The Water Molecule Kit Activity
Draw your water molecule in the space provided.
Label the hydrogen and oxygen on your water molecule. Describe what happens when your water molecule is brought near the water molecule of someone near you.
Draw a picture of three water molecules interacting in the space provided.
17.1 – Liquid Water and its Properties
Water has polar bonds due to a difference in electronegativity of ______
Water is a polar molecule and has a bent shape due to lone pair electrons on the central element, oxygen.
Water molecules are attracted to each other by _____________________________.
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 ______________________ shape.
A sphere has the smallest surface area for a given volume.
Water’s surface tension is stronger than most ____________.
Surface tension reduces vapor pressure.
o ________________ – substance that interferes with the hydrogen bonds between water molecules. Surface tension breaks down and the water spreads out.
Specific heat capacity – the amount of energy required to raise the temperature of 1.0 g
of water by 1C. q = mCT
- C = ______________________________________________ - m = ____________________________ ____________ - ∆T = _____________________________________________ - q = ______________________________________________
Water allows for more temperate climates
17.2: Water Vapor & Ice
_________________ – the change of state from a liquid to a gas at the surface of a liquid that is not boiling.
Condensation - the change of state from a gas to a liquid o Water has a high heat of vaporization (____________)
o 2260J of energy are needed to change 1.0 g of water from a liquid to a gas or from a gas to a liquid
o 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.
___________________ – the change of state from a liquid to a solid
CHAPTER 17
& 18: WATER
AND
SOLUTIONS
Draw a watermolecule and label its negative and positive ends.
My water molecule
Draw arrows showing the pull of surface tension on the drop of water below.
Three molecules interacting.
Why would a burn from steam at 100C be worse than a burn from water at 100C?
o Water has a high heat of fusion (334J/g)
o 334J of energy are needed to change 1.0 g of water from a solid to a liquid or a liquid to a solid.
o Density-the ratio of the mass of an object to its volume.
D = m/v or Density = ________________
Review Problems
1. Calculate the heat released when a cup of tea cools from 61C to 25C. The mass of the tea is 225g. (Assume the specific heat of the tea is equivalent to that of water)
2. Calculate the amount of heat needed to boil (vaporize) a kettle filled with water (250g).
3. How much energy is needed to melt 30.0 g of ice at 0⁰C to water at 80⁰C?
4. Which atom in the water molecule is most electronegative? _____________ 5. How are water molecules held together? ___________________________ 6. Water has a ________________ vapor pressure due to __________________. 7. Water has a ____________ heat capacity and a __________ heat of vaporization. 8. Due to high heat capacity and vaporization energy of H2O, coastal areas have
_____________________ temperature.
9. What are the characteristics of surface tension? a. _________________________________ b. _________________________________ c. _________________________________ d. _________________________________
10.A surfactant is a substance that interferes with _____________________ and decreases the _____________________________.
17.3 Aqueous Solutions
Aqueous solution – a water solution containing dissolved substances
__________________ – the dissolving medium.
Solute – particles dissolved in the solution.
Solvation – the process that occurs when a solute ____________ in a solvent
“Like Dissolves Like”
Polar substances dissolve in polar solvents.
What are some benefits of ice floating?
Is the freezing of water endothermic or exothermic?
o H2O: would dissolve things that are ____________________________
Nonpolar substances dissolve in nonpolar solvents
o Gasoline: would dissolve things that are nonpolar like mineral oil
__________________– compounds that conduct an electric current in aqueous solutions or In a molten state
o Includes all ionic compounds
o Some very ______________ molecules dissolve in H2O
Nonelectrolytes – compounds that do not conduct an electric current in either aqueous solutions or the molten state
o ________________________________
o Organic compounds (carbon containing compounds)
o Nonpolar compounds
There are strong and weak electrolytes
o In a strong electrolyte, nearly all the ions dissolve in aqueous solution o Examples: NaOH, HCl and NaCl
o In a weak electrolyte, only very small amounts of ions dissolve in aqueous solution
o Examples: Distilled H2O, ammonia, acetic acid
How electrolytes form:
Water of Hydration – water in a crystal
o When copper (II) sulfate is dissolved in water and then the water allowed to evaporate, copper (II) sulfate pentahydrate is formed
_________________________________________
o _____________ - compound that contains water of hydration
o When cobalt (II) chloride is dissolved in water and then the excess water is allowed to evaporate, cobalt (II) chloride hexahydrate is formed
Practice: Calculate the percent water in CuSO4•5H2O
_______________________ – process in which a hydrated compound loses water to its surroundings.
o Occurs when a substance has a vapor pressure higher than that of water.
Deliquescence – process in which anhydrous or somewhat hydrated compounds ____________ water from the surroundings.
o Occurs when the solution formed has a lower vapor pressure than that of the water in the air
Desiccants – hygroscopic (water absorbing) substances that are used as drying agents.
o Small silica gel packets used in electronic merchandise shipping
o Sodium hydroxide is deliquescent and becomes a solution quickly (dissolves itself) when exposed to water in the air
Write soluble next to the compounds listed below that would dissolve in water.
Gasoline ____ Salt ____ Alcohol ____ Vegetable oil ____
In the hydrate CuSO45H2O
how many water molecules would be present in 3 formula units? ________
17.4 Heterogeneous Aqueous Systems
____________________ – mixtures from which particles settle out upon standing. o Suspensions have particle sizes larger than solutions
o Generally the sizes are larger than ________ o The particle size in a solution is about 1 nm
_________________________ is a good example
Colloids – heterogeneous mixtures containing particles that are intermediate in size between solutions and suspensions
o Generally the sizes are between1 and 100 nm
o Examples include __________, ____________, paint, aerosols and smoke o _______________________ - the scattering of light in all directions.
Suspensions also exhibit this effect, but solutions do not.
o Brownian Motion – the chaotic movement of colloidal particles. Under a microscope the particles seem to be moving about erratically.
Emulsion – a colloidal dispersion of liquids in liquids.
o Emulsifying agents are used to keep the emulsion _____________. o Soap and detergents are good emulsifying agents
o Mayonnaise is an emulsion. Do you know the main ingredients?
Factors affecting rate of solution:
1. Agitation -brings fresh solvent in ______________ w/ solute -does not affect the amount of substance that dissolves
2. Temperature -heat increases rate of solution by increasing kinetic energy and motion of particles
3. Particle size -smaller particles dissolve _________ because of greater surface area
Solubility - a measure of the amount of solute that will dissolve in a given amount of solvent.
- we usually use ________________________ solvent
Factors affecting solubility:
1. The nature of the solute and solvent a. “Like dissolves like”
2. The temperature
a. Most solids become more soluble at a higher temperature. A few become _________________________.
b. The solubility of a gas decreases as temperature increases. 3. Pressure (for solutions of gases in liquids)
a. increasing ________________ increases the solubility of a gas
Saturated solution -contains the maximum amount of solute that will dissolve in a given amount of solvent at a given temperature.
_______________________ solution- more solute could be dissolved -indicated by no solid present
Supersaturated solution- more solute is dissolved than is theoretically possible at a given temperature.
Describe the following as solutions, suspensions, colloids, or emulsions. Paint ______ Italian dressing _______ Jello _______ Milk _______ Tea _______ Kool-aid _____
What would dissolve faster? -a cube of sugar -granulated sugar -powdered sugar
EXAMPLE:
How could you determine if a solution is saturated, unsaturated or supersaturated? ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________
Miscible - liquids that are soluble in each other -Ex. Ethanol and water
Immiscible- liquids that are insoluble in each other -Ex. Oil and water
Henry’s Law- At a given temperature, the solubility of a gas in a liquid is proportional to the pressure of the gas above the liquid
EXAMPLE:
At 25oC, the solubility of a certain gas in H
2O is 0.75 g/L of H2O at a pressure of 1.0 atm.
What is the solubility of the same gas at 10.0 atm pressure?
Concentration -a measure of the amount of solute per given amount of solvent or solution.
Measured in units of molarity
Dilute solution- Contains a small amount of solute
Concentrated solution- Contains a large amount of solute
Molarity (M): moles of solute Liters of solution
A 1 M solution contains 1 mole of solute per 1 L of solution. A 0.5 M NaCl solution has 0.5 mol NaCl in 1 L total solution.
EXAMPLES:
What is the concentration in molarity of a solution made with 1.25 mol NaOH in 4.0 L of solution?
Dilutions
Diluting a solution won’t change the number of moles of solute. It only changes the concentration.
M1V1 = M2V2
This formula works only for dilution of a solution!!!! Do not use this formula for a reaction!!!!
How would you make 500. mL of 6.0 M NaOH from 12.0 M NaOH?
Which of the following would be miscible in a polar solvent? HCl
NaOH Gasoline MgBr2
Sugar Olive oil LiCl
Pressurized CO2 is pumped
into three cans of soda. The first can is at 10ºC, the second is at 20ºC and the third is at 50ºC. In which can will the most gas dissolve and why?
S1 = S2 P1 = P2
A student measures 58.5 g of NaCl and dissolves it into 1.0 liter of water. What is the molarity of the solution?
How many grams of NaOH would be necessary?
EXAMPLE:
For a lab we need 500. mL of 4.25 M HCl. Concentrated HCl is 12.0 M. How do we make up the solution?
Add _________ of concentrated HCl to enough water to make ______ total solution.
Solution Stoichiometry
-use Molarity as a conversion factor
EXAMPLES:
What volume of 0.246 M nitric acid is required to react completely with 0.386 L of 0.0515 M Ba(OH)2?
Calculate the number of grams of carbon dioxide that can react with 0.135 L of a 0.357 M solution of potassium hydroxide, according to the following reaction:
% Solutions
Percent by volume % v/v = volume of solute (ml) x 100
volume of solution (ml)
Percent mass/volume % m/v = mass of solute (g) x 100 volume of solution (ml)
EXAMPLES:
Rubbing alcohol is 70.0% isopropyl alcohol by volume. How many mL of isopropyl alcohol are in a 250 mL bottle of this solution?
If the % mass/volume (m/v) for a solute is 6.80 %, and the volume of the solution is 42.6 mL, what mass of the salt is present?
1L # mol # mol