How do you say stoichiometry? Stoy – KEY – Om – met – tree
How does stoichiometry relate to real life? Will I even use stoichiometry ever again?
After high school or college you may never need to say the word stoichiometry ever again, but you’ll use it even if just in your head.
Stoichiometry is mainly used often in calculating the amount of something needed or produced. Below are some real life stoichiometry examples to make this all make sense.
What is stoichiometry?
Stoichiometry is a method of converting a given amount of something from one unit to another. Yes it uses fractions, called conversion factors, but stoichiometry is much simpler than it sounds.
If you’ve ever figured out how many minutes you’ve been alive, or if all the ants of the world are bigger than the grand canyon, or how much medicine you should take, you’ve used stoichiometry.
Conversion factors
Conversion factors are fractions that have equal amounts and different units on the numerator and denominator. For example 12 eggs / 1 dozen eggs . 12 eggs equals 1 dozen eggs so this fraction reduces to 1 which means if you use this conversion factor the original amount will not be changed, just the number in proportion to the units.
What does that mean? Let’s explain further…
Say I have lots of chickens and we brought in 144 eggs (nice number for ease purposes) and I need to know how many egg cartons to get out of the garage. You may be able to do this in your head, but what’s happening is this:
144 eggs * 1 dozen eggs / 12 eggs = 12 dozen eggs
Notice the original unit became the denominator (bottom) of the conversion factor (fraction) and then the unit moving toward the answer was on top (the numerator).
Example in pharmacology (medicine)
In pharmacology, dosage uses conversion factors and stoichiometry often. For example, to determine the amount of amoxicillin to include in each capsule for a specific disease, dosage is used. I got this info from medical news today.
For children, especially infants, weight is also accounted for in the conversion.
“A toddler has an ear infection and goes to the doctor. The doctor measures the weight 20lb and converts it to 9 kg. The dosage for a toddler is 25 mg of amoxicillin per kg of child per day, but divided into two doses. “
Let’s calculate the prescription for our example toddler.
The doctor generally would prescribe the common amount closest, but above the needed dose for the child. So for this example, this toddler received a prescription for 125 mg per 5mL taken 2 times per day. Close enough.
Notice how the conversion factor of the amount of amoxicillin per kg of child was used to get the needed amount per day. This is how stoichiometry works; changing one unit (kg of toddler) to another (mg of amoxicillin) proportionally.
Now that we’ve gone through a few examples, let’s try a challenge question about our body.
Challenge question: How much iron is in your blood?
I like giving challenging questions that are intriguing and potentially interesting. This challenge question involves the blood and how much iron is generally flowing around our body at any given moment. The resources for information gathered are included at the bottom of this post.
Question: How much iron (g) is needed in an average person’s body to transport oxygen in their blood?
Our starting point is an average person’s body. In your brain, you may skip this step, but I’ll still write it here: Given 1 human
Humans have about 1.5 gal (aka 10 units) of blood. The conversion factor from the one human to the amount of blood is 1.5 gal / 1 human. Human is on the bottom here to cancel out the given unit at the beginning.
Then after google’s help we know 1.5 gal equals 5.678 L. Why are we converting to liters? Scientists generally use liters, miters, and grams instead of gallons, yards, and pounds so our information on hemoglobin and iron will be based in liters, miters, and grams. The conversion factor would be set up as follows: 5.678 L blood / 1.5 gal blood.
Next, the amount of hemoglobin per Liter of blood, can be personalized for men and women but I chose an overlapping amount of 140g hemoglobin per L. The conversion factor for hemoglobin could be: 140 g hemoglobin / 1 L blood . You may choose to have a different g of hemoglobin based on your body, but for this article we’re going as average as average can be.
The molar mass is a sum of the atomic mass of every atom within a molecule. Hemoglobin is an enormous molecule (actually it’s an enzyme aka protein) so looking up it’s molar mass will be best: hemoglobin 64,000g/mol so the conversion factor here will have g hemoglobin in the denominator to cancel with the previous conversion factor and have mol of hemoglobin on top.
Almost to the finish line!
In the protein hemoglobin there are 4 mol iron ions per 1 mol of the hemoglobin protein. This is an easy 4 mol Fe / 1 mol hemoglobin. This tells us the number of moles of atoms of iron in the blood. Now just to convert moles to grams.
Lastly the conversion from moles to grams of iron needs the molar mass. Iron’s molar mass is 55.85 g/mol which will be the same as our conversion factor and our paper should look like this:
Same question with less parts: Given 5.678 L blood, how many g Fe are present?
Answer: click here
2.77g Fe
Further Research
LINK how iron is used in body
LINK how oxygen moves in body
LINK humans have about 1.5 gal (aka 10 units) of blood = 5.678 L
LINK although different for men and women, estimated 140g hemoglobin per L
LINK molar mass hemoglobin 64,000g/mol