How much carbon is present in 22.0 g of CO2? QUESTION: How much carbon is present in 22.0 g of CO2? A. 6.00 g, B. 9.43 g, C. 12.0 g One mole of CO2 contains 1 mol C and 2 mol O: 1 mol C: 1 mol C x 12.01 g/mol = 12.01 g 2 mol O: 2 mol O x 16.00 g/mol = 32.00 g The total mass of one mole of CO2 is 44.01 g Compounds have definite composition: masses of elements and total mass are directly proportional. mass C How much carbon is present in 22.0 g of CO2? A. 6.00 g, B. 9.43 g, C. 12.0 g PAUSE Anytime we’re asked to determine the amount of element present in a compound, it’s a good strategy to lay out the composition of one mole of the compound. CLICK In the case of carbon dioxide, we know from the subscript that one mole of carbon dioxide contains one mole of carbon and 2 moles of oxygen. CLICK We can look up the molar mass of carbon and find it to be 12.01 grams per mole. Therefore, one mole of carbon has a mass of 12.01 grams. CLICK Similarly, we can find the molar mass of oxygen to be 16.00 grams. Therefore, the mass of 2 moles of oxygen is 32.00 grams CLICK Therefore, the total mass of one mole of carbon dioxide is 44.01 grams.... 12.01 grams plus 32.00 grams equals 44.01 grams. CLICK Compounds are said to have a definite composition. What this means is that the masses of the elements that make up the compound and the total mass of the compound are directly proportional quantities. Therefore, in the case of carbon dioxide, we can say that for any carbon dioxide sample, the ratio of the mass of carbon to the mass of carbon dioxide is a constant. We have information here to get the value of this constant... For one mole of carbon dioxide, it is equal to... 12.01 grams of carbon over 44.01 grams of carbon dioxide. Rearranging this equation to solve for the mass of carbon, we essentially end up multiplying the mass of carbon dioxide which is 22.0 grams CLICK CLICK by the ratio 12.01 grams carbon over 44.01 grams carbon dioxide. CLICK Note that the ratio of the mass of the element present in one mole of compound to the total mass of one mole of the compound essentially serves as a conversion factor. Carrying out this calculation... SHOW UNIT CANCELLATION gives us 6.00 grams of carbon. Note that the least precise term in this calculation is 22.0. It has 3 significant figures. Therefore, our answer should also have 3 significant figures. The correct answer is A. 6.00 grams. CONTINUED ON NEXT SLIDE 12.01 g C = mass CO2 44.01 g CO2 12.01 g C 22.0 g CO2 x = 6.00 g C 44.01 g CO2
Other ways this question can be phrased: How much carbon can be extracted from 22.0 g of CO2? To produce 22.0 g of CO2 from carbon, how much carbon is needed? How much carbon can be obtained from the decomposition of 22.0 g of CO2 to its constituent elements? Here are some other ways that this question might be phrased CLICK ...How much carbon can be extracted from 22.0 grams of carbon dioxide? ... CLICK ...Or ...To produce 22.0 grams of carbon dioxide from carbon, how much carbon is needed? ...How much carbon can be obtained from the decomposition of 22.0 grams of carbon dioxide to its constitutent elements. CLICK PAUSE END RECORDING
Video ID: 4-6-2 © 2008, Project VALUE (Video Assessment Library for Undergraduate Education), Department of Physical Sciences Nicholls State University Author: Glenn V. Lo Narrator: Funded by Louisiana Board of Regents Contract No. LA-DL-SELECT-13-07/08