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Hello everyone.
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Thanks for joining me, ms.
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Hulstrom, as we discuss solubility calculations.
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Today we're going to focus on a problem that asks us to perform a solubility calculation for a solution at two different temperatures.
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Before we get started, i'd like you to take a quick look at this image i've included.
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This particular graph shows us the relationship of solubility to temperature.
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This says it's for solids, but if you'll look right here, you'll see that solids are the solid lines.
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This one also includes some gases, which are beyond the scope of what we're going to take a look at today.
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But the solid lines are what we're going to consider.
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You'll notice that temperature is on our x -axis, and we're going from zero to 100, which makes sense for water.
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And the substance we're going to be looking at today is potassium nitrate, which is the red line.
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That goes from here to here, from here to here.
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And if you take a look at this image, you'll see that potassium nitrate, kno3, is the substance most affected by a change in temperature.
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On the y -axis, we are given solubility in terms of grams of solute per 100 grams of solvent.
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In this case, since these are all aqueous solutions, it's per 100 grams of water.
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Now, on the line, the quantities that we see on the line, for instance, if i'm looking right, i'm going to try to pick something that's sort of close to being right on a line so i can read it easily.
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This one's pretty close.
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I can see that at 20 degrees c, about 29 grams of solute for both of these two, both k -n -o -3 and nacl, that's the maximum amount of solute that can dissolve in 100 grams of water.
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That would be the amount to prepare a saturated solution.
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And a saturated solution contains the maximum amount of solute that can be dissolved.
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The problem we're given today was going to take me a moment to write down.
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We are going to be working with a solution of k -103 potassium nitrate.
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And we're starting with exactly, and notice since we are given exactly a 100 gram aliquot or sample of a solution at, 75 degrees c and this solution is saturated.
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This is a saturated solution in 75 degrees c and we are given two solubilities.
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First we're given the solubility at 75 degrees celsius.
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We are given that 155 grams potassium nitrate will dissolve to to create a saturated solution in 100 grams water.
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Now we're going to talk we're told we're going to cool this solution to 25 degrees c.
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And at 25 degrees c, we are given that 38 .0 grams of potassium nitrate will be present in a saturated solution containing 100 grams of water.
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What we need to find out, what we're asked to find out, is in the process of cooling down 100 grams of sample from 75 degrees to 25 degrees, how much kno3 is going to precipitate out of solution? how much is going to crystallize out of solution? so we're going to make a plan to do this.
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And our plan is going to have three steps.
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Our first part of our plan is we are going to find mass of solute and mass of our solvent, which is water, in 100 grams of a saturated, k -03 solution at 75 degrees celsius.
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That's step one.
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Our second step, we are going to find the mass of solute of a saturated solution at 25 degrees celsius, given the mass of water from step one.
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And last but not least, super easy step.
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We're going to take the mass of solute that can be contained at 75 degrees c minus the mass of solute at 25 degrees c to find out the mass of solute that will crystallize.
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So that's what we're going to do.
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Let's begin.
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And if you need to, i'll try to jot all of our numbers back down again...