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Unit 9 Solutions and thermochemistry Student Handout Anticipation Guide 1) A solution can be made of not only liquids but gases as well and looks homogeneous. Agree ______ Disagree ______ Why? 2) Orange juice cartons that say “made from concentrate” are better because they are made from pure orange juice with no additional water. Agree ______ Disagree ______ Why? Questions/Main Ideas Objective1: Describe what a solution is and what allows a solute to dissolve in a solvent What Is a Solution? 1) Suspension 2)Aqueous Solution 3) Colloid What is a Solution continued… Components of a solution Dissolving process • When you add the solute to a solvent, the solute dissolves as it makes contact with the solvent 1 Solubility Concentration Key Questions Answer the following questions about a 12M sugar water solution. 1) What kind of solution is it? 2) What is the solute? 3) What is the solvent? 4) What is the concentration? CER 1 Determine if you agree or disagree with the statement below and provide at least 2 pieces of evidence and your reasoning to support your view. Mayonnaise is an example of a Colloid that has eggs as one of the solutes and oil as the solvent 2 1) Oil and water do not mix because water repels oil. Agree ______ Disagree ______ Why? 2) Soap is able to remove dirt from your hands because it is nonpolar like dirt is. Agree ______ Disagree ______Why? Questions/Main Ideas Objective: Learn how to describe a solution and how to make a solution. Concentrations of a solution 1) concentrated 2) dilute 3) saturated 4) unsaturated 5) supersaturated Water: The universal solvent Solubility and Liquids Wax does not repel water Ionic solids 3 Detergents Key Questions: 30 mL of salt solution is added to 100 mL of water. A) What is the solvent? 1) salt solution 2) water 3) both B) What is the solute? 1) salt solution 2) water 3) neither C) What ions are present in the salt solution? 1) Na+ 2) Cl− 3) both D) The following figure represents soap. Which end of the anion is hydrophobic? left end, right end E) How will the anions on the surface of a beaker of water prefer to arrange themselves: A, B, C F) How does soap interact with grease (see below)? A, B CER 2 Determine if you agree or disagree with the statement below and provide at least 2 pieces of evidence and your reasoning to support your view NH3 is not able to dissolve in water because NH3 has a lone pair of electrons around the nitrogen that makes in nonpolar and thus unable to dissolve in water. 4 Questions/Main Ideas Objective: Learn what solutions conduct electricity and how to calculate concentration. Aqueous solutions Electrolytes Weak electrolytes Nonelectrolytes Concentration of solutions • there are 4 different ways of calculating concentration • for all calculations set up following table with info given and plug in relevant values Species Grams Moles kg Solute Solvent Total 1) Molarity - moles of solute per liter of solution M= moles solute Liters solution Ex. A solution is prepared by dissolving 25.0 g of MgCl 2 in enough water to make 450 mL of solution. Calculate the molarity. 2) Mass percent - percent by mass of solute in solution - is value between 0 and 100 Mass %= mass solute x 100 Mass solution Ex. Calculate the mass percent of ethanol (CH3CH2OH) in an ethanol- water solution if 25.0 g of ethanol are dissolved in 125 g of water. Species Solute Solvent Total Grams Moles 5 kg 3) Parts per million (ppm) -used for very dilute solutions and often used to show the amount of contaminants in a sample of water • Calculation similar to mass percent • Ppm= mass solute X 106 mass of solution Ex. Calculate how many ppm of ethanol you have in the water solution from the previous question 4) Molality -moles solute per kg solvent -m= number of moles of solute kg solvent Calculate molality of ethanol given in last problem Key Question:A solution is prepared by mixing 85.0g of hexane, C6H14 and 45.0g of decane, C10H22. Species Solute Solvent Total Grams Moles 1) Calculate the molality. Calculate the mass percent of decane. kg 2) Calculate the ppm of decane CER 3 Determine if you agree or disagree with the statement below and provide at least 2 pieces of evidence and your reasoning to support your view. When 20g of NaOH dissolves in 1000 g of water creates a 0.50m solution that conducts electricity very well. 6 3) Anticipation Guide 1) If you want a solid to dissolve faster you can either heat the mixture, mix it or break the solid into smaller pieces. Agree ______ Disagree ______ Why? 2) Cooks add salt into hot water when making pasta only because it makes the pasta taste better. Agree ______ Disagree ______ Why? 3) It will be harder to freeze Kool Aid into ice cubes than regular water. Agree ______ Disagree ______Why? Questions/Main Ideas Objective: Predict the effect of changing physical condition on dissolving and the impact of a solute on the boiling point and freezing point. Effect of Temperature Effect of pressure Effect of surface area Freezing point depression 7 Boiling point elevation Number of particles and fp and bp What causes boiling? Vapor Pressure • Pressure created by every liquid as a result of the liquid evaporating • The higher the vapor pressure the faster boiling can occur Key Questions A) Determine which of the following would produce a lower freezing point 1) C6H12O6 2) MgCl2 3) AlCl3 B) Which of the following would have a higher boiling point 1) C6H12O6 2) MgCl2 3) AlCl3 C. Why does warm soda taste so different than cold soda? 8 CER 4 Determine if you agree or disagree with the statement below and provide at least 2 pieces of evidence and your reasoning to support your view. Two friends decide to do an experiment to see what effect atmospheric pressure has on water boiling. One goes to big bear mountain and the other stays here in the neighborhood. They simultaneously start boiling water but the friend in the neighborhood really wants to win so he decides to add salt to his water and claims his boiled faster. He argues this is because atmospheric pressure is lower here which is why his boiled faster. Questions/Main Ideas Objective: Calculate the change in freezing point and boiling point as a result of adding a solute to a solvent Boiling Point Elevation Freezing Point Depression Boiling Point Elevation and Freezing Point Depression 9 Ex. What are the freezing and boiling points of naphthalene when 10.0g of nicotine, C10H14N2, is dissolved in 50.0g of naphthalene? Kf= 6.94 ˚C/m kb= 6.2 ˚C/m Freezing point= 80.29˚C Boiling point= 217.96˚C Grams Moles nicotine 10g 0.06 Naphthalene 50g Total 60g kg 0.010kg 0.050kg 0.060kg Question: Calculate the freezing point depression in a 0.0100 m aqueous solution of MgSO4 with a kf= 1.86ºC/m CER 5 Determine if you agree or disagree with the statement below and provide at least 2 pieces of evidence and your reasoning to support your view. The boiling point of 80g of NaOH dissolved in 1000g of water is 107.44°C and the freezing point is -2°C. 10 1) When an object feels cold it is because“coldness” is traveling to your hand from the object. Agree_____ Disagree______ Why?_____ 2) Heat and temperature are the same thing Agree_____ Disagree______ Why?_____ 3) It is easier to burn your tongue eating a hot piece of toast then eating a hot bowl of soup. Agree_____ Disagree______ Why?_____ 4) A piece of ice melts because it absorbs heat from the surroundings. Agree_____ Disagree______ Why?_____ Questions/Main Ideas Objective Explain how energy can be measured and transferred in a solution and how How is energy and temperature related? objects absorb heat differently. Energy • is the capacity to do work or supply heat PE(Potential energy) Heat vs. Temperature Temperature Measurements 11 KE(kinetic energy) Units of Energy • Measured in calories • A calorie is defined as The amount of heat energy needed to raise the temperature of one gram of water one degree Celsius. A) When you touch an object and it burns you, which direction does the heat flow? 1) From object to hand 2) from hand to object B) You put ice on your knee because of some soreness. Which direction is heat flowing? 1) From knee 2) from ice 3) Heat not flowing C) If a thermometer shows that the temperature is increasing, than the liquid inside the thermometer is 1) Expanding 2) contracting 3) doing nothing Heat capacity • is the amount of heat it takes to change an object’s temperature by exactly 1 Celsius • Basically depends on what the substance is and how much of it you have Specific heat Capacity • is the amount of heat it takes to change the temperature of 1 g of substance 1 Celsius • Basically depends only on the identity of the substance and is a constant 12 CER 6 Determine if you agree or disagree with the statement below and provide at least 2 pieces of evidence and your reasoning to support your view.A 10. g cube of copper at a 80°C is placed in an insulated cup containing 10g of water at a temperature 50°C. (The specific heat of copper is 0.385 J/g°C and the specific heat of water is 4.18J/ g°C.). After heat was transferred to the water from the copper it was noticed that the temperature of the copper changed more than the temperature of the water since it had a lower specific heat capacity Questions/Main Ideas Objective Calculate the heat of a reaction and explain if a reaction is exothermic or endothermic Calculating heat of a solution • to calculate you need to know the specific heat capacity of the substance (c), the mass of solution (m) (solute +solvent) and the change in temperature(∆t which is final temperature – initial temperature) Ex. 1 Water only Calculate the heat absorbed by 100g of water when it has its temperature raised by a chemical reaction from 30˚C to 50˚C. Specific heat capacity of water is 4.18J/˚C g. q= mc∆T = 100g (4.18J/˚C g) (50˚C− 30˚C) = 8360 J Ex. 2 Water and chemical 80g of sodium hydroxide dissolves in 120g of water and causes an increase in temperature from 20˚C to 30˚C. Calculate the heat of the reaction. 13 Key Questions 1) What is the amount of heat released when 10 grams of a ammonium chloride causes the temperature of 40 grams of water to go from 30˚C to 10 ˚C ? 2) Why does it take longer to boil a gallon of water compared to a cup of water? 3)Which would reach 100 ˚C faster, 50g of a piece of iron or 50g of water? A. System and surroundings 1) Exothermic -“exit” of heat - energy flows out of system (ex. Fire) 2) Endothermic - “entrance” of heat - energy flows into system (ice melting) Chemical Reaction in water • All data collected from experiments carried out in water is from point of view of water Calorimetry 14 Calorimeter Changes in energy due to state changes CER 7 Determine if you agree or disagree with the statement below and provide at least 2 pieces of evidence and your reasoning to support your view. I add 20g of NaOH to 80g of water and I notice that the temperature rises from 25°C to 28°C. I calculate the heat of the reaction as 250.8J which means the reaction is Endothermic and is absorbing energy from the surroundings 15 Questions/Main Ideas Objective Draw a heating and cooling curve to show the energy associated with a substance going from a solid to a liquid and a gas. What are some things that happen as we heat a sample up? Heat In chemistry heat is measured in Joules (J) and is transfer of energy Heat is dependent on mass, temperature change and specific heat (or ability of a substance to absorb heat) Temperature is a measure of warmth or coldness. What is the heating curve? 16 Why is the curve flat at some portions? What can you determine at flat lines? What is heat of fusion? What is heat of vaporization? 17 Summary • The heating curve is a useful tool to show us the changes in temperature, energy, and state as a sample is heated up. Cooling Curve Using the heating curve of water as a guide, draw a cooling curve for water beginning with steam at 140°C and ending at -40°C. Indicate on your graph at which points KE or PE changes 18