MATTER- SOLUTIONSChemistry 2012

QUESTION?

What is a solution? How is a solution made? Is it a mixture or a compound? How can we tell the difference?

ENGAGE

In a large test tube or jar, mix 10 mL of sodium silicate (sometimes called water-glass solution) and 40 mL of water. Carefully drop solid-colored crystal compounds of cobalt, copper, nickel, iron, and/or manganese in different locations inside the jar.a) Is there evidence of a change immediately? In

several minutes? In several hours? In several days?

b) Is the phenomenon you see the result of a physical or a chemical change? Explain your answer.

INVESTIGATE- PART 1 Prepare a data table in your Journal There should be 4 columns and 8 rows. One column

for what was done another for what is observed, and the 4th for physical or chemical change. Record your observations. Label each interaction as being a physical or a chemical

change. What are some examples of chemical and physical changes

you encounter in your everyday life?

DATA TABLE 1Reactions Prediction Observations Chemical/Physical

1. Add lemon juice to chocolate milk-

2. Add vinegar to baking soda

3. Add salt to water-

4. Add phenolphthalein to KOH-

5. Add sodium carbonate to sodium hydrogen sulfate-

6. Add copper sulfate to water

7. Add ammonia to copper sulfate-

8. Add vinegar to marble chips or chalk-

MAKE ANOTHER CHART

In your Journal, make a chart. Use an entire page, leaving room to record observations.

Observations: color change and/or formations of precipitate (sometimes observed as a cloudy solution).

DATA TABLE 2

LAB ACTIVITY

Now it is time to mix the solutions. After mixing the pairs of solutions, make note on your chart of any changes you observe.

Complete your data table with your observations. Do not use more than two drops and do not allow the tips of the pipettes to touch the chemicals. If a precipitate forms, record its color in the table in your log by using the notation “Ppt (color).” If no precipitate forms, record “Sol” (for solution) in the table. Notice that the symbol (aq) has been added to the

solutions to indicate that the chemical is dissolved in water (aqueous solution). The symbol (s) has been added to identify the solid precipitate.

BACKGROUND INFORMATION

There are thousands upon thousands of reactions that occur in the world, and most of them take place in water (aqueous) solutions. When certain cations and anions are combined, water-insoluble ionic compounds may form. (Cations are positively charged ions and anions are negatively charged ions.) When these ions are in separate aqueous solutions and then brought together, an insoluble solid, or precipitate forms. The precipitate is an ionic compound (often called a salt) that forms because certain ions attract each other so strongly that they are removed from the water solution as the product of a chemical reaction. A double-replacement reaction is one type of precipitation reaction where a precipitate forms when one of the products is insoluble.

Look at the example of the reaction between solutions of zinc nitrate and sodium carbonate that you observed in the activity:

Zinc nitrate(aq) + sodium carbonate(aq) → sodium nitrate(aq) + zinc carbonate(s)

Zn(NO3)2(aq) + Na2CO3(aq) → 2NaNO3(aq) + ZnCO3(s) Note that (aq) means a compound is in aqueous solution, and (s) means that a solid has formed (the precipitate).

SIMPLE RULES FOR SOLUBILITY OF COMPOUNDS IN WATER

1. Most nitrate (NO3–1), acetate (CH3COO–1), and perchlorate (ClO4

–1) compounds are soluble.

2. Group 1A metal (Li+1, Na+1, and K+1) and ammonium (NH4+1) compounds are

soluble. 3. Most chloride (Cl–1), bromide (Br–1), and iodide (I–1) compounds are soluble. The

most notable exceptions are when these anions are combined with Cu+1, Ag+1, Pb2+, Hg2+, and Hg2

2+.

4. Most sulfate (SO42–) compounds are soluble, except when they are combined

with Ba2+, Hg22+, Sr2+, and Pb2+. Ca2+ compounds are slightly soluble.

5. Carbonate (CO32–) and phosphate (PO4

3–) compounds are only slightly soluble.

6. Most hydroxide (OH–) compounds are insoluble except when combined with group 1A cations. Ca(OH)2 is slightly soluble. An ionic compound is said to be soluble if a large amount of it dissolves in water. How much

is a “large amount”? Typically, this means a solution with a concentration of at least 0.1 mol/L (mole per liter) at room temperature. An insoluble ionic compound is defined as one that will not dissolve in water, typically producing an aqueous solution of less than 0.001 mol/L at room temperature. A slightly soluble compound falls somewhere between these two boundaries, usually forming a precipitate in water.

ANALYSIS 1. How can mixing two clear solutions produce a solid

material? What is happening at the molecular level? Provide a specific example in your discussion.

2. What experimental data do you have that shows how a pigment can form from a precipitation reaction?

3. Predict the products when the following aqueous solutions are combined; a) copper sulfate plus sodium hydroxide b) potassium iodide plus iron (III) bromide

4. Use the solubility rules to determine which of the following are insoluble in water: a) lithium acetate b) ammonium chloride c) silver bromide

INVESTIGATE PART 3- DEMONSTRATION

Your teacher will show you a solution of sodium acetate in a 250-mL flask. Observe the solution carefully. Your teacher will then add one crystal of sodium acetate to the flask. a) Record your observations in your Active

Chemistry log.b) What happens? Record your observations in

your log.c) Was this a chemical or physical change?

EXPLAIN – QUESTION?

Imagine a situation where two colorless solutions are mixed together. There is no color change, no precipitate is formed, and no gas is released. However, heat is released as the solutions are mixed. Even though dissolving is a physical process, it very often results in a change in temperature, which can be either positive or negative, depending on the solute and solvent. Is this an example of a chemical or physical

change? Explain your choice.

EXPLAIN-CHEM TALK Read the Chem Talk on pp. 436-437 and answer

the following questions:1. What is a physical change? Provide two examples.

What does it mean when substances undergo physical change?

2. Is making a solution a chemical or physical change? Explain your answer.

3. Explain the meaning of a solution, a solute, and a solvent.

4. How do you describe the concentration of a solution?5. Explain the difference between an unsaturated

solution, a saturated solution, and a supersaturated solution.

6. Did you have difficulty at the beginning of this activity in telling the difference between physical and chemical changes? What about solutions?

INVESTIGATE PART 4

What are the factors that affect how a solution is formed?

How would you test the factors?

DATA TABLE

Station Factor being tested

Observations

Copy the data table and use it to perform the investigation.

INVESTIGATE- STATION 1

1. Pour 200 mL hot water into one beaker and 200 mL ice water into another beaker. Add a tea bag to each. a) Record your results. b) Describe the relationship between temperature and

the rate of solution.

INVESTIGATE- STATION 2

2. Prepare two beakers, each containing equal amounts (about 200 mL) of room temperature water. Obtain two sugar cubes. Crush one and leave the other whole. Simultaneously add the crushed cube to one beaker and the whole cube to the other beaker. a) Record your observations. What factor was being

studied? b) Describe the relationship between that factor and the

rate of reaction.

INVESTIGATE- STATION 3

3. Prepare two large test tubes, each containing equal amounts (about 10 mL) of room temperature water. Add a scoop of table salt to each test tube. Using a stopper, place the stopper in only one test tube and shake the solution for 1 minute. a. Compare the two test tubes. Describe your

observation. b. What factor are you testing? Explain how it affects

your solutions.

EXPLAIN- ANALYSIS

1. What is happening at Station 1? What is causing the difference to occur?

2 What is happening at Station 2? What is causing the difference to occur?

3. What is happening at Station 3? What is causing the difference to occur?

Write a ½ page summarizing the factors affecting the formation of a solution.

EVALUATE- THE DIAPER DILEMMA Obtain a sample of diaper material. Determine it’s

mass and record. Place the material from the disposable diaper into a

large beaker. Predict how much liquid the diaper material will be

able to hold. Record your prediction in your Journal.

DIAPER EXPLAIN: POLYMERSodium Polyacrylate- Sodium polyacrylate is a polymer. It is made up of

many (poly) repeating units of a smaller group of elements (the monomer called acrylate).

The polymer is used in disposable diapers Unique property-can absorb more that 800 times

its own mass in distilled water

ELABORATE-LAB REPORT -ROUGH DRAFT

Problem: Which brand is the better diaper? Background Information: (What do you already know

about the absorbency of a disposable diaper?) See if you can find information about how much liquid a typical disposable diaper should hold. How much liquid can a disposable diaper actually hold?

Hypothesis: Hypothesis must be testable Materials: List all materials and equipment necessary

to carry out the experiment. Procedure: List procedures in order. Design an

investigation to measure which diaper can absorb the greatest amount of liquid. Record your procedure in your Journal.

Data table: (Have this set up so that you can easily record all data collected during the experiment)

Analyze your data.

EVALUATE- FINAL LAB REPORT Present your lab in a formal lab report. Write your conclusion: Restate and answer

your hypothesis. Briefly write about the procedure. Was your hypothesis correct? If not, how could the experiment be changed to retest the problem? What may be some sources of error?