HASPI Medical Chemistry Lab
How do you feel? No, really, how is it that when you touch something your brain immediately knows something about it? The texture, the temperature, even the size without even looking at it? This is due to electrical impulses that pass through your body, known as an action potential. This works because your neurons are full of electrolytes. Electrolytes are any ion that dissociates in water, allowing the solution to conduct electricity. Sodium, chloride, potassium and calcium ions are all essential parts of this process. All along the neuron, specific electrolytes are pumped on to either side of the cell membrane, and to send a signal, electrolytes rush across the membrane, allowing the signal to move. The ion pumps then re-set these ions so that the next signal can be sent. http://www.bem.fi/book /03/03.htm When you are low in electrolytes your body can’t communicate with your brain as well and your muscles may cramp. You may feel more fatigue when you are low on electrolytes. You might even crave salty foods, because table salt contains sodium ions, which are a key component needed for nerve signals. Your sweat is full of electrolytes, which is why you need to drink fluids rich in potassium, calcium and sodium when you work out. Sports drinks also contain large amounts of sugar to help give you extra energy when you drink them. http://webspace.ship.edu/cgboer/the neuron.html When a patient has diarrhea, one of the key things they lose is electrolytes. For this reason, it is important to drink more than plain water when you have diarrhea, because you need to replace your electrolytes to keep you strong. You also need to have electrolytes to help you absorb water because your body absorbs water through osmosis, which means that water follows the electrolytes. Pediatricians recommend that kids drink Pedialyte when they are sick so that they get the right mix of electrolytes in their liquids, but this works for any age. If you don’t have Pedialyte then you can use Gatorade or another sports drink, however the large amount of sugar is not always a good idea when you’re sick, so drink sports drinks in moderation or pick up some Pedialyte liquid or freezer pops! http://canigivemyb aby.com/pedialyte/
http://www.bbc.co.uk/schools/gcsebit esize/science/add_ocr_21c/natural_en vironment/hydrosphererev2.shtml Ionic, Covalent & Metallic compounds each have physical properties that relate to their structures, so there are some tests we can do to help identify the type of bonding in a substance.
An ionic bond is made when ions of opposite charges come together to create a crystal lattice structure. In order to melt an ionic compound the temperature has to rise until the ions move with enough force to break away from the oppositely
charged ions around them. For table salt, this means you would need a temperature of 801 °C to hit the melting point (that’s over 1,000°F!). Covalent compounds don’t break apart when they melt, so they only have to reach a temperature strong enough to pull them away from the other molecules to melt them. This is why most small covalent molecules are liquid or gas at room temperature because they have such low melting points. http://www.utdallas.edu/~brikowi/Teachin g/Field_Methods/Lab_3_Background.html
Solubility & Conductivity
http://zube.brinkster.net/SCH3U21/Reac tions/Reading/stateparticles.jpg Ionic compounds dissolve very easily in water to create an aqueous solution. Since water is a polar molecule (meaning it has partial charges) it attracts the ions and surrounds each one as the compound dissociates in the water. Once water is full of charged particles it can conduct electricity very easily. This is why tap water conducts electricity the chemicals used to treat the water are ions, so it makes the water into a conductor.
Non-polar covalent compounds do not dissolve well in water. They have no charges on their outsides, so they are not attracted to the polar water. Some polar-covalent compounds do dissolve well in water; however they do not conduct electricity in the water because they do not have charges. By testing a substance’s melting point, solubility and conductivity you will be able to predict what type of bond it has.
Define the following terms on a separate sheet of paper
Electrolyte melting point Conductivity Solubility 1.
ionic List some examples of electrolytes. action potential 2.
covalent neuron https://chemistry11mrstandring.wikispaces.co
m/The+Conductivity+of+Aqueous+solutions polar What are two causes of low electrolytes? 3.
List the expected physical qualities of an ionic substance 4.
Research these chemicals and fill out the data table
Paraffin Wax Ionic, Polar Covalent or Non-Polar Covalent List the expected physical qualities of a covalent substance Chemical Formula Molar Mass Medical Use Fructose Sodium Bicarbonate 2
Name(s): Period: Date:
HASPI Medical Chemistry Lab
Today you will test substance A, B and C to determine which are paraffin, fructose and sodium bicarbonate based on some of their physical properties. In the pre-lab, you researched these chemicals so you know which one is ionic, which one is covalent, and which one is polar covalent. As you complete each part of the lab, record your findings. At the end of the lab you will be asked to look at your compiled data and determine the identity of each substance.
Wear your lab goggles and closed toed shoes at all times in the lab.
It’s important to understand what is happening at the atomic level when you are doing a lab. Think about what you already know about each type of compound and draw what you think is happening. Use a pencil so you can revise your drawing. Draw an example of what you think an ionic compound looks like at an atomic level Draw an example of what you think a covalent molecule looks like at an atomic level Draw an example of what you think a polar covalent molecule looks like at an atomic level Once you have drawn your models, discuss them with a partner. Look back over the prelab pictures and see if you can gather more information from those pictures. Look in your notes or textbook to see if you can refine your drawing to be more accurate.
Draw an example of what you think an ionic compound looks like at an atomic level when added to water Draw an example of what you think a covalent molecule looks like at an atomic level when added to water Draw an example of what you think a polar covalent molecule looks like at an atomic level when added to water
Look back to your pre-lab and think about which type of substance has a low melting point, which has a very high melting point, then answer these questions to help you better understand what is about to happen. What kind of substance do you expect to melt first? What kind of substance has a very high melting point?
Aluminum Foil Step Procedure 1 2. Hot Plate Substance A, B and C Create a foil boat with 3 sections Add ¼ tsp or small scoop of the each substance to different sections of your foil boat. Carefully wipe the spoon out after each use to be sure no contamination occurs but do not use any water.
3. 4. 5. 6. Small scoopula or ¼ tsp Tongs Observations, Changes or Comments Note any differences in the three compounds Turn the hot plate to medium. Wait for your substances to melt. It they are not melting you can turn the hot plate up. When the first substance melts, record a 1 below. When the second substance melts, TURN OFF THE HOT PLATE and remove your foil boat using tongs. Record a 2 for the melting order For the third substance you merely have to record that it would melt 3 rd . Do not attempt to melt it as the melting point would be very high! Observations: Observations: Data Table Part 2: Melting Points Substance A Observations about the solid substance Melting Order Ionic, Covalent or Polar Covalent? Substance B Substance C Reasoning
In the pre-lab you read that an ionic compound is very easily dissolved in water because the ions are attracted to the polar water molecules and the compound will dissociate, or break apart, as it dissolves. Polar covalent molecules are also fairly soluble because they are attracted to the water, although polar covalent substances do not break apart as they dissolve. Non-polar covalent molecules are not soluble in water because they are not attracted to the polarity of water, and they will either sink or float depending on their density. 4
Beaker A: Substance A in water Beaker B: Substance B in water Beaker C: Substance C in water Step Procedure Changes or Comments 1 2. 3. Pick up the first beaker labeled substance A in water. Write down your observations. Do you see any solid remaining? Do you see any liquid layers? If the substance is fully dissolved, write SOLUBLE If the substance is not dissolved, write INSOLUBLE Repeat for remaining substances Observations Data Table Part 3: Solubility in water Solubility Ionic, Covalent or Polar Covalent? Reasoning for identification Substance A Substance B Substance C
Look back at your pre-lab and think about which type of substance will conduct electricity. Do you expect different results for each of the three substances? Which types of substances may have the same results?
Conductivity meter, Paper Towels, Pre-filled and labeled well plate with water, electrolyte solution, and Substance A, B and C in water. Step Procedure Observations, Changes or Comments 1 2. 3. 5. Find your conductivity meter and turn it on. Look at the key on the back to see how you will measure conductivity. Rinse the probes on the conductivity meter with DI water then dry them well. Now place the dry probes into substance A. Record any conductivity. Use a paper towel to carefully clean the probes and ensure they are still dry. Now place the dry probes into substance B. Record any conductivity. Repeat for substance C. You will now use the conductivity meter to test each substance in an aqueous solution. Start by testing the conductivity of pure DI water and the electrolyte solution What kind of bond does water have? What kind of bond do the atoms in the electrolyte solution have? 6 Use a paper towel to carefully clean off the probes on the conductivity meter. Now test each of the substances, drying the meter between each test.
DI Water Data Table Part 4: Conductivity Conductivity in water Ionic or covalent Reasoning Electrolyte solution Substance A Substance B Substance C
Compile your data from above to figure out which substance is which. Analysis Data Table –Compiling & Interpreting Results Substance A Substance B Substance C Melting Point Order Solubility Conducts as a pure substance? Conducts when dissolved in water? 1.
Ionic, Covalent or Polar Covalent? What is the identity of substance A? What is your evidence and reasoning for this identification? 2.
What is the identity of substance A? What is your evidence and reasoning for this identification? 3.
What is the identity of substance A? What is your evidence and reasoning for this identification? 6
Extensions: Make your own conductivity meter: http://scifun.chem.wisc.edu/homeexpts/CondTester/SolutionConductivity.htm http://www.instructables.com/id/Conductivity-Meter/ Fructose Reading: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2467321/
http://www.livestrong.com/article/268996-symptoms-of-low-potassium-of-electrolytes/ http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_21c/natural_environment/hydrospherere v2.shtml