Biochemistry- Solutions

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Published on February 16, 2014

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Biochemistry- SOLUTIONS

Solutions IB 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).

Concentration  As 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.

Molarity  Molarity is a term we use to describe concentration. = mol/dm3, Molarity = moles (n) of solute dissolved in 1 dm3 of solution. M is the molarity of 2.98g of NaCO3 in 500cm3 of solution?  What

Dilutions  Sometimes, 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 Mixtures  Classified by:  Size of the particles  Whether they exhibit the Tyndall effect

Types of Mixtures  Solution:  Particles are evenly distributed and do not separate on standing  No Tyndall Effect  Example: 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 Mixtures  Suspensions:  Particles are not evenly distributed. Particles are suspended but will eventually settle into layers  Exhibits Tyndall Effect  Examples: Dirt and water mixture

Suspensions The larger particles in a suspension settle out over time. Particles are only physically combined.

Types of Mixtures  Colloids:  Particles are not evenly distributed. Particles are suspended but will eventually settle into layers  Exhibits Tyndall Effect  Examples: milk

Colloids Looks 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

Hydrates  An example of a hydrate is:  CuSO4  5H2O  This 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  If a solute dissolves, the solute molecule is surrounded by water molecules. 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+ ClNa+ ClNa+ Cl- Na+ Cl- Cl- 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) NaCl(s)  Na+ (aq) + Cl-(aq) CaCl2 (s)  Ca2+ (aq) + 2Cl-(aq) (1 particle being dissolved, not ionic) (2 particles being dissolved, ionic) (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 Electricity  If 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.

Electrolytes  Importance 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 Electrolytes  Strength 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 Properties  1. 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????

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