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CH104 Lab 10: Solubility (F15) 127

LAB 10: SOLUBILITY: SOLUBILITY RELATIONSHIPS OF SALTS AND GASES

PURPOSE: To observe and describe with net ionic equations the formation of insoluble salts. To measure the solubility of KNO3 at various temperatures and graph a solubility

curve.

To derive from experiment the relationships between Pressure (P), Temperature

(T), and Water Solubility of gases.

SAFETY CONCERNS: Always wear safety goggles. Handle and dispose of broken glass safely.

SOLUBILITY:

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 (BaSO4) 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+

, NH41+

,

Na1+

, NO31-

K1+

, C2H3O21-

Except

Salts with

OH1-

,

CO32-

, S2-

,

PO43-

Most Chlorides,

Cl1-

Except

AgCl, Hg2Cl2, PbCl2,

Most Sulfates,

SO42-

Except

CaSO4 PbSO4

SrSO4

BaSO4,

Table of Common Solubilities:

NO31-

C2H3O21-

Cl1-

SO42-

OH1-

CO32-

S2-

PO43-

Li1+

S S S S S S S S

Na1+

S S S S S S S S

K1+

S S S S S S S S

NH41+

S S S S S S S S

Ca2+

S S S I I I I I

Sr2+

S S S I I I I I

Ba2+

S S S I I I I I

Pb2+

S S I I I I I I

Ag1+

S S I S I I I I

Hg1+

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) AgCl(s) + NaNO3(aq)

Soluble Salts Insoluble Salt

Total Ionic Equation: (Shows all ions present)

Na1+

(aq) + Cl1-

(aq) + Ag1+

(aq) + NO31-

(aq) AgCl(s) + Na1+

(aq) + NO31-

(aq)

Net Ionic Equation: (Shows only the reaction that has occurred)

Ag1+

(aq) + Cl1-

(aq) 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) as T where gases are less

soluble (S) as T),

pressure (most solids and liquids are not affected by pressure but gases are more soluble (S) as P)

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 (O2), Nitrogen (N2), or Carbon Dioxide (CO2) 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.


PROCEDURES: ACTIONS:

I. SOLUBLE & INSOLUBLE SALTS: 1. Obtain dropper bottles of 0.1 M aqueous solutions

1 of

NaCl, Na2SO4, Ba(NO3)2, AgNO3, Na3PO4, CaCl2, NaOH,

and Na2CO3.

2. Obtain a transparent spot plate and place it over a dark or

colored background. 2

3. Choose a pattern of wells on your spot plate similar to that

shown3 and place drops of the following solutions:

Into the 1st column of 5 wells place 3 drops of silver

nitrate, AgNO3, solution.

Into the 2nd

column of 5 wells place 3 drops of barium

nitrate, Ba(NO3)2, solution.

Into the 3rd

column of 5 wells place 3 drops of calcium

chloride, CaCl2, solution.

4. Make mixtures by adding 3 drops of the following solutions

to those already in the wells. Observe any insoluble salts

formed and report your observations. (Column I3.)

1. To the AgNO3, add sodium chloride, NaCl.

2. To the AgNO3, add sodium sulfate, Na2SO4.

3. To the AgNO3, add sodium hydroxide, NaOH.

4. To the AgNO3, add sodium carbonate, Na2CO3.

5. To the AgNO3, add sodium phosphate, Na3PO4.

6. To the Ba(NO3)2, add sodium chloride, NaCl.

7. To the Ba(NO3)2, add sodium sulfate, Na2SO4.

8. To the Ba(NO3)2, add sodium hydroxide, NaOH.

9. To the Ba(NO3)2, add sodium carbonate, Na2CO3.

10. To the Ba(NO3)2, add sodium phosphate, Na3PO4.

11. To the CaCl2, add sodium chloride, NaCl.

12. To the CaCl2, add sodium sulfate, Na2SO4.

13. To the CaCl2, add sodium hydroxide, NaOH

14. To the CaCl2, add sodium carbonate, Na2CO3.

15. To the CaCl2, add sodium phosphate, Na3PO4.

5. Write the ions that are present in each of the two solutions

mixed in each reaction (Column I2.).

6. Using the solubility rules, draw a circle around the ions that

would form an insoluble salt.

7. For any chemical reactions that took place write the net ionic

equations (Column I4) showing the correct formulas for any

insoluble salts formed. Use the symbols (aq) and (s) for

those ions or compounds that are aqueous or solid.

NOTES:

1Verify, using the solubility

tables, that these compounds

are indeed soluble in water.

2In the absence of a

transparent spot plate a

transparent plastic sheet can

be used. Place it on a non-

white background so that the

formation of any white solid

precipitate will be visible.

3Pattern of spot plate wells:

AgNO3 Ba(NO3) 2 CaCl2

NaC

l

1

O 6

O

11

O

Na 2

SO

4 2

O

7

O

12

O

NaO

H

3

O

8

O

13

O

Na 2

CO

3 4

O

9

O

14

O

Na 3

PO

4 5

O

10

O

15

O


II. SOLUBILITY OF POTASSIUM NITRATE, KNO3:

The temperature at which KNO3 is soluble is determined by heating

and cooling a KNO3 solution.

1. Weigh out a portion4 of solid potassium nitrate, KNO3, as

instructed5 on a tared weighing paper or tared container.

2. Report the mass of the potassium nitrate you weighed to the

accuracy of your balance.

3. Place 5.0 mL of water in a large test tube and add your weighed

amount of KNO3.

4. Clamp the test tube of KNO3 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 KNO3 dissolves.

5. As soon as all the KNO3 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 gently7 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. 8

6. 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 closely agree.

7. Set the test tube aside. In 15-20 minutes, observe the

appearance of the crystals in the test tube.

8. To discard, add water and heat until the KNO3 dissolves. Pour

the solution in proper waste container.

9. From your data, express the solubility of KNO3. in g’s per 100

mL water. 9

10. Collect the solubility data obtained by other members of the

class from other sample sizes.

11. On the same grid where you reproduced the text book solubility

curve for KNO3 create another curve using the class solubility

data. (Plot solubility (g KNO3/100 mL water) on the vertical axis (Y) and

the temperature (0-100oC) on the horizontal axis (X).) Distinguish the 2

curves using different colors or symbols or line styles.

4To reduce the amount of

KNO3 used, each group of

students will be assigned to

weigh out an amount of KNO3

from 2 to 7 grams. The results

will be shared with the class. 5Weigh out an amount of

KNO3 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 KNO3 to

obtain exactly 3.00 g. Weigh

carefully and record the actual

mass of your sample to the

accuracy of your balance. 6Heating the solution.

7Without gentle stirring there

is a chance of “super cooling”

where a temporarily

supersaturated solution forms.

If this happens crystals may

not precipitate until a lower

temperature than expected.

8This is the temperature at

which the solution becomes

saturated. The amount of

KNO3 in that solution is the

solubility of KNO3 at that

temperature.

9Solubility 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 5.0

mL of water are both

multiplied by 20.

g KNO3 x 20 = g KNO3

5.0 mL H2O 20 100 mL H2O


PROCEDURES: ACTIONS:

III. HENRY’S LAW: SOLUBILITY VS PRESSURE 8. Pour ice cold

10 carbonated water (CO2 dissolved in H2O)

into a vacuum flask to a level of about 1 inch.

9. Set the tightly stoppered flask in an ice water bath to keep

it cold.

10. Connect the flask to the vacuum source and turn it on full

force. On the report sheet (IIIA) record your

observations. Indicate increasing solubility (Ability of gas

to dissolve) (S) of CO2 gas with up arrows, and

decreasing solubility (S) of CO2 gas with down arrows.

11. Detach the vacuum tubing from the source to allow the

flask to return to atmospheric pressure. Record your

observations. (IIIB)

12. Formulate Henry’s Law by summarizing your results in

the space provided on the report sheet. (IIIE)

PHYSIOLOGICAL APPLICATION: THE BENDS 13. 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)11

Record

your hypothetical results (IIIC).

14. 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? 12

Record your hypothetical results

(IIID)

10

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

CO2. Temperature also affects

solubility of gases in water, so to

change the temperature changes

the experiment.

11

At the atmospheric pressure of

sea level we all have a certain

amount of Oxygen (O2) and

Nitrogen (N2) 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.

12

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 IV3

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”.


IV. SOLUBILITY VS TEMPERATURE As you follow the instructions given in this section you will answer the given question by

practicing the scientific method. Use the example given in the discussion section at the

beginning of the Burners and Flames lab chapter to help you. The question we’ll tackle is:

What is the relationship between the solubility of a gas and the

temperature of the liquid in which it is dissolved? 1. On the report sheet (IVA) make an educated guess, or

hypothesis, to answer the question. Explain why

you came up with the hypothesis you did based on

what you have learned so far or past experiences.

2. Create experimental procedures (IVB/C) to test

your hypothesis.13

3. Perform your experiment and record the results14 on

the report sheet (IVD).

4. Write a conclusion statement (IVE) that sums up

the answer to the original question giving factual

evidence from your experiment to support your

answer.

5. Analyze any potential for errors, and record (IVF)

any hints to achieving reliable results.

PRACTICAL OR PHYSIOLOGICAL APPLICATION: 6. Report a practical application or a physiological

application where this relationship between gas

solubility and temperature might be important. (IVG)

13Your experimental procedures must

be clear enough to be followed by

another person. Be clear about what

results to look for.

Depending on the type of experiment

you choose, you may need to include

a “control” experiment so that you

are confident that you are seeing

solubility and temperature

relationships and not just water

boiling.

14

Be sure that you are correct in the

description of your results. For

example, if your experiment requires

you to look for bubbles escaping are

you sure that the gas bubbles you

see are dissolved gases escaping or

are you just seeing water boil?


LAB 10: SOLUBILITY NAME_____________

PRE LAB EXERCISES: DATE______________

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. ___The correct name(s) for the formula PbSO4 is(are)

A. Plumbous Sulfate B. Plumbic Sulfate C. Lead Sulfate D. Lead (I) Sulfate

3. ___The correct formula for Calcium Nitrate is

A. CaNO3 B. Ca(NO3) 2 C. Ca2NO3 D. Ca3N2 E. Ca(NO2)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. 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 balanced ionic equations for the reaction between silver nitrate and sodium carbonate. Use symbols (aq) and (s) to indicate aqueous and solid components of the equation.

Total ionic equation

Net ionic equation

6. On the grid in part II of your report sheet reproduce the theoretical solubility curve for KNO3 using

the graphed data from the solubility curve in your text.

7. What effect would “super cooling” have on the solubility of KNO3? How can you prevent it?


LAB 10: SOLUBILITY NAME___________________

REPORT: PARTNER_________DATE___

I. SOLUBLE AND INSOLUBLE SALTS 1. Compounds in

Mixture

2. Ions present in

mixture

3. Observations

4. Write the balanced net ionic equation (if none put NR)

1.

AgNO3(aq) + NaCl(aq)

Ag1+

NO31-

Na1+

Cl1-

Observations

Net ionic equation

2.

AgNO3(aq) + Na2SO4(aq)

Observations

Net ionic equation

3.

AgNO3(aq) + NaOH(aq)

Observations

Net ionic equation

4.

AgNO3(aq) + Na2CO3(aq)

Observations

Net ionic equation

5.

AgNO3(aq) + Na3PO4(aq))

Observations

Net ionic equation

6.

Ba(NO3)2(aq) + NaCl(aq)

Observations

Net ionic equation

7.

Ba(NO3)2(aq) + Na2SO4(aq)

Observations

Net ionic equation

8.

Ba(NO3)2(aq) + NaOH (aq)

Observations

Net ionic equation


1. Compounds in

Mixture

2. Ions present in

mixture

3. Observations

4. Write the balanced net ionic equation (if none put NR)

9.

Ba(NO3)2(aq) + Na2CO3(aq)

Observations

Net ionic equation

10.

Ba(NO3)2(aq) + Na3PO4(aq)

Observations

Net ionic equation

11.

CaCl2(aq) + NaCl(aq)

Observations

Net ionic equation

12.

CaCl2(aq) + Na2SO4(aq)

Observations

Net ionic equation

13.

CaCl2(aq) + NaOH(aq)

Observations

Net ionic equation

14.

CaCl2(aq) + Na2CO3(aq)

Observations

Net ionic equation

15.

CaCl2(aq) + Na3PO4(aq)

Observations

Net ionic equation

Summary & Conclusions: Complete the following solubility table using Theoretical value (THR) and

your own Experimental (EXP) results. Use S for soluble, and I for insoluble. Circle any unexpected results:

NO31-

Cl1-

SO42-

OH1-

CO32-

PO43-

THR EXP THR EXP THR EXP THR EXP THR EXP THR EXP

Na1+

S S S S S S

Ca2+

S

Ba2+

S

Ag1+

S

Explanation/Analysis: Were your results as expected? Explain specifics.


II. SOLUBILITY OF KNO3: Group Names:

Circle your own

Actual Mass KNO3 used Temperature (crystals appear)

Solubility ( g KNO3/100 mL H2O)

2g.

3g.

3.5g.

4g.

4.5g

5g.

5.5g

6g.

6.5g

7g.

Solubility Curve for KNO3

So

lub

ilit

y (

g K

NO

3/1

00

mL

H2O

)

200

150

100

50

0

0 25 50 75 100

Temperature (oC)

Summary:

1.___ The solubility of KNO3 in water _____ as the temperature increases.

A. decreases B. increases, C. does not change

Explanation/Analysis: How does your solubility curve compare to that of KNO3 presented in your textbook? Explain.


III. HENRY’S LAW: SOLUBILITY VS PRESSURE

Action Observations Effect on

Pressure P or P

Effect on

gas

Solubility S or S

A. Vacuum source turned on

with carbonated solution in

flask.

B. Vacuum hose detached

with carbonated solution in

flask.

C. A diver is deep in the

ocean with gases dissolved in

the blood

Imagine what you would see.

D. A diver, deep in the ocean

with gases dissolved in the

blood, comes rapidly to the

surface.

Imagine what you would see.

E. Conclusion: 1.___ The solubility of a gas in water (the ability of a gas to dissolve) _____ as the pressure _____.

A. decreases, increases B. increases, increases. C. does not change, changes

2.___ Henry’s Law: The solubility of a gas ____________ the pressure.

A. varies directly with B. varies inversely with C. is unrelated to

Explanation/Analysis: Were your results as expected? Explain specifics.


IV. SOLUBILITY VS TEMPERATURE

QUESTION:

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. Hypothesis: (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. Experimental Procedure: (Give details that others could follow; include instructions for what to look for and how to

determine if your experiment is accomplishing your goal.) 1.

2.

3.

4.

C. Experimental Control: If your experiment requires you to look for bubbles escaping how will you insure that the gas bubbles you see are

dissolved gases escaping and not just water boiling? If your experiment requires you to look for gases filling a balloon how will you insure that the

inflation of a balloon is from dissolved gases escaping and not just hot gases expanding (Charles Law)?

D. Results:

Action Observations Effect on

Temperature

T or T

Effect on gas

Solubility

S or S

E. Summary/Conclusion: 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:______________________________________

F. Explanation/Analysis: (Give warnings or advice for modifications to your experiment. Give potential for errors. Explain)

G. Practical or Physiological Application: (Where might this temperature/solubility relationship be observed in nature, health, or

everyday life?)


LAB 10: SOLUBILITY NAME____________

RELATED EXERCISES:

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 KNO3 with temperature.

C. The variation of solubility of CO2 with pressure.

D. The variation of solubility of CO2 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.

5. A. The solubility of sucrose (common table sugar) at 70oC is 320 g/100 g H2O. How much sucrose

(a common carbohydrate) can possibly dissolve in a cup of tea (about 240 g of water) at 70oC?

(Show calculations and circle your answer.)

B. How many Food Calories (kcals) would the cup of tea in part A provide? (Show calculations and

circle your answer.)

C. A can containing 355 mL of soft drink contains 42 g sugar (sucrose). How many Food

calories would come from drinking this soda? (Show calculations and circle your answer.)

REFERENCE SEARCH: 6. A. Solubility is not an all or nothing concept but rather every substance has degrees of solubility. Substances in which a

“high” number of grams will dissolve in 100 mLs water are labeled soluble (S). Substances in which a “low” number of

grams will dissolve in 100 mLs water are labeled insoluble (I). Use the CRC Handbook to look up solubility data that would complete the table. Record the solubility

and label S or I.

Solubility of Selected Salts (g/100 mL) in cold water

NO31-

Cl1-

SO42-

OH1-

CO32-

PO43-

Ca2+

121.2 = S

B. How does the CRC solubility information compare to your results in Part I? At what point do you think

compounds are considered to be soluble or insoluble? Explain

lab 10: s - chemeketa community college faculty web …faculty.chemeketa.edu/jcammack/ch104/ch104...

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