SOLUTIONS. Heterogeneous Mixtures. Section 8.1: Solutions and Other Mixtures. Heterogeneous Mixtures (cont d) CHAPTER 8.

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1 Section 8.1: Solutions and Other Mixtures CHAPTER 8 SOLUTIONS Key Questions What is a heterogeneous mixture? What is a homogeneous mixture? Heterogeneous Mixtures The tree of matter branches into two distinct types: pure substances and mixtures. Mixtures can be classified as either heterogeneous or homogeneous based upon the composition of the mixture. Heterogeneous mixtures do not have a fixed composition. Heterogeneous Mixtures (cont d) Each sample of a heterogeneous mixture contains a differing amount of all the components. No two samples are the same. Heterogeneous mixtures can be further classified as suspensions, colloids, or emulsions. Each type has distinct properties.

2 Suspensions are heterogeneous mixtures in which the particles within the mixture are suspended and eventually settle. Suspensions Particles of suspensions are larger than normal. Over time these particles must be agitated to be placed back in phase. These larger particles can be filtered out. Examples include orange juice with pulp and Italian salad dressing. Colloids are mixtures in which the particles are intermediate in size (between nm in diameter). Colloids contain particles that medium sized that are suspended in a solid, a liquid, or a gas. Colloids can t be effectively filtered out due to the smaller particle size. Colloids can scatter light that passes through them. This is called the Tyndall effect. Examples of colloids include muddy water, whipped cream, gelatin, smoke, and fog. Colloids Some colloids are composed of two immiscible liquids (liquids that don t mix together). Emulsions are found in various places, including your refrigerator or pantry. Emulsions are mixtures of two or more immiscible liquids in which one liquid is dispersed in the other. Examples include mayo, bile salts, cream Emulsions Homogeneous Mixtures Unlike heterogeneous mixtures, homogeneous mixtures have fixed compositions. Even when examined under a microscope, homogeneous mixtures look uniform because the individual components of the mixture are too small to be seen. Homogeneous mixtures are also called solutions. Solutions are made up of two components solute and solvent.

3 Homogeneous Mixtures (cont d) In a solution, the substance that is being dissolved is called the solute. In a solution, the substance in which the solute dissolves is called the solvent. Water is called the universal solvent due to its ability to dissolve many compounds. Not all solutions are made up of solid solutes. Some are composed of two miscible liquids like rubbing alcohol. Homogeneous Mixtures (cont d) Other states of matter can also form solutions. The air that you breathe is a solution of nitrogen, oxygen, argon, and other gases. Vinegar is a solution of acetic acid and water. Solids can dissolve in other solids to create metal solutions called alloys. Example of alloys include brass (mix of Cu and Zn) and bronze (mix of Sn and Cu). Section 8.2: The Dissolving Process Water: A Common Solvent Key Questions Why is water called the universal solvent? Why do substances dissolve? Two-thirds of Earth s surface is water. 75% of your body weight is water. Water is called the universal solvent because of its ability to nearly dissolve everything.

4 Water Can Dissolve Ionic Compounds Why is water such a good solvent? ITS STRUCTURE! Because water is a polar molecule, electrons are creating partially positive and negative regions within a water molecule. These partially charged areas attract oppositely charged ions in an ionic compound. Tear the House Down! The polarity of the water molecule allows for each type of ion in an ionic compound to orient itself to an oppositely charged region of a water molecule. This pairing up continues until the attraction between water molecules and ions is greater than the attraction between ions in the crystal. The crystal gets torn apart when the crystal dissolves into the water solution. Water dissolves many ionic compounds, but not all. Use the Force! An ionic compound will dissolve in water if the attraction between water molecules and ions in the crystal are greater than the attraction between the ions in the crystal. In order to dissolve a substance, the force between solvent molecules and particles of a substance must be greater than the force between particles in the crystal. Who Want Some Water? Water has many special properties such as low molecular mass, high density, and high boiling point due to the strength of intermolecular forces, in particular hydrogen bonding (H bonding). H bonding occurs when partially positive H atoms of one molecule are strongly attracted to partially negative O atoms of a nearby molecule. H bonds allow water to dissolve polar compounds like ethanol, vitamin C, and table sugar. These bonds help pull the polar compound into the water solution.

5 That s What I Like That s What I Like Like Dissolves Like! This rule means that a solvent will dissolve a solute that has a molecular structure like that of the solvent. Polar dissolves ionic compounds, therefore would dissolve polar solutes. Nonpolar compounds do not dissolve in water (polar). The Break Up According to kinetic theory of matter, molecules are always in motion. The energy transferred from solvent to solute, as well as the attractive forces between solute and solvent molecules, causes molecules at the surface of the crystal to dissolve. What Can Cause a Break Up? Solute Surface Area There are 3 factors that will affect the dissolving process: Solute Surface Area Agitation Temperature In other words, how can I get myself out there in the most places? Solutes that cover a larger surface area will dissolve quicker. By covering a larger surface area, the solute/solvent molecular collisions increase causing faster dissolution.

6 Shaken or Stirred? It s Getting Hot In Here Undisturbed, a solute will start to diffuse very slowly. Shaking or agitating the solution will increase the rate of diffusion which in turn will increase the distance from the crystal. According to kinetic theory of matter, all molecules are in constant motion. When the temperature is raised, the kinetic energy of the molecules of solvent and solute increases resulting in an increasing number of collisions and faster dissolution. Section 8.3: Solubility and Concentration Key Questions What is solubility? What happens when you add more solute to a saturated solution? How do you describe how much of a solute is in a solution? Solubility in Water Some substances are insoluble in water. Insoluble refers to substances that will not dissolve in water. Other substances, such as sugar and baking soda, are soluble in water they dissolve easily in water. The solubility of a substance is the maximum mass of a solute that can dissolve in 100 g of solvent at a certain temperature and standard atmospheric pressure.

7 Solubility in Water (cont d) Some substances, such as acetic acid, methanol, and glycerol, are completely soluble in water. Any amount of these substances will mix with water to make a solution. Some ionic compounds, like AgCl, are almost completely insoluble in water. Different substances have different solubilities. Solubilities depends on the strength of the forces acting between the solute particles and the strength of the forces acting between water molecules and solute particles. In a highly soluble substance, the forces between water molecules and the solute particles are stronger than those between solute particles. Concentration Not all solutions have all of the solute that can be dissolved. Because the amount of a substance that is dissolved can vary greatly, the amount of solute that is dissolved in a given solution must be specified. A solution may be classified as weak if only a small amount of solute is dissolved. A solution may be classified as strong if a large amount of solute is dissolved. Concentration The concentration of a solution is the quantity of solute that is dissolved in a given volume of solution. A concentrated solution has a large amount of solute; whereas, a dilute solution has a small amount of solute. Saturated Solutions A saturated solution is a solution in which the dissolved solute is in equilibrium with undissolved solute. Unsaturated solutions contain less solute than a saturated solution does and are able to dissolve additional solute. Supersaturated solutions hold more dissolved solute than is required to reach equilibrium at a given temperature.

8 Concentration of Solutions The terms concentrated, dilute, saturated, and unsaturated do not reveal the quantity of dissolved solute. Molarity Sample Problem 1 Calculate the molarity of sucrose, C12H22O11, in a solution of 124 g of solute in L of solution. Scientists express the quantity of solution in several ways. One of the most common ways of expressing concentration of a solution is molarity. molarity = (moles of solute)/ (liters of solution) M = mol/l Molarity Sample Problem 2 What is the molarity of 2 mol of calcium chloride, CaCl2, dissolved in 1 L of solution? Molarity Sample Problem 3 What is the molarity of 525 g lead (II) nitrate, Pb(NO3)2 dissolved in 1,250 ml of solution?

9 Molarity Sample Problem 4 Express the molarity of a solution that contains 0.5 mol of calcium acetate per 1.0 L of solution. Molarity Sample Problem 5 Calculate the molarity of a solution that contains 35.0 g of barium chloride, BaCl2, dissolved in 450 ml of solution. Molarity Sample Problem 6 How many moles of lithium chloride, LiCl, are dissolved in 3.00 L of a M solution of lithium chloride? Molarity Sample Problem 7 Potassium sulfate, K2SO4, has a molar mass of 174 grams/mole. If potassium sulfate is the solute in a 2 L solution that has a concentration of 0.25 M, how many grams of potassium sulfate are in the solution?