College Prep Chemistry Core Lab #11

50 points

A Solubility Curve of KNO3

Objective:

To determine how the solubility of a salt, KNO3, varies with temperature.
To prepare a solubility curve from experimental data.
To determine the solubility of KNO3 at 60.0oC.

Pre-Lab:

Define the term precipitate.
When might a precipitate form with regards to solutions?

Hypothesis:

Address Objective 1 in sentence format and Objective 2 with a small-sketched graph.
Determine the solubility of KNO3 in 100 g of water at 60 oC using the solubility curve from your notes. Express this in sentence format.

Procedure:

***CAUTION!! This lab involves using a hot plate, glassware, and handling hot liquids – be sure safety goggles and closed toed shoes are worn for the entirety of the lab procedure.***
Begin heating the water bath. (If you were assigned as the 6 gram group –you will receive alternate directions. Please wait to begin.)
Accurately weigh the amount of solute assigned to your group. Record the exact value into Table 1.
Group 1: 6.00 g (cool in ice water)
Group 2: 11.00 g
Group 3: 15.00 g
Group 4: 20.00 g
Group 5: 25.00 g
Group 6: 33.00 g
Pour the measured KNO3 into a clean test tube.
Add 25 mL of water to the test tube and put the test tube in the water bath.
Stir, very carefully, with a thermometer until the solute completely dissolves. Continue heating for a short while longer.
Remove test tube from the water bath and allow the solution to begin cooling.

Stir constantly and note the exact temperature at which the crystals first appear.
Record this temperature in Table 1. This completes the first trial.

Repeat steps c-g for trial 2.
When finished, turn off/ unplug hotplate, wipe off lab bench, and rinse all glassware with water and set to dry.

Data:

Table 1: Group Data of Precipitate Formation

Mass of Sample (g) / Temperature When Precipitate Forms (oC)
Trial 1
Trial 2
Median

Table 2: Class Data for Precipitate Formation

Mass of KNO3 / 25 g of H2O / Mass of KNO3 / 100 g H2O / Temperature Precipitate Forms (oC)

Analysis:

Construct a full-page graph of Mass KNO3/ 100 g of H2O as a function of Temperature with point protectors. (Hint: You’ve seen graphs like this already.)
Construct a smooth curve connecting all the data points.
Extrapolate to the temperature limits using a dotted line.
Determine the solubility of KNO3 in 100 g of water at 60 oC from the graphed data. (Experimental value)

Calculate percentage error. (formula, substitution, labeled answer)

Results:

Identify and report (1) the class value for the solubility of KNO3 in 100 g of water at 60 oC and also (2) the actual value for the solubility of KNO3 in 100 g of water at 60 oC (from reference chart)
Report percent error
Sentence format

Conclusion:

See rubric for guidelines

RST:

In this lab, you determined the solubility curve of KNO3. You will analyze your data and results (Source A), the information in the paragraph below (Source B), and Table 1 (Source C) to gather information and formulate a written explanation of why these deposits form in the boilers.

Source B: Excerpt from Chemistry Matters 2012

Boilers are sometimes used to heat large buildings. Boilers heat large amounts of tap water, which is often filled with a variety of minerals or other chemicals, to high temperatures. Deposits of substances such as calcium carbonate, CaCO3, will precipitate out of the water as it heats within the boiler and hinder the operation of the boiler. Aqueous solutions of hydrochloric acid are commonly used to remove these deposits.

Source C: Solubility Table (www.intro.chem.okstate.edu)

Ion / Solubility / Exceptions
NO3– / soluble / None
ClO4– / soluble / None
Cl– / soluble / except Ag+, Hg22+, *Pb2+
I– / soluble / except Ag+, Hg22+, *Pb2+
SO42- / soluble / except Ca2+, Ba2+, Sr2+, Hg2+, Pb2+, Ag+
CO32- / insoluble / except Group IA and NH4+
PO43- / insoluble / except Group IA and NH4+
OH– / insoluble / except Group IA, *Ca2+, Ba2+, Sr2+
S2- / insoluble / except Group IA, IIA and NH4+
Na+ / soluble / None
K+ / soluble / None
NH4+ / soluble / None

College Prep Chemistry Core Lab #11

50 points

A Solubility Curve of KNO3

Format 5 points

Written in pencil (1)
Underline appropriate titles (1)
Use appropriate units throughout and significant digits (1)
Title all tables, graph, and figures (1)
Tables and graphs are drawn with straight edge (1)

Introduction, Hypothesis and Pre-Lab ______7 points

Restate the objective and incorporate how the objective was met by performing this lab (3)
Discuss how solubility varies with temperature
Definition(s)

Pre-lab defined and answered correctly (2)
Hypothesis written appropriately (2)

Data /Analysis 16 points

Table 1 and 2 completed appropriately (4)

Full page graph (solubility curve) (6)
Scaled axis, labels , Titles
Trend line

Solubility at 60oC marked and recorded on graph (4)

Percent Error (2)
Formula, substitution, and answer

Results 5 points

Identify and report the class value and experimental value for the half-life (2)
Report percent error (2)
Sentence format (1)

Conclusion 7 points

Address the objective. Support your answer with lab data and results (2)
Defend the hypothesis (2)

Conclusion quality: well organized and cohesive and contains no mechanical/grammatical errors. (3)
Well organized and cohesive but contains grammatical or mechanic (2)
Somewhat organized but does not contain any errors (2)
Somewhat organized with some errors (1)
Disorganized with errors (0)

RST 10 points

Thesis statement (2)
Comprehension of key ideas and details (3)
Cites convincing evidence to support analysis, showing full comprehension of complex ideas expressed in the texts provided.
Development of ideas and organization (2)
Student response addresses the prompt and provides effective development of the claim by using clear and convincing reasoning, details, and evidence.
Appropriate integration of source material/information (3)
Student response utilizes information in a way where the sources “speak with one another” are used adequately to support the student’s claims and lab conclusions.