Solutions Chapter 10

Review of Mixtures: Heterogeneous Homogeneous Heterogeneous Mixtures: suspension: large particles that settle out colloid: particles are uneven throughout the sample (positive Tyndall Effect)

solute: substance being dissolved solution: a substance is dissolved in another substance and evenly distributed Solution Parts: solute: substance being dissolved solvent: substance doing the dissolving

Phases and Solutions

Solid Solution 14-karat gold is a mixture of gold, silver, and copper

What would a mixture of gases look like? Gas Solution What would a mixture of gases look like?

Liquid Aqueous Solution Solutions with water as the solvent

SATURATION

saturated solution: contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature. unsaturated solution: contains less solute than the solvent has the capacity to dissolve at a specific temperature.

supersaturated solution: contains more solute than a solvent has the capacity to dissolve at a specific temperature, more than a saturated solution

Saturation Examples

SOLUBILITY CURVES

Solubility Curves The x-axis: Temperature (oC) The y-axis: Solubility in 100g of water When is the solution saturated, unsaturated, and supersaturated? Solubility in 100g H2O Temperature oC

What do you get from a solubility curve? Identify the solubility at a specific temperature. Identify the temperature at which something can dissolve. Identify whether something is saturated, unsaturated, or supersaturated. Identify solubility in different amounts of water. Identify how much will crystallize with a temperature change.

SOLUBILITY

Soluble when a substance IS capable of being dissolved in another substance Insoluble when a substance is NOT capable of being dissolved in another substance

Soluble and Insoluble Ionic Compounds

How do you know if something will dissolve?

“like dissolves like” Two substances with similar intermolecular forces will be soluble in each other.

non-polar molecules are soluble in non-polar solvents CCl4 in C6H6 polar molecules are soluble in polar solvents C2H5OH in H2O ionic compounds are more soluble in polar solvents NaCl in H2O

Water Molecule Polarity polar molecule A ________ ____________ has an uneven distribution of electrical charge, which means that each molecule has a _________  __________   region at one end and a __________  __________ region at the other end. The water molecule has a _________ or V-shape, NOT linear H-O-H. The __________ is an electrically negative region that has a greater concentration of _____________. The two _____________ are electrically positive. slightly positive slightly negative bent oxygen electrons hydrogens

In the picture of water below, label the atoms and indicate the partial electrical charges. Element: ______ Charge: ______ Element: ______ Charge: ______

Ionic crystals are made up of two types of ions, cations and anions. What charge is associated with a cation? What charge is associated with an anion?   In the example sodium chloride, identify the cation and the anion: Sodium: ________ Chlorine: __________

Hydration – What happens when salt dissolves? Color in the molecules and ions below. Next to each molecule and ion identify the charge. Hydrogen: White Oxygen: Red Sodium: Blue Chlorine: Green DISSOLVED means: surrounded by WATER MOLECULES Solvation Process Simulation

What will make a solute dissolve in a solvent faster? Stirring or shaking increase contact between the solute and solvent Break up solute increase the surface area for more contact Increase temperature more collisions between solute and solvent

ELECTROLYTES

Electrolytes Electrolytes: When a solute dissolves in water and the solution conducts electricity The electricity comes from the ions that form in solution when the solute is dissolved. Strong and weak electrolytes differ in the degree of ionization.

Strong electrolyte: high conductor because of high number of ions in solution. Weak electrolyte: low conductor because of small number of ions in solution. Non-electrolyte: solution that does not conduct electricity because there are no ions. strong electrolyte weak electrolyte non-electrolyte

THE IONS!!! How do electrolytes conduct electricity? Cations (+) and Anions (-) Strong Electrolyte – 100% ions Weak Electrolyte – very few ions Non-Electrolyte – no ions

Light Board Demo Sample Prediction Actual Ions Present? Water NaCl Sugar Gatorade Vinegar

Concentration

Concentration concentration: measure of the amount of solute in a given amount of solvent or solution. measured in: molarity, molality, parts per million (ppm), parts per billion (ppb) The opposite of concentrated is dilute.

Molarity (M) moles of solute M = liters of solution Mol M L Molarity: is the number of moles of solute in one liter of solution. M = moles of solute liters of solution Mol M L

Example Problem 1 You have 3.50 L of solution that contains 1.54 mol of sodium chloride, NaCl. What is the molarity of that solution?

Example Problem 1 Solution Given: solute = 1.54 mol NaCl solution volume = 3.50 L Unknown: molarity Solution:

Example Problem 2 You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl does this solution contain?

Example Problem 2 Solution Given: volume of solution = 0.8 L concentration of solution = 0.5 M HCl Unknown: moles of HCl Solution:

Colligative properites

Colligative Properties colligative properties: properties that depend on the concentration of solute particles but not on their identity

What happens when a substance boils normally?

Boiling-Point Elevation To cook the pasta faster, you add salt to the water. Adding salt to the water is like turning the escape route of the particles into a puzzle. Since it requires more energy to escape, the water boils at a higher temperature (cooking the pasta faster).

What happens when a solution boils? Draw lines to show how the particles on the bottom of the pan boil to the surface through the “puzzle”. This is called boiling point elevation.

What happens when a substance freezes normally?

Freezing-Point Depression In the winter, salt is thrown on the road to melt the ice. When the salt comes in contact with the ice, the ice melts and cannot reform to a solid at the same temperature. Since the salt particles are in the way, it requires a lower temperature to get the water molecules to connect to form ice. Therefore, the water freezes at a colder temperature.

What happens when a solution freezes? Connect the dots below (again with straight lines) this time with salt particles in the way. This is called freezing point depression.