Colligative Properties Does solute change the properties of

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Colligative Properties

Colligative Properties

Does solute change the properties of a solvent? • Consider aqueous solutions – Solvent

Does solute change the properties of a solvent? • Consider aqueous solutions – Solvent = water • How do properties of aqueous solution compare to properties of pure water?

Conductivity • Pure water does not conduct electricity – Some aqueous solutions do •

Conductivity • Pure water does not conduct electricity – Some aqueous solutions do • To conduct current, solution must contain ions • Conductivity depends on nature of the particle – Molecular (covalent) solutes do not conduct; ionic solutes do conduct

Colligative Properties • Depend on number particles in solution not on type particles –

Colligative Properties • Depend on number particles in solution not on type particles – i. e. doesn’t matter what kind of particles: can be ions or molecules – Concentration of particles does matter

What are some colligative properties? • • Vapor Pressure (↓) Freezing Point (↓) Boiling

What are some colligative properties? • • Vapor Pressure (↓) Freezing Point (↓) Boiling Point (↑) change in Osmotic Pressure • higher the concentration of solute particles, the larger the effect

Does it matter if solute is ionic or covalent? • number of particles will

Does it matter if solute is ionic or covalent? • number of particles will vary • Ionic solutes – dissolve to produce (+) & (-) ions more particles per mole of solute • Covalent solutes – 1 -to-1 relationship between moles of solute and moles of dissolved particles

C 6 H 12 O 6 • Covalent substances: – dissolve as molecules: C

C 6 H 12 O 6 • Covalent substances: – dissolve as molecules: C 6 H 12 O 6(s) + H 2 O(l) C 6 H 12 O 6(aq) 1 mole sugar → 1 molecules

Na. Cl • Ionic substances: – dissolves (dissociates) as ions: Na. Cl(s) + H

Na. Cl • Ionic substances: – dissolves (dissociates) as ions: Na. Cl(s) + H 2 O(l) Na+1(aq) + Cl-1(aq) 1 mole salt 2 moles ions

Mg. Cl 2 • Ionic substance: – dissolves as ions Mg. Cl 2(s) +

Mg. Cl 2 • Ionic substance: – dissolves as ions Mg. Cl 2(s) + H 2 O(l) Mg 2+(aq) + 2 Cl-(aq) 1 mole salt 3 moles ions

As solute is added to a solvent, what happens to freezing point & boiling

As solute is added to a solvent, what happens to freezing point & boiling point of solution? 1) The freezing point ↓ & the boiling point ↓ 2) The freezing point ↓ & the boiling point ↑ 3) The freezing point ↑ & the boiling point ↓ 4) The freezing point ↑ & the boiling point ↑ Answer: 2

Which solution containing 1 mole of solute dissolved in 1000 g of water has

Which solution containing 1 mole of solute dissolved in 1000 g of water has the lowest freezing point? 1) C 2 H 5 OH(aq) 2) Na. Cl(aq) Be careful! - do you want greatest or least change? 3) KOH What if question asked which solution has highest freezing point? 4) Ca. Cl 2 Answer: 4

Of the following solutions, the one that will freeze at the lowest temperature contains

Of the following solutions, the one that will freeze at the lowest temperature contains 1 mole of nonvolatile solute dissolved in 1) 2) 3) 4) 250 g of solvent 500 g of solvent 750 g of solvent 1000 g of solvent Answer: 1

Which solute, when added to 1000 g of water, will produce a solution with

Which solute, when added to 1000 g of water, will produce a solution with the highest boiling point? 1) 29 g of Na. Cl 2) 58 g of Na. Cl 1 mole of Na. Cl → 2 moles of ions 3) 31 g of C 2 H 6 O 2 4) 62 g of C 2 H 6 O 2 1 mole of C 2 H 6 O 2 → 1 mole of molecules

Which solution will freeze at the lowest temperature? 1) 1 g of Na. Cl

Which solution will freeze at the lowest temperature? 1) 1 g of Na. Cl dissolved per 100 g of H 2 O 2) 1 g of Na. Cl dissolved per 1000 g of H 2 O 3) 1 g of C 12 H 22 O 11 dissolved per 100 g of H 2 O 4) 1 g of C 12 H 22 O 11 dissolved per 1000 g of H 2 O

Which solution will freeze at the lowest temperature? 1) 1 g of Na. Cl

Which solution will freeze at the lowest temperature? 1) 1 g of Na. Cl dissolved per 100 g of H 2 O __1 g____ 58. 8 g/mol = 0. 017 mol → 0. 034 mol of ions (Na. Cl) (Na+1 and Cl-1) 2) 1 g of C 12 H 22 O 11 dissolved per 100 g of H 2 O __1 g___ 232 g mol = 0. 0043 mol of molecules

Effect of Nonvolatile Solute • Boiling Point Elevation (↑) • Freezing Point Depression (↓)

Effect of Nonvolatile Solute • Boiling Point Elevation (↑) • Freezing Point Depression (↓) • The more particles, the bigger the effect!

Applications of colligative properties Salting roads in the winter time Using salted ice to

Applications of colligative properties Salting roads in the winter time Using salted ice to make ice cream