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LL^ ABAB^121 2::^ SS^ OLOLUUBBIILLIITTYY^ ::
SS^ OOLLUUBBIILLIITTYY^ RR^ EELLAATTIIOONNSSHHIIPPSS OOFF^ SS^ AALLTTSS AANNDD^ GG^ ASASEESS
P P UURRPPOOSSEE :: To observe and describe with net ionic equations the formation of insoluble salts.
To measure the solubility of KNO 3 at various temperatures and graph a solubility curve. To derive from experiment the relationships between Pressure (P), Temperature (T), and Water Solubility of gases..
S S AAFFEETTYY CC OONNCCEERRNNSS ::
Always wear safety goggles. Handle and dispose of broken glass safely.
S S OOLLUUBBIILLIITTYY ::
Soluble and Insoluble Salts:
Although many ionic compounds (salts) dissolve in water (are soluble) there are some that do not. These are known as insoluble salts. A slurry of the insoluble salt barium sulfate (BaSO 4 ) is often used in medicine as an opaque substance to help outline the gastrointestinal tract in x-ray images.
The solubility of ionic compounds can be predicted by using the simple rules given in the following tables:
Solubility Rules for Ionic Compounds: Soluble in Water Insoluble in Water Any salt with Li1+^ , NH 4 1+^ , Na1+^ , NO 3 1- K 1+^ , C 2 H 3 O 2 1-^ Å Except
Salts with OH 1-^ , CO 3 2-^ , S 2-^ , PO 4 3- Most Chlorides, Cl1-^ Except Æ
AgCl, Hg (^) 2Cl 2 , PbCl2,
Most Sulfates, SO 4 2- Except Æ
CaSO 4 PbSO (^4) SrSO (^4) BaSO (^) 4,
Table of Common Solubilities: NO 3 1-^ C (^) 2H (^) 3O 2 1-^ Cl1-^ SO 4 2-^ OH 1-^ CO 3 2-^ S 2-^ PO 4 3- Li1+^ S S S S S S S S Na 1+^ S S S S S S S S K 1+^ S S S S S S S S NH 4 1+^ S S S S S S S S Ca 2+^ S S S I I I I I Sr2+^ S S S I I I I I Ba 2+^ S S S I I I I I Pb 2+^ S S I I I I I I Ag 1+^ S S I S I I I I Hg 1+^ S S I S I I I I
When solutions of two soluble ionic compounds are mixed, the formation of an insoluble solid precipitate indicates that a chemical reaction has occurred. A solid forms when the positive ion of one substance in solution, and the negative ion in solution are more attractive to each other than they are to water. For example, mixing solutions of the soluble salts NaCl(aq) and AgNO3(aq) will produce a white solid, which is the insoluble salt AgCl (^) (s).
NaCl (^) (aq) + AgNO3(aq) Æ AgCl(s) + NaNO3(aq)
Soluble Salts Insoluble Salt
Total Ionic Equation: (Shows all ions present)
Na 1+(aq) + Cl 1-(aq) + Ag1+(aq) + NO 3 1-(aq) Æ AgCl (^) (s) + Na1+(aq) + NO 3 1-(aq)
Net Ionic Equation: (Shows only the reaction that has occurred)
Ag 1+(aq) + Cl 1-(aq) Æ AgCl(s)
Solubility Values:
The solubility (ability to dissolve) of a solid in a liquid depends upon the
- polarity of the solute and solvent (like dissolves like) ,
- temperature , (Generally, the dissolving of a solid solute is endothermic, which means that solubility increases with an increase in temperature. So most solids are more soluble ( S K) as T K where gases are less soluble ( S L) as T K),
- pressure (most solids and liquids are not affected by pressure but gases are more soluble ( S K) as P K)
A solution that holds the maximum amount of solute possible at a certain temperature it is said to be saturated. When more solute is added to a saturated solution the excess appears as a solid in the container. The maximum amount of solute that dissolves in a particular solvent is called the solubility. Solubility is usually stated as the number of grams of solute that dissolve in 100 mL ( or 100g) of water. Solubility = g solute or = g solute 100 mL water 100 g water
Solubility of Gases:
Gases, like some solids or liquids, are able to dissolve partially in water. Some gases, such as Oxygen (O 2 ) , Nitrogen (N 2 ) , or Carbon Dioxide (CO 2 ) easily dissolve in water. We say these
are soluble gases. However, some gases such as Helium (He) dissolve only a little bit. Gases
that do not dissolve in water very much are said to be either insoluble or partially soluble depending on just how much does dissolve.
Unlike the solubility of solids or liquids, the ability of gases to dissolve in water ( the solubility
of gases ) changes if either the surrounding pressure or the surrounding temperature changes.
In the laboratory exercises that follow you will discover the relationships between Pressure (P),
Temperature (T) and the Solubility of a gas, and be able to derive Henry’s Law for yourself.
II. SOLUBILITY OF POTASSIUM N ITRATE , KNO 3 : The temperature at which KNO 3 is soluble is determined by heating and cooling a KNO 3 solution.
- Weigh out a portion^4 of solid potassium nitrate, KNO 3 , as instructed^5 on a tared weighing paper or tared container.
- Report the mass of the potassium nitrate you weighed to the accuracy of your balance.
- Place 5.0 mL of water in a large test tube and add your weighed amount of KNO 3.
- Clamp the test tube of KNO 3 to a ring stand and place the test tube in a beaker of water. Use a hot plate or Bunsen burner to heat the water. 6 Stir the mixture and continue heating until all the KNO 3 dissolves.
- As soon as all the KNO 3 dissolves, turn off the burner or hot plate. Loosen the clamp and remove the test tube from the hot water. As the test tube and contents cool, stir gently with a thermometer. Look closely for the first appearance of crystals. As soon as you see some solid crystals, read and record the temperature of the solution. 7
- Place the test tube back into the hot water bath and begin heating again. Repeat the warming and cooling of the solution until you have obtained three or more temperature readings that agree.
- Set the test tube aside. In 15-20 minutes, observe the appearance of the crystals in the test tube.
- To discard, add water and heat until the KNO 3 dissolves. Pour the solution in proper waste container.
- From your data, express the solubility of KNO 3. in g’s per 100 mL water. 8
- Collect the solubility data obtained by other members of the class from other sample sizes.
- Prepare a graph of the solubility curve for KNO 3. Plot the solubility (g KNO 3 /100 mL water) on the vertical axis (Y) and the temperature (0-100oC) on the horizontal axis (X).
(^4) To reduce the amount of KNO 3 used, each group of students will be assigned to weigh out an amount of KNO 3 from 2 to 7 grams. The results will be shared with the class. (^5) Weigh out an amount of KNO 3 that is close to your assigned amount. It does not have to be exact. For example, if you are assigned an amount of 3 grams, measure out a mass such as 3.10 g or 3.25 g or 2.85 g. It is not necessary to add or remove KNO 3 to obtain exactly 3.00 g. Weigh carefully and record the actual mass of your sample to the accuracy of your balance. (^6) Heating the solution.
(^7) This is the temperature at which the solution becomes saturated. The amount of KNO 3 in that solution is the solubility of KNO 3 at that temperature. (^8) Solubility is expressed as the number of grams of solute in 100 mL of water. Because you used a sample of 5.0 mL of water, the mass of the solute you measured out and the 5. mL of water are both multiplied by 20.
g KNO 3 x 20 = g KNO 3 5.0 mL H 2 O 20 100 mL H 2 O
P P ROROCCEEDDUURREESS ::
ACTIONS :
III. HENRY ’S LAW : S OLUBILITY VS P RESSURE
- Pour ice cold 9 carbonated water (CO 2 dissolved in H 2 O) into a vacuum flask to a level of about 1 inch.
- Set the tightly stoppered flask in an ice water bath to keep it cold.
- Connect the flask to the vacuum source and turn it on full force. On the report sheet (IVA) record your observations. Indicate increasing solubility (Ability of gas to dissolve) (S K ) of CO 2 gas with up arrows, and decreasing solubility (S L ) of CO 2 gas with down arrows.
- With the aspirator water still running, detach the vacuum tubing 4 from the sink aspirator to allow the flask to return to atmospheric pressure. Record your observations. (IVB)
- Formulate Henry’s Law by summarizing your results in the space provided on the report sheet. (IVE)
PHYSIOLOGICAL APPLICATION: THE BENDS
- Now that you have discovered Henry’s law, imagine what would happen to the solubility (S) of air (oxygen and nitrogen gases) in the blood (a water solution) of a diver that descends to the depths of the ocean (P K )^10 Record your hypothetical results (IVC).
- Now imagine that the diver in the depths of the ocean quickly rises to the surface. What happens to the atmospheric pressure and what happens to the solubility of gases in the blood? 11 Record your hypothetical results (IVD)
(^9) We keep the solution cold because we want to look at only one condition at a time. We are now looking at the effects of pressure on the solubility of the CO (^) 2. Temperature also affects solubility of gases in water, so to change the temperature changes the experiment. (^10) At the atmospheric pressure of sea level we all have a certain amount of Oxygen (O 2 ) and Nitrogen (N (^) 2) gases dissolved in our blood. When a scuba diver descends to the bottom of the ocean there is a greater amount of atmosphere, including water, pressing down. (^11) When a diver ascends too quickly from a high pressure atmosphere under the ocean, to a low pressure atmosphere at sea level, the change in solubility of the blood gases occurs too rapidly. Imagine that the carbonated beverage in step IV is blood containing dissolved air and that putting it under reduced pressure is similar to the diver rising quickly from the depths of the ocean to the surface. Bubbles in the blood, joints, and muscles cause the diver to bend over in pain with “the bends”.
L L ABAB 121 2:: SS OLOLUUBBIILLIITTYY NN AMAMEE (^) __________________________
PP (^) RREE LL (^) AABB EE (^) XXEERRCCIISSEESS (^) :: DD ATATEE (^) ____________________________
1.___ An insoluble salt is _____ A. an ionic compound that dissolves in water at room temperature. B. an ionic compound that does not dissolve in water at room temperature. C. a covalent compound that dissolves in water at room temperature. D. a covalent compound that does not dissolve in water at room temperature.
2.___ A correct name for the formula PbSO 4 is A. Plumbous Sulfate B. Plumbic Sulfate C. Lead Sulfate D. Lead (I) Sulfate
3.___ The correct formula for Calcium Nitrate is A. CaNO 3 B. Ca(NO 3 ) 2 C. Ca2 NO 3 D. Ca3 N 2 E. Ca(NO 2 ) (^2)
4.___ Which of the following is true about the solubility of substances in water? A. Atmospheric pressure has no effect on the quantity of any substances that will dissolve in water. B. Atmospheric pressure has a large effect on the quantity of a solid that will dissolve in water. C. Atmospheric pressure has a large effect on the quantity of a liquid that will dissolve in water. D. Atmospheric pressure has a large effect on the quantity of a gas that will dissolve in water. E. More than one of these is correct.
5.___ The solubility of sucrose (common table sugar) at 70o^ C is 320 g/100 g H 2 O. Will 400 g of sucrose dissolve in a teapot that contains 200 g of water at 70 o^ C? A. Yes B. No C. Not enough information
- A. Write a balanced chemical equation for the reaction between silver nitrate and sodium carbonate. Use symbols (aq) and (s) to indicate aqueous and solid components of the equation.
B. Write the net ionic equation for the reaction between silver nitrate and sodium carbonate. Use symbols (aq) and (s) to indicate aqueous and solid components of the equation.
1. Compounds in 3. Observations Mixture 2. Ions present in mixture (^) 4. Write the net ionic equation (if none put NR)
- Observations
Ba(NO 3 ) (^) 2(aq) + Na 2 CO3(aq) Net ionic equation
- Observations
Ba(NO 3 ) (^) 2(aq) + Na 3 PO4(aq) (^) Net ionic equation
- Observations
CaCl (^) 2(aq) + NaCl(aq) (^) Net ionic equation
- Observations
CaCl (^) 2(aq) + Na 2 SO4(aq) (^) Net ionic equation
- Observations
CaCl (^) 2(aq) + NaOH(aq) Net ionic equation
- Observations
CaCl (^) 2(aq) + Na 2 CO3(aq) (^) Net ionic equation
- Observations
CaCl (^) 2(aq) + Na 3 PO4(aq) Net ionic equation
Summary & Conclusions: Complete the following solubility table using your own results. Use
S for soluble, and I for insoluble.
NO 3 1-^ Cl 1-^ SO 4 2-^ OH1-^ CO 3 2-^ PO 4 3-
Na 1+^ S S S S S S
Ca
2+
S S
Ba 2+^ S
Ag
1+
S
Error Analysis:
II II.. (^) SS (^) OOLLUUBBIILLIITTYY OOFF KNKNOO (^33) Group Names Actual Mass KNO 3 used Temperature (crystals appear)
Solubility ( g KNO 3 /100 mL H 2 O) 2g.
3g.
3.5g.
4g.
4.5g
5g.
5.5g
6g.
6.5g
7g.
Solubility Curve for KNO 3
0 25 50 75 100
Solubility ( g KNO
3/100 mL H
2O)
200
150
100
50
0 Temperature ( oC) Conclusion: 1.___ The solubility of KNO 3 in water _____ as the temperature increases. A. decreases B. increases, C. does not change
Error Analysis: How does your solubility curve compare to that of KNO 3 presented in your textbook?
IV IV.. SS OLOLUUBBIILLIITTYY VVSS (^) TT EMEMPPEERRAATTUURREE
Q Q UUEESSTTIIOONN ::
What is the relationship between the solubility of a gas (the ability of a gas to
dissolve in water) and the temperature of the solvent in which it is dissolved?
A.A. HH YYPPOOTTHHEESSIISS :: (Do before any experiment is done. Use complete sentences; give rationale based on previous information.)
I believe that as the temperature of a liquid increases the solubility of dissolved gases will _______. I believe this because ………………
B. B. EE XXPPEERRIIMMEENNTTAALL PP ROROCCEEDDUURREE :: (Give details that others could follow; include instructions for what to look for and
how to determine if your experiment is accomplishing your goal. If your experiment requires you to look for bubbles escaping how can you be sure that the gas bubbles you see are dissolved gases escaping and not just water boiling?)
C.C. RR ESESUULLTTSS ::
Action Observations Effect on Temperature T K or T L
Effect on gas Solubility S K or S L
D. D. CC ONONCCLLUUSSIIOONN ::
1.___ The solubility of a gas in water (the ability of a gas to dissolve) ___ as the temperature ___. A. decreases, increases B. increases, increases.
2.___ The solubility of a gas ____________ the temperature. A. varies directly with B. varies inversely with C. is unrelated to
3.___ My original hypothesis was___ A. totally incorrect. B. correct as written. C. correct with the following revisions:______________________________________
E. E. EE RRRROORR AA NNAALLYYSSIISS :: (Give warnings or advice for modifications to your experiment. Give potential for errors.)
F. F. PP RARACCTTIICCAALL OORR PP HYHYSSIIOOLLOOGGIICCAALL AA PPPPLLIICCAATTIIOONN :: (Where might this temperature/solubility relationship
be observed in nature, health, or everyday life?)
L L (^) AABB 121 2:: (^) SS OLOLUUBBIILLIITTYY NN AMAMEE (^) ________________
RR ELELAATTEEDD EE XEXERRCCIISSEESS ::
1.___ Gas being evolved when the cap is removed from a cola drink illustrates B. Boyle’s Law C. Charles’s Law H. Henry’s Law N. None of these
2.___ Which of the following portions of today’s laboratory experiments most illustrates the “bends”? A. The precipitation of an insoluble salt at atmospheric pressure. B. The variation of solubility of KNO 3 with temperature. C. The variation of solubility of CO 2 with pressure. D. The variation of solubility of CO 2 with temperature. N. None of these
3.___ When sea divers who are suffering from the “bends” are transported to the hospital pressure chamber which of the following would be most advisable? A. Apply ice packs to the diver. B. Apply heat packs to the diver.
4.___ When an airplane suddenly looses cabin pressure the pilot will quickly decrease the altitude because decreasing the altitude will ____________ A. increase the temperature and thus prevent the bends. B. decrease the temperature and thus prevent the bends. C. decrease the pressure and thus prevent the bends. D. increase the pressure and thus prevent the bends. E. give the passengers less distance to fall when they have to jump out of the plane.
- A. The solubility of sucrose (common table sugar) at 70o^ C is 320 g/100 g H 2 O. How much sucrose can dissolve in a cup of tea (about 240 g of water) at 70 o^ C? (Show calculations and circle your answer.)
B. How many Food Calories (kcals) would this cup of tea (in part A) provide? (Show calculations and circle your answer.)
R R EFEFEERREENNCCEE SS EEAARRCCHH ::
- A. Use the CRC Handbook to look up solubility data that would complete the table:
Solubility of Selected Salts (g/100 mL) in cold water
Cl
1-
SO 4
2-
OH
1-
CO 3
2-
PO 4
3-
Ca 2+ S 74. Ba 2+
Ag 1+
B. How does this information compare to your results in Part I?
