Colligative Properties Does solute change the properties of
- Slides: 17
Colligative Properties
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 • 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 – 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 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 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 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 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) + 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 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 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 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 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 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 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 (↓) • The more particles, the bigger the effect!
Applications of colligative properties Salting roads in the winter time Using salted ice to make ice cream
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