Lab: Solubility Curve of Magical Mystery Salt



Name: ____________________________________________ Lab Grade: _________

Date Due: ________________Lab Partners: ________________________________

Lab: Solubility Curve in Water of the Magical Mystery Salt

Purpose: to identify an unknown salt by creating a solubility curve and comparing the data to the solubility curves on Reference Table G.

Introduction:

How will the solubility curve be generated? First, measure out a mass of solute, then add the solute to a measured mass of water. In this experiment, 10.0 grams of water will be used. The salt doesn’t dissolve entirely? No problem! Heat the salt up in a water bath. Eventually, the amount of precipitate will diminish until precipitate is all gone! Then the test tube will be removed from the hot water bath and the test tube with now unsaturated solution will be let to cool. Once the solution cools past its solubility temperature, a precipitate will begin to form in the test tube. This precipitation or crystallization will look like it’s flurrying inside the test tube. Record the temperature that this first begins to happen! Heat the test tube with the solution up again to dissolve the precipitate and then let the solution cool again to get a second temperature. The two temperatures will be reported to the class by posting. Different groups in the class will be assigned different amounts of solute to use, but all groups will use 10.0 grams of distilled water as the solvent.

Once the solubility data for the class has been gathered, the average of the two temperatures for each group will be calculated and a graph based on the data will be constructed. By comparing the graph’s general shape and specific numbers with those on Reference Table G, the identity of the salt can be determined. The curve on Reference Table G that matches the data the most is the salt!

Prelab Questions: Complete Sentences required (restate the question in the answer- no pronouns)

1) Identify the solvent, which is going to be used in this lab.

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2) The solute, which is going to be used, is a solid. Based on reference table G, explain what should be the relationship, direct or indirect, between the temperature and solubility of the solute.

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3) Initially, not all of the solute will dissolve in the 10.0 mL of the solvent. What will be done to dissolve in order to dissolve all the solute?

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4) An unsaturated solution can be made saturated by either adding more solute or cooling down the solution. Which method will be used in this lab?

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5) What change in the solution will indicate that the solution is now saturated?

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6. How will the identity of the Magical Mystery Salt be determined?

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Materials:

|Balance |Plastic spoon |Bunsen burner or hot plate |Test tube |

|Test tube holder |test tube clamp |test tube rack |weigh boat (2) |

|400 mL beaker |thermometer |ring stand |iron ring (2) |

|10 mL graduated cylinder |wire gauze |beaker tongs |goggles |

|assigned mass of Magical Mystery Salt |10.0 mL distilled water | |

|Assigned # of Grams of Magical Mystery Salt | |

Procedure:

1) Grab your goggles and strap ‘em on! Gather your equipment and set it up as shown on the diagram on the next page.

2) Fill the beaker to the 300 mL line with tap water. Set it on the ring stand and begin heating it with the Bunsen burner.

3) Using one of your weigh boats, get a spoonful of mystery salt from the stock container and bring it back to your station. Be careful, as the salt is in the form of pellets, which roll around easily.

4) Weigh the weigh boat and then set the balance ahead by the number of grams you were assigned. Add mystery salt using a spoon until the balance evens out.

5) Place this salt into a DRY test tube.

6) Measure out 10.0 mL of distilled water using the 10 mL graduated cylinder and add it to the salt in the test tube. Remember, the density of water is 1.00 g/mL, so the volume in mL will be equal to the mass in grams. 10.0 mL will weigh 10.0 grams.

7) Place a test tube holder at the top of the test tube and slide the test tube into the somewhat loose test tube clamp that is high on the ringstand. Use the thermometer to stir the salt in the test tube, but do not poke! You might break a hole through the bottom of the test tube if you do. Just stir.

8) The amount of undissolved salt will steadily decrease until it is all gone. Once you can’t see any undissolved salt (the solution is clear), remove the test tube from the hot water bath and let it cool.

9) Eventually the solution will cool enough that precipitate will start to form. Keep a close eye on the bottom of your test tube! A strand of dust does not a precipitate make! When you start to see what looks like light flurries in your test tube, record the temperature. You now have a solution that is saturated!

10) Repeat steps 8-10 to get your second trial in.

11) Average the two trials and put your result on the front board chart with the class results on it.

To make the cooling process work better, use the following chart to see your method of cooling for your given amount of mystery salt:

|Given amount of salt |Cooling Method |

|3 g |Cool the bottom of the test tube by dipping it in an ice water bath. Cool for a few seconds while stirring with the |

| |thermometer, then check for the precipitate. As the temperature decreases, use the ice water less and less. Get a large|

| |beaker filled with ice and water! |

|4 g | |

|5 g |Cool the bottom of the test tube by running cold water from the tap over it. Cool for a few seconds while stirring with |

| |the thermometer, then check for the precipitate. As the temperature decreases, use the water less and less. |

|6 g | |

|7 g |Just let the solution air cool. |

|8 g | |

Reference Table G gives solubility in grams of solute per 100 grams of water. You used 10.0 grams of water. Use a proportion to convert grams of solute per 10.0 grams of water to grams of solute per 100 grams of water.

Solubility Curve of Magical Mystery Salt Data

This page will be turned in with your graph and completed questions on a separate sheet of paper stapled to the back.

Data:

|Assigned grams of salt / 10.0 g|1st Crystallization |2nd Crystallization |Average Crystallization Temperature |Grams of salt |

|of H2O |Temperature (oC) |Temperature (oC) |(oC) |100 grams H2O |

| | | |(X-Axis on Graph) |(Y-Axis on Graph) |

|3.0 g | | | | |

|4.0 g | | | | |

|5.0 g | | | | |

|6.0 g | | | | |

|7.0 g | | | | |

|8.0 g | | | | |

Analysis:

1) Calculate the quantity of mystery salt in 100. g of water for each quantity of the mystery salt used in the lab. Use a proportion. For example: (2.000 g / 10.0 g) = (x g / 100. g)

Show one sample calculation below:

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2) Graph the class data, placing the Temperature (starting at 0oC) on the X-axis and Solubility (starting at 0 g salt / 100 g H2O) on the Y-Axis. Use all of the features that a good graph should have and connect the data points not with straight lines, but rather with a smooth curve.

3) Color your solubility curve, using one color for the line, another color to show the areas of the graph that represents a supersaturated solution and a third color to represent an unsaturated solution. Color lightly.

4) Create a key on the graph to indicate which colors represents a saturated solution , a supersaturated solution and an unsaturated solution

Questions: Complete Sentences required (restate the question in the answer- no pronouns)

1) Based on your data, what is the identity of the magical mystery salt from reference table G?

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2) Using your Solubility Curve for the mystery salt, classify the following solutions as saturated, unsaturated or supersaturated. Explain your answers.

a) 75 g of mystery salt / 100. g of H2O at 40oC

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b) 50 g of mystery salt / 100. g of H2O at 50oC

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3) Using Reference Table G:

a) How many grams of NaNO3 will dissolve in 100.0 g of H2O at 25oC?

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b) How many grams of NaNO3 will dissolve in 200.0 g of H2O at 25oC? Must show work!

4) Using Reference Table G:

a) How many grams of HCl will dissolve in 100.0 g of H2O at 30oC?

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b) How many grams of HCl will dissolve in 50.0 g of H2O at 30oC? Must show work!

5) Using Reference Table G: No sentence required. Must show work!

a) A solution containing 50 grams of KNO3 in 100 grams of water at 60oC is unsaturated. How many grams of KNO3 can be added to make the solution saturated? Must show work!

b) A solution containing 80 grams of KNO3 in 100 grams of water at 30oC is supersaturated. How many grams of KNO3 will precipitate out to make the solution saturated? Must show work!

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