1B. Looking at Water & Its Contaminants Objectives: 1) Learn about the chemistry of water and how substances interact with water. 2) Define and identify physical properties of water. 3) Classify samples of matter in terms of elements, compounds and mixtures. 4) Distinguish among different types of mixtures (solutions, colloids and suspensions). 5) Learn about chemical symbols, formulas and equations. 6) Learn about protons, neutrons and electrons.
Water is very common… on Earth • 70% of Earth’s surface covered by oceans – average depth of 3 km (2 mi) • Water is one of the rarest and most unusual substances in the universe. • Unmatched by any planet or moon in our solar system
Water is a form of matter Matter is anything that has mass & occupies space. Water is one form of Matter. What else is matter? All solids, liquids and gases are classified as matter. 4
Water has Physical Properties Matter can be distinguished by its properties. Physical properties are those that can be observed and measured without changing the chemical makeup of the substance Ex.- color, odor, density, melting point, boiling point, freezing point, surface tension
Physical Properties of water: • Color – colorless, clear • Odor - odorless • Density = mass/ volume • Temperature dependent • Freezing point = 0°C • Boiling point = 100°C • Surface tension
Water has Physical Properties • Density – Water’s density is 1.00 g/cm3 or 1.00 g/mL at 25oC – varies by temperature • Freezing Point – 0oC at normal atmospheric conditions • What physical property of water explains the sheeting action under the swimmers right arm? • Other properties?
Why does ice float? • Because ice floats, we can infer that ice must be less dense than water • Density = mass/ volume • D = grams / mL • Temperature dependent
Based on your observations in the Foul-Water Lab, what has the greater density, oil or water?
Do Now • What physical property of water explains the “sheeting action” under the swimmers right arm?
Surface Tension: • Forces of attraction between the hydrogen and oxygen atoms in water that keep the atoms close together. • Almost as if they form a barrier and make the water molecules “stick” together. • Held together by cohesive forces. • Responsible for creating a meniscus. • Responsible for “spherical” water drops. • Doesn’t stick to wax (on cars etc.). • Beading effect of water on surfaces.
1B.2 Density • Density = mass / volume • D = grams/mL or grams/cm3 Mass is usually measured in grams. Volume is measure in mL if the substance is a liquid (graduated cylinder). Volume is measured in cm3 if the object is a regularly shaped solid.
1B.2 Density • Density = mass / volume • D = grams/mL or grams/cm3 Mass is usually measured in grams. Volume is measure in mL if the substance is an irregularly shaped solid by measuring volume displaced. (marbles in the graduated cylinder). 18
1B.2 Density • Classwork: Answer questions 1-3 • on page 28 • Density worksheet • Due today!
Do Now • Draw: • A) a water molecule (H2O) • B) 2H2O
Objectives • Identify physical properties of substances • Differentiate between mixtures and substances and heterogeneous and homogenous mixtures • Review the differences between types of mixtures. • Differentiate between symbol, element, compound, and molecule.
“Pure” Water • “Pure” water is water with absolutely nothing else dissolved or suspended in it • Properties of pure water • Clear • Colorless • Odorless • Tasteless
Substances Dissolve in Water • Aqueous solutions – water based solutions (something dissolved in water) • Surface water (river or lakes) contains dissolved minerals & other substances • Rainwater contains dissolved gases – so does distilled water used in car batteries • Tap water contains dissolved substances, which give it its taste
Matter is anything that has mass & occupies space. Matter is divided into a mixture or a puresubstance We will look at each of these more closely
Mixtures • A mixture is the result of two or more substances coming together but keeping their individual properties. • “Foul Water” was a mixture of water, used coffee grinds, oil, garlic powder, salt • Examples include: sugar dissolved into water, brass, chocolate chip cookie and air.
Heterogeneous mixture • Heterogeneous mixture – not uniform or evenly distributed • Components of the mixture can be separated by physical means (filtration) • Example: “Foul Water” was a mixture of water, used coffee grinds, oil, garlic powder, salt • Another example: sand and water. The heavier sand settles to the bottom.
2 Types of Heterogeneous Mixtures • Suspension – heterogeneous mixture containing large, solid particles that can settle out or be separated by filtration • Colloid – heterogeneous mixture containing particles too small to settle out – cloudy – Tyndall effect examples Tyndall effect
Solutions • Homogeneous mixture – uniform or evenly distributed • All solutions are homogeneous mixtures • A solute dissolves in a solvent to make a solution • Solutions are clear but not necessarily colorless • A conductivity test indicates the presence of dissolved charged particles
Solutions • Homogeneous mixture • Can occur between any state of matter. • Solid in liquid- Kool-aid • Liquid in gas- water vapor • Liquid in liquid- antifreeze in a car radiator • Gas in gas- air (oxygen, nitrogen and argon) • Solid in solid - brass
Aqueous solutions – water based solutions • SOLUTE- substance that is being dissolved (usually in lesser amount) • SOLVENT- substance that dissolves the solute (usually water, in aqueous solutions it is water)
Examples of Solutions Salt dissolved into water Sugar dissolved into water Sugar dissolved in coffee SoluteSolvent salt water sugar water sugar coffee
Pure Substances • In contrast to a mixture, a puresubstanceis always homogeneous. • A pure substance has a fixed composition. • Every sample of a given pure substance has exactly the same characteristic physical and chemical properties. • Every sample of a pure substance has exactly the same composition.
Pure Substances Pure substances are either elements (listed on the periodic table)or compounds.
Elements • Element – a pure substance made of only one kind of atom. • Element Examples – carbon, hydrogen gold, silver and oxygen. • The periodic table lists all the elements.
Compounds • Compound – a substance that is made from the atoms of two or more elements that are chemically bonded. • A compound can be broken down, or decomposed, into two or more simpler elements by a chemical change. • Water is made from hydrogen and oxygen atoms bonded together. H2O
Compound Examples: • methane gas is made of carbon and hydrogen. • sugar is made from carbon, hydrogen and oxygen. • table salt - ?
SUMMARY Matter is divided into a mixture or a substance • Pure Substance: • Definite composition, not physically able to separate (gold, silver, aluminum, table salt, pure water, sugar) • Mixture: • two or more substances coming together but keeping their individual properties (heterogeneous and homogeneous mixtures)
Classwork: • Page 50 (1-3, 5, 6 and 7a-f) Homework: • Worksheet • Due:Today
Lab Demo Objectives • Make and record proper observations for each demonstration. • Compare and contrast surface tension between water and alcohol • Define matter and discuss the physical properties of water. • Calculate density
Demo – pg 26 • How many drops of water can a penny hold without spilling over? • How many drops of isopropyl alcohol can be added to the surface of a penny? • Can a paper clip float in water? • Calculate the density of water, using 20.0 mL of water
Particulate Level So far we have focused on properties that are observable: density, surface tension, boiling point – physical properties. To understand the macroscopic (large scale & readily observed) properties of water, you have to understand water’s behavior at the particulate level – the level of small particles – the level of atoms and molecules.
Pure Substances • A pure substance has a fixed composition. • Every sample of a given pure substance has exactly the same characteristic physical and chemical properties. • Not physically separable. 47
Pure Substances Pure substances are either elements (listed on the periodic table)or compounds. 48
Types of Substances • Elements: • One type of atom (gold) • All elements are on the periodic table • Compounds: • Two or more types of atoms chemically bonded together (NaCl-table salt)
Substances • Atoms – all matter is composed of atoms, “building blocks of matter” • Elements – made of one kind of atom (hydrogen, oxygen, gold) • Represented by symbols (H, O, Ne)