How many moles of CH4 are in 4.00 g of CH4?

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Presentation transcript:

How many moles of CH4 are in 4.00 g of CH4? QUESTION: How many moles of CH4 are in 4.00 g of CH4? A. 0.249 mol, B. 64.0 mol, C. 0.307 mol Molar mass of CH4: 16.04 g/mol moles CH4 1 mol CH4 = mass CH4 16.04 g NH3 How many moles of CH4 are in 4.00 g of CH4? A. 0.249 mol, B. 64.0 mol, C. 0.307 mol PAUSE By now, you should know how to calculate the molar mass given a formula. CLICK For CH4, you should be able to calculate that the molar mass is 16.04 grams per mole. To do a mass to mole conversion, it is important to recognize that these two quantities are directly proportional. This means that the ratio of the two quantities is constant. In this case, The ratio of the moles of methane CLICK to the mass CLICK CLICK is equal to the ratio of 1 mole to 16.04 grams We can rearrange this equation to solve for the moles of methane. Essentially, what we would end up doing is multiply the given mass of methane, 4.00 grams CLICK by the ratio... 1 mole methane over 16.04 grams CLICK CLICK CLICK The ratio serves as a conversion factor. SHOW CANCELLATION OF UNITS The answer we get should be rounded off to three significant figures... since the the least precise factor, 4.00 CALLOUT “3 significant figures” has only three significant figures. 16.04 grams has four significant figures, CALLOUT and the number 1 in the numerator is exact. CALLOUT 4.00 divided by 16.04 gives us 0.2494, which we round off to 0.249. Therefore, the correct answer is choice A....0.249 moles. Here’s another way of looking at this calculation. CLICK if we want to convert grams to moles.. we simply divide the mass HIGHILIGHT by the molar mass HIGHLIGHT CLICK 4.00 grams divided by 16.04 grams per mole, equals 0.249 moles CLICK PAUSE END RECORDING 1 mol CH4 4.00 g CH4 x = 0.249 mol CH4 16.04 g CH4 To convert grams to moles: Moles = Mass / (Molar Mass) = 4.00 g / (16.04 g/mol) = 0.249 mol

Video ID: 4-5-4 © 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