Chapter 17 Water & Aqueous Systems 17.1 Liquid Water and its Properties Why do we care about water? 3/4 of earths surface, 60% of our body weight Unique properties make life possible

Water Molecule Polar Bonds – difference in electronegativity is 1.4 Polar Molecule – has a bent shape due to lone pair electrons on the central element, oxygen O: 3.5 H:2.1 How polar is it? Address angle

Water Molecule Molecules are attracted to each other by hydrogen bonds ∂- Polar Covalent bond O ∂+ H H Remember ∂ means partial or slightly. Intermolecular vs. Intramolecular ∂- O H H Hydrogen bond ∂+

Surface Tension The inward force, or pull, that tends to minimize the surface area of a liquid Tends to hold a drop of liquid in a spherical shape A sphere has the smallest surface area for a given volume Skin like properties (waterstrider) Surface molecules attracted to each other through H-bonding and can’t h-bond to air H-bonding is the reason for water beading up Cohesion-attraction of water to water (surface tension) Adhesion -attraction of water to non water (water sticking to a surface)

Surface Tension Water’s surface tension is stronger than most liquids reduces vapor pressure Define vapor pressure, h-bonds hold liquid together, h-bonds must break to increase vapor pressure

Surface Tension Surfactant – substance that interferes with the hydrogen bonds between water molecules. Surface tension breaks down and the water spreads out. Surface active agent Why we use soap Decreases surface tension

Thermochemistry Specific heat capacity – the amount of energy required to raise the temperature of 1.0 g of water by 1C. q = m  C  T C = 1.00 cal/g°C or 4.18 J/g°C m = mass in grams ∆T = change in temperature in °C q = heat in joules or calories Thermochem properties of water are incredibly important

Impact of Thermochemical Properties Water allows for more temperate climates. Water cools more slowly at night and heats more slowly during the day reducing temp variations

Chapter 17 Water & Aqueous Systems 17.2 Water Vapor & Ice

Water Vapor Evaporation – the change of state from liquid to gas at the surface of a liquid that is not boiling Ever left a glass out over night? Endothermic- ex: sweat, Rubbing alcohol (colder because evap is faster, less h-bonds)

Water Vapor Condensation – the change of state from a gas to a liquid Water has a high heat of vaporization (2260 J/g) 2260 J of energy is needed to change 1.0 g of water from liquid to gas 2260 J of energy is given off when 1.0 g of water is changed from a gas to a liquid Breathing on a cold day A cold glass sweating Exothermic Where does the water come from that condenses on the cup? In the breath?

Water Vapor Why would a burn from steam at 100C be worse than a burn from water at 100C? Liquid water 2260 J/g more heat in steam than liquid 100°C steam ∆q

Water Vapor Water’s high boiling and melting points are caused by hydrogen bonding When compared to ammonia (NH3) the H – bonds in water are stronger It takes more energy to disrupt these bonds, giving water a higher boiling and melting point H2o: 2 lone pairs 2 hydrogens more polar bonds (1.4) Nh3: 1 lone pair 3 hydrogens (.9)

Ice Freezing – the change of state from a liquid to a solid Water has a high heat of fusion (334 J/g) 334 J of energy is needed to change 1.0 g of water from a solid to a liquid

Ice Density – the ratio of the mass of an object to its volume M D = V

Ice What happens when water freezes?

Ice What are some benefits of ice floating? Insulates fish in winter, ground & air cold, ice keeps water warm, like eskimos

Review Problems Calculate the heat released when a cup of tea cools from 61C to 25C. The mass of the tea is 225g. (Assume the specific heat of the tea is equivalent to that of water) C = 4.18 J/g°C m = 225 g ∆T = 61°C - 25°C = 36°C q = ? q = m  C  T = 225g  4.18 J/g°C  36° C = 33900 J Variables, formular, plug in, solve, units, sig digs 100°C 0°C Heat change

Review problems Calculate the amount of heat needed to boil (vaporize) a kettle filled with water (250 g). m = 250g Hvap= 2260 J/g q = ? q = m • Hvap q = 250g • 2260 J/g q = 565000 J Assume water is already at 100°C

Review Problems How much heat energy is needed to melt 30.0 g of ice at 0C to water at 80C? C = 4.18 J/g°C Hfus= 334 J/g m = 30 g ∆T = 80°C - 0°C = 80°C q = ? q1 = m • Hfus q2 = m  C  T = 30g * 334 J/g = 10020 J = 30g  4.18 J/g°C  80° C = 10032 J + 2. T when there is temp change, no temp change during phase change 20100 J 100°C 1 0°C 2 Heat change

Review Which atom in the water molecule is most electronegative? a. Hydrogen b. Oxygen c. neither

Review How are water molecules held together? a. magic b. dispersion forces c. covalent bonds d. hydrogen bonds

Review Water has a ________________ vapor pressure due to _________________. a. low; magic b. high; no reason c. low; hydrogen bonds d. high; hydrogen bonds

Review Water has a ________________ heat capacity and a __________________ heat of vaporization. a. high; low b. high; high c. low; high d. low; low

Review Due to the high heat capacity and vaporization energy of H2O, coastal areas have ___________________ temperatures. a. moderate b. extreme c. low d. high

Review Which of the following are characteristics of surface tension? a. reduces vapor pressure b. holds liquids in spherical shapes c. is caused by hydrogen bonding d. is very strong in water e. all of the above

Review A surfactant is a substance that interferes with ________________ and decreases the _________________. a. free time; productivity b. hydrogen bonding; surface tension c. intramolecular forces; vapor pressure

Chapter 17 Water & Aqueous Systems 17.3 Aqueous Solutions

Solutions Aqueous solution – a water solution containing dissolved substances Solvent – the dissolving medium Solute – particles dissolved in the solution Would the salt or the water be the solute in a salt-water solution? Salt

Solutions Solvation – the process that occurs when a solute dissolves in a solvent EXAMPLE: Liquid water is constantly in motion, particle collisions break up solute into ions

Solutions “Like Dissolves Like” Polar substances dissolve in polar solvents. H2O: polar and ionic Nonpolar substances dissolve in nonpolar solvents Gasoline: oil

Solutions Electrolytes – compounds that conduct an electric current in aqueous solutions or in a molten state All ionic compounds Some very polar molecules dissolved in H2O Electrolytes in gatorade: citric acid, salt, sodium citrate, monopotassium phosphate, sucrose acetate isobutyrate

Solutions Nonelectrolytes – compounds that do not conduct an electric current in either aqueous solutions or the molten state Molecular compounds Organic compounds (carbon containing compounds) Nonpolar compounds Cane sugar, rubbing alcohol, not composed of ions H C H H H

Solutions Strong electrolytes: Weak electrolytes: Nearly all the ions dissolve in aqueous solution NaOH, HCl and NaCl Weak electrolytes: Very small fraction of ions dissolve in aqueous solution Distilled H2O, ammonia and acetic acid

Solutions How electrolytes form: NH3 + H2O → HCl + H2O → NH4+ + OH- H3O+ + Cl-

Hydration Water of hydration – water in a crystal When copper (II) sulfate is dissolved in water and then the water allowed to evaporate, copper (II) sulfate pentahydrate is formed CuSO4 + 5H2O ↔ CuSO45H2O Hydrate - compound that contains water of hydration Dot used to connect formula of compound and # of water molecules per unit CoCl2 is blue CoCl2•6H2O is red Give them words have them predict products/reactants

Hydration When cobalt (II) chloride is dissolved in water and then the water allowed to evaporate, cobalt (II) chloride hexahydrate is formed CoCl2 + 6H2O ↔ CoCl2 6H2O

Naming Hydrates To name a hydrate, use the following: They are named by giving the name of the salt followed by a prefix denoting the number of water molecules associated with a formula unit of the salt. Ex: CuSO4 • 5H2O copper (II) sulfate penta hydrate

Hydration Calculate the percent water in CuSO4•5H2O. Cu 1 S 1 Total mass of hydrate: 249.6 g Mass H2O: H 2 O 1 Total mass of H2O: 18.0 g X 5 = 90.0g x 63.5 = 63.5 x 32.1 = 32.1 x 16.0 = 144.0 x 1.0 = 10.0 + x 1.0 = 2.0 x 16.0 = 16.0 +

Hydration Mass H2O Mass Hydrate X 100 = % H2O 90g X 100 = 36.1% 249.6g

Compound(high pressure) H2O(low pressure) Hydration Compound(high pressure) Efflorescence – process in which hydrated compounds lose water to its surroundings. Occurs when a substance has a vapor pressure higher than that of water Some hydrated compounds can effloresce and will form anhydrous compounds In this process the compound loses water

Compound(low pressure) H2O(high pressure) Hydration Compound(low pressure) Deliquescence – process in which anhydrous or somewhat hydrated compounds gain water from the surroundings. Occurs when the solution formed has a vapor pressure lower than that of the water in the air Some anhydrous or somewhat hydrated compounds will deliquesce and form hydrated, or more hydrated, compounds In this process water is gained

Hydration Desiccants – hygroscopic (water absorbing) substances that are used as drying agents. Small silica gel packets used in electronic merchandise shipping Sodium hydroxide is a dessicant and becomes a solution quickly (dissolves itself) when exposed to water in the air

Chapter 17 Water & Aqueous Systems 17.4 Heterogeneous Aqueous Systems

Suspensions Suspensions – mixtures from which particles settle out upon standing. Suspensions have particle sizes larger than solutions Generally the sizes are larger than 100 nm The particle size in a solution is about 1 nm Muddy water is a good example

Colloids Colloids – heterogeneous mixtures containing particles that are intermediate in size between solutions and suspensions Generally the sizes are between 1 nm and 100 nm Examples include glues, gelatin deserts, paint, aerosols and smoke Define heterogeneous- 2 substances can be separated Whipped cream, marshmellows, milk Appear cloudy maybe even clear if very dilute, will not settle out Cannot be filtered with paper filters (like coffee filters)

Colloids Tyndall effect - the scattering of light in all directions. Suspensions also exhibit this effect, but solutions do not. Fog, ever turned on headlights in fog seen everything light up? That is the tyndall effect H2O constant motion hitting colloid and causing them to move as well Called brownian because it was discovered by Robert Brown-Scottish Botanist

Colloids Brownian motion – the chaotic movement of colloidal particles. Under a microscope the particles seem to be moving about erratically. Example

Emulsions Emulsion – a colloidal dispersion of liquids in liquids. Emulsifying agents are used to keep the emulsion stable. Soap and detergents are good emulsifying agents Mayonnaise is an emulsion. Know the main ingredients? How emulsifying agents work- one polar end 1 not polar end Ex: oil is attracted to non polar end water attracted to polar end Vinegar, oil, egg yolk

Review What is the purpose of a surfactant? To decrease surface tension by disrupting h-bonds

Review What type of process is the freezing of water? Exothermic, heat is released

Review What type of molecule is water? Nonpolar/polar/ionic

Review What types of compounds dissolve in water? Polar/ionic

Review Which of these compounds would dissolve in water? CH4 NH3 NaNO3 N2

Review What is solvation? Process that occurs when a solute dissolves

Review In the hydrate CuSO45H2O how many water molecules would be present in 3 formula units? 15

Review In the hydrate CuSO45H2O how many hydrogen atoms would be present in 3 formula units? 30