Mole Fraction - Video Tutorials & Practice Problems
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Mole Fraction (X) represents the mole component by total moles.
Calculating Mole Fraction
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concept
Mole Fraction
Video duration:
36s
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Now the concept of the mole fraction, which is represented by the variable x, represents the mole component divided by your total moles. Now mole component itself represents the element or compound whose mole fraction we must determine. Taking this information, we now have our mole fraction formula. So mole fraction again, which is x equals your mole component, so what they're asking you to find the mole fraction of, divided by your total moles. Now that we know the formula for mole fraction, continue on to the next video and let's take a look at an example question.
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example
Mole Fraction Example 1
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3m
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In this example question, it says we have 25 grams of dichloromethane, which is c h two c l two, and it's dissolved in a 125 grams of water. They They say here, what is the mole fraction of dichloromethane? So we're gonna start out with step 1, and in step 1, we have to convert all the masses given to us into moles. Now to avoid rounding errors, make sure you have at least 4 decimal places when you convert to moles. We're gonna take the 25 grams of dichloromethane, and we're gonna say it's composed of 1 carbon, 2 hydrogens, and 2 chlorines. Looking up their atomic masses from the periodic table and adding them together, we get a combined mass of 84.926 grams of c h two c l 2 for every one mole. So here the grams cancel out and then I'll get 0.2944 moles of our dichloromethane. Now take the 125 grams of water. At this point, we've seen water so many times you know that the mass of 2 hydrogens and 1 oxygen is 18.016 grams for every 1 mole of water. So again our grams cancel out, and now we're gonna have 6.9383 moles for water. Step 2, we're now going to place the mole component as the numerator of the mole fraction formula. So remember, the mole fraction of the mole component is based on who we're asked to find the mole fraction of. And we're asked to find the mole fraction of dichloromethane. So we're gonna say here, mole fraction equals the moles of dichloromethane and then determine the total value of moles added together and place it as the denominator of the mole fraction formula. So here we're gonna take the 0.2944 moles of dichloromethane plus the moles of the water, and that'll give you my total moles which is 7.2327. So those moles here go on the bottom, so again this is our total moles for matting up the moles of dichloromethane and water together. Now this is important, your final answer should have no units because mole fraction is a unitless expression. That makes sense because the moles here would cancel out. So when we do that we'll get as our final answer 0.04070 as our mole fraction. This has 4 sig figs just like 0.2944 moles had 4 sig figs. So this is all we need to do when it comes to the mole fraction formula. Just remember who your mole component is. It's based on who you need to determine the mole fraction for. If you know that, that goes as your numerator, and then just total moles on the bottom as your denominator, and you'll get your mole fraction at the end.
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Problem
Problem
A reaction vessel is composed of 20.3 g Cl2, 4.27 g N2 and 10.8 g Ne. Calculate the mole fraction of nitrogen.