chapter 15: solutions...chapter 15: solutions 3/30/2011 what does “dissolve” mean? • when a...
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Chapter 15: Solutions
3/30/2011
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What does “dissolve” mean?
• When a compound dissolves, the atoms in thecompound break apart and spread out.
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• Substance 1 breaks apart the crystal lattice ofsubstance 2 by pulling on it:
Substance 1
Substance 2
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• Substance 1 is called the solvent. It does the breaking.
• Substance 2 is called the solute. It gets broken apart.
Substance 1 Solvent
Substance 2 Solute
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• Dissolving is NOT a chemical reaction.
• The atoms are NOT rearranged into new substances, they are just separated temporarily.
• If you remove the solvent, the solute will goback to its crystal lattice.
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Dissolving:
• Dissolving is when two substances mix andone compound is broken apart by the other.– The solute is the substance that breaks apart
(usually a solid)
– The solvent is the substance that does thebreaking (usually a liquid)
• Dissolving is NOT a chemical reaction, so there are no reactants or products.
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Think!
• A teaspoon of dry coffee crystals dissolves when mixed in a cup of hot water. The original crystals are classified as a
A. solute.B. solvent.C. reactant.D. product.
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What is a solution?
• When a substance dissolves in anothersubstance, the whole thing is called a solution.
Ocean water is a solution of salt
dissolved in waterSteel is a solution
of carbon dissolved in iron
Air is a solution of oxygen dissolved in
nitrogen
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May exist in all states of matter (gas, liquid, solid)• Examples:
• Oxygen and Nitrogen gas (gas/gas)• Carbon Dioxide in water (gas/liquid)• Water in air (Liquid/gas)• Alcohol in water (Liquid/Liquid)• Mercury in Silver (Liquid/Solid)• Sugar in water (solid/liquid)• Copper in Nickel (Solid/Solid)
Types of Mixtures
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• Solutions are homogeneous mixtures of a solute anda solvent. Looks the same
throughout
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Solutions:
• Solution – a homogeneous mixture of a soluteand a solvent
• Homogeneous means that it looks the same throughout.
• Ex: Sugar dissolves in water to make sugar water
Solute Solvent Solution (homogeneous
mixture)
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Think!
• Label the picture using the vocabulary words:
homogeneous, heterogeneous
Heterogeneous
Homogeneous
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Think!
• Label the picture using the vocabulary words:
solution, solvent, solute
Solute
Solution
Solvent
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Chapter 15, WS #1
Dissolving & Solutions
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Why do substances dissolve?
Start today’s notes on theFRONT of a NEW PAGE
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Why do substances dissolve?
Remember:
• Particles are in constant, random motion– Gases move quickly and freely
– Liquids flow
– Solids vibrate in place
• So all particles bump into each other (whetherthey are solid, liquid, or gas)
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Even though they bump into each other, compounds hold together because of:– Intramolecular forces (within compounds)
– Intermolecular forces (between compounds)
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• But what if they bump into a different substance that they are more attracted to?
Na+ Cl–
H+ O–2
H+
Attraction!
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• If the intermolecular attraction (between compounds) is stronger than the intramolecular attraction (within the compound), the compound will dissolve (break apart)
Na+
H+ O–2
H+
Cl–
Stronger Intermolecular
Attraction!
Weaker Intramolecular
Attraction
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Polar dissolves polar
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Why do substances dissolve?
• Particles are in constant, random motion.
• Particles are bumping into each other.
• If a particle bumps into another particle that it is more attracted to, it can break apart from its crystal lattice and dissolve.
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Which particles will be mostattracted to each other?
• Some compounds do not share their electrons evenly.
• They are called polar molecules.
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• Other molecules share their electrons evenly.
• They are called nonpolar molecules.
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Dissolving Rule:
• Like dissolves like– Nonpolar solvents will dissolve nonpolar solutes– Polar solvents will dissolve polar solutes
• Ex: water is polar and NaCl is polar, so NaCl will dissolve in water
• Ex. chalk is nonpolar and ethanol is nonpolar, sochalk will dissolve in ethanol
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Polar dissolves polar
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• Label each solute as polar or nonpolar:
– NH4Cl
– C10H8
– C2H5OH– CO(NH2)2
Think!Polar Nonpolar
Polar
Nonpolar
½ is Polar & ½ is Nonpolar
Polar
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Chapter 15, WS #2
Like Dissolves Like
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How fast will something dissolve?
• Three things affect how quickly a substancewill dissolve:– Temperature
– Pressure
– Surface Area
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Which dissolves faster?
• Sugar in ice water
• Sugar in hot water
• Heat makes things dissolve faster!
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• Heat makes things dissolve faster– Heat makes particles move faster
– Then they bump into each other more
– This makes them dissolve faster
Temperature
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Pressure
• Higher pressure makes things dissolve faster– When pressure increases, particles are forced
closer together
– Then they bump into each other more
– This makes them dissolve faster
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When you want something todissolve faster, what do you do?
• Drop it in water and leave it alone
• Drop it in water and crush it up
• More surface area makes things dissolve faster
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Surface Area
• More surface area makes things dissolve faster– If particles have more surface area, they will have
more places to get bumped
– More surface to bump into means more chances to dissolve
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Chapter 15, WS #3
Dissolving Rates
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Which cup of tea has the mosttea dissolved in it?
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Concentration
• The concentration of a solution is how much solute is dissolved in a specific amount of solvent.
• Levels of concentration:– Dilute (not much solute dissolved)
– Concentrated (lots of solute dissolved)
– Saturated (the maximum amount of solute dissolved)
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Think!
• Label each beaker as dilute, concentrated, orsaturated.
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Is there a limit to how muchsolute will dissolve?
• Will 1 teaspoon of salt dissolve in a cup of hot water?
YES
• Will 1 tablespoon of salt dissolve in a cup of hot water?
YES
• Will 1 cup of salt dissolve in a cup of hot water?
MAYBE
• Will 1 container of salt dissolve in a cup of hot water?
NO
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Yes, there is a limit!
• The limit is called the solubility• It is a number with a unit• It is different for every solute• It depends on the temperature and pressure
• Example:– The most sugar that will dissolve in 100 grams of
water at 25°C is 67.9 grams.
– The solubility of sugar in water at 25°C is 67.9 g/100 g H2O.
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Solubility
• The solubility is the maximum amount of solute that can be dissolved in a given amount of solute.
• Example:– The most salt that will dissolve in 100 grams of
water at 25°C is 36.2 grams.
– The solubility of NaCl in water at 25°C is 36.2 g/100 g H2O.
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Think!
• If the solubility of NaCl at 25°C is 36.2 g/100g H2O, what mass of NaCl can be dissolved in50.0 g of H2O?
½ as much solvent
½ as much solute
Solute Solvent Temperature
36.2 g NaCl 100 g H2O 25°C18.1 g NaCl 50 g H2O 25°C
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Chapter 15, WS #4
Concentration
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• Molarity (M) = moles of solute
• Example: How many moles of HNO3 are needed to prepare 5.0 L of a 2.0 M solution of HNO3?
liters of solution
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Molarity (M) = moles of solute liters of solution
2.0 M = moles of solute 5.0 L
(2.0 M) × (5.0 L) = moles of solute
10 moles of solute (HNO3)
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Chapter 15, WS #7
Molarity