Using the information in Table 9.4, describe how you would prepare each of the following solutio

step 1 Okay, we have some molarity calculations to do. And we have four pretty easy problems that we're

Using the information in Table 9.4, describe how you would...

Key Concepts

Dilution Principle

The dilution principle is used to prepare solutions of a desired concentration by adding solvent to a concentrated stock solution. It is based on the concept that the number of moles of solute remains constant during the dilution process, which leads to the relationship M1V1 = M2V2, where M represents molarities and V represents volumes.

Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. This concept is central to calculating how much of a concentrated substance is needed to achieve a desired dilute solution, and it is essential for precise solution preparation and stoichiometric relationships in chemical reactions.

Stock Solutions

Stock solutions are highly concentrated solutions that are diluted down to the needed concentration for specific applications. Understanding how to work with stock solutions involves careful calculation and measurement to ensure that the correct volume is taken so that when diluted, the final solution has the intended molarity.

Volumetric Analysis

Volumetric analysis involves the use of precise glassware, such as volumetric flasks and pipettes, to measure out volumes accurately during the preparation of solutions. This technique ensures that both the volume of the concentrated aliquot and the final solution are exact, which is critical for maintaining the integrity of the desired concentration.

Transcript

00:01 Okay, we have some molarity calculations to do.

00:04 And we have four pretty easy problems that we're going to be working on.

00:09 For each one of these problems are required volume.

00:12 We're going to be asked how to prepare to solutions, how to prepare, and we're going to be preparing two liters for each one.

00:27 So how to prepare dot, dot, dot.

00:31 First problem, we are asked, how to prepare.

00:33 And i'm going to write the whole thing out for this one, two liters, of 0 .250 molar sodium hydroxide.

00:47 And our first order of business is going to be to figure out how many grams of the sodium hydroxide we need.

00:55 And to figure out how many grams we're going to have to get moles.

00:59 So we're going to find moles, and then we're going to go from moles to grams.

01:12 And then after that, we're going to do explain how to find the process that would be involved.

01:21 Okay, so we know that molarity equals moles per liter.

01:29 And we also know that we were given malarity.

01:34 That doesn't look like a very nice leader.

01:37 I'll go fix that.

01:43 Leader.

01:45 So now we can rearrange this equation to find moles.

01:49 Moles equals molarity times liters.

01:54 And i'm not going to do this again, but moles equals, remember, for molarity is moles per liter times liter, so liters cross out.

02:05 Let's substitute our values in.

02:07 Moles equals our malarity, 0 .250.

02:12 I'll write moles per liter times 2 .00 liters.

02:20 Do the math, and you get 0 .5 .0 moles.

02:29 I need half a mole.

02:32 Okay, whenever we're dealing with the solid, you have to find the molar mass.

02:36 So i'm just going to change colors here a little bit and find molar mass, which you will find.

02:46 You probably already know this is 40 .00 grams per mole.

02:51 And then we're going to take our moles times our mass equals moles times molarity or excuse me, times molar mass equals 20 .0 grams of n -a -o -h.

03:20 Okay, i'm going to the next page.

03:23 Checking my camera it's on so i'm going to um to prepare this carefully weigh two 0 .0 grams sodium hydroxide and i would weigh that using a weighing dish and be careful sodium hydroxide is um a pretty strong base it's pretty caustic second place transfer the n a h to a two two liter volumetric flask and even i have a two -liter volumetric flask so they're not that hard to find so you're going to place that into a two -liter volumetric flask add enough and i'm going to call it lab grade water it could be distilled it could be deionized in my building we use a reverse a deionizer reverse ro system to allow easy agitation so you can agitate until all the noh is dissolved.

05:30 And then once all the sodium hydroxide is dissolved, fill with lab grade water to the mark.

05:50 And every volumetric flask has a mark.

05:53 If it's glass, you want to fill it so if that's your mark, so the meniscus is right there.

06:04 So if it's glass, make sure your meniscus is right there.

06:06 Be careful because if you overshoot, you overshoot.

06:10 So when i get close, i just use, i'll even use a dropper if it's a narrow enough flask.

06:19 And once you've done that, this often generates a little heat.

06:24 So i usually let it set.

06:28 Sodium hydroxide is very exothermic.

06:31 Let's set for a few hours if you have time and then check your volume again.

06:42 Because as it cools it might move a little bit.

06:44 Okay, so that's how we do our first one.

06:47 And i'm going to tell you that we are going to do the next problem that requires mass the exact same as this, but we're going to change this, this, and i think that's it.

07:05 We're just going to put our new stuff in here and fill it the same way.

07:10 So it'll be the exact same process as this.

07:12 I won't write it again.

07:15 Next.

07:16 I'll do this one in my favorite color on this.

07:20 Okay.

07:22 Next, we're asked to prepare two liters, two liters, and i better get my sig -figs on here, of a 0 .250 molar solution from a stock solution that is 1 .0 molar, and it's sodium hydroxide.

08:04 And to do this one, to figure out the quantity, we're going to use the malarity times volume equals malarity times volume equation...

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