Law of Multiple Proportions Problem

Law of Multiple Proportions Problem This is a worked example of a chemistry problem using the law of multiple proportions. Two different compounds are formed by the elements carbon and oxygen. The first compound contains 42.9% by mass carbon and 57.1% by mass oxygen. The second compound contains 27.3% by mass carbon and 72.7% by mass oxygen. Show that the data are consistent with the law of multiple proportions. Solution The law of multiple proportions is the third postulate of Daltons atomic theory. It states that the masses of one element which combine with a fixed mass of the second element are in a ratio of whole numbers. Therefore, the masses of oxygen in the two compounds that combine with a fixed mass of carbon should be in a whole number ratio. In 100 grams of the first compound (100 is chosen to make calculations easier), there are 57.1 grams oxygen and 42.9 grams carbon. The mass of oxygen (O) per gram of carbon (C) is: 57.1 g O / 42.9 g C 1.33 g O per g C In the 100 grams of the second compound, there are 72.7 grams oxygen (O) and 27.3 grams carbon (C). The mass of oxygen per gram of carbon is: 72.7 g O / 27.3 g C 2.66 g O per g C Dividing the mass O per g C of the second (larger value) compound: 2.66 / 1.33 2 Which means that the masses of oxygen that combine with carbon are in a 2:1 ratio. The whole-number ratio is consistent with the law of multiple proportions. Solving Law of Multiple Proportions Problems While the ratio in this example problem worked out to be exactly 2:1, its more likely chemistry problems and real data will give you ratios that are close, but not whole numbers. If your ratio came out like 2.1:0.9, then youd know to round to the nearest whole number and work from there. If you got a ratio more like 2.5:0.5, then you could be pretty certain you had the ratio wrong (or your experimental data was spectacularly bad, which happens too). While 2:1 or 3:2 ratios are most common, you could get 7:5, for example, or other unusual combinations. The law works the same way when you work with compounds containing more than two elements. To make the calculation simple, choose a 100-gram sample (so youre dealing with percentages), and then divide the largest mass by the smallest mass. This isnt critically important- you can work with any of the numbers- but it helps to establish a pattern for solving this type of problem. The ratio wont always be obvious. It takes practice to recognize ratios. In the real world, the law of multiple proportions doesnt always hold. The bonds formed between atoms are more complex than what you learn about in a 101 chemistry class. Sometimes whole number ratios dont apply. In a classroom setting, you need to get whole numbers, but remember there may come a time when youll get a pesky 0.5 in there (and it will be correct).

5 Super Tips On How to Get Your Resume Noticed

5 Super Tips On How to Get Your Resume Noticed You’ve come of age in the era of social media. Which probably means you assume everything can be done online: networking, socializing, job applications. And that’s more or less true. But there’s one vestige of the old world that will still be crucial to you in finding yourself a satisfying job: a resume. Don’t be fooled into thinking you don’t need one. Everybody does. Do concern yourself with making sure your resume gets in the right hands. It doesn’t have to be perfect; you’ll likely tinker with it for the entirety of your career. But you need to start somewhere. Here are five tips for how to get your resume noticed and read, so you can get that job and get your start.1. Think like a computerYour cover letter and your interview need to be geared towards the human recruiters who’ll be reading it. Your resume, on the other hand, will probably be read first by a search engine. Keep that simple fact in mind and gear your document to get through the machines.2. OptimizePart of this strategy means using the right words to get through the computer programs that will sort your resume. Part of it is simply making sure you’re showing a hiring manager that you can do the job. Start by reverse-engineering the job description and peppering your resume with the keywords necessary to showcase your skills. You can also create a â€Å"core competencies† section at the top and listing your most valuable skills there. And if you have to cheat, and include keywords for skills you don’t quite have, you can try putting them in in white font, so computer searches will pick up on it, but human recruiters won’t see that text.3. Make it easyMake sure to get all the basics covered: school, major, GPA, objective. When writing your objective, err on the side of specifics. Don’t just say you want a great job doing great things; make sure to let the recruiter know you mean business. Be clear about th e location and the industry you’re looking for. Take the guess work out of it.4. Go electronic with your cover letterMore often than not, you’re going to need to email a cover letter rather than sending the traditional hard copy. Again, there’s no guarantee a human is going to see it. But you shouldn’t cut any corners all the same. Start with as personal an opening as possible- whether a friend referred you, or you have a mutual acquaintance, or you have a particular affinity for this particular position. Then use the rest of the message to contextualize the bullet points on your resume. Again, be as specific as possible.5. Think â€Å"means to an end†Your resume doesn’t have to be perfect. It doesn’t have to do everything. But it does need to be attention-grabbing. And it needs to present your brand clearly and effectively to the people who will hire you. Be honest and showcase your unique qualities and talents and you’ll do f ine.