Unit 4: TOXINS Stoichiometry, Solution Chemistry, and Acids and Bases Living By Chemistry Unit 4: TOXINS Stoichiometry, Solution Chemistry, and Acids and Bases

In this unit you will learn: how toxins are defined how chemists determine toxicity the mechanisms by which toxic substances act in our bodies and what this has to do with chemical reactions

Section III: Toxic Substances Lesson 13 Bearly Alive Lesson 14 Drop In Lesson 15 Holey Moley Lesson 16 Is It Toxic?

Lesson 13: Bearly Alive Solution Concentration

ChemCatalyst Five gummy bears have been placed overnight in five different aqueous sugar solutions. Each solution contains a different amount of dissolved sugar. Which solution do you think has the greatest amount of sugar in it? Explain your reasoning. What do you think caused the bears to change size?

Key Question How can you keep track of compounds when they are in solution?

You will be able to: define the terms solution, saturated solution, solute, and solvent explain what the concentration and molarity of a solution represent complete calculations involving molarity

Prepare for the Lab Work in groups of four. Solution: A mixture of two substances that is uniform throughout.

Discussion Notes A solution is a mixture of two or more substances that is uniform throughout. Solute: The substance dissolved in a solution. Solvent: The substance in which the solute dissolves in a solution.

Discussion Notes (cont.) A solution is saturated when no more solute will dissolve. Saturated solution: A solution that contains the maximum amount of solute for a given amount of solvent.

Discussion Notes (cont.) Concentration refers to the amount of solute that is dissolved in a solution. Molarity (M) = Concentration: A measure of the amount of solute dissolved in a specified volume of solution. n (moles) V (liters of solution)

Discussion Notes (cont.) Molarity: The concentration of a solution expressed in moles of solute per liter of solution.

Discussion Notes (cont.) The gummy bears changed size depending on the concentration of the solution they were soaked in. Molecules move from areas of higher concentration to areas of lower concentration.

Wrap Up How can you keep track of compounds when they are in solution? When two or more substances mix together uniformly at a molecular, ionic, or atomic level, they form a solution. The concentration of a solution can be expressed in moles per liter. This is also called the molarity of the solution, or M. The concentration of a solution can also be expressed in moles per kilogram. This is called the molarity of the solution, or m.

Check-in Suppose 10.0 g of salt, NaCl, are dissolved in 0.50 L of water. What is the molarity of this solution?

Lesson 14: Drop In Molecular Views

ChemCatalyst Examine the gummy bear in the sugar solution you prepared in class yesterday. What does the gummy bear’s appearance suggest about the solution? Is the solution saturated? Why or why not? Imagine that you have 1 L of a 2.0 M sugar solution in a large container. You pour out 100 mL into a beaker. Did the concentration of sugar in the large container change? Did the number of moles of sugar in the large container change?

Key Question How can you convert from molarity to moles of solute?

You will be able to: describe solution concentration on a particulate level calculate the number of moles of particles from the molarity and the volume of a solution differentiate between particles in ionic and molecular solutions

Prepare for the Activity Work in groups of four. Never taste substances in the laboratory.

Discussion Notes The particle views represent molecules dissolved in water. 4 in. 3 in. Particle view 1 120 particles Number density: 10 particles/in2 Particle view 2 60 particles Number density: 5 particles/in2 Particle view 3 30 particles Number density: 2.5 particles/in2 Particle view 4 15 particles Number density: 1.25 particles/in2

Discussion Notes (cont.) Any sample cut out of the original Particle View 1 has the same concentration of dots per square inch as the large sample.

Discussion Notes (cont.) Concentration does not depend on the size of the sample. In order to create solutions C and D, you must dilute the original solution to half its molarity.

Discussion Notes (cont.) The relationship between the number of moles of particles in a solution and the volume of the solution is proportional. Number of moles = k • volume of solution (in liters)

Wrap Up How can you convert from molarity to moles of solute? The relationship between moles of molecules in a solution and liters of solution is a proportional one described by the formula M = mol/L, where M is the molarity of the solution. The concentration (or molarity) of a solution does not change with the size of the sample. In calculating the number of moles of particles in an ionic solution, it is necessary to take into account all the ions in the formula.

Check-in How many moles of sugar, C12H22O11, are in 52 mL of a 0.50 M solution? How many moles of sugar, C12H22O11, are in 26 mL of a 0.50 M solution?

Lesson 15: Holey Moley Preparing Solutions

ChemCatalyst Imagine that you want to make 5 L of 0.60 M NaCl solution for a saltwater aquarium. You need to determine the correct mass of NaCl needed to obtain the correct concentration, or the fish will die. What information do you have? What information do you need?

Key Question How can you make a solution with a specific molarity?

You will be able to: calculate the amounts necessary to create a solution with a desired volume and molarity determine the number of grams of solute in a sample with a specific volume and molarity

Prepare for the Lab Work in groups of four.

Discussion Notes You can use a hydrometer to measure the density of a solution. The 0.60 M solution comes closest to resembling ocean water. There are several possible sources of error in this experiment.

Discussion Notes (cont.) Molarity relates moles and liters. Molarity = moles/liters If you know the molarity of a solution and the size of the sample, you can calculate the number of grams of substance dissolved in that solution. Grams = moles • molar mass

Wrap Up How can you make a solution with a specific molarity? In order to calculate the amount of solute needed to make a solution with a certain molarity, you must use the molar mass of the solute to convert moles to mass. Solutions of specific concentrations can be made by weighing out the appropriate amount of the substance dissolved in the solution. If you know the molarity and volume of a sample of solution, you can figure out the mass of the dissolved substance in that sample.

Check-in How many grams of salt are in 0.100 L of 2.50 M NaCl?

Lesson 16: Is It Toxic? Mystery Solutions

ChemCatalyst Suppose you wanted to determine if your tap water contains lead (II) nitrate, Pb(NO3)2, which is toxic. Do you expect the mass of 100 mL of pure water to be the same as that of a solution containing Pb(NO3)2? Explain your reasoning. What is the molar mass of lead nitrate? What would be the mass of 0.100 mole of lead (II) nitrate?

Key Question Can molarity calculations be used to identify a toxin?

You will be able to: explain the relationship between the mass of a solution sample and the molar mass of the solute

Prepare for the Classwork Work in pairs.

Discussion Notes The molarities of the 100 mL samples of solute solution were all 1.00 M. To figure out the identities of the solutions, we determined the molar mass of each from the periodic table. It is important to know the toxicity of a substance in moles per kilogram.

Wrap Up Can molarity calculations be used to identify a toxin? Solution samples can have different masses depending on the molar mass of the substance dissolved in the solution. In some situations, it is important to compare numbers of moles of a substance rather than masses.

Check-in You have three aqueous solutions, 200 mL of each: 1.5 M NaCl, 1.0 M KCl, and 1.0 M CaCl2. Which has the greatest mass? Which has the least?