AP Chemistry 3/10/15

Applications of Le Chatelier’s Principle

Lab Write-Up of “Applications of LeChatelier’s Principle” Due Monday, March 30th

Overview for Write Up (details below)

  • Lab title, student name(s) and data
  • Part I. Answer and define
  • Part II. Pre-lab questions and Safety Precautions
  • Part III. Introductory Activity Procedure and Expected Results
  • Part IV. For your group Introductory Activity
  • Analyze the results
  • Write a balanced equation for each of the equations possible in Activities A-E
  • Design an experiment for each mini-experiment (A-E) investigating the effect of one of the following: concentration, temperature or pressure; on the concentration of at least one reactant or product.
  • Part V. For each mini-experiment (A-E) include the following:
  • Hypothesis
  • Procedure (part IV c)
  • Results (observations) relating to the equilibrium reaction (provided in a table)
  • Data analysis with a consideration of problems, how the problems were addressed and what to do next time
  • One paragraph RACES conclusion that includes detailed claim and evidence which refers to specific tables or figures in the results
  • Part VI. AP Chemistry Review Questions

Pre-Lab Due Thursday before Class (Read LeChatelier’s Lab- attached as a separate pdf)

Part I: Answer/Define

1)What does it mean for a reaction to “proceed to completion”?

2)Define what equilibrium means in chemistry.

3)Define the following

  1. Dynamic equilibrium
  2. Chemical equilibrium
  3. Equilibrium constant

4)What factor(s) could cause the ratio of products and reactants to change?

5)Define LeChatelier’s Principle

6)Explain how predicting and interpreting shifts in equilibrium can be determined:

  1. qualitatively
  2. quantitatively

7)Define Q

8)What happens to an equilibrium reaction if:

  1. Q=k?
  2. Q<K?
  3. Q>K?

9)What happens if the concentration is changed of

  1. reactants (increased and decreased)
  2. products (increased and decreased)

10)How does increasing temperature alter a reaction that is:

  1. exothermic
  2. endothermic

11)Define partial pressure

12)Write the mathematical equation for determining the pressure from the partial pressure of several gases.

13)Explain how one can change the pressure of a system to shift equilibrium towards the left or right.

14)What is the introductory activity?

15)What is the purpose of this lab?

16)Define solubility.

Part II

  1. Answer the two pre-lab questions
  2. List safety precautions and reasons for them.

Part III

Draw a cartoon of the introductory procedure and indicate the expected results.

Thursday, March 12th.

Using examples from the pre-lab and introductory activity, students were taught how to qualitatively (Le Chatelier’s principle) and quantitatively (compare Q to K) determine equilibrium shifts.

The Introductory Activity results and table of reactions were provided (the table is attached seperately as a pdf file).

Part IV. Thursday Night Homework

With the group of students who will be your lab partners,

1)analyze the introductory activity results

2)write a balanced equation for each of the five reactions possible in activities A-E (provided in the following table)

3)For each activity, design a testing procedure to investigate the effect of either concentration, temperature or pressure on the color or appearance of the products or reactants. Suggestions for each activity are given in the table.

Friday, March 13th. Double Lab Period

Part IV Continued. The introductory activity was demonstrated and student’s filled notes into the following tables:

Table 1. Colors of each solution of crystal

KSCN
Fe(NO3)3
KSCN crystal
KNO3 crystal
NaH2PO4 crystal

Table 2. Experimental results and explanation

Part A Observations
20 mL KSCN (aq)
Add 3 drops Fe(NO3)3 (aq)
Add KNO3 crystals
Add NaH2PO4 crystals
Add 1 drop Fe(NO3)3 (aq)
Add KSCN crystals
Part B Observations
Solution is Chilled
Solution is Heated

Part IVc. Students were asked to pick a station and explore adding a stressor(s) that would push the reaction forward or reverse. Identifying the reaction as moving forward or reverse was determined by a color and / or precipitation change. Students were asked to write a rudimentary procedure for their station, if possible.

Part V. After exploring for 15 minutes, students were given about 10 minutes per station to complete the following procedures, which were provided as shown below.

Procedure for Activity A

1)Measure 2 mL of dH2O and add to a test tube

2)Add 5 drops of 0.04% bromothymol blue. Swirl gently and observe and record color.

3)Add 0.1 M HCl dropwise. Observe and record color changes.

4)Add 0.1 M NaOH dropwise. Observe and record color changes.

5)Add additional drops of HCl and NaOH. Observe and record color changes.

Procedure for Activity B

1)Add 5 mL of 0.2 M CuSO4 to a test tube

2)In fume hood, add concentrated ammonium hydroxide solution dropwise. Observe and record changes.

3)Add 1.0 M HCl dropwise. Observe and record changes.

4)Add additional drops of NH3. Observe and record changes.

Procedure for Activity C

1)Label three test tubes A-C and place them in a test tube rack

2)Use a graduated, beral-type pipet, add about 2 mL of the cobalt chloride solution to each test tube. Observe and record the color and phase of each tube.

3)Add 6.0 M HCl dropwise to test tube B. Observe and record the color and phase.

4)Add 0.1M AgNO3 dropwise to test tube B. Observe and record the color and phase.

5)Add distilled water dropwise to test tube C. Observe and record the color and phase.

6)Add 5-6 grams fo CaCl2 to test tube C. Observe and record the color and phase.

7)Place test tube C in an ice-water bath for 2-3 minutes. Observe and record the color and phase.

8)Place tests tube C in a hot-water bath for 2-3 minutes. Observe and record the color and phase.

9)What was the purpose of test tube A?

Procedure for Activity D

1)Obtain 10 mL of seltzer water in a 50 mL beaker

2)Add about 20 drops (we amended to 4) of 0.04% bromocresol green indicator. Swirl to mix the solution. Observe and record color changes.

3)Draw up about 10 mL of this mixture into a 30 mL syringe.

4)Ask a teacher to demonstrate.

5)She will seal the tube and pull back on the syringe to create a decrease in pressure (larger overall volume). Hold plunger steady and shake until bubble stop forming. Observer and record color changes.

6)She will then push the syringe to increase pressure (decrease volume). Hold plunger steady. Observe and record color changes and match them to the pH paper.

Procedure for Activity E

1)Obtain 10 mL of milk of magnesia solution

2)Measure 50 mL of distilled water

3)Use some of this water to rinse the milk of magnesia into a 250 mL beaker

4)Add remainder of the 50 mL distilled water

5)Add 5-10 drops of universal indictor solution. Swirl to mix and observe and record color.

6)Add one drop of 3M HCl with constant stirring. Swirl to mix and observe and record color.

7)Add additional drops of 3M HCl with constant stirring. Swirl to mix and observe and record color.

8)Add additional drops of 3M HCl with constant stirring. Swirl to mix and observe and record color.