Review of Activities 35-40

Mystery Liquids – Activity #35 We explored the fact that substances in a liquid phase have characteristic properties, just as solids do. We tried to identify two different liquids. One was water and one was ethanol (an alcohol). We investigated qualitative properties such as appearance, odor, feel on the skin, cohesiveness, phase and tendency to evaporate at room temperature. We also measured quantitative properties such as melting and boiling points, and density. We should have learned that water has some unusual properties and that most measurement scales tend to be defined relative to water.

Vocabulary words learned Particle – small pieces or parts Phase – the three forms that a substance can be in – solid, liquid, or gas Physical change – distance b/w particles changing Vapor - water in the gas phase

Objectives to Activity 35 Substances have characteristic properties, such as density, melting point, and boiling point, that are independent of the amount of the sample. Substances generally exist in one or more of three phases: solid, liquid and gas. Phase changes, such as melting and boiling, are physical changes. Scientists set the standards of density and the Celsius temperature scale based on water’s melting and boiling points.

Notes to remember When we froze water in the freezer, it turned to ice. When we froze ethanol, it never froze in our freezer. Remember that the lower the temperature, the less amount of energy so the particles vibrate but they stay in place. Higher temperature means more energy so the particles move faster to fill the container. The basic particles do not change – only the arrangement and distance between the particles change during a phase change.

Main ideas Substances can be identified based on their properties. Liquid A was water based on its properties. Lack of color Lack of odor Round drop Density was 0.98 – 1.02 g/mL Boiling point was 97 – 103 degrees Celsius (higher than alcohol) Melting point Liquid B was ethanol based on its properties Had an odor Did not form a drop on the wax paper Boiling point was 75 – 81 degrees Celsius (lower than water) Density was g/mL One plus one does not always equal two……. Space between molecules

Activity #36 – Making Molecules We created models of basic compounds such as Water Methanol Ethanol We created models of molecules of diatomic elements such as Hydrogen Oxygen Nitrogen

Can you identify the molecule? Methanol Ethanol

Vocabulary terms Element – a basic substance that can’t be simplified Atom – smallest particle of an element Molecule – 2 or more atoms held together with a covalent bond Compound – two or more elements chemically bonded – a molecule that contains more than one element A is for Atom

Further Review We worked with four different elements: carbon, hydrogen, oxygen and nitrogen The ‘sticks’ in our models represented ‘bonds’ with another atom. In the molecular formula H 2 O – what doe the 2 stand for? The number 2 represents the number of hydrogen atoms in the molecule. Remember that elements are a substance composed of only one type of atom whereas a compound is any substance made up of two or more elements chemically bonded together. Water and alcohols are similar in that they all include hydrogen and oxygen in OH groups. However, alcohols have carbon and water does not. Alcohol molecules are larger.

Activity 37 “What Dissolves?” We investigated the solubility of four solids in water. Sodium chloride Copper chloride Cornstarch Iron chloride We further explored solutions and solubility. Key vocabulary Dissolve – sugar mixing into water – sugar dissolves Solute – the sugar – what YOU are putting in Solvent – the water – universal solvent is water Solution – the mixture that results of you putting two things together

Questions Must a mixture be clear to be a solution? Yes, a mixture must be clear to be a solution. If it isn’t clear, there are still large particles in the mixture. Must a mixture be colorless to be solution? No. Even when the copper chloride completely mixed into the water and no particles remained, the solution was blue. If it is clear, it is a solution, even if it has color.

Activity #38 – Dissolving Duel We compared water and ethanol as solvents. We performed a controlled experiment that tested for the relative solubilities of eight solutes. Water can dissolve many different solutes and is often called the universal solvent. Water’s ability to dissolve many substances is both helpful and harmful to living organisms. Industrial activity can introduce undesirable substances into the environment.

Concept Map Solvent Solute Solution Less solubleMore soluble Saturated Dissolves in dissolves Can be Less solute dissolves before More solute dissolves before form May be

Questions In a solution of sugar and water: Which is the solute? Which is the solvent? Which one is a solution? Coffee with cream Hot tea Soda Black coffee Muddy water milk Milk, muddy water and coffee with cream are not solutions because they are not clear. Black coffee, tea and soda are solutions because they are clear

Objectives A solution exists when one substance, the solute, dissolves in another, the solvent. Solubility, the amount of a substance that can dissolve in a particular solvent such as water, varies from substance to substance. Dissolved particles may be detected by sight as a color change of the solution; un-dissolved particles are always visible. A filter can remove only un-dissolved solid particles from a mixture.

Questions continued What could be done to a sugar solution to make it more dilute? Adding more water to a sugar solution would make it more dilute What could be done to a sugar solution to make it more saturated? Adding more sugar or evaporating some of the water The longer you leave a tea bag in hot water, the darker the tea becomes. Explain why this happens in terms of dissolving and concentration? Dark tea is more concentrated than light colored tea made from the same tea leaves. The deeper the color, the more tea is dissolved in the solution.

Activity 39 Contaminants We did an activity which followed a water molecule in a droplet of water through the water cycle – very similar to what we did in the weather unit however, the piece that was added was the contaminants. Started as fairly pure precipitation. Water circulates through the earth’s crust, oceans, and atmosphere in the water cycle. It evaporates from the surface, rises, cools at higher elevations, condenses as rain or snow, and falls to the surface where it collects in lakes, oceans, soil, and rock layers underground.

Water Cycle

Pass out Transparency 39.1 Use this as a reference – tape it into Activity #39 Notice that the solid arrows represent water which has picked up contaminants Notice that the black outlined arrows represent water as either vapor or no significant contaminants

Activity #40 Parts Per Million We were introduced to the concept of serial dilution. We can quantify relative concentration of solutions in parts per million. Dilution reduces the amount of solute relative to the amount of solution but without eliminating the existence of solute, even when it becomes imperceptible to the naked eye Mathematical relationships are involved in serial dilution and the expression of concentration of a solution.

Parts per million 1 second in 12 days 1 penny out of $10,000 1 grain of salt in 2 pounds of potato chips 1 inch in 16 miles 1 postage stamp in an area the size of a basketball court