โ๏ธ Quick & colourful revision notes โ by @edugrown
๐ Table of Contents
1
Classifying Mixtures
A mixture is made of two or more substances mixed physically. Based on composition, mixtures are of two types:
| Homogeneous Mixture | Heterogeneous Mixture |
|---|---|
| Uniform composition throughout (e.g. sugar solution) | Non-uniform composition (e.g. sand + water) |
| Particles not visible; also called a solution | Particles are visible & settle with time |
| Example: vinegar, soda, sugar-water | Example: muddy water, oil + water |
REMEMBER
A solution always remains homogeneous โ same composition in the first sip and the last sip!
A solution always remains homogeneous โ same composition in the first sip and the last sip!
2
Solutions & Concentration
KEY TERMS
Solute = substance that gets dissolved. Solvent = substance that dissolves the solute.
Concentration = amount of solute dissolved in a given amount of solvent/solution.
Solute = substance that gets dissolved. Solvent = substance that dissolves the solute.
Concentration = amount of solute dissolved in a given amount of solvent/solution.
๐น Three Ways to Express Concentration (%)
MASS BY MASS %
% m/m = (Mass of solute รท Mass of solution) ร 100
used for solids in solids/liquids โ e.g. milk powder composition
MASS BY VOLUME %
% m/v = (Mass of solute รท Volume of solution) ร 100
used in medicines/labs โ e.g. 5% glucose IV solution
VOLUME BY VOLUME %
% v/v = (Volume of solute รท Volume of solution) ร 100
used for miscible liquids โ e.g. 5% v/v acetic acid in vinegar
GOOD TO KNOW
Numerically, % m/m and % w/w are the same โ mass & weight are used interchangeably in daily/industrial use.
Numerically, % m/m and % w/w are the same โ mass & weight are used interchangeably in daily/industrial use.
3
Solubility
DEFINITION
Solubility = maximum amount of solute that dissolves in a fixed amount (100 g/100 mL) of solvent at a given temperature.
A solution that cannot dissolve any more solute at that temperature is called saturated.
Solubility = maximum amount of solute that dissolves in a fixed amount (100 g/100 mL) of solvent at a given temperature.
A solution that cannot dissolve any more solute at that temperature is called saturated.
- Solubility of a solid in a liquid โ generally increases with temperature.
- Solubility of a gas in a liquid โ generally decreases with temperature.
- A solubility curve is a graph of solubility (g/100 g water) vs temperature (ยฐC).
USE
Solubility differences at different temperatures is the whole principle behind crystallization!
Solubility differences at different temperatures is the whole principle behind crystallization!
4
Crystallization
DEFINITION
Process of forming crystals (particles arranged in a regular geometric pattern) from a saturated solution, by cooling it slowly.
Process of forming crystals (particles arranged in a regular geometric pattern) from a saturated solution, by cooling it slowly.
- Used to separate two solids (one present in small quantity), both soluble in the same solvent.
- Also used for purification of solids (removes soluble/insoluble impurities).
- Slow cooling โ large, well-shaped crystals. Fast cooling โ small, poorly-formed crystals.
- Natural crystals: rock salt, sugar candy (mishri), snowflakes, frost, quartz.
STEPS
Prepare saturated solution (hot) โ Filter to remove insoluble impurities โ Cool slowly โ Filter & collect crystals โ Dry.
Prepare saturated solution (hot) โ Filter to remove insoluble impurities โ Cool slowly โ Filter & collect crystals โ Dry.
5
Distillation
DEFINITION
Separates a homogeneous mixture of two miscible liquids by heating till the liquid with the lower boiling point vaporises, then cooling the vapour back to liquid.
Separates a homogeneous mixture of two miscible liquids by heating till the liquid with the lower boiling point vaporises, then cooling the vapour back to liquid.
- Works best when boiling points of the two liquids differ by at least ~25 ยฐC.
- Can also separate a liquid from a solution containing dissolved solids.
- Fractional distillation โ used when boiling point difference is less than 25 ยฐC (e.g. separating petrol, diesel, kerosene from crude oil).
INDIA'S CONTRIBUTION
Mitti ka Ittar (earthy perfume) from Kannauj, UP, is made using the traditional Deg-Bhapka distillation method โ capturing the fragrance of first rain on soil! ๐ง๏ธ
Mitti ka Ittar (earthy perfume) from Kannauj, UP, is made using the traditional Deg-Bhapka distillation method โ capturing the fragrance of first rain on soil! ๐ง๏ธ
6
Paper Chromatography
DEFINITION
A technique to separate components of a mixture (like dyes/pigments) based on differences in how fast they move with a solvent through paper.
A technique to separate components of a mixture (like dyes/pigments) based on differences in how fast they move with a solvent through paper.
- "Chromatography" (Greek) = chroma (colour) + graphein (to write) โ "writing with colour".
- The solvent (e.g. water) rises up the paper by capillary action, carrying dissolved substances at different speeds โ separates into spots/bands.
- Used to separate ink colours, plant pigments (chlorophyll in leaves), food dyes.
- Important: the solvent level must stay below the sample spot at the start โ never above it!
7
Immiscible Liquids & Sublimation
๐น Separating Funnel (Immiscible Liquids)
- Immiscible liquids do not mix โ they form separate layers based on density (e.g. oil floats on water).
- A separating funnel is used โ open the stopcock to drain the denser (lower) liquid first.
๐น Sublimation
DEFINITION
Sublimation = solid changes directly to vapour (without becoming liquid) on heating, below its melting point.
Deposition = the reverse โ vapour directly changes back to solid on cooling.
Sublimation = solid changes directly to vapour (without becoming liquid) on heating, below its melting point.
Deposition = the reverse โ vapour directly changes back to solid on cooling.
- Used to separate a sublimable solid (camphor, naphthalene, dry ice) from a non-sublimable one (sand).
8
Suspensions & Centrifugation
DEFINITION
A suspension is a heterogeneous mixture where solid particles do not dissolve but remain suspended in the medium โ visible to the naked eye, settle over time (e.g. muddy water, sawdust in water).
A suspension is a heterogeneous mixture where solid particles do not dissolve but remain suspended in the medium โ visible to the naked eye, settle over time (e.g. muddy water, sawdust in water).
๐น Centrifugation
PRINCIPLE
High-speed spinning โ heavier particles move outward & settle
- Used to separate blood into plasma, RBCs, WBCs & platelets.
- Also used widely in dairies & chemical industries.
๐น Coagulation
- Adding a coagulant (like alum/fitkari) makes fine suspended particles clump together and settle down (sedimentation).
- Example: purifying muddy water; making paneer from milk using lemon juice/vinegar as coagulant.
9
Colloids
A colloid is a mixture "in between" a solution and a suspension โ e.g. blood, milk, tomato sauce, ice cream, fog, smoke.
| Property | Solution | Colloid | Suspension |
|---|---|---|---|
| Particle size | < 1 nm | 1 โ 1000 nm | > 1000 nm |
| Visible to eye? | No | No | Yes |
| Settles on standing? | No | No | Yes |
| Separated by filtration? | No | No | Yes |
| Scatters light (Tyndall)? | No | Yes | Yes |
KEY TERMS
Dispersed phase = the solute-like component of a colloid. Dispersion medium = the substance in which it is dispersed.
When both phases are liquids โ called an emulsion (e.g. milk = oil-in-water).
Dispersed phase = the solute-like component of a colloid. Dispersion medium = the substance in which it is dispersed.
When both phases are liquids โ called an emulsion (e.g. milk = oil-in-water).
10
Tyndall Effect
DEFINITION
Tyndall Effect = scattering of a light beam by particles in a colloid or suspension, making its path visible. Named after scientist John Tyndall.
Tyndall Effect = scattering of a light beam by particles in a colloid or suspension, making its path visible. Named after scientist John Tyndall.
- Seen in: a light beam through a colloid/suspension, sunlight through tree leaves, headlight beams in fog/dust, stadium floodlights.
- NOT seen in true solutions โ particles are too small (< 1 nm) to scatter light.
11
Quick Formula Sheet
| Concentration Type | Formula |
|---|---|
| Mass by mass % | (Mass of solute รท Mass of solution) ร 100 |
| Mass by volume % | (Mass of solute รท Volume of solution) ร 100 |
| Volume by volume % | (Volume of solute รท Volume of solution) ร 100 |
| Method | Best For |
|---|---|
| Crystallization | Separating/purifying a solid from a saturated solution |
| Distillation | Two miscible liquids (ฮ boiling pt โฅ 25 ยฐC) |
| Fractional distillation | Miscible liquids (ฮ boiling pt < 25 ยฐC) |
| Paper chromatography | Separating dyes / pigments |
| Separating funnel | Two immiscible liquids |
| Sublimation | Sublimable solid + non-sublimable solid |
| Centrifugation | Fine suspended particles in a liquid (e.g. blood) |
| Coagulation | Clumping fine suspended impurities to settle them |
๐งช Homogeneous = Solution
๐ซ๏ธ Heterogeneous = Suspension/Colloid
๐ Crystallization โ pure solid
โจ๏ธ Distillation โ boiling pt. diff.
๐ Centrifugation โ density diff.
โจ Tyndall Effect โ light scattering
๐ That's a wrap!
Chapter 5 ยท Exploring Mixtures and their Separation โ Notes by @edugrown