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Biochemistry- SOLUTIONS
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SolutionsIB Chemistry: Chapter 1 Section 1.5
What parts make up a solution?Solution is a mixture of two components.
1. Solute: less abundant component, the substance being dissolved
2. Solvent: more abundant component, the dissolver
Solutions in water are called aqueous (aq).
ConcentrationAs more and more solute gets dissolved, the solution becomes
more concentrated.
When the solvent can no longer dissolve any more solute, it is saturated. (If less solute is dissolved, unsaturated.)
Solution can dissolve more solute than usual under particular circumstances – supersaturated.
MolarityMolarity is a term we use to describe concentration.
M = mol/dm3, Molarity = moles (n) of solute dissolved in 1 dm3 of solution.
What is the molarity of 2.98g of NaCO3 in 500cm3 of solution?
DilutionsSometimes, we need a diluted solution for a particular
procedure.
In order to dilute, you add water to a more concentrated solution.
The equation we use to determine how much concentrated solution we need is:
M1V1=M2V2
Types of MixturesClassified by:
Size of the particlesWhether they exhibit the Tyndall effect
Types of Mixtures
Solution:Particles are evenly distributed and do not
separate on standingNo Tyndall EffectExample: food coloring and water mixture
Solution Example
Notice how you cannot see a distinction between solute and solvent. It is the same throughout the solution.
Types of MixturesSuspensions:
Particles are not evenly distributed. Particles are suspended but will eventually settle into layers
Exhibits Tyndall EffectExamples: Dirt and water mixture
SuspensionsThe larger particles in a suspension settle out over time. Particles are only physically combined.
Types of MixturesColloids:
Particles are not evenly distributed. Particles are suspended but will eventually settle into layers
Exhibits Tyndall EffectExamples: milk
ColloidsLooks like a solution to the naked eye. Particles are suspended. The particle size is the “in betweener”, larger than a solutions’ particles but smaller than a suspensions’ particles.
What is this “Tyndall effect”?Light scattering by particles.
Found in colloids and suspensions, but not solutions.
Tyndall Effect
Hydrates
Hydrates are ionic compounds that have water molecules absorbed into the crystal lattice.
Hydrates are still solid, just have certain amounts of water attached to the ions.
An example of a hydrate is Copper (II) Sulfate pentahydrate:CuSO4 ● 5H2O
HydratesAn example of a hydrate is:
CuSO4 5H2OThis means that for every 1 unit of copper sulfate, there
are 5 units of water.Or, for every 1 mole of copper sulfate there are 5 moles of
water.
Solve for the molar mass. (The dot does not mean multiply, just add the mass of water to mass of copper sulfate.)
Properties of Solutions: Dissociation
When a solute dissolves, the solute molecule is surrounded by water molecules.
If the solute is ionic, than the ions separate and are surrounded by water molecules.
Example: NaCl Na+ + Cl-
Model of NaCl dissolving in water
Na+
Cl-
Cl-
Cl- Cl-
Cl-
Na+ Na+
Na+ Na+
Na+
Dissociation Continued Because of this, ionic substances have more of an effect on the boiling point
and freezing point than a covalent bond (something that is not ionic).
C6H12O6 (s) C6H12O6 (aq) (1 particle being dissolved, not ionic) NaCl(s) Na+ (aq) + Cl-
(aq) (2 particles being dissolved, ionic) CaCl2 (s) Ca2+ (aq) + 2Cl-
(aq) (3 particles being dissolved, ionic)
CaCl2 will have the largest effect (higher melting/boiling pts) and glucose the least effect (lower melting/boiling pts).
Ability to Conduct ElectricityIf ions are present in solution, it will conduct eletricity……all
ionic substances will conduct electricity when dissolved.Ex: Tap water, salt water
Solutes that conduct electricity when dissolved are called electrolytes.
ElectrolytesImportance of electrolytes:
The movement of calcium ions allows muscles to contract and relax
Presence of sodium and potassium ions allow your nerve cells to respond to stimuli.
STRONG vs. weak ElectrolytesStrength depends on number of ions in solution
More ions = stronger electrolyte, Fewer ions = weaker electrolyte
For strong electrolytes, increasing concentration increases conductivity
Weak electrolytes, increasing concentration does not effect conductivity
Think about it!!!For strong electrolytes, increasing concentration
increases conductivity
Weak electrolytes, increasing concentration does not effect conductivity
WHY????
Colligative Properties1. Boiling point of the solvent elevates
2. Freezing point is lowered
Vapor pressure is lowered, fewer molecules of solvent are escaping to the gas phase when a solute is present. The solvent molecules cannot escape because they are “busy” keeping the
solute dissolved.
Salting the Roads!
Rock salt (CaCl2) is used to keep the roads from freezing in the winter. Ever wonder why that
happens????