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General Chemistry

Learn the toughest concepts covered in Chemistry with step-by-step video tutorials and practice problems by world-class tutors

7. Gases

Mole Fraction -

Mole Fraction (X) represents the mole component by total moles. 

Calculating Mole Fraction

Mole Fraction

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Now, the concept of the mole fraction, which is represented by the variable X, represents the mold component divided by your total moles. Now, more component itself represents the element or compound. Who's more fraction You 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 to find the mole fraction off 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.

Mole Fraction Example 1

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in this example question. It says we have 25 g of decorum methane, which is ch two c l two, and it's dissolved in 125 g of water. They say here, what is the mole fraction of diet cola methane. So we're gonna start out with step one and step one. We have to convert all the masses given to us in two moles. Now, to avoid rounding errors, make sure you have at least four decimal places. When you convert two moles, we're gonna take the 25 g of declawed methane, and we're gonna say it's composed of one carbon to hydrogen and two Korans looking up their atomic masses from the periodic table and adding them. Together we get a combined mass of 84.926 g of ch two c l two for every one mole. So here the grams, cancel out and then I'll get 0.2944 moles, our diet cola, methane. Now take the 125 g of water. At this point, we've seen water so many times you know that the mass of two hydrogen and one oxygen is 18.16 g for every one mole of water. So again, our grants cancel out. And now we're gonna have 6.9383 moles for water. Step two, we're not gonna place the mole component as the numerator off the mole fraction formula. Remember the mole fraction off? The more component is based on who were asked to find the mole fraction off and were asked to find a little fraction of dick low methane. So we're going to stay here. Mole fraction equals the moles of declawed methane and then determine the total value of moles added together and place it as the denominator off the mole fraction formula. So here we're going to take the 0.2944 moles of dicho methane plus the moles of the water. And that will give you my total moles, which is 7.23 to 7. So those moles here go on the bottom. So again, this is our total moles from adding up the moles of declare methane and water together. Now, this is important. Your final answer should have no units because mole fraction is a unit list expression that makes sense because the moles here would cancel out. So when we do that, we'll get as our final answer point 04070 as our mole fraction. This has four sig figs, Just like 40.2944 moles had four sig figs. So this is all we need to do when it comes to the mole fraction formula. Just remember who you're more component is. It's based on who you need to determine the mole fraction for if you know that, that goes as you numerator and then just total moles on the bottom as a denominator and you'll get your mole fraction at the end.

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.