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Primarily due to polarity. Video1 Properties of water – 4 ½ min Why is ice less dense than water? How does ice floating on water impact the survival of.

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Presentation on theme: "Primarily due to polarity. Video1 Properties of water – 4 ½ min Why is ice less dense than water? How does ice floating on water impact the survival of."— Presentation transcript:

1 Primarily due to polarity

2 Video1 Properties of water – 4 ½ min Why is ice less dense than water? How does ice floating on water impact the survival of the living organisms Draw the water structure. How does the term polar describe the water molecule? What is the intermolecular force between water molecules called? Explain surface tension in water

3 Molecule two hydrogen atoms and one oxygen atom v-shaped triangular molecule hydrogen bonds Polarity properties

4 Water is a molecule made up of two hydrogen atoms and one oxygen atom. It has the formula H2O. When oxygen and hydrogen combine (H-O-H) they form a v-shaped triangular molecule. While water molecules are electrically neutral, the oxygen atom holds a small negative charge and the two hydrogen atoms hold small positive charges. Water molecules are attracted to each other, creating hydrogen bonds. These bonds determine almost every physical property of water and many of its chemical properties too. Scientists believe this unusual electrical balancing, called polarity, gives water some of its remarkable properties

5 Polarity Hydrogen bond Cohesion Adhesion Surface tension Capillary action Specific heat

6 Water Physical Properties (review) At what temperature in Celsius does water start boiling? At what temperature in Celsius does water start melting? At what temperature in Celsius does water start freezing? What is the density of water?

7 Water has a high specific heat capacity Water has the ability to absorb a lot of heat with a relatively small increase in temperature Water has one of the highest specific heat capacity This allows marine organisms to avoid drastic temperature fluctuations in the seawater. This allows orchards grown on the coast to survive hot summers and severe winters.

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11 Thinking critically Videos5&6 If matter expands when heated, and contracts when cooled, why does ice expand (increase in volume) when water freezes?

12 When water freezes, it goes from a mixed up liquid state where all these V's are just sliding around each other, to an ordered crystalline solid state where all the V's have to connect with each other in nice orderly solid shapes.

13 The closest and easiest solid crystal shape for something that exists as a degree V is a hexagonal (really tetrahedral in 3D) crystal. Think of it as a flat hexagonal snowflake shape, but it really goes in three dimensions. The water molecules want to do this because to them it "feels" nicer--that is: they feel less strain and they can get into a lower energy state by getting into this nice orderly hexagonal crystal.

14 Critical Thinking: If ice were more dense than liquid water, how would this impact the survival of the marine life? (The floating layer of ice insulates the liquid water below, so that it wouldnt freeze – this makes the ocean environment to easier to live in)

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16 As we know – water is neutral (equal number of e- & p+ = zero Net Charge) But because the O atom is more electronegative than the H atoms – electrons spend more of their time nearer the oxygen. (O atom attracts more than its fair share of electrons). This gives water a slight overall charge. The oxygen end acts negative. The hydrogen end acts positive. This charge is called polarity

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20 What is electronegativity? How does it change across a period? Down a group? What is the most electronegative element on the PT? Least electronegative? Which of the two elements, S or N, has a greater ability to attract another atoms valence electrons?

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24 Carbon is more electronegative Oxygen is more electronegative

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26 Water can dissolve more substances than any other solvent. Give examples of substances that water can dissolve. The dissolving power of water is very important for life on Earth. Wherever water goes, it carries dissolved chemicals, minerals, and nutrients that are used to support living things.

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28 Water (polar) + Styrofoam (non-polar)Acetone (nonpolar) + Styrofoam (non- polar)

29 Polarity really does allow bonding They are hydrogen bonds and they are weak They last for fractions of a second Continuously break and reform video clip Water molecule Part 1 - bonds breaking and reforming

30 Opposites attract

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32 Cohesion Adhesion

33 Cohesion (water is sticky) Attraction between particles of the same substance (why water is attracted to itself) Attraction between particles of the same substance ( why water is attracted to itself) Results in Surface tension (a measure of the strength of waters surface)Results in Surface tension (a measure of the strength of waters surface) Produces a surface film on water that allows insects to walk on the surface of water

34 Inside a drop of water polar water molecules attract to each other in a random fashion At the surface of the drop, water does not attract to the air A unified layer of molecules at the surface creates surface tension There the water behaves like an flexible sheet allowing denser objects to sit on the surface.

35 Can be seen as water droplets form Helps insects walk across water

36 Attraction between two different substances. Water will form hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton Adhesion Causes Capillary Action, which gives water the ability to climb structures.

37 * Can be seen as water droplets form on the spider web (another polar surface) Form spheres & hold onto plant leaves

38 * We know that gravity is ALWAYS pulling on objects with mass * Yet water can move up a paper towel with relative ease – How can this happen? * Because the positive and negative charges in the paper attract the polar water molecules (adhesion) * This property of adhesion is called capillary action.

39 Explain the following water properties in both words and drawings(2 min) Polarity- Like dissolves like- Heat capacity Water acts as a magnet- Trade notebooks with your partner write one constructive comment in your partners notebook. Hand them back their notebook( 1min)

40 How do heterogeneous and homogeneous mixtures differ?(Left Side) Salt solution and Oil in water 2 min - Quick Write: Based on your prior knowledge about mixtures, explain why a salt solution is classified as a homogeneous mixture and a mixture of oil and water is said to be a heterogeneous mixture. White boards activity: Homo- or Hetero - ? COKE AIR STEEL A JAR OF PENNIES Coke (mixture of CO 2 gas, water, sugar, caramel color, food flavorings) Air (mixture of O 2 and N 2 ) Steel (alloy – mixture of Fe and C) A jar of pennies and nickels Notes

41 By the end of the day you will know: Solute Solvent Solution Soluble Insoluble Immiscible Separation Solvation Factors affecting the rate of dissolution Next notes…

42 Complete the sentences. When you put salt into water it______. The salt dissolves because it is ________in the water. The substance which dissolves is called the ______. The substance that does the dissolving is called the _______. When something dissolves you get a _______. Water is a ________. Salt is a ________. When a substance does not dissolve it is________ Dissolution of salt in water water.jsp

43 Animation - Dissolution of an Ionic compound (results in dissociation) and a covalent compound (no dissociation) wf Animation – Strong electrolyte (complete dissociation into ions) – many ionic compounds – conduct electricity - (+ strong acids and bases – will cover in more detail in Bundle 11) Animation – Weak electrolyte (partial dissociation) – weak acids and bases (if a conductivity meter is used - light is not as bright (dim) compared to a strong electrolyte) Animation – Non-electrolyte ( no dissociation) - no disruption of its molecular (covalent) structure – does not conduct electricity

44 The dissolved components of ionic and covalent compounds are: a. All ions b. Ions for ionic and molecules for covalent compounds c. Ions for covalent and molecules for ionic

45 The dissolution of KNO 3 and C 3 H 6 O (acetone) in water occurs: a. Molecules by molecules for both KNO 3 and C 3 H 6 O b. Ion by ion for KNO 3 and molecule by molecule for C 3 H 6 O c. Ion by ion for C 3 H 6 O and molecule by molecule for KNO 3

46 Based on your observations of the dissolution process on the animation, how do you think substances get dissolved? a. Each solvent molecules gets separated from other molecules and is surrounded by ions in ionic substances or molecules in covalent substances b. Each ion in covalent substances and each molecule in ionic substances gets separated from other molecules or ions and is surrounded by solvent molecules c. Each ion in ionic substances and each molecule in covalent substances gets separated from other molecules or ions and is surrounded by solvent molecules.

47 Warm up 2/25/13 For the following reaction identify the products as insoluble or soluble. Na 2 CO 3 + CaCl 2 CaCO 3 + 2NaCl Classify the type of reaction Activity Sketch the process of dissolution of calcium chloride. Find a partner - compare each others drawings – make corrections if needed(4min)

48 Factors that Affect the Rate of Dissolution Pre-assessment: If you wanted to dissolve a substance in water as quickly as possible what could you do?

49 The three methods to increase the rate of dissolving for a solid are? Heat it! Crush it! Stir it!

50 How can you achieve the following: Increased number of collisions between solvent and solute Agitation Increased surface area Increased kinetic energy

51 Notes –Solubility the amount of solute that will dissolve in a given amount of solvent at a specified temperature and pressure (for gases) grams of solute per grams of solvent grams of solute per 100ml of solvent

52 Example: at C, the solubility of sodium chloride is 35.0 grams per 100 ml of water. You can dissolve up to 35.0 grams of sodium chloride in 100 ml of water. If you add more than 35.0 grams the solid will simply not dissolve.

53 Based on solubility we can have three types of solutions: Unsaturated – a solution that could dissolve MORE solute at a specific temperature Saturated – a solution that contains the MAX amount of solute that can dissolve at a specific temp (stable) Visual evidence: a small quantity of un-dissolved solute remains in solution Supersaturated – a solution that contains more dissolved solute than a saturated solution. (Prepared by heating the solvent, adding solute, and cooling slowly – very unstable) DEMO. Supersaturated solution of Sodium Acetate

54 Grams solute/100 g H 2 O NaClO 3 KNO 3 KBr NaCl Temperature Grams of solute per 100 g of water

55 How much solute will dissolve? Grams solute/100 g H 2 O NaClO 3 KNO 3 KBr NaCl Temperature A solubility curve shows the amount of each solute that will dissolve in 100g H 2 0 at each temperature. Saturated is on the line. Unsaturated is below the line. Supersaturated is above the line.

56 A solubility curve shows the amount of each solute that will dissolve in 100g H 2 0 at each temperature. Saturated is on the line. Unsaturated is below the line. Supersaturated is above the line. Grams solute/100 g H 2 O Saturated

57 What is the solubility of KNO 3 at 60 o C in 200 g of H 2 O? How many grams of KBr can dissolve in 300 gr of H 2 O at 100 o C? Grams solute/100 g H 2 O NaClO 3 KNO 3 KBr NaCl Temperature

58 Grams solute/100 g H 2 O Unsaturated

59 Grams solute/100 g H 2 O How much NaClO 3 would you have to add to 100 g of water at 50 o C to make a saturated solution? 50 o Look at the intersection. Approx. 140 – 142 g

60 Mini Lab: WHAT FACTORS INFLUENCE DISSOLUTION Surface Area (Solid Solute) 1) Record the time 1 sugar cube needs to dissolve in 200 ml of tap water. ______ 2) Crush 1 sugar cube in the mortar & pestle. Record the time the crushed sugar cube needs to dissolve in 200 ml of tap water. _____________ Temperature (Solid Solute) 3) Obtain 200 ml of warm water from the front lab table. Color one side of the sugar cube with a Vis-A-Vis marker. Add the sugar cube to the warm water & record the time the cube needs to dissolve. _____________ 4) Obtain 200 ml of cold water from the front lab table. Color one side of the sugar cube with a Vis-A-Vis marker. Add the sugar cube to the cold water & record the time the cube needs to dissolve.___________ Stirring (Solid Solute) 5) Place 1 sugar cube in 200 ml of tap water. Record the time the cube needs to dissolve without stirring.______________ 6) Place 1 sugar cube in 200 ml of tap water. Record the time the cube needs to dissolve while you stir the solution._____________

61 Homework: Lab analysis questions 1) How do you increase the surface area of a solid? 2) How is surface area of a solid solute related to dissolution? WHY? 3) How is temperature related to the dissolution of a solid solute? WHY? 4) What effect does stirring have on the dissolution of a solid solute? WHY?

62 Checking for understanding

63 The Great Soda Mystery! 1.What is the difference between the hot soda and cold soda? Why? 2.As temperature _______, solubility of a gas ______. 3. Does pressure affect the amount of gas in the soda? How? 4. As pressure _____, solubility of gases ______.

64 In general solubility of solids increases with increasing temperature. Solubility of gases in water decreases with increasing temperature.

65 Solubility of Gases When something is heated it will favor the gas phase, therefore, heating solutions with gaseous solutes will decrease the solubility. For example, carbonated water can dissolve more carbon dioxide at lower temperatures. The following is a solubility curve for gases

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67 Pressure Pressure has little effect on the solubility of liquids or solids in liquid solvents.(cant not be compressed) The solubility of a gas in a liquid solvent INCREASES when pressure increases. The pressure holds the solute (CO 2 gas) in the solution.

68 Electrolyte - An ionic compoud whose aqueous solution conducts electricity. (Dissolved in water, the positive and negative ions are free to move (mobile ions) and can conduct elect.) Solid ionic compounds cant conduct electricity (ions are present but they are NOT mobile) Strong (HCl, KCl) – completely ionize in water. Weak (vinegar – acetic acid) – partially ionize in water Ex: NaCl almost completely ionizes in solution and produces positive and negative ions, which will conduct electricity. Electrolytes can be found in sports drinks (ex. Gatorade) – maintain homeostasis.

69 Warm up 3/5/13 1) When the attractive forces within the particles of a solid substance are weaker than the attractive forces between the solid particles and its liquid solvent, what will happen to the solid substance? Draw a picture representing the above scenario.

70 Exit Pass- What do all of the following have in common? KCl (aq) NaCl (aq) AgNO 3(aq) NaOH (aq) HCl (aq) They are all homogeneous mixtures= solutions Which is the solute and solvent in each one?

71 Concentration of Solutions How would you describe the concentration of the Kool-Aid solutions? How do you know which solution contains more or less solute?

72 Concentration – a measure of how much solute is dissolved in a specific amount of solvent. Concentration may be described qualitatively using the words: 1. Concentrated- contains a LARGE amount of solute 2. Dilute – contains a SMALL amount of solute

73 Although qualitative descriptions of concentration can be useful, solutions are more often described quantitatively. One of the commonly used quantitative descriptions is MOLARITY. B. Calculating Concentration 1. Molarity (M) – The # of moles of SOLUTE dissolved per LITER of solution. M = moles solute L of solution a. Ex: An IV solution contains 5.10 g of glucose (C 6 H 12 O 6 ) in ml of solution. What is the molarity of the solution? b. Ex: How many grams of Na 2 SO 4 would be dissolved in 1.5L of a.24M solution of Na 2 SO 4 ?

74 In the laboratory, you may use concentrated solutions of standard molarities called stock solutions. For example, concentrated hydrochloric acid (HCl) is 12M. You would rarely use this concentration in a lab. How would you prepare a LESS CONCENTRATED (dilute) solution? You can prepare a less concentrated solution by taking a concentrated solution (stock solution) and diluting it with solvent

75 M 1 V 1 = M 2 V 2


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