A Look at Water and its Contaminants

Unit 1 Section B ChemCom Hon I Ms. Brandi Thomas

**B.1 Physical Properties of Water

Properties that can be observed and measured without changing the chemical makeup of substance This section focuses on the physical properties of water –
    

density, physical state, surface tension, boiling and freezing points and the solvent characteristics Water based solutions

Aqueous Solutions

** Mixtures and Solutions


Two or more substances that retain there individual properties Composition is not the same or uniform throughout.
• Suspension

Heterogeneous Mixture

Particles are large enough to settle out and can be filtered Particles are smaller than in suspension can not settle out… cloudy appearance Particles smaller than particles in colloids and separate into particles so small they can not be seen.

• Colloid

• Dissolves

** Mixtures and Solutions
 Homogeneous Mixture

A mixture that is uniform throughout
• Solutions are homogeneous • Solute

The dissolved substance The dissolving agent

• Solvent

**Molecular view of Water
 


All matter is composed of atoms Matter made up of only one type of atom 90 different elements found in nature A substance with two or more elements linked together chemically in fixed positions Each element and compound. A uniform and definite composition and distinct properties Molecule
• Smallest unit of a pure substance that retains properties • “glue” that holds atoms of a molecule together.

 


Pure substance
 

Chemical Bond

**B.4 Symbols, formulas, and Equations
 An introduction to symbols, formulas, and

equations and to the significance of subscripts and coefficients.

International “chemical language” to represent atoms, elements, and compounds. Chemical Symbols = “letters” of chemical lang.
• Each element is assigned a chemical symbol. • Only first letter is capitalized

**B.4 Symbols, formulas, and Equations
 All elements are organized into the

periodic table.  Chemical formula = “the word” in chemical lang.
 

Ex:H2O = Water A subscript indicates how many atoms of each element are in the molecule or unit of substance Ex:C3H8 = Propane (3 Carbon molecules and 8 Hydrogen)

**B.4 Symbols, formulas, and Equations
 Chemical equations = the “sentences” of

chemical lang.

Each chemical equation represents a chemical reaction that happens or that someone predicts might happen.

 Chemical Reactions = breaking and the

forming of chemical bonds, causing atoms to rearrange into new substances.

**B.4 Symbols, formulas, and Equations
 Reactants = the original substances in a

chemical equation.  Products = the new substance formed from the rearrangement of the reactant

**B.4 Symbols, formulas, and Equations

Diatomic Molecules

They exists as two bonded atoms of the same element. Gen-U-ine Diatomic molecules

Elements that exits as Diatomic Molecules Element Formula Hydrogen H2 Nitrogen N2 Oxygen O2 Fluorine F2 Chlorine Cl2 Bromine Br2 Iodine I2

**B.5 The Electrical Nature of Matter
 The Electrical nature of matter is

discussed in terms of interaction among charges, and in terms of neutrons, protons, and electrons.
  

Water is described as a polar molecule Like forces repel each other Unlike charges attract each other.

**B.5 The Electrical Nature of Matter
 Neutral atoms have equal numbers of

positively charged particles called Protons and negatively charge electrons. Neutrons are electrically neutral atoms  Protons = (+)  Electrons = (-)  Positive neutrons and negative elections form the glue that holds atoms together.

**B.6 Ions and Ionic Compounds
 Molecules make one type of compound
 

Another type of compound = ions Ions are charged atoms. Atoms can gain or lose electrons to form positive or negative ions. Ionic compounds are composed of both positive and negative ions. (no net charge)
• When an cation sticks to an anion = ionic compounds

**B.6 Ions and Ionic Compounds
 Anions
 

When and atom gains one or more electron Resulting in an negative charge An atom losing one or more election resulting in a positive charge. An ion consisting of a group of bonded atoms Figure 18 (page 33)

 Cations

 Polyatomic (many atom) ion
 

***Figuring out how many electrons atoms gain or lose…
  

 

Count forward from it on the periodic table until you reach the next noble gas Count backward from it on the periodic table until you reach the last noble gas. If the forward < than backward, the element will gain elections (amount you counted) for a negative charge If backward is < than forward then you will lose the number of electrons that you counted. Important: SKIP OVER TRANSITION METALS WHEN COUNTNG TO NOBLE GASES,

Practice Problem
 What will the charges of the following

elements be when they gain or lose electrons to gain the same electron figuration as the nearest noble gas?  A) Magnesium (Mg)  B) Calcium (Ca)  C) Bromine (Br)

~Properties of Ionic Compounds
 Ionic compounds form

Crystals  Ionic compounds often have high melting and boiling points  Ionic compounds are hard and brittle  Ionic compounds conduct electricity when dissolved in water or melted

~Writing Ionic Names from Formulas
 Step 1

Determine the base name
• The first word is the cation • The second word is the anion (if polyatomic ion just look up on polyatomic chart)

 Step 2

Determine whether or not the compound will require a roman numeral Step 3

***Writing Ionic Formulas from names
 Step 1

From the base name, determine the formula and charge of ions Write the formulas of the cations and anions next to each other. Devise an ionic formula that gives the compound a neutral charge.

 Step 2

 Step 3

Writing Ionic Formulas from Names Example “Beryllium Hydroxide”
“Beryllium” indicates Be+2 and “hydroxide” indicates OH-1  Putting them together we get Be+2OH-1.  Because Beryllium hydroxide has to be electrically neutral, there needs to be two hydroxide ions for each beryllium ion. As a result the formula of beryllium hydroxide is Be(OH)2

Write the formula of the following ionic Compound
 A) Lithium acetate  B) sodium


Write the formula of the following ionic Compound
 A) Lithium acetate


 B) sodium



Group Activity
 In Groups of 4

do building skills on page


B.7 Water testing
 Purpose: allow you to use a method that

chemist, including those investing the Riverwood fish kill , use to detect specific ions in water solutions  Confirming test: A positive test confirms the ion in question is present.

Change in color or appearance of precipitate indicate a positive test.

B.7 Water testing
 A negative test does not equal an absent

ion.  Qualitative test vs. Quantitative test. (This lab is qualitative…(only test for presence not amount)

Testing for
• • • • Iron (III) (Fe+3) Calcium (Ca 2+ ) Chloride (Cl-) Sulfate (SO42-)

B.7 Water testing
 Reference Solutions

Contains the ions of interest Does not contain the ion of interest Natural Water/Mystery Water Tap water
• Are to be compared to the reference solutions • Lab video

 Control

 The other samples
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B.7 Water testing
 Post Lab
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Questions 1-4 page 38 For the next 5 min:
• With your partner go over questions 1-4

B.8 Pure and Impure Water
 Most families in the US have clean water

but not pure water.

Pure is almost impossible since so many substances dissolve in water, (even atmospheric gases like nitrogen, hydrogen, and carbon dioxide.

B.9 The RiverWood Mystery
 Making Decisions Group activity

In groups of 4 read over the directions and questions on page 38-39 and answer questions. Put the answers in your notes section of class binder. We will come back to these for a group discussion and for our town council meeting

B.10 What are the possibilities
 Bridge to part C  Identifies the processes just used by

students as typical work of scientist.

Now that we know about the types of substances that can be dissolved or suspended in water, we can determine which ones are potentially harmful to aquatic life.