How to Calculate Mass Percent Composition

How to Calculate Mass Percent Composition This is a worked example problem showing how to calculate mass percent composition. Percent composition indicates the relative amounts of each element in a compound. For each element, the mass percent formula is: % mass (mass of element in 1 mole of the compound) / (molar mass of the compound) x 100% or mass percent (mass of solute / mass of solution) x 100% The units of mass are typically grams. Mass percent is also known as percent by weight or w/w%. The molar mass is the sum of the masses of all the atoms in one mole of the compound. The sum all the mass percentages should add up to 100%. Watch for rounding errors in the last significant figure to make sure all the percentages add up. Key Takeaways Mass percent composition describes the relative quantities of elements in a chemical compound.Mass percent composition is also known percent by weight. It is abbreviated as w/w%.For a solution, mass percent equals the mass of an element in one mole of the compound divided by the molar mass of the compound, multiplied by 100%. Mass Percent Composition Problem Bicarbonate of soda (sodium hydrogen carbonate) is used in many commercial preparations. Its formula is NaHCO3. Find the mass percentages (mass %) of Na, H, C, and O in sodium hydrogen carbonate. Solution First, look up the atomic masses for the elements from the Periodic Table. The atomic masses are found to be: Na is 22.99H is 1.01C is 12.01O is 16.00 Next, determine how many grams of each element are present in one mole of NaHCO3: 22.99 g (1 mol) of Na1.01 g (1 mol) of H12.01 g (1 mol) of C48.00 g (3 mole x 16.00 gram per mole) of O The mass of one mole of NaHCO3 is: 22.99 g 1.01 g 12.01 g 48.00 g 84.01 g And the mass percentages of the elements are mass % Na 22.99 g / 84.01 g x 100 27.36 %mass % H 1.01 g / 84.01 g x 100 1.20 %mass % C 12.01 g / 84.01 g x 100 14.30 %mass % O 48.00 g / 84.01 g x 100 57.14 % Answer mass % Na 27.36 %mass % H 1.20 %mass % C 14.30 %mass % O 57.14 % When doing mass percent calculations, its always a good idea to check to make sure your mass percents add up to 100% (helps catch math errors): 27.36 14.30 1.20 57.14 100.00 Percent Composition of Water Another simple example is finding the mass percent composition of the elements in water, H2O. First, find the molar mass of water by adding up the atomic masses of the elements. Use values from the periodic table: H is 1.01 grams per moleO is 16.00 grams per mole Get the molar mass by adding up all the masses of elements in the compound. The subscript after the hydrogen (H) indicates there are two atoms of hydrogen. There is no subscript after oxygen (O), which means only one atom  is present. molar mass (2 x 1.01) 16.00molar mass 18.02 Now, divide the mass of each element by the total mass to get the mass percentages: mass % H (2 x 1.01) / 18.02 x 100%mass % H 11.19% mass % O 16.00 / 18.02mass % O 88.81% The mass percentages of hydrogen and oxygen add up to 100%. Mass Percent of Carbon Dioxide What are the mass percentages of carbon and oxygen in carbon dioxide, CO2? Mass Percent Solution Step 1: Find the mass of the individual atoms. Look up the atomic masses for carbon and oxygen from the Periodic Table. Its a good idea at this point to settle on the number of significant figures youll be using.  The atomic masses are found to be: C is 12.01 g/molO is 16.00 g/mol Step 2: Find the number of grams of each component make up one mole of  CO2. One mole of CO2 contains 1 mole of carbon atoms and 2 moles of oxygen atoms. 12.01 g (1 mol) of C32.00 g (2 mol x 16.00 gram per mole) of O The mass of one mole of CO2 is: 12.01 g 32.00 g 44.01 g Step 3: Find the mass percent of each atom. mass % (mass of component/mass of total) x 100 And the mass percentages of the elements are For carbon: mass % C (mass of 1 mol of carbon/mass of 1 mol of CO2)  x 100mass % C (12.01 g / 44.01 g) x 100mass % C   27.29 % For oxygen: mass % O (mass of 1 mol of oxygen/mass of 1 mol of CO2)  x 100mass % O (32.00 g / 44.01 g) x 100mass % O 72.71 % Answer mass % C 27.29 %mass % O 72.71 % Again, make sure your mass percents add up to 100%. This will help catch any math errors. 27.29 72.71 100.00 The answers add up to 100% which is what was expected. Tips for Success Calculating Mass Percent You wont always be given the total mass of a mixture or solution. Often, youll need to add up the masses. This might not be obvious! You may be given mole fractions or moles and then need to convert to a mass unit.Watch your significant figures!Always make sure the sum of the mass percentages of all components adds up to 100%. If it doesnt, you need to go back and find your mistake.

Sample Appeal Letterâ€Academic Dismissal from College

Sample Appeal Letter- Academic Dismissal from College If youve been dismissed from college for poor academic performance, your college will most likely give you an opportunity to appeal that  decision. The best approach is to appeal in person, but if the school doesnt allow face-to-face appeals or if the travel costs are prohibitive, you should plan to write the best appeal letter possible. (In some cases, you might be asked to do both- the appeals committee will ask for a letter in advance of the in-person meeting.) Qualities of a Successful Appeal Letter Demonstrates an understanding of what went wrongTakes responsibility for academic failuresOutlines a clear plan for future academic successConveys points in an honest tone In the sample letter below, Emma was dismissed after she ran into academic trouble because of difficulties at home. She uses her letter to explain the extenuating circumstances that caused her to perform below her potential. After reading the letter, be sure to read the discussion of the letter so that you understand what Emma does well in her appeal and what could use a little more work.   Emmas Appeal Letter ThoughtCo. Dear Dean Smith and Members of the Scholastic Standards Committee: I am writing to appeal my academic dismissal from Ivy University. I was not surprised, but very upset to receive a letter earlier this week informing me of my dismissal. Im writing with the hope that you will  reinstate me for next semester. Thank you for allowing me the opportunity to explain my circumstances. I admit I had a very difficult time last semester, and my grades suffered as a result. I dont mean to make excuses for my poor academic performance, but I would like to explain the circumstances. I knew that registering for 18 credit hours in the spring would require a lot of me, but I needed to earn the hours so that I was on track to graduate on time. I thought I could handle the workload, and I still think I could have, except that my father became very ill in February. While he was home sick and unable to work, I had to drive home every weekend and some weeknights to help out with household duties and to care for my little sister. Needless to say, the hour-long drive each way cut into my study time, as did the chores I had to do at home. Even when I was at school, I was very distracted with the home situation and was unable to focus on my schoolwork. I understand now that I should have communicated with my professors (instead of avoiding them), or even taken a leave of absence. I thought I could handle all of these burdens, and I tried my best, but I was wrong. I love Ivy University, and it would mean so much to me to graduate with a degree from this school, which would make me the first person in my family to complete a college degree. If I am reinstated, I will focus much better on my schoolwork, take fewer hours, and manage my time more wisely. Fortunately, my father is recovering and has returned to work, so I should not need to travel home nearly as often. Also, I have met with my advisor, and I will follow her advice about communicating better with my professors from now on. Please understand that my low GPA that led to my dismissal does not indicate that I am a bad student. Really, Im a good student who had one very, very bad semester. I hope you will give me a second chance. Thank you for considering this appeal. Sincerely, Emma Undergrad A quick word of warning before we discuss the details of Emmas letter: Do not copy this letter or parts of this letter in your own appeal! Many students have made this mistake, and academic standards committees are familiar with this letter and recognize its language. Nothing will torpedo your appeal efforts faster than a plagiarized appeal letter. The letter needs to be your own. Critique of Sample Appeal Letter Any student who has been dismissed from college has an uphill battle to fight. The college has indicated that it lacks confidence in your ability to succeed academically, so the appeal letter must re-instill that confidence.   A successful appeal must demonstrate that you understand what went wrong, take responsibility for the academic failures, outline a clear plan for future academic success, and demonstrate that you are being honest with yourself and the committee. Many students who appeal an academic dismissal make the mistake of attempting to place the blame for their problems on someone else. Certainly external factors can contribute to academic failure, and it is fair to describe extenuating circumstances. However, it is important to own up to your own mistakes. In fact, acknowledging mistakes is a major sign of maturity. Remember that the appeals committee does not expect college students to be perfect; instead, they want to see that you recognize your mistakes and have learned from them. Emmas appeal succeeds fairly well in all of the above areas. First of all, she does not try to blame anyone but herself. She has extenuating circumstances- her fathers illness- and she is wise to explain them, but she doesnt make excuses. Instead, she acknowledges that she did not handle her situation well. She owns up to the fact that she should have been in contact with her professors when she was struggling, and ultimately should have withdrawn from classes and taken  a leave of absence  when her fathers illness started to dominate her life. The overall tone of Emmas letter is sincere. The committee now knows  why  Emma had such bad grades, and the reasons seem both plausible and pardonable. Assuming she did earn solid grades in her earlier semesters, the committee is likely to believe Emmas claim that she is a good student who had one very, very bad semester. Emma also presents a plan for her future success. The committee will be pleased to hear that she is communicating with her advisor. In fact, Emma would be wise to have her advisor write a letter of support to go with her appeal. A few elements of Emmas future plan could use a little more detail. She says that she will focus much better on [her] schoolwork and manage [her] time more wisely. The committee is likely to want to hear more on these points. If another family crisis arises, what will Emma do to ensure that she is able to stay focused on schoolwork? What is her time management plan? She wont become a better time manager simply be saying she will do so. How exactly is she going to learn and develop more effective time management strategies? Are there services at her school to help with her time management strategies? If so, she should mention those services and describe how she will utilize them. On the whole, Emma comes across as a student who deserves a second chance. Her letter is polite and respectful, and she is honest with the committee about what went wrong. A severe appeals committee may reject the appeal because of the mistakes Emma made, but many colleges would be willing to give her a second chance. More on Academic Dismissals Emmas letter provides a good example of a strong appeal letter, and these six tips for appealing an academic dismissal can help guide you as you craft your own letter. Also, there are many less sympathetic reasons for being kicked out of college than we see in Emmas situation. Jasons appeal letter takes on a more difficult task, for he was dismissed because alcohol took over his life and led to academic failure. Finally, if you want to see some common mistakes students make when appealing, check out Bretts weak appeal letter.