3.4 Real-world applications 🌍

• Soda & soft drinks 🥤: CO₂ is pumped in at high pressure to keep fizz locked in.
• Scuba diving 🤿: At depth, extra pressure dissolves more N₂ in blood; fast ascent forms nitrogen bubbles and causes “bends”.
• High mountains 🏔️: Lower oxygen pressure means less O₂ in blood, leading to anoxia.

3.5 Worked example 📝

At 293 K, bubbling N₂ into 1 L water under 0.987 bar dissolves 0.716 mmol of the gas (using \(K_H = 76.48\;\text{kbar}\)). :contentReference[oaicite:10]{index=10}

4 • Key takeaways 🎯

• Remember the equilibrium arrow – it captures the essence of saturation.
• Check the heat change to predict how temperature shifts solubility for solids.
• Use Henry’s law any time a gas meets a liquid under pressure.
• Link textbook ideas to everyday experiences – that’s the fun part! 😄