Aqueous Solutions And Colloids

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Aqueous Solutions and Colloids Solutions in living systems are aqueous solution (aq.), that they are made with water.

Types Of Solutions: The result of mixing sugar with water is a homogenous mixture called a (solution). Solution : is a homogenous mixture of the molecule, atoms, or ions of two or more different substances. The substances that make up a solution are called (components). There is usually more of one component than the other component in a solution. The component present in excess is called (solvent), the others are called (solutes). In a solution of sugar in water, water is the solvent and sugar is the solute.

Solubility : there is a limit to the amount of solute that can be dissolved in a solvent at a particular temperature. When this limit is reached. No more solute will dissolve in the solvent. In this case the solvent is saturated with the solute (saturated solution). Solubility : is the amount of solute that dissolve in a given quantity od solute to form a saturated solution. The solubility depends on many factors: 1. Kind of solvent 2. Kind of solute 3. Temperature 4. Pressure above the solvent Remember always the golden rule (like dissolve like) :  polar dissolve polar. Ex: water is a good solvent for NaCl  non polar dissolve non polar Ex: gasoline in a good solvent for greases and oil. Liquid in liquid solution: 1. Completely miscible like water and ethanol. 2. Partially miscible 3. Immiscible The temperature of the solvent affect its solubility, as solutes are more soluble in hot than cold solvent. But gases solubility decreases with increasing temperature like in boiling water, as the temperature of water increases gases escape from solution. The solubility of gas is affected by the pressure of the gas above the solution, so the solubility of gases increase as the pressure of the gas above the solution is increased.

(ex: beverages contain CO2 dissolved in water and are bottled under high pressure . When the bottle is opened the partial pressure of CO2 decreases and the solubility of CO2 decreases. The solubility of solids and liquids are unchanged with the change in pressure.

Concentration and solutions: 1.w/w % % by wt. solute =

wt. of solute in (g)  100 wt. of solute (g)  wt. of solvent (g)

Ex: what is the % by wt. of sugar in a solution made by dissolving 10 g of sugar in 90 g of water? Answer: % wt. =

10  100 10% 10 90

2. Vol./Vol. % % by wt. volume solute =

volume of solute (ml)  100 volume of the solution (ml)

Ex: what is the % by vol.. of ethanol in a solution made by diluting 10 ml of ethanol to 100 ml with water? Answer: % by vol. ethanol =

10  100 10% 100

4.Wt./Vol. % % by wt./Vol. solute =

wt . of the solute (g)  100 total vol of solution (ml)

Ex: what is the % by wt./vol of NaCl in a solution made by diluting 1.5 g of NaCl to 100 ml with water? Answer: % by wt./vol

NaCl =

1.5(g)  100 1.5% 100(ml)

Low concentration of solute are expressed in mg/100ml. This wt/volume % unit is defined as follows: wt . of the solute (mg) mg/100ml = 100 ml of solution (ml)

Ex: 1 ml sample of blood plasma is found to contain 3.3 mg of sod.ions. express this conc. In mg/100ml? 3.3 X   X 330mg 1ml 100ml Answer: 330(mg) mg/100ml  100(ml)

5.Parts per million and parts per billion (ppm and ppb) these are used to report very small amounts of solute in a solution. ppm =

wt . of the solute in (mg) wt.of solution (in Kg)

Notice : Kg = 106mg. One parts per million (ppm) contains and part of solute per 1 million (106) parts of solution. A part mean ant unit of measure such as (gm, L, …etc). Concentration of small quantities of solid in water, the unit ppm is defined as mg of solute per liter of solution because 1 million mg (1Kg) of water occupies 1 L. Air pollution is measures in ppm as volume rather than wt. So1ppm means that there is 1μL of pollutant (solute) per 1 million (106) μL (1L) of air (the solution).

The amount of Hg in the fish exceed the max. FDA tolerance. The fish is contaminated with Hg.

ppb contains 1 part of solute per 1 billion (109) parts of solution. Parts Ex: The maximum food and drug administration (FDA) tolerance of Hg in fish is 05 ppms. A 10 g sample of fish is found to contain 72 μg of Hg.

Does this amount of Hg in fish exceed the FDA maximum tolerance?

Answer:

72μ2

10g

X

1Kg

ppm 

X

72μ2 103 1mg  1Kg  3  7.2mg 10g 1Kg 10 μg

wt. of solute (mg) 7.2   7.2ppm 1Kgofsolut ion 1

refer to wt. and Vol. depending on whether the solution is a gas, liquid or solid.

Molar Concentrations: Molar concentration or molarity is the no. of moles of solute per liter of solution. no. of moles of solute M= no. of liter of solution

Ex: determine the molar concentration of a solution that contains 25g of glucose, C6H112O6 In 500ml of solution. M.wt.of glucose = 180g/mole 25g No.of moles =  0.139mo 180g/mole 500 0.139mole  0.5L,M  0.278M 1000 0 5L

The important of molar concentration is that we can determine the wt.of the solute contained in any vol. of solution. Ex: a patient is fed IV 0.5 L of a 1M glucose solution. How many moles of glucose has the patient received?

1 mole X

1L

X= 0.5L

Milliequivalents per Liter:

0.5 X 1  0.5moleglucose 1

this unit is used to express low concentration of ions in body fluids. One equivalent of an ion (Eq.) : is 1 mole of that ion multiplied by the absolute value its change. Ex: 1 mole of sod. Ions contains one equivalent of sod. Ions. +

+

no.of milliequivalent of ion 1 mole Na+ = 1 Eq. Na+ Milliequivalent per liter (mEq/L) =   volume of solution, In L 1Eq.Na 1mEq.Na 1  Or 1molNa 0.001 molNa 1molC  1Eq. ClOr 1Eq.Cl 1mEq.Cl 1  1molCl 0.001 molCl  0.001 molNa 1mEq.Na 1mEq. Na    L L 0.001molNa   0.001 molCl 1mEq. Cl 1mEq. Cl   L L 0.001 molCl

Ex: express the concentration of sod. And chloride ions in a 0.001M NaCl solution in terms of mEq/L. Answer: 0.001MNaCl  0.001 MNaCl Na  0.001M Cl 0.001MNaCl 0.001 MNaCl Na 0.001M Cl   L L L

Electrolytic And Nonelectrolytic: Electricity is the flow of e- in a circuit from a battery of electrical generator. Solution s that conduct electricity called (electrolytic solution) and that doesn't is called (nonelectrolytic solution). The solute that forms an aqueous electrolytic solution is called (electrolyte). Ex: NaCl, Kl, LiF,CaCl2, are electrolytes. Sucrose, ethanol, oxygen, Co, are non electrolytes.

Arrhenius Theory of Electrolytes:

all the electrolytes are compound that contain ionic bonds.. Such compounds are solid at room temperature and contain ions arranged in a crystal lattice. When these are dissolved in eater, the ions are released and distribute themselves uniformly in water. Such close association of water molecules with ion is called (hydration). The total no. of ions formed per mole of electrolyte depends on the chemical formula of the electrolyte. Ex: NaCl, Na+ Cl2  6.02  10 23 LiBr, Li+ Br2  6.02  10 23 +

We can use Arrhenius model to explain how solutions of electrolytes conduct electricity; in an electrical circuit, one of the electrodes has a positive charge and the other has a negative charge. The positive ions (cations) in an electrolytic solution are attracted to the negatively charged electrode and the other has a negative ions (anions) are attracted to the positively charged electrode. This results in a transport of electrical charge from one electrode to the other. The net effect is a flow of electrons through the solution. While in a nonelectrolyte solution there is no attraction to any of the electrodes because the solution is neutral. So no electric current flows through the solution.

Osmosis and Osmotic Pressure: Cells have membranes called (plasma membranes). These membranes not only keep the cell intact but also allow the exchange of material into and outside the cell. Dialysis and osmosis are two ways exchange of material occurs.

Osmosis: Is the movement of water through an osmotic membrane form an aqueous solution that is less concentrated to one that is more concentrated. Membranes that allow only certain molecules to pass through are called (semipermeable membranes) or (Osmotic membranes).

We can prevent osmosis from occurring by applying pressure to the right arm of the U-tube ( the one that contains the glucose solution). The pressure needed to prevent osmosis is called (osmotic pressure), so the level in both arms will be the same. Water moves from dilute to more concentrated solution to make the concentration of the solutions equal. Osmotic membranes contain small holes. Molecules larger than the holes will not pass through, so membranes act as a molecular sieve. Certain molecules pass through but not others. The greater the number of particles, whether ions or molecules, in a solution, the greater the osmotic pressure. Ex: The osmotic pressure of 1M NaCl solution is twice that of 1M glucose solution. The reason is that NaCl is an electrolyte will glucose is a nonelectrolyte. 1 mole NaCl contains 1 Mole of Na+ and 1 Mole of Cl-, so 1M NaCl contains twice as many particles as glucose. The solution that have the same osmotic pressure are called (isotonic). If one has a higher osmotic pressure than the other it's (hypertonic) with respect to the other. A lower osmotic pressure solution is called (hypotonic). The plasma membrane of red blood cell (RBC) behaves as osmotic membranes. The cells contains an aqueous fluid made up of dissolved compounds and exert osmotic pressure determined by the concentration of dissolved molecules and ions in the fluid. Osmotic occurs when the RBC is placed in water, so water enters the cell that the cell is ruptured. This is called (hemolysis).

Osmosis occurs when RBC are places in concentrated solution (NaCl). But in this case, the solution inside the cell is hypotonic compared to saline and osmosis occurs in the reverse direction. Water leaves the cell and passes into the solution. This causes the RBC to shrink called (crenation). A 0.95% saline solution is isotonic compared to the solution inside RBC. RBC placed in such a solution undergo neither shrinking nor hemolysis. For this all IV solution should be isotonic with blood. Fluids in living system carry not only dissolved ions and molecules but also larger particles called colloids.

Colloids and colloidal Dispersions: Solutions are homogenous mixtures of solute and solvent molecules. The size of atoms and molecules (particles) in a solution is 0.05 – 0.25 nm. Sometimes intermolecular attraction between molecules cause them cluster together. The size of these clusters 1-100 nm. Matter containing particles of this size is called a (colloid). A uniform dispersion of a colloid in water is called is a (colloidal dispersion). the colloid in a colloidal dispersion is called the dispersed substance. The contentious matter in which the colloid is dispersed is called the dispersing substance. The dispersion is similar to a solution in that the particles don't settle down on standing. But a colloidal dispersion usually appears cloudy. There are 8 types of colloidal dispersions:

Particles in a colloidal dispersions are charged so repel each other and cannot from particles large enough to settle out.

Other colloids are stabilized in water by the action of a third substance called (emulsifying agent). Ex: mixture of oil in water, oil is immiscible with water but if soap is added the oil is emulsified by the soap. So soap is emulsifying agent. The soap breaks up the oil into small drops. The soap forms a negatively charged layer on the surface of each oil drop. This causes the oil to repel each other and they disperse through the water. Ex: Bile salts are emulsifying agents. They break the fats we eat into small globules that can be more effectively digested.

Dialysis and living systems: Osmotic membranes aloe water molecules but not solute particles to pass through. Membranes that allow small molecules and ions to pass while holding back large molecules and colloidal particles are called (dialysis membranes). A plasma selective passage of small molecules and ions in either direction by a dialyzing membrane is called (dialysis). Dialysis differs from osmosis in that osmotic membrane allow only solvent molecules to pass. Ex: The kidneys which cleanse the blood by removing the waste products of metabolism and control the concentration of electrolytes.