Scenario
You work for a company called, Merky Pharmaceuticals. Your team has been asked to give a presentation on how a new drug the company has developed. This drug helps to control the concentration of iron in the blood of people who have a genetic disease. The disease suppresses the protein that regulates blood-borne iron. Your team has been asked to present a 10 minute explanation of chemical equilibrium. Your audience is the stockholders. Most of them know little about chemistry except for the chemistry they took in high school.
Background
Many chemical reactions take place in our blood. We will look at the basics of two kinds of reactions that our blood performs every day: buffering and iron balancing. Buffers in our blood prevent our blood from becoming too acidic or too basic. When we exercise, for instance, the acidity of our blood tends to increase. If the acidity isn’t controlled, then all kind of nasty things can happen. Our blood contains chemicals that remove excess acids.
The amount of iron (in the form of iron ions) in our blood needs to be regulated chemically. We need just the right amount of iron to make hemoglobin that carries oxygen to every cell in our body. When the level of iron gets too high, chemical reactions remove iron from the blood. When the level of iron gets too low, other reactions occur that add more iron to our blood.
How can substances like acids and iron be removed? What does that mean? How can something as small as an ion of acid or iron be removed? (Very small tweezers?)
How can more iron be added to our blood? Do chemical reactions occur that release the iron trapped in substances in our body? How do these substances “know” when to release and when to capture the iron?
In this lab you will study a chemical law known as equilibrium. A French chemist by the name of Henri Louis Le Chatelier made sense of the rather complicated mathematics surrounding chemical equilibrium. In this lab you will see how equilibrium is applied in two chemical systems and use Le Chatelier’s Principle to interpret what you will experience.
Materials
For Part I - Per Group For Part II - Per Group
Quantity Item Quantity Item
1 dropper bottle Fe(NO3)3 (0.045M) 1 dropper bottle HCl (0.1M)
1 dropper bottle KSCN (0.002M) 1 dropper bottle NaOH (0.1M)
1 dropper bottle deionized water 1 dropper bottle acetate buffer
Small crystals of KSCN 1 dropper bottle bromcresol green indicator solution
Small crystals of Na2HPO4
1 24 well plate or spot plate
1 small plastic cup or 125mL beaker
1 scoopulas
1 beral pipet
1 plastic stirrer
Tasks
Part I: Can reactions go in reverse?
This lab will follow a format different from the format used in other labs. Begin by writing the names of the two ionic compounds used and write down the two kinds of ions in each of the two substances. Then read the directions at the right and write down your observations or responses on the left, as you go along step by step.
Part I
Name of Fe(NO3)3
Color:
Name of KSCN
Color:
Step 1: Place 45 drops of the KSCN solution into the plastic cup. Place one drop of the Fe(NO3)3 solution into the plastic cup, and swirl the cup to mix. On the report sheet write down your observation. Your teacher will help you determine the chemical equation for the reaction.
Step 2: Use the beral pipet to separate the contents of the plastic cup into 4 wells of the spot plate. You want to separate the solution so that all the wells will look the same color. Don’t completely fill each well, and you may have some solution left over. Well #2 will be the reference, so that you can compare the color changes in the other wells to it.
Step 3: Add one or two tiny crystals of KSCN to well #1. Stir gently with a stirrer. Compare the color in well #1 to the reference well #2. Record your observation on the report sheet, and answer the question for step 3 on the report sheet.
Step 4: Add one drop of the Fe(NO3)3 solution to well #3. Stir gently with a clean stirrer. Compare the color in well #3 to the reference well #2. Record your observation on the report sheet, and answer the question for step 4 on the report sheet.
Step 5: Add one or two tiny crystals of Na2HPO4 to well #4. Stir gently with a clean stirrer. Record your observation on the report sheet, and answer the question for step 5 on the report sheet.
Clean out the well plate. Your teacher will give you directions.
Your teacher will give you directions for the debrief of Part I.
Ions present in solution
+ Ions present in solution
+ SCN-
Step 1: Observation:
Chemical Equation:
Step 3: Observation
Step 3: If cell #2 turned darker, more FeSCN2+ was produced. Which reactant, Fe3+ or SCN-, must have been present in excess in well #2 before you did step 3?
Step 4: Observation
Step 4: If cell #3 turned darker, more FeSCN2+ was present.
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