Objective 4: 9a, b, d: Solution Chemistry The student is expected to relate the structure of water to its function, relate the concentration of ions in a solution to physical and chemical properties such as pH, electrolytic behavior, and reactivity; and demonstrate how various factors influence solubility including temperature, pressure, and nature of the solute and solvent.

Solutions Most of chemistry is based on solution chemistry, where water is the solvent (called aqueous solutions). Solutions—homogeneous mixture of two or more substances completely dispersed(same throughout). H 2 O universal solvent Brass-solution of solids Cu & Zn Air-solution of gases

The Solution Process

Component present in greater proportion is called the solvent, the one in lesser proportion is called the solute Oceans are salt water solutions—water is the solvent, salt is the solute. Sweet tea in another example — sugar is the solute and water is the solvent Solute and solvent

What is solubility? The amount of a substance that dissolves in a given volume of solvent at a given temperature. Common units: grams solute/ 100 grams of solvent or grams solute/ 100mL of water

Solution Process Step 1. The solute molecules separate. This process requires energy. Step 2: The solvent molecules must separate. This process requires energy Step 3: The solute and solvent attract. This process releases energy.

Factors Affecting Solubility Solute-solvent interactionSolute-solvent interaction - Like dissolves like Polar liquids tend to dissolve in polar solvents. “Likes dissolve likes”. Example Water and Ethanol are both polar, and are miscible. Polar water and non-polar oil are immiscible. Miscible liquids: mix in any proportions. Immiscible liquids: do not mix. Stirring and crushing, increase the surface area, and therefore increase the rate of solution.

Temperature Factor -Temperature Factor - Solids/Liquids- Solubility increases with Temperature. Increased K.E. increases motion and collisions between solute / solvent. Gas - Solubility decreases with Temperature. Increased K.E. result in gas escaping to atmosphere. Experience tells us that sugar dissolves better in warm water than cold. Experience tells us that carbonated beverages go flat as they get warm. Therefore, gases get less soluble as temperature increases.

Pressure Factor -Pressure Factor - Solids/Liquids - Very little effect. Solids and Liquids are already close together, extra pressure will not increase solubility. Gas - Solubility increases with Pressure. Increased pressure squeezes gas solute into solvent.

Substances that don’t dissolve are called insoluble E.g. Petroleum (crude oil), which are non-polar So if you want to dissolve grease which is non-polar, you need to use a non-polar solvent. Petroleum in a non-polar organic molecule

When an ionic solid dissolves in water, the ions that form the solid are released into solution, where they become associated with the polar solvent molecules. NaCl(s)  Na + (aq) + Cl - (aq) We can generally assume that salts dissociate into their ions when they dissolve in water.

+ - The positive end of the water molecule is attracted to the anion (negative ion) and the negative end of the water molecule is attracted to the cation (positive ion). Solutions of ionic compounds are strong electrolytes.

Electrolytes Strong Weak Non Electrolyte Electrolyte Electrolyte solution

Electrolytes compounds which when dissolved in water produce solutions that conduct an electric current. The strength of an electrolyte is due to the number of ions in solution. Strong electrolytes conduct a much stronger current than weak electrolytes because they have more ions. Nonelectrolytes compounds which when dissolved in water produce solutions that do not conduct an electric current. These solutions do not contain ions.

Ionic Solutes

Sugar is a molecular solid. When sugar dissolves in water, the weak bonds between the individual sucrose molecules are broken, and these C 12 H 22 O 11 molecules are released into solution. Sugar does not form ions in solution.

Properties of Water 2-2-  + Water is polar Water forms hydrogen bonds Ice is less dense than water

Saturated Solutions

1. Which substance’s solubility increases the most with temperature? 2. Which substance’s solubility changes the least with temperature? 3. What is the solubility of KI at 8 o C? 4. What temperature is needed to dissolve 160 g of potassium iodide, KI, in 100 g of water?

O O Covalent acids form ions in solution. Some covalent compounds IONIZE in solution H H H H H Cl H If the molecule ionizes completely it is a strong electrolyte, if it partially ionizes it is a weak electrolyte. HCl, hydrochloric acid, is a strong electrolyte and HC 2 H 3 O 2 (vinegar) or acetic acid, is a weak electrolyte.

Saturated/unsaturated solutions The solubility of a solute in a solvent is also related to temperature (if T ↑, solubility ↑ ) Solutions whose solute concentration is at a maximum are called saturated. Solutions where the solute concentration is below its solubility are called unsaturated. Some solutions can be super-saturated, a concentration of solute > than solubility

To dissolve 120 g the temp must be raised to 80 o C at 50 o 88.0 g of KNO 3 will dissolve

Acids (Properties) Taste Sour Turn Red litmus Blue Neutralizes bases Reacts with metals pH below 7 Examples: Juices: Tomato, Orange, Grapefruit Wine Banana Coffee Vitamin C Soda Acids-Bases Characteristics Base (Properties) Taste Bitter Turn Blue litmus Red Neutralizes acids Turns metal into hydroxides pH above 7 Slippery Examples: Milk of Magnesia Lime water Lye, Drano Ammonia blood Soap