Write a Conversion Factor for the Relationship Between Grams and a Mole of Fe.
Weekly Web Work #9:
a Calculations Using Chemical Equations
&
Exam Preparation Check-up
This assignment was due by noon on Tuesday, March 11, 2003.
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The assignment this week has two objectives. The first objective is to solve problems using balanced chemical equations. The second objective is find out how your Exam 2 preparation is going.
Calculations using Chemical Equations
A balanced chemical equation indicates the relative numbers of molecules involved in a chemical reaction. Rust, iron (III) oxide, forms when iron and oxygen react. The balanced chemical equation for this process is:
From the balanced chemical equation 4 iron atoms react with 3 oxygen molecules to yield 2 iron (III) oxide formula units. Or 4 moles of iron atoms react with 3 moles of oxygen molecules to yield 2 moles of iron (III) oxide.
These mole ratios can be used as conversion factors.
| Fe and O2 | Fe and Fe2O3 | O2 and Fe2O3 | |||
 |  |  |  |  |  |
These mole ratio conversion factors can be used in many calculations. If you want to know the number of moles of oxygen needed to completely react with 6 moles of iron, you would see from the balanced chemical equation that 3 moles of oxygen are needed for every 4 moles of iron. How would you set up the calculation? Which mole ratio would you use?
How moles of iron (III) oxide can be produced from 6 moles of iron?
If you want to produce 6 moles of iron (III) oxide, how many moles of iron do you need to start with? (Assume you have all the oxygen that you need.)
The ability to convert from moles of one substance to moles of another substance using mole ratios from balanced chemical equations is a useful skill. However, one can't just go to the shelf and count out numbers of atoms or numbers of moles of a substance. Instead, we weigh the substance and calculate the corresponding number of moles using the molar mass.
The molar mass of Fe is 55.845 grams (1 mole Fe = 55.845 grams Fe).
The molar mass of O2 is 2 x 16.00 or 32.00 grams (1 mole O2 = 32.00 grams O2).
The mass of a mole of Fe2O3 is (2 x Fe) + (3 x Oxygen) = (2 x 55.845) + (3 x 16.00) = 159.69 grams (1 mole of Fe2O3 = 159.69 grams Fe2O3).
What is the mass in grams of 4.5 moles of O2?
How many moles of Fe2O3 are in 75 grams Fe2O3?
Putting it all together.
How many grams of lithium can be formed from 27 grams of lithium nitride according to the following chemical equation?
First, you would need to convert the 27 g of lithium nitride to moles of lithium nitride (using the molar mass of lithium nitride as a conversion factor).
Next, you would need to convert moles of lithium nitride to moles lithium (using the mole ratio from the balanced chemical equation.)
Finally, you would convert moles lithium to grams lithium (using the molar mass of lithium as a conversion factor).
We would report the answer as 16 g lithium. An extra significant figure was kept in each step to avoid rounding errors. Rounding was done at the end to give us the appropriate number of significant figures in our answer.
Now it is your turn.
Sodium chlorate decomposes into sodium chloride and oxygen according to the following chemical equation:
| 1. | How many moles of sodium chloride form when 4 moles of sodium chlorate decompose? |
| 2. | Explain how you arrived at your answer. What conversion factor(s) did you use? Explain with words without using equations. |
| 3. | How many moles of oxygen, O2, form when 4 moles of sodium chlorate decompose? |
| 4. | Explain how you arrived at your answer. What conversion factor(s) did you use? Explain with words without using equations. |
| 5. | How many moles of oxygen form when 2.2 moles of sodium chlorate decompose? |
| 6. | Explain how you arrived at your answer. What conversion factor(s) did you use? Explain with words without using equations. |
| 7. | How many grams of oxygen form when 5.3 grams of sodium chlorate decompose? (Be careful. Oxygen in the above equation is diatomic oxygen, O2. Hint: its molar mass is not 16 g/mol.) |
| 8. | Explain how you arrived at your answer. What conversion factor(s) did you use? Explain with words without using equations. |
Exam Preparation Check-up--How's it going?
Explain how your preparation for Exam 2 is going. Some questions you might answer are: How are you using the lecture notes? Is this different from how you used them when preparing for Exam 1? How much homework have you done? Is this a higher or lower percentage than what you did from chapters 1-3? What about the practice exams? Textbook usage? Mentoring?
What other strategies do you use to learn chemistry?
In order to receive a satisfactory score, you must answer all questions and provide explanations for your answers as requested.
Remember, since this file is in the archive, you can no longer submit it.
Write a Conversion Factor for the Relationship Between Grams and a Mole of Fe.
Source: http://webphysics.iupui.edu/webscience/courses/chem101/chem101/archive/www9archive.html