Solutions and Mixtures Chapter 7 By Daniella Perruzza

Introduction It is important to study and build on our background about pure substances and their properties. Both solutions and colloidal dispersions compose our very own bloodstream. It is amazing to know how some substances dissolve in water and how others do not. Dialysis gives an insight to how important the kidney is in our bodies. The human body maintains concentrations of all the substances that circulate in the bloodstream.

Properties of Mixtures l Mixtures can either be homogenous or heterogeneous, but are made up of two pure substances in variable proportions. l A property of mixtures is that they can be separated into their original components without requiring any chemical reaction. Allowing the water to evaporate over boiling bath water can separate sugar and water. Solutions have different particle sizes, which distinguish one homogeneous mixture from another. l Solutions are also known to be transparent, where one could see right through them. It may however, obtain a color but still be transparent. The mixture remains stable and does not separate after standing for any period of time.

Type 1: Solutions l A solution is a homogeneous mixture with no definite composition. It usually refers to liquids but can also be gases and solids. Water solutions can contain solutes that are normally solids, liquids and gases. l The substance that is present in much larger quantity then the other is referred to as the solvent. The gases, liquids, or solids dissolved in the solvent are the solutes. At least two substances must be mixed in order to have a solution.

Electricity by Aqueous Solutions l Aqueous solutions of some substance conduct electricity. These substances are known as electrolytes. Ions are produced when an electrolyte dissolves in water. Ions are responsible for conducting electricity in the solutions. l Strong electrolytes conduct electricity very easily, because in the solution the electrolytes exist almost entirely as ions. Weak electrolytes form solutions that are poor conductors, because there are few ions present. l Aqueous solutions that cannot conduct electricity are known as non-electrolytes. Water molecules are polar with negative charges on their oxygen atoms and positive charges on the hydrogen atoms.

Type 2: Colloidal Dispersion l l Another type of a homogeneous mixture is a colloidal dispersion. Colloids consist of clumps of molecules. The particles have dimensions between 2 to 1000 nanometers. Fog and Jell-O are examples of a colloid. Colloids frequently appear opaque, such as milk. The particles are large enough to scatter light, such as the way fog interacts with the light from car headlights. The particles may be seen in a beam of light such as dust in air in a ray of sunlight.

Type 3: Suspension l l l A suspension is a homogeneous mixture with particles visible to the naked eye. The particles have diameters greater then 1000 nanometers. Blood is an example of a suspension. In circulating blood, red cells, white cells, and platelets are suspended. Suspensions do not transmit light. However, they separate on standing for a period of time and can be separated by filtration.

Replacement Reactions l l There are three types of single replacement reactions that occur in aqueous solutions. In the first type, a free metal displaces a less active metal. In the second type, a free active metal displaces hydrogen from water. The last type occurs when an active halogen displaces a less active halogen. In double replacement reactions, the product produced distinguishes when a double replacement reaction has occurred. Three different products will form after the reaction has taken place.

Factors Affecting Solubility l l l There are definite factors that effect the solubility, or the ability to be dissolved, of gases in liquids. The solubility of a gas in water always decreases with increasing temperature. The dissolving of gases in liquids is always an exothermic process. An undissolved gas plus a solution equals a more concentrated solution and heat. Pressure is another factor that affects the solubility of a gas. Henry’s Law states that the concentration of a solute gas in a solution is directly proportional to the partial pressure of that gas above the solution.

Solute VS. Solvent l Solutions have different properties than either the solutes or the solvent, with slightly higher boiling points and lower melting points. These effects depend on the ratio of solute to solvent. These properties can be divided in two groups, colligative and non-colligative. Colligative properties depend on the number of dissolved particles in a solution and not their identity. Very few of the physical properties of a solution are colligative properties.

Movement of Water Osmosis is the passage of water from a region of high water concentration through a semipermeable membrane to a region of low water concentration. Cell membranes for example are semipermeable, which simply means that they are very thin. They allow some things to pass but prevent other harmful things from passing through. Cell membranes allow small molecules like oxygen, water and carbon dioxide to pass through, but larger molecules like sucrose or starch are unable to.

History of Osmosis l l French botanist, Henri Dutrochet , was the first to discover osmosis in 1830. A semi-permeable membrane allows water pass through, but not other substances. Water molecules can move in both direction, but less readily from the solute side, where particles get in the way of transport. Since water molecules move into the solution, the solution becomes more diluted as well as larger in volume. Macromolecules contribute a specific osmotic pressure called the colloidal osmotic pressure of a solution.

Ways of Movement l Active transport and dialysis control the movement through the membranes. Active transport is the pumping of molecules or ions through a membrane. This requires a trans-membrane protein called a transporter to push molecules or ions into the membrane against their concentration gradient. Energy in the form of ATP is also required. l Dialysis involves the movement of specific dissolved substances in a solution. Smaller molecules are able to pass through the pores in the membrane, while larger molecules cannot pass.

Osmotic Pressure l Osmotic pressure is the pressure necessary to reverse osmosis. At a given temperature, it depends upon the molar concentration and is considered potential pressure. Thus, the value of osmotic pressure is directly proportional to the molar concentration. l Osmotic pressure can be measured by using an osmometer. Osmotic pressure depends solely on the concentrations of the particles, and is a colligitave property. This pressure can build up in a space that is enclosed by a membrane that is permeable to a solvent, such as water. The pressure called the osmotic pressure stops the flow of the solvent through a membrane.

Dialysis l l l Dialysis is similar to osmosis, except that the membrane is more permeable. Ions and molecules are able to move through the membrane. A dialyzing membrane has larger pores to enable larger molecules to enter. The function of the kidneys serves as the body’s natural filtration system. The body maintains concentrations of all substances that circulate in the bloodstream. If these complicated mechanisms fail to function, the consequences can be life threatening. The kidney’s cleanse the bloodstream of nitrogen wastes, such as urea. Dialysis replaces the function of the kidneys through this special type of treatment. The treatment uses a blood filter and a chemical solution known as dialysate, which removes waste products and excess fluids from the bloodstream.

Type 1: Hemodialysis l Hemodialysis is the most prescribed type of dialysis used in the United States. Patient’s blood is circulated outside of the body through an extracorporeal circuit or dialysis circuit. Two needles are inserted into the patient’s vein and attached to the dialysis circuit. A dialysis machine monitors and maintains blood flow and administers dialysate, which is a chemical bath that removes waste products from the bloodstream. l The dialysate should be isotonic with the blood and have the same concentrations as the essential substances that should be left in the blood. The dialysate is kept very low in the concentrations of the wastes, so the rate at which wastes leave the blood is greater than the rate at which they can get back in.

Urea Reduction Ratio l l A blood test is required at the beginning of treatment, which is generally a high level. After the treatment is finished the blood urea nitrogen (BUN) should be lower. The amount of blood urea nitrogen removed is calculated before and after treatment is finished. This calculation is called the Urea Reduction Ratio (URR). The desired minimum is that the BUN in dialyzed blood should be reduced by 70% during each treatment. Patients feel better by having more energy to live their life to their optimal fullest.

Type 2: Peritoneal Dialysis l The other type of dialysis, peritoneal dialysis is the lining of the abdomen, which acts as a blood filter. A catheter is inserted into the patient’s abdomen, and it is used to fill the abdominal cavity with dialysate. Waste products travel from the patient’s bloodstream into the dialysate solution. l After waiting for about twentyfour hours, the waste is drained from the abdomen and replaced with clean dialysate. Creatinine is the substance that is observed to determine if treatment is adequate. The minimum value of creatinine should be at least 60 liters a week.

Importance of Red Blood Cells l Red blood cells are more concentrated internally than if placed in a container of water. Dialysis brings more fluid into the normal red blood cell causing the red cells to hemolyze or burst. l Red blood cells are responsible for transporting sufficient oxygen. Some diseases can cause premature breakdown of red blood cells which interfers with oxygen transportation. Hemolysis is the breakdown of red blood cells. Red blood cells normally live for 110 days and then die and break down.

Osmolarity l Osmolarity is a measure of the osmotic pressure exerted by a solution across a perfect semi-permeable membrane, one which allows free passage of water and completely prevents movement of solute, compared to pure water. l Osmolarity is dependent on the number of particles in solution, yet independent of the nature of the particles. Osmotic Pressure in atm. = Molarity ( R ) (Kelvin Temp. )