Presentation on theme: "Activity 35 Analysis 1.Did in class 2.In this activity you compared two liquids. a.What properties and measurements were the most helpful in identifying."— Presentation transcript:
Activity 35 Analysis 1.Did in class 2.In this activity you compared two liquids. a.What properties and measurements were the most helpful in identifying the two liquids? b.Explain your answer density and boiling point were the most helpful (they were most exact) all properties observed and measured could be used to tell the substances apart except general appearance All the alcohols had similar qualitative and quantitative properties (it could be ethanol or isopropyl alcohol)
3.A liquid forms rounded droplets because of its degree of cohesiveness. a.Which of the two liquids was more cohesive? b.Explain the observations that support your answer. Liquid A was more cohesive formed a round drop held together could be moved around as a single drop Liquid B formed a flatter drop didnt stay round or hold together smeared out over the plastic
4.Why should you keep liquid samples capped or covered while studying them? they can spill they might evaporate can spread fumes 5.Which do you predict would evaporate more quickly at room temperature: methanol or acetone? (Refer to the data in Table 1.) Explain why. acetone lower boiling point it would evaporate faster at a lower temperature observed this with water and ethanol
Common states of matter, cohesiveness is a property of liquids Quantitative properties, color is qualitative All qualitative properties, temperature is a measurement All properties of the unknown samples, comparison is not a property 6. Follow steps a, b, c, and d. a. Look for a relationship among the words in List 1. Cross out the word or phase that does not belong. b. In List 1 circle the word or phrase that includes the other three. c. Explain how the word or phrase you circled is related to the others. d. Repeat steps a–c for each of the remaining lists. List 1List 2List 3List 4 LiquidDensityOdorProperty SolidBoiling PointFeelCohesive GasQuantitative PropertyColorLiquid CohesiveColorTemperatureComparison States of MatterMelting PointQualitative PropertyClear
Activity 36 Analysis 4.What does the 2 in the molecular formula H 2 O stand for? Explain. Number of hydrogen atoms in the molecule 5.In this activity, you modeled ethanol, hydrogen, methanol, nitrogen, oxygen, and water. Why are oxygen gas, hydrogen gas, nitrogen gas, and carbon called elements, while water and ethanol are called compounds? An Element is composed of only one type of atom like carbon, hydrogen, nitrogen, and oxygen A compound is composed of two or more different atoms chemically bonded together. Water and ethanol both have two or more different elements (atoms) bonded together
6.Methanol and ethanol are both alcohols. a.Compare: How are the molecules of methanol and ethanol similar? Both are made of the same three elements and both contain an OH and a CH 3 b.Contrast: How are the molecules of methanol and ethanol different? Methanol contains one carbon atom Ethanol contains two carbon atoms Ethanol has more of a chain structure since it has more carbons
7.a. Why is the formula for methanol usually written as CH 3 OH instead of CH 4 O? The formula CH 3 OH better describes the structure of the methanol molecule From the formula CH 4 O, you cant tell how the oxygen atom is involved in bonding without building a model b.Looking at its structure, propose two ways other than C 2 H 5 OH to write the formula for ethanol. Describe the advantages and disadvantages of each. C 2 H 6 O,gives correct # of each kind of atom, but doesnt show structure CH 3 CH 2 OH is long, but it most clearly suggests the structure of the molecule
This is called a molecular isomer They have the same number and type of atoms, but they are arranged differently Molecular size and structure have many effects on the physical properties of a substance –Density –Melting point –Boiling point Liquid at room temperature Gas at room temperature
8.Compare and contrast water with the two alcohols you modeled. How are they the same? How are they different? Water and alcohols both include hydrogen and oxygen in OH groups Alcohols have carbon and water does not Alcohols are larger molecules
Water Contamination Water is not always pure. Dissolved substances can be helpful: –Salts dissolved in our blood and in our food and drink. Substances may be unpleasant to smell or taste or are harmful to humans or other organisms. Water contamination refers to undesirable materials dissolved in water. You will begin to investigate how things dissolve in water.
Read C-39 Problem: What makes a mixture of a solid and a liquid a solution? Hypothesis/Initial Thoughts:
Sugar Mixed in Water As the sugar mixes in: Dissolving When all sugar has disappeared: Dissolved Sugar dissolves in water: Soluble The mixture that results after a solute dissolves in a liquid such as water: Solution Flour does not dissolve: Insoluble
Procedure: Follow procedure on pgs. C-40 to C-42 1. Put solid in appropriate cup instead of on a paper towel. Note: In step 5, Using Table 2, make sure you put the correct number of scoops in the assigned cup listed in the table. In step 11, demo on how to use filter paper.
Did it dissolve? If the solute (solid) dissolves, the solvent (liquid) will be clear. If the solution is cloudy and you cannot see through it easily, it is not a solution. The material is suspended in the liquid, it is not dissolved.
Vocabulary sentences: Solute Solvent Solution Write a sentence to describe your observations in the vocabulary section of your notebook for the above vocabulary words.
Saturation In some cups, the water (solvent) dissolved some, but not all of the solid (solute) When there is solid left over after you have stirred and seen some dissolution, it means that the solvent can hold no more, the solution is saturated.
In which cups did you see saturation? Cup 2: sodium chloride Cups 7 & 8: iron chloride Cornstarch cannot be considered a saturated solution since there was no evidence that any cornstarch dissolved at all
Variables in this Investigation Controlled variable: the variable(s) which is held constant –The amount of water added to each cup –The temperature Independent variable: An independent variable is the variable you have control over, what you can choose and manipulate. It is usually what you think will affect the dependent variable. –The four solids –The two amounts used for each solid Dependent variable (or responding variable): It is the variable that depends on other factors. –Whether or not the solids dissolve to form a solution