๐งช
Chapter 9 โ The Amazing World of Solutes, Solvents & Solutions
Table of Contents
- 9.1 What Are Solute, Solvent & Solution?
- 9.2 How Much Solute Can a Solvent Dissolve?
- 9.2.1 Temperature & Solubility of Solids
- 9.3 Solubility of Gases
- 9.4 Why Do Objects Float or Sink?
- 9.5 What is Density?
- 9.5.1 Measuring Mass & Volume
- 9.5.2โ3 Temperature & Pressure on Density
- ๐ Quick Summary & All Formulas
9.1 What Are Solute, Solvent & Solution?
@edugrown
Fig 9.3 โ Solute evenly distributed in Solvent
Salt in water, sugar in tea, ORS โ all are solutions !
- Two or more substances mixed to form a uniform mixture
- Components are evenly distributed โ can't see them separately
- Non-uniform: Sand + Water, Sawdust + Water, Chalk + Water
- Air is also a solution โ a uniform mixture of gases!
๐ The 3 Key Terms โ
solid / less qty liquidSolute
๏ผ
liquid / more qtySolvent
โ
uniform mixtureSolution
- Solute โ substance that dissolves
- Solvent โ substance that dissolves the solute
- Two liquids mixing โ smaller quantity = Solute, larger = Solvent
@edugrown
Fig 9.4 โ Gulab Jamun Chashni (sugar syrup solution)
In Gulab Jamun Chashni โ even though sugar is MORE than water, water is still the Solvent and sugar is the Solute!
ORS โ salt + sugar + water. Every sip tastes same because all components are evenly distributed throughout the solution!
Key Definition
Solution = a uniform mixture where the solute dissolves completely in the solvent. Components are not visible separately. e.g. Salt water, sugar water, air (mixture of gases).
โฆ โฆ โฆ
9.2 How Much Solute Can a Solvent Dissolve?
@edugrown
Fig 9.5 โ Unsaturated Solution
@edugrown
Fig 9.6 โ Saturated Solution (undissolved salt at bottom)
Unsaturated Solution
More solute CAN still dissolve at given temperature
Saturated Solution
No more dissolves โ excess settles at the bottom!
- Concentration = amount of solute in a fixed quantity of solution
- Dilute Solution โ less solute dissolved
- Concentrated Solution โ more solute dissolved
- Dilute & Concentrated are relative terms โ compare to each other
Key Definition
Solubility = the maximum amount of solute that dissolves in a fixed quantity (100 mL) of solvent at a particular temperature. A saturated solution at one temp becomes unsaturated if temperature is raised!
โฆ โฆ โฆ
9.2.1 Temperature & Solubility of Solids
@edugrown
Fig 9.7 โ Dissolving baking soda by heating
๐ฌ Baking Soda + Water Experiment:
- At 20ยฐC โ some baking soda left undissolved
- Heat to 50ยฐC โ undissolved solid dissolves โ
- Heat to 70ยฐC โ even more dissolves โ โ
- Conclusion: More heat โ more dissolving!
20ยฐC
Least dissolves
๐ก๏ธโ
Least dissolves
50ยฐC
More dissolves
๐ก๏ธโ
More dissolves
70ยฐC
Even more! ๐ฅ
Even more! ๐ฅ
Key Rule
For most solid solutes: Solubility INCREASES as temperature increases. A saturated solution at a lower temperature becomes unsaturated at a higher temperature!
Asima Chatterjee โ developed anti-epileptic & anti-malarial drugs using solvents & solutions to extract compounds from medicinal plants. First woman to win Shanti Swarup Bhatnagar Award in Chemical Science. Awarded Padma Bhushan.
โฆ โฆ โฆ
9.3 Solubility of Gases
@edugrown
Fig 9.8 โ Aquatic life survives on dissolved Oโ
- Many gases like oxygen dissolve in water
- This dissolved Oโ sustains all aquatic life ๐๐
- Gas + Water = uniform mixture
- Gases dissolve evenly โ it is a solution!
Gas Solubility โ OPPOSITE to Solids!
For gases: Solubility DECREASES as temperature increases. Cold water holds more Oโ โ supports aquatic life. Warm water โ less Oโ dissolved โ danger for fish!
| Solute Type | Temp โ | Solubility | Example |
|---|---|---|---|
| Solid in Liquid | Higher ๐ฅ | ๐ Increases | Salt, Sugar in Water |
| Gas in Liquid | Higher ๐ฅ | ๐ Decreases | Oโ in Water |
โฆ โฆ โฆ
9.4 Why Do Objects Float or Sink?
@edugrown
Fig 9.9 โ Some objects float, others sink
- Objects less dense than liquid โ FLOAT ๐ถ
- Objects more dense than liquid โ SINK ๐ชจ
- Oil floats on water โ oil is less dense than water
- Rice husk floats, rice grains sink โ different densities!
Unpeeled orange floats โ air pockets in peel lower its overall density. Peeled orange sinks โ no air, denser than water! Density of substance is NOT the only factor โ shape & trapped air also matter!
โฆ โฆ โฆ
9.5 What is Density?
@edugrown
Fig 9.10a โ Dense forest = high density
@edugrown
Fig 9.10b โ Less dense forest = low density
Density = Mass รท Volume
D = M / V | mass per unit volume of a substance
@edugrown
Fig 9.11 โ 1 litre oil = only 910g โ Density < water!
- SI unit: kg/mยณ | Common: g/mL or g/cmยณ
- Density is independent of shape & size
- Depends on temperature & (for gases) pressure
- 1 mL of water โ 1 g at room temperature
- 1 litre oil = 910 g โ oil density < water density โ oil floats!
๐ Relative Density
Relative Density = D(substance) รท D(water)
No units | e.g. Aluminium = 2.7 g/cmยณ โ Rel. Density = 2.7
- Rel. Density < 1 โ substance floats in water
- Rel. Density > 1 โ substance sinks in water
@edugrown
Fig 9.20 โ Earth's layers, density increases toward centre
๐ Earth's Layers โ Density increases โ
โฆ โฆ โฆ
9.5.1 Measuring Mass & Volume
Mass
Quantity of matter. Units: g / kg
Tool: Digital Weighing Balance
Tool: Digital Weighing Balance
Volume
Space occupied. Units: mL, cmยณ, L
Tool: Measuring Cylinder
Tool: Measuring Cylinder
โ๏ธ How to Measure Mass โ Steps:
@edugrown
Step 1: Switch ON โ bring to zero
@edugrown
Step 2: Place watch glass โ tare/reset to zero
@edugrown
Step 3: Place object โ read mass (16.400 g)
๐งช How to Measure Volume of Liquids:
@edugrown
Fig 9.15 โ Measuring cylinders of different sizes
- Use a narrow transparent Measuring Cylinder
- Pour liquid slowly to the required mark
- Water forms a curved surface = Meniscus
- Read at bottom of meniscus (colourless liquids)
- Read at top of meniscus (coloured liquids)
- Eyes must be level with meniscus!
@edugrown
Fig 9.16 โ 100 mL measuring cylinder
@edugrown
Fig 9.17 โ Pouring water into cylinder
@edugrown
Fig 9.18 โ Reading the meniscus at eye level
๐ฆ Volume of Regular Solids (Cuboid):
Volume = Length ร Width ร Height
V = l ร w ร h (in cmยณ)
๐ชจ Volume of Irregular Solids โ Displacement Method:
- Fill cylinder with water โ note initial level (A)
- Lower the solid into water using a thread
- Note the new water level โ final level (B)
- Volume of object = B โ A (mL = cmยณ for solids)
Volume of Object = B โ A
Final water level โ Initial water level
Why are measuring cylinders narrow & tall? A narrow cylinder makes even a tiny volume change produce a bigger, more visible rise in liquid level โ gives more accurate readings!
โฆ โฆ โฆ
9.5.2โ3 Temperature & Pressure Effects on Density
Temperature โ
Particles spread โ Volume โ โ Mass same โ Density decreases
Temperature โ
Particles closer โ Volume โ โ Mass same โ Density increases
@edugrown
Fig 9.22 โ Hot air balloons rise due to lower density of hot air
Hot Air Balloon: Heated air expands โ less dense than cool surrounding air โ balloon rises! Same principle as hot air rising up from the ground.
๐๏ธ Effect of Pressure on Density:
| State | Pressure Effect | Reason |
|---|---|---|
| ๐ฌ๏ธ Gases | Large effect | Compressible โ Vol โ โ Density โ |
| ๐ง Liquids | Small effect | Nearly incompressible |
| ๐ชจ Solids | Negligible | Particles already very close |
@edugrown
Fig 9.23 โ Ice floats on water (density of ice < liquid water)
Special Case โ Ice floats on Water!
Water's density is highest at 4ยฐC. When cooled to 0ยฐC, water freezes โ particles rearrange โ takes more space (expansion) โ same mass, more volume โ density decreases โ ice floats! ๐ง
Ice layer on top keeps water underneath warm โ fish & aquatic life survive in winter. โ๏ธ๐
@edugrown
Fig 9.21 โ Bamboo raft floats due to low density of bamboo
In ancient times, people used bamboo & wooden logs to travel rivers & seas. Bamboo is light, hollow & floats easily โ less dense than water. People tied bamboo poles to make rafts for fishing, trading & crossing water bodies.
โฆ โฆ โฆ
Quick Summary & All Formulas
- Uniform mixture = Solution
- Solid in solution = Solute | Liquid = Solvent
- Saturated = no more solute dissolves at that temperature
- Unsaturated = more solute CAN still be dissolved
- Solid solubility โ with temperature โ
- Gas solubility โ with temperature โ
- Density = Mass / Volume
- Density โ when temperature โ (generally)
- Ice floats โ water's density is highest at 4ยฐC
- Pressure mainly affects density of gases; solids โ negligible effect
All Formulas at a Glance
DensityD = Mass / Volume
Vol. of CuboidV = l ร w ร h
Displacement MethodVol = B โ A (mL)
Relative DensityD(sub) รท D(water)