Academic Chemistry
Solutions
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Scratch Paper For Warm Up Activities
Solutions & Water Notes
Water (H2O) – a unique compound
- Lewis dot structure
- EN for O ® 3.5
H ® 2.1
- bent shape, polar molecule
- STRONG hydrogen bonds between water molecules
- explains high boiling point, high heat of vaporization, and high surface tension
- density of liquid water to ice (not typical)
temp. density
(°C) (g/cm3)
100 0.9584
50 0.9881
25 0.9971
10 0.9997
4 1.000*
water 0 0.9998
ice 0 0.9168
Aqueous solutions – water samples containing dissolved substances (solid, liquid, or gas)
Solution has 2 parts:
1. Solvent – dissolving medium, substance in greater
amount, usually liquid (H2O is most common)
2. Solute – substance being dissolved, substance in
lesser amount, usually solid
Solvation – process that occurs when a solute dissolves
Prediction of whether solubility will occur:
“like dissolves like”
Water is a POLAR compound, so
(one end “-“, one end “+”)
Notes Solubility
Solute
Ionic / PolarCovalent / Nonpolar
Covalent
soluble*
electrolyte / soluble
nonelectrolyte* / insoluble
nonelectrolyte
Electrolyte – compound that conducts an electric current in aqueous solution or the molten state
Can an aqueous solution be made with CCl4?
No – CCL4 is Nonpolar covalent;
Insoluble
What is solubility?
The number of grams of solute that dissolves in a given quantity of a solvent (usually 100 g) at a given temperature to produce a saturated solution
Factors affecting solubility (how much solute dissolves)
1. Temperature – generally, solubility with rise in T (gases are opposite)
2. Nature of solute or solvent
3. Pressure (for gases) – only a factor for gases, pressure results in solubility of a gas in a liquid (ex. soda pop)
CO2 in solution stays as long as soda is under pressure.
Explains how sodas go “flat” if left open.
Factors affecting RATE of solubility (how fast solute dissolves)
1. Stirring (agitation) – more contact with surface of solute
2. Temperature – greater kinetic energy, more collisions
3. Particle size – finer particles expose more surface area so faster dissolving
Solutions Homework # 1
1. Describe the hydrogen bonding between molecules in water.
+ Hydrogen atoms are attracted to – oxygen atoms
2. Explain why water has a relatively high boiling point and heat of vaporization.
Because of Strong Hydrogen Bonding between molecules
3. What is the difference between the structure of liquid water and the structure of ice?
Water is not connected when it is a liquid but when it is
Ice it looks like this:
How does this explain why ice floats in water?
Empty space between molecules gives ice a lower density than liquid water
4. What is the significance of the statement “like dissolve like”?
Polar compounds dissolve polar compounds
Nonpolar compounds dissolve nonpolar compounds
What does the “like” refer to?
Solvent and Solutes
5. Distinguish between an electrolyte and a nonelectrolyte.
Ionic compounds are electrolytes and conduct electricity
Covalent compounds are nonelectrolytes and do not conduct electricity
Give an example of each.
Salt NaCl = Electrolyte Sugar C6H12O6 = Nonelectrolyte
6. Identify the solvent and the solute in vinegar, a dilute aqueous solution of acetic acid.
H2O = Solvent Acetic Acid = Solute
7. Distinguish among a solution and an aqueous solution.
Aqueous is when water is used as the solvent.
Solution anything can be used as the solvent.
8. Name three factors that influence the rate at which a solute dissolves in a solvent.
Stirring, Temperature, Particle Size
9. Use the solid substances listed in Table 18.1 (next page in your packet) to complete this general statement relating a change in the solubility of a solid to a change in temperature.
As temperature Increases solubility of a solid in a liquid Increases
10. What is the effect of pressure on the solubility of gases in liquids?
As pressure increases solubility of a gas increases.
Section 18.1 Notes
Properties of Solutions
miscible – when two liquids dissolve into each other (water and alcohol)
immiscible – two liquids that are not soluble in each other (water and oil)
As T , can dissolve more and more solute (except gases)
1) saturated solution – contains the maximum amount of solute for a given amount of solvent at a constant T
2) unsaturated solution – contains less solute than a saturated solution
3) supersaturated solution – a solution that contains more solute than it should theoretically continue to hold at a constant T (when a saturated solution slowly cools and crystallization does not immediately occur)
Solubility Tables – provide solubility data at various T
Questions:
1. Do the last three substances in the Table 18.1 increase or decrease their solubility in water as temperature increases? Why? Decrease, because they are Gases
2. Is a solution of 45 grams of KCl dissolved in 100 grams of water at 50 °C unsaturated, saturated, or supersaturated? Super Saturated
3. Is a solution of 222.0 grams of AgNO3 dissolved in 100 grams of water at 20 °C unsaturated, saturated, or supersaturated? Saturated
4. Is a solution of 3.5 grams of KClO3 dissolved in 100 grams of water at 0 °C unsaturated, saturated, or supersaturated? Unsaturated
5. Which solute has the highest solubility at 20 °C?
Sucrose
6. Which solute has the highest solubility at 50 °C?
Silver Nitrate
Notes Solubility Graphs – provides saturation curve with unsaturated and supersaturated regions easily identifiable
Questions (Graph on Left):
1. What solute dissolves best when the water is 60 °C?NaNO3
2. What solute has the lowest solubility at 60 °C?
Yb2(SO4)3
3. How much NH4Cl dissolves in 100 mL of water that is 65 °C?
50 g
4. How much KBr will dissolve in 500 mL of water that is 45 °C?
70 x 5 = 350 g
5. If you stir 150 grams of KNO3 in 100 mL of water that is 70 °C, will all of it dissolve?
NO
6. If you stir 200 grams of NaNO3 in 100 mL of water that is 45 °C, how many grams of it won't dissolve?
100 g
7. How many grams of NaCl dissolve in 200 mL of water that is 50 °C?
35 x 2 = 70 g
8. You have 100 grams of KNO3 in 100 mL of water at 100 °C. Is this an unsaturated, saturated, or supersaturated solution?
Unsaturated
9. If you only had 50 ml of water as a solvent, how many grams of solid NaCl could you dissolve in 100 °C water?
30 / 2 = 15 g
10. How many grams of sodium nitrate would be needed to saturate 100 mL of water at 65 °C?
100 g
11. A test tube with 85 g of KNO3 in 100 mL of water at 40 °C would look clear (unsaturated), clear (saturated), cloudy, or similar to green Kool-Aid?
Super saturated
Questions (Graph on Right):
1. How does solubility change with temperature for gases? Is this a direct or inverse relationship?
Inverse Temperature increases solubility decreases
2. Use the Kinetic Molecular Theory to explain the behavior of all 3 of these gases at 100 °C.
Molecules move faster and gases do not mix
Home work # 2 INTERPRETING A GRAPH OF SOLUBILITY DATA
1. What is the solubility of KNO3 at 30oC?
45 g
2. What is the solubility of KNO3 at 70oC?
125 g
3. How many grams of KCl will dissolve in 200.0 grams of water at 45oC?
84 g
4. How many grams of NaNO3 are required to make a saturated solution in 100.0 g of water at 70oC?
125 g
5. How many grams of NH4Cl will dissolve in 50.0 grams of water at 70oC?
30 g
6. At what temperature will a saturated solution of SO2 hold 20 grams of solute?
5 °C
7. What change occurs in the solubility of LiCl as the temperature of the solution increases?
Solubility Increases
8. Will the solubility of KI increase or decrease with a decrease in temperature?
Decreases
Home work # 2 INTERPRETING A GRAPH OF SOLUBILITY DATA
9. State whether the following are saturated or unsaturated solutions.
50.0 g of KCl in 100.0 g of water at 80oC Saturated
135 g of KI in 100.0 g of water at 90oC Super Saturated
40.0 g of NaNO3 in 50.0 g of water at 10oC Saturated
35.0 g of NaCl in 100.0 g of water at 80oC Un Saturated
10. What happens to a saturated solution of KCl at 30oC when it is heated to 40oC?
Goes from 38 g to 40 g
11. The graph for NaCl is practically a straight horizontal line. What does this mean about
the solubility of NaCl?
Does not change with temperature
12. What is the solubility of SO2 at 20oC? 12 g
What is the solubility of SO2 at 90oC? 0.0 g
Did the solubility increase or decrease as temperature increased? Decreased
13. 105 grams of NaNO3 are put into 100.0 g of water at 40.0oC. If more NaNO3 is added, will it dissolve?
NO Why?
It is Saturated
14. At what temperature is the solubility of NaNO3 equal to the solubility of KNO3?
73 °C
15. 25.0 grams of CsCl is placed in 100.0 grams of water at 25.0oC. Will all of the CsCl dissolve?
YES
If not, should the solution be cooled or heated for complete dissolution?
______
16. Will the following number of grams of solute dissolve in 100.0 grams of water at the given temperature?
10.0 grams of KNO3 at 20.0oC YES 10.0 grams of NH4Cl at 10.0oC YES
40.0 grams of KNO3 at 60.0oC YES 10.0 grams of NH4Cl at 20.0oC YES
80.0 grams of KNO3 at 30.0oC NO 1 10.0 grams of NH4Cl at 50.0oC YES
Notes: Section 18.2 – Concentrations of Solutions
dilute solution – one that contains only a low concentration of solute
concentrated solution – one that contains a high concentration of solute
Use MOLARITY to better express concentration of solution
Molarity (M) – number of moles of solute dissolved per liter of solution
M = moles of solute
Liters of solution
Example – 2.5 M HCl means 2.5 mols HCl
1 Liter solution
Problem 1: Find the molarity of a solution that is made by dissolving 0.35 moles of ammonium iodide in 100 mL of solution.
100 mL / 1 L / = 0.1 L / M = / 0.35 mol NH4I / = 3.5 M NH4I1000 mL / 0.1 L
Problem 2: Find the molarity of a solution that is made by dissolving 53.0 g of potassium chloride in 500.0 mL of solution.(convert to liters)
53 g KCl / 1 mol KCl / = 0.71 mol KCl / M = / 0.71 mol KCl / = 1.42 M NH4I74.55 g KCl / 0.5 L
Problem 3: How many grams of sodium chloride are needed to make 1.500 L of a 2.00 M solution?
2.00 M= / mol NaCl / = 3.0 mol NaCl / 3 mol NaCl / 58.44 g NaCl / = 175.32 g NaCl1.5 L / 1 mol NaCl
Problem 4: What volume of 1.25 M sodium hydroxide can be prepared using 60.0 grams of sodium hydroxide?
60 g NaOH / 1 mol NaOH / = 1.5 mol NaOH / 1.25 M = / 1.5 mol NaOH / = 1.20 L NaOH40 g NaOH / ? L NaOH
Dilutions
When diluting, moles of solute DO NOT change!
A solution is diluted by simply adding more solvent.
M1 V1 = M2 V2
M1 = molarity (mols/L) of initial solution
V1 = volume (mL or L) of initial solution
M2 = molarity of new solution
V2 = volume of new solution
Problem 1: How would you prepare 100 mL of 0.40 M magnesium sulfate from an initial solution of 2.0 M magnesium sulfate M1 V1 = M2 V2
(2.0 M)V1 = (0.40 M) (0.1 L) V1 = 0.02 L
Or you can use mL
(2.0 M)V1 = (0.40 M) (100 mL) V1 = 20 mL
Problem 2: If you dilute 20.0 mL of a 3.5 M solution to make 100.0 mL of solution, what is the molarity of the dilute solution? M1 V1 = M2 V2
(3.5 M)(0.02 L) = M2(0.1 L) M2 = 0.7 M
Or you can use mL
(3.5 M)(20 mL) = M2(100 mL) M2 = 0.7 M
Homework # 3 Molarity
1. What is the molarity of 250 mL of solution that contains 0.70 mol NaCl?
M = / Moles / = / 0.70 mol / = 2.8 M NaCLLiters / 0.250 Liter
2. How many moles of solute are present in 1.5 L of 0.24 M Na2SO4?
M = / Moles / 0.24 M= / mol / = 0.36 mol Na2SO4Liters / 1.5 Liter
3. How many grams of CaCl2 are in 250 mL of 2.0 M CaCl2 solution?
M = / Moles / 2.0 M= / mol / = 0.5 mol CaCl2 / 110.98 g CaCl2 / = 55.49 g CaCl2Liters / 0.25 Liter / 1 mol CaCl2
4. How many liters of solvent are required to make a 1.3 M KCl solution with 1.0 mol KCl?
M = / Moles / 1.3 M= / 1.0 mol / = 0.76 L KClLiters / Liter
5. What is the molarity of 1.5 L of solution that contains 0.50 mol MgCl2?
M = / Moles / = / 0.50 mol / = 0.333 M MgCl2Liters / 1.5 Liter
6. How many moles of solute are present in 500 mL of 2.0 M KNO3?
M = / Moles / 2.0 M= / mol / = 1 mol KNO3Liters / 0.5 Liter
7. What is the molarity of a solution prepared by dissolving 80.0 grams of NaOH in enough water to make one liter of solution?
80 g NaOH / 1 mole NaOH / = 2 mol NaOH / M = / Moles / = / 2 mol / = 2 M NaOH40 g NaOH / Liters / 1 Liter
8. How many grams of NaBr are required to prepare 500. mL of 4.00 M NaBr solution?