Behavior of Molecules in Solution

The state a substance is in at a particular temperature and pressure depends on two factors Kinetic Energy of the Particles Strength of the attraction between the particles

IMF IMF = Intermolecular Forces Attractive forces between molecules Much weaker than chemical bonds within molecules

Overcoming Bonding Forces IMF control how molecules bond together Depending on the state of matter, molecules behave differently In order for a molecule to change state (i.e. liquid to solid) the IMF of the molecules must be overcome. The kinetic energy of the molecules need to overcome the IMF in order to change state ---Remember *What is kinetic energy??

Overcoming Bonding Forces IMF can be determined by the properties of the atoms/molecules.  Boiling Point (BP)  Melting Point (MP)  Vapor Pressure (VP) Higher BP,MP,VP = stronger IMF

Specific Heat Specific heat measures the amount of heat, in joules, needed to raise the temperature of 1 g of substance by 1°C. This means that water must absorb or release more heat for its temperature to change by one Celsius degree than any of the other substances.

Specific Heat The specific heat of water is 4.18J/g°C. (The unit is read “joules per gram per degree Celsius.”) In order to raise the temperature of 1 g of water by 1°C, you must add 4.18 J of heat. On the other hand, you must remove 4.18 J of heat from a 1-g sample of water to lower its temperature by 1°C.

Water is such a versatile solvent that it is sometimes called the universal solvent. Its ability to act as a solvent is one of its most important physical properties.

A Model of the Dissolving of NaCl

Like Dissolves Like Although water dissolves an enormous variety of substances, both ionic and covalent, it does not dissolve everything. The phrase that scientists often use when predicting solubility is “like dissolves like.” The expression means that dissolving occurs when similarities exist between the solvent and the solute.

Concentrated Versus Dilute Chemists never apply the terms strong and weak to solution concentrations. Instead, use the terms concentrated and dilute

Preparing 1 L of an NaCl Solution How would you prepare 1.0 L of a 0.15M sodium chloride solution? First, determine the mass of NaCl to add to a 1.0-L container. The 0.15M solution must contain 0.15 moles of NaCl per liter of solution.

Preparing 1 L of an NaCl Solution The proper setup, showing the conversion factors, is as follows.

Preparing 1 L of an NaCl Solution = 8.8 g NaCl The result means you need to measure 8.8 g of NaCl, add some water to dissolve it, and then add enough additional water to bring the total volume of the solution to 1.0 L.

Practice Problems How would you prepare 5.0L of a 1.5M solution of glucose, C 6 H 12 O 6 ? You add 32.0 g of potassium chloride to a container and add enough water to bring the total solution volume to 955 mL. What is the molarity of this solution?

Dilution M 1 V 1 =M 2 V 2 M = Molarity V =Volume Ex: If I add 45 mL of water to 325 mL of a 0.15 M NaOH solution, what will the molarity of the diluted solution be?