Flashcards
Solutions and their properties
Cards in this deck (31)
- 1What is a solution? What is solvent? What are solutes?Solution: homogenous mixture containing two or more substances in proportions that can be varied
Solvent: A medium (large quantity) for solutes to interact
Solutes: things to be dissolved into solvent - 2What forms solutions can be?Gas, liquid and solid
- 3What are the methods of calculating the concentration in a solution?Percentage Notation: Mass %(m/m), Volume% (v/v), Mass/Volume%(m/v)
Parts-per Notation: ppm, ppb, ppt
Mole-based Notation: Mole Fraction, Mole %
Molarity(mol/L) and Molality (Mol/solv. kg) - 4Why some substances mix to form solutions and others do not?when forming solutions
heat change is involved.
resulting of redistribution of intermolecular forces
related to enthalpy change - 5What components is in the enthalpy diagram?1) enthalpy change for breaking the solvent-solvent attractions (Endo)
2) enthalpy change for breaking the solute-solute attractions (Endo)
3) enthalpy change for forming solvent-solute attractions (Exo) - 6What are the four scenarios that can be resulted according to the relative strengths of these intermolecular forces?1) enthalpy of solution is 0
2)enthalpy of solution <0
3)enthalpy of solution is >0
4)enthalpy of solution is >>0 - 7Explain what happens when the enthalpy of solution is 0.The breaking the solvent-solvent +solute-solute interactions are the same as the forming of solute-solvent interactions.
homogeneous mixture/ ideal solution achieved - 8Explain what happens when the enthalpy of solution is <0.solvent-solute interactions are stronger than solvent-solvent and solute-solute interactions
Non-ideal solution is formed, properties cannot be predicted - 9Explain what happens when the enthalpy of solution is >0.Solvent-solute interactions are somewhat weaker than solvent-solvent and solute-solute interactions
Non-ideal solution is formed, properties cannot be predicted - 10Explain what happens when the enthalpy of solution is >> 0.Solvent-solute interactions are much weaker than solvent-solvent and solute-solute interactions
the two things are in a heterogeneous mixture - 11How to form aqueous solutions?The formation of aqueous solutions of ionic compounds involves interactions between ions and water dipoles
- 12Mechanism of forming ionic solutionsNegative ends of water dipoles point toward the positive ions
Positive ends of water dipoles point toward the negative ions
known as ion-dipole forces
ions surround by water are called hydrated - 13What is Lattice energy?Lattice energy is the energy released when separated gaseous cations and anions come together to form one mole of a solid ionic compound
- 14What Lattice energy measures?1)it is an exothermic process for ionic bonds are formed between the separated gaseous ions
2) measure of ionic bond strength
3) Determined indirectly through the Born-Haber cycle - 15What's the tendency of the dissolution of solutes?Gibbs free energy
G=H-TS
as long as G is <0 then the reaction is spontaneous
1) relative small value for H 2) large increase in entropy to have G<0 - 16Solution formation and equilibrium that might occurStage 1): only dissolution occurs, no crystallization takes place
Stage 2): Dissolution rate > Crystallization rate
Stage 3): Dissolution = Crystallization rate to have dynamic equilibrium - 17Define Saturated, Unsaturated and Supersaturated solution.Sat: solution having solute concentration equals its solubility
Unsat: Solution having solute concentration less than in the saturated solution
Supersat: Solution containing quantity of solute greater than in a saturated solution - 18Solubility as a Function of Temperature, so what trend will that be?In most cases (~95% of ionic substances), solubility increases with increasing temperature (positive slope of the solubility curves)
- 19Explain the relationship of Enthalpy and Solubility?Enthalpy of solution >0 raising temp. stimulates dissolution. This increases the solubility of the solute
Enthalpy change of solution <0, raising temperature stimulates crystallization This decreases the solubility of the solute - 20What is Recrystallization?Recrystallization is a common method for separating a relatively pure homogeneous solid from impurities
- 21How recrystallization works?When temperature decreases, the solution can always become saturated for the desired solute (but not for impurities)
When the concentrated solution cools, the impurities remain in solution while the desired solute crystallizes. - 22What is the principle of recrystallizationImpure crystal lattice dissolution in a hot solvent, then undergone filtration, then slow cooling. At the end pure crystal lattice is selectively produced
- 23Why can recrystallization obtain pure products?Crystallization is a selective process. When a solid crystallizes at the right speed under the right conditions (conc. & solvent) an almost perfectly pure crystalline material is formed. (only molecules of the right shape fit into the crystal lattice)
- 24Why use a fluted filter paper?Highly folded, faster filtration rate, the temp decrease of sol. is minimal, prevent premature crystallization
- 25Recrystallization technique procedures1) Selection of an appropriate solvent
2) Dissolving the Solid
3) Filtering Insoluble Impurities
4) Cooling the solution
5) Collecting the Crystals
6) Drying the Crystals - 26How to select an appropriate solvent?The solute should have a max. solubility in the hot solvent, and a min. solubility in the cold solvent (permits recovery of the purified product in high yield) The impurities should either be insoluble in the solvent at all T or retain soluble in the cold solvent.
- 27What is solvent should used?The solvent should be of low boiling point (lower than melting point of the solid being purified)
- 28What are the steps of Recrystallization?First, take a small sample (20-30mg) of the compound to be recrystallized, place it in a test tube, and add 5-10 drops of a trial solvent. Shake the tube for mixing.
The formation of crystals in 10-20 min suggests that the solvent is a good one - 29Why shake the tube for mixing?if the compound dissolves immediately-> no good (too soluble)
If no solubility is observed, heat the solvent to its b.p., if solubility is then observed, cool the solution to observe crystallization. - 30What are included in when we consider the polarity of a solvent?Dipole moment (microscopic)
Dielectric constant (Macroscopic): the larger value, more polar
* Petroleun ether-> not ether, only a mixture of alkane - 31—
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- Flashcards on Solutions and their properties, created by Holim Chung on 28/04/2016.
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- Holim Chung
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