Warm up What we have learned so far…….. Use the word bank to fill in the blanks: –Soluble –Conservation –Reactants –Contaminants –Products –Trade-offs –Solute –Chemical –Insoluble –Atoms –Solvent –biological

What we have learned so far… Clean water is necessary for life. People need clean water that has no. Contaminants can be (from industrial pollution) or (like bacteria and viruses). The cholera epidemics we learned about were caused by a biological contaminant. Scientists must clean up water to make sure that water is clean for people to drink. Biological contaminants can be destroyed with chemicals or filtered out of the water, but chemical contaminants are sometimes harder to get rid of. Remember that the law of of matter states that the number and types of in the products of a chemical reaction must equal the number and types of atoms in the reactants. (The are what you begin with in a chemical reaction and the are what you end up with.) contaminants chemical biological conservation atoms reactants products

1. Label the side of the equation as “reactants” or “products” 2. Count the number and types of atoms in the reactants and products of this reaction. 3. Is this reaction balanced? If not, which elements are unbalanced? SnO 2 + H 2 → Sn + H 2 O Atoms do not disappear or appear on their own, so when chemical contaminants are mixed in with the water, scientists must find ways to remove them. When something is, it does not dissolve and can be filtered out of a solution with a filter. We saw an example of this with cornstarch in a previous activity. When a (solid) does dissolve in a (liquid) to form a solution, the chemicals that were added to the water cannot be filtered out. Something that dissolves is in a liquid. We saw this case with copper sulfate in water. We will look at several more methods scientists can use to remove contaminants from water. We will examine dilution and precipitation as ways to purify contaminated water and discuss the (good and bad features) of these methods. insoluble solute solvent soluble trade-offs reactantsproductsReactants: 1Sn, 2O, 2H Products: 1Sn, 1O, 2H

Think far back to Unit B to answer the following questions. You can use a periodic table to help you. Of the elements listed in the reaction for conservation of mass, which elements are metals? Which elements are non-metals? Sn ___________ H___________ O ______________ How does the melting points of metals compare to that of non- metals? Sn is the element tin. The atomic number of Sn is 50 and the atomic mass is 119. How many protons, neutrons, and electrons does tin have? What would the atomic mass be for an isotope of tin with 72 neutrons? Why can’t we have an atom of tin with 49 or 51 protons? MetalNon-metal They are higher 50 protons, 50 electrons and 69 neutrons = = 122 The number of protons defines the element. If you have a different number of protons, you have a different element.

Title: Part Per Million Activity 40

Review Activity 37: What Dissolves? You made solutions with 2 different amounts of solute (1 scoop or 5 scoops) in the same amount of solvent (10 drops) Concentration is the amount of solute per solution (or relative amount of solute in a solution)

Dilute and Concentrated Solutions Can you think of other examples?

How can we describe the relative amount of solute in the solution? Many substances we are concerned about in the environment (drink water) are present in relatively low amounts. Not reasonable to express as fractions: 1/10,000 We use parts per million to express concentrations of substances present in very small amounts.

The Activity: You will be diluting a solution of food coloring that is 10% solution by mass. What does percent mean? –Parts per hundred The red food coloring is made from powdered dye and water –1 part red powdered dye in 9 parts water How would you prepare (give amounts in grams) a 10% saltwater solution? –10 g of salt in 90 g or 90 mL of water

Read C-52 Problem: How much is one part per million of a solute, such as food coloring, and when is it a useful measurement tool? Hypothesis/Initial Thoughts:

How to use dropper bottles: Hold dropper bottles vertically Don’t touch the dropper tip to the solutions, as this could result in contamination

Data/Observation: Table: Serial Dilution

Record the first cup that was colorless on the bar graph on the document camera Cup number Number of student pairs

Why might pairs have different answers for the number of the cup in which the solution first appeared colorless? Droppers could be dispensing unequal drops Human error in the number of drops that are squeezed out Ability to detect color may vary slightly

How would you describe both quantitatively and qualitatively the differences between the solution in Cup 1 and Cup 2? Quantitative: parts per million, percent, fraction, and ratio Qualitative: color of the solutions

One drop of red dye solution One drop of water

Serial Dilution Each cup is successively diluted by 1/10 Cup 2 is one part in 100, cup 3 is one part in 1,000 Cup 6 is where the concentration is one part in 1,000,000 or one part per million (ppm) A serial dilution by 1/10 th is called a 1/10 th serial dilution.

If you change the original solution of food coloring in the bottle of one part in 10 (10%) to five parts in 10 (50%), what would the concentration of the food coloring be in Cup 6? 50/10,000,000 5/1,000,000 1/200, %