SOLUTIONS Chapter 6.7

A solution is a homogeneous mixture of two or more substances; the dissolved substance is called the solute and the substance in which the solute is dissolved is called the solvent. The relative amounts of the substances in the solution determine which is solvent and solute; the one in the greater amount is solvent and solute; the one in the greater amount is considered the solvent.

Concentration of a solution refers to the amount of solute in a given amount of solution. Methods of expressing concentration are: Dilute and Concentrated

A dilute solution contains a relatively small proportion of solute, while a concentrated solution contains a relatively large proportion of solute. Concentrated solutions are only possible when the solute is very soluble.

An unsaturated solution is one that can still dissolve more solute at that temperature. A saturated solution is one in which the solute in solution is in equilibrium with the pure undissolved solute; in other words, the solution contains all of the solute it can dissolve at that particular temperature. A supersaturated solution contains more solute in solution than it would ordinarily hold at that temperature. Example: If in hot coffee one dissolves all the sugar it can possibly hold and carefully cools it, the coffee still holds all the sugar that was dissolved and a supersaturated solution exists. If a small crystal of sugar is introduced into this cooled coffee, some sugar will crystallize out and a saturated solution will remain.

Types of Solutions

gas in liquid carbonated beverages
liquid in liquid alcohol in water
solid in liquid salt in water

gas in solid hydrogen in platinum
liquid in solid mercury in silver (dental fillings)
solid in solid copper in silver (sterling silver)

PERCENT COMPOSITION - Think in terms of 100

1. Percent - Mass in a total volume (m/v) Most frequently used form of %.
    A 5% solution means 5 grams in 100 mL volume. Or 2.5 grams in 50 mL volume.
    A 5 mg% solution means 5 mg in 100 mL volume. Same as 5 mg/dL. (dL = 100 mL)

2. Percent- Mass of solute and mass of solution (m/m)
    This refers to the amount of solute in grams in the total solution also in grams.
    Example: A 10% aqueous NaCl solution contains 10 g of NaCl in 90 g of water (or 10 g NaCl per 100 g of solution).

3. Percent - Volume of solute in volume of solution. (v/v)
    This refers to relative amounts of two liquids in solution. Example: An alcoholic beverage that is 7% alcohol contains 7 ml of alcohol per 100 ml of solution.
    Ratios of individual liquids is generally given rather than %. Example: A chromatography solvent was chloroform: methanol: water (6:3:1).

1. How many grams of sugar are needed to make 100 ml of a 20% solution?

2. What is the concentration in mg % of 100 mg of NaCl dissolved in 500 ml of solution?

3. How many grams of sugar are needed to make 150 ml of a 30% solution:

4. I have 250 ml of a .9% NaCl solution (saline). How many grams of salt do I have ?

5. How many grams of sugar are need to make 50 grams of a 3% solution?

MOLAR SOLUTIONS Pages 181 - 183

Molar solutions are used more frequently and are more precise than the percent solutions.

1. How would I make up 500 mL of a 1 M solution of NaCl?

moles = grams                     Molarity = moles
              MW                                           L

                                                1       =  x moles
                                                                  0.5 L

                                                x       = 0.5 moles

0.5 = x grams
           58.5

x = 29.25 grams

Put 29.25 g NaCl in flask, stir, add H₂O and bring up to 500 ml

2. How would we make up 250 mL of a 3 M solution of NaCl?

3. How much NaCl would I need to make up 10 ml of a 6 M solution?

4. How many grams of Ca(CO₃) would I need for 100 ml of a 2 M solution?

5. I have 29.25 g NaCl in 500 ml. What is its molarity?

Isotonic means the same osmotic strength on both sides of the semipermeable membrane. Physiological saline (0.89% NaCl) is isotonic with blood. The cell retains is=s shape and function.

Hypotonic means the solution has a lower concentration of particles than the cell. If a red blood cell were placed in distilled water, there would be more water moving into the cell and eventually burst it. Hemolysis (If you soak limp lettuce in water it will perk up. Why/)

Hypertonic means the solution has a higher concentration of particle than the cell. If a red blood cell were place in brine (concentrated NaCl), the cell would shrivel up. This method is used for curing meats like country ham. The bacteria can=t survive in the high salt concentration. (What is on the outside of country ham?)

In osmosis the membrane allows only the solvent to pass through the semi-permeable membrane. The pores of the membrane can be increased selectively to allow passage of different molecular weight compounds. Quite often it is used to remove salt or other ions from a solution.

Hemodialysis uses this principle to filter out the buildup of toxic compounds in the body. The function of the kidneys is to remove these waste products through dialysis. The kidneys can also reabsorb ions to keep a balance. There is a threshold for reabsorption for glucose. When the blood concentration is 150 mg%, the sugar is seen in the urine.

In the dialysis machine the blood is circulated through a long tube of cellophane in an isotonic solution and then returned to the patient=s vein. The ions can pass out and the large proteins remain. When protein is found in the urine, that means there is some type of damage to the kidney. The isotonic solution has 0.6% NaCl, 0.04% KCl, 0.2% NaHCO₃ , and 0.72% glucose (w/v). Thus no sodium ions or glucose is lost from the blood. The isotonic solution is changed every 2 hours and the patient stays on the dialysis machine for 4 to 7 hours.

Rate a solute dissolves depends on
    1. surface area
    2. agitation
    3. temperature

Factors Affecting Solubility
    1. pressure - gas in soda
    2. temperature
    3. chemical structure

1. Calculate the molar concentration of the following solutions

a. 36.5 g HCl in 1 liter of solution ________________________

b. 36.5 g HCl in 5 liters of solution _______________________

c. 36.5 g HCl in 0.25 L of solution _________________________

d. 73.0 g HCl in 1 liter of solution ________________________

e. 73.0 g HCl in 5 L of solution ____________________________

f. 73.0 g of HCl in .25 L of solution________________________

2. Calculate the weight of solute contained in each of the following solutions

a. 250 mL of a 1 M solution of H₂SO₄ _______________________

b. 3000 mL of 0.5 M solution of HC₂H₃O₂ _________________

c. 2 liters of 1.5 M solution of H₂CO₃ _______________________

d. 100 mL of 2 M solution of KOH __________________________

3. Calculate the volume of solution (1.5 M) that would contain

a. 40 g of NaOH _______________

b. 80 g of Ca(OH)₂ _______________

c. 20 g of HCl _______________

d. 40 g H₂CO₃ ________________

Wednesday, March 21, 2007 01:28:03 PM