Chemistry
Water and Solutions
Century High School
Chemistry Instructors: Moertel, Stroh and Handlon
Name ___________________________________________Hour____
General Chemistry Standards Unit 9 Water & Solutions
I.
I can describe the dynamic process by which solutes dissolve in solvents, and
calculate concentrations including percent concentration, molarity and parts
per million.
A. I can use describe how a polar solvent such as water dissolves an ionic solute (like salt) or
polar solute (like sugar).
B. I can use calculate the percentage by mass of a solute in a solution given the grams of solute
and solvent or by using a solubility graph to determine the grams of solute per 100 grams of
water at a given temperature.
C. I can calculate the molarity of a solute in a solvent given the formula and mass of the solute
and liters of solution.
Unit 9 Review
1. Draw a model of the water molecule and use it to describe how water would dissolve a solute
like potassium iodide.
2. Methanol (CH3OH) is an alcohol that is polar. Why does it dissolve in water? Why doesn’t
methane (CH4) which is not polar dissolve in water? You may use diagrams to explain the
process.
3. Calculate the mass percentage of salt in water which has a solubility of 35.0 grams in 100.0
grams of water.
4. Calculate the Molarity of 47.9 grams of Copper (II) Sulfate (CuSO4) dissolved in 100.0 ml of
water.
5. What is the mass percentage of ammonium chloride if 35.0 grams dissolve in 50.0 grams of
water at 90o C
6. If 26.7 grams of aluminum chloride (AlCl3) are dissolved into 500 ml of solution, what is the
molarity?
7. Why does the solubility of a gas in a water solution go down (like CO2 in pop) when the
solution is heated?
3. Calculate the mass percentage of salt in water which has a solubility of 35.0 grams in 100.0
grams of water.
4. Calculate the Molarity of 47.9 grams of Copper (II) Sulfate (CuSO4) dissolved in 100.0 ml of
water.
5. What is the mass percentage of ammonium chloride if 35.0 grams dissolve in 50.0 grams of
water at 90o C?
6. If 26.7 grams of aluminum chloride (AlCl3) are dissolved into 500 ml of solution, what is the
molarity?
7. Why does the solubility of a gas in a water solution go down (like CO2 in pop) when the
solution is heated?
World of Chemistry Video Questions: Water
1. What is the annual rate of consumption of water per person? What percent is for
agriculture?
2. What are the main uses of water in industry?
3. What is meant by a polar molecule?
4. What is hydrogen bonding?
5. What are some properties of water that are due to hydrogen bonding?
6. What is unusual about the density of ice compared to the density of water?
7. Briefly describe the dissolving process.
8. What generalization may be made about whether or not one material will dissolve in
another?
Water and Solutions
I.
The Molecular Structure of Water
A. Draw the molecular structure of water (H2O). Start by drawing an electron dot diagram of an
oxygen atom (how many outer electrons does it have?). Then bond the two hydrogen atoms to
the oxygen. Remember atoms can bond by sharing a pair of electrons. What is this type of bond
called?
B. Now “build” a model of the water molecule with the model kit. Use a red ball for oxygen and white
ones for hydrogen. How would you describe the shape of the water molecule? Redraw your
structure from Part A like the molecule you built.
II.
Physical Properties of Water
A. “Polarity” – because of water’s structure the molecule has some partial charge to it which makes
the molecule act like a charged particle like a magnet. Answer these questions:
1. What are the two types of electrical charge? _________________ and ______________
2. What are the two “ends” of a magnet?
_________________ and _______________
3. Name a material a magnet will attract ______________________________.
4. Name two materials a magnet will NOT attract. ______________________ and _____________
B. Demonstration – of polarity. Answer these questions from the teacher demonstration:
1. What “charge” is given to the black rod? ________
2. What charge is given to the glass rod? ________
3. How does the ball behave when the black rod is brought near it?
_______________________________
4. How does the ball behave after the black rod is brought near it and touches it?
___________________________
5. How does the ball behave after the black rod touches it and then the glass rod is brought near it?
_____________
6. What happens to the stream of water when the black rod is brought near it?
______________________________
7. Make a prediction of what you think will happen to the stream of water when the glass rod is
brought near it? Then record the observation of what actually happens when the glass rod is
brought near the stream.
8. Describe at least three properties water has because of its “polarity”.
9. What geometry does a water molecule have (linear, tetrahedral, etc.)?
10. Based upon what you know about opposite charges, why do you think water molecules tend to
“stick” together?
11. Draw examples of different ways that two water molecules could be arranged so that they
“stick” together. Draw the models of water.
Lab Activity: The Solution Process
What happens when water dissolves a substance? How is water able to do this? What type of
substances will water dissolve? What types of substances will water not dissolve? These are some of
the questions you will investigate in this lab activity. FOLLOW ALL DIRECTIONS AND WEAR
GOGGLES AT ALL TIMES!
I.
When does 4 + 4 ≠ 8?
1. Use only the equipment on the lab table! Record all observations in the table below.
2. Use the graduated cylinder to measure 4.0 ml of water and place the water into one of the small
test tubes. Leave this for the next step.
3. Measure out 4.0 ml of the methanol in the graduated cylinder. The methanol is a type of alcohol
and this has green food coloring. Then add the 4.0 ml of water from the test tube to the
methanol in the graduated cylinder. Stopper the graduated cylinder and shake.
4. Record the volume in the graduated cylinder in the table on back and your description. Then
rinse out the graduated cylinder (pour the contents down the sink).
5. Now measure another 4.0 ml of water and place into one of the small test tubes.
6. Measure 4.0 ml of liquid paraffin from the small plastic bottle labeled “PW” into the graduated
cylinder. Describe the paraffin in your table.
7. Add the 4.0 ml of water from the test tube to the cylinder. Stopper and shake this. Record the
total volume in the table and your description of the two after mixing them.
8. DISPOSE OF THE PARRAFIN BY POURING IT INTO THE BEAKER IN THE FUME HOOD.
9. Then record your data of the volumes in the spreadsheet below.
Water Description
(4.0 ml)
Methanol Description
(4.0 ml)
Volume after
mixing (ml)
Description after mixing
Water Description
(4.0 ml)
Paraffin Description
(4.0 ml)
Volume after
mixing (ml)
Description after mixing
II. Questions
1. Examine the class results. What happened to the volume when the water and alcohol were mixed?
Did 4 + 4 = 8?
2. Examine the class results. What happened to the volume when the water and paraffin were mixed?
Did 4 + 4 = 8? Which was closer to 4 + 4 = 8, the water and methanol or the water and paraffin? Explain
why?
Lab Activity: The Solution Process Part II
What happens when water dissolves a substance? How is water able to do this? What type of
substances will water dissolve? What types of substances will water not dissolve? These are some of
the questions you will investigate in this lab activity. FOLLOW ALL DIRECTIONS AND WEAR
GOGGLES AT ALL TIMES!
1. Use only the equipment on the lab table! Record all observations in the table.
2. Use the graduated cylinder to measure 4.0 ml of water and place the water into one of the small
test tubes.
3. Measure out A SMALL AMOUNT of copper (II) sulfate [CuSO4] with the blue spatula. Place this
in the 4.0 ml of water. Then stopper and shake the test tube. Record your observations in the table
then rinse out the test tube.
4. Then add 4.0 ml of water into another test tube. Measure out A SMALL AMOUNT of cobalt (II)
chloride [CuCl2] with the blue spatula. Place this in the 4.0 ml of water. Then stopper and shake the
test tube. Record your observations in the table. Then rinse out the test tube.
5. Then add 4.0 ml of water into another test tube. Measure out A SMALL AMOUNT of “salol” with
the blue spatula. Place this in the 4.0 ml of water. Then stopper and shake the test tube. Record your
observations in the table. Then rinse out the test tube INTO THE BEAKER IN THE FUME HOOD!
6. Sit down and complete the table by writing in the other information.
7. Your teacher will then demonstrate the solubility of Iodine (I 2) in water and it’s solubility in the
paraffin. Also the solubility of the copper (II) sulfate in the paraffin will be shown as well. Record all
of your observations in the table.
Part II. Solubility of Solids
Solute Formula
Iodine (I2)
Describe Solubility in
Water
Describe Teacher Demo –
Solubility in Paraffin
Ions (+) and (-) in the
Solution
1. Which solutes dissolved in water?
________________________________________________
2. These solutes were “ionic”. Ionic solutes are composed of a metal ion and nonmetal ion
or group. Use your Periodic Table to write the ions that are present in each ionic solute
in the table.
3. What happened when the paraffin was mixed with water? Does this make a solution?
Which was on top and why.
4. Give an example of a water solution you might find at home and two items that are NOT
soluble you might find at home.
Solubility Curves Questions
1. Write a definition or explanation for each of these terms from the reading in the book:
A. Solute
B. Solvent
C. Saturated
D. Unsaturated
E. Solution
F. Mixture
2. Why does the amount of solute increase as the temperature of the solvent increases for
most solid solutes dissolved in a liquid? Use the model of the molecules behavior to
explain.
3. What type of solute (physical state) has a lesser amount dissolved at a higher
temperature? Explain why using the molecules behavior.
4. Use the solubility graph below to answer these questions. The solubility is the number
of grams of solute dissolved in 100 grams of water.
A. How many grams of KCl dissolve in water at 40 C? __________
B. What mass of NH4Cl saturates 100 g of water @ 70 C? __________
C. Would 50 grams of KNO3 dissolved in 100 grams of water @ 30 C be a saturated or
unsaturated solution? _______________________
5. What temperature must the water be so that 40 grams of CuSO4 dissolve in 100 grams
of water? __________________________
6. How much is the mass percentage of Li 2SO4 @ 90 C? Show work.
7. How much is the mass percentage of KClO3 @ 70? Show all work.
8. How many grams of NaNO3 dissolve in 100 g of water @ 10 C? Then determine how
many grams would dissolve in 50 grams of water. Show all work.
Concentration Units for Solutions
Mass Percentage =
•
Mass of Solute
Total Mass of Solution
(Water + Solute)
Molarity (M)
•
=
Moles of Solute
Volume (L) of Solution
1000 ml = 1 Liter
Steps to Finding Molarity:
•
1. First convert grams of solute into moles.
•
2. Convert volume to Liters of solution.
•
3. Divide Moles of Solute by Liters of Solution.
Example:
What is the Molarity of 20.0 grams of Ca(OH) dissolved into 250 ml of solution? Use a
2
conversion factor to find moles.
1.
Molar mass of Ca(OH) Ca = 40.1 +2 O =32.0 + 2 H = 2.0
2
total = 74.0 grams in 1 mole
2. Setup 20.0 g
x ( 1 mole )
= 20.0
( 74.0 g )
3. Volume = 250 ml x (1 Liter)
= 0.27 moles
74.0
=
0.25 L
(1,000 ml)
4. Molarity = 0.27 moles
0.25 L
= 1.08 M or 1.1 M
Practice:
1. What is the molarity of 185 grams of CrCl dissolved into 500 ml of solution? Show work
4
with a conversion.
2. What is the molarity of 185 grams of FeSO4 dissolved into 100 ml of solution? Show
work with a conversion.
3.
What is the molarity of 95 grams of sodium chloride dissolved in 200 ml of water?
4.
How many grams of NaCl would I need to add to make one liter of 2.5 molar salt
solution?
5.
How many grams of C6H12O6 do I need to make 1 liter of a 3 molar solution with
water?