 Well, hello again, been a long time. I know you miss me Let's do some molarity molarity is one of the ways that scientists Quantify the concentration of a solution In our everyday life, we can use words like Concentrated or dilute whenever we're talking about things, you know, you go to the grocery store and you go to buy thing of laundry detergent it might say three x concentrated on it and Fantastic makes you buy it Might work might not who knows that that's daily life, you know, we run into things that might or might not work all the time In science, however, particularly in chemistry, we got to be very careful with the amount of stuff that we're dealing with so We need a better way to approach it We need a way to quantify it or put numbers on it and molarity is one of those things we can do I'm looking out the window here going wow, I've never seen this in your life So empty I could have driven to work today and got out on time Make sure all you seniors watch my molality video because I did teach today molarity abbreviated with a capital M equals the moles of solute over the leaders of Solution Again abbreviated with capital M That's important because the other one molality that I'll be doing the video for next is abbreviated with a lowercase m So they do mean two different things make sure you're aware of that not only when you write your measurements down But when you read test questions and things like that as well, make sure you know capital M from molarity And it's moles of solute on top solute is what is dissolved in the solution and its leaders of solution on the bottom This is a total There's nothing in here about the solvent and that's important because in the next equation there will be You got to read these things carefully and make sure you know what you're dealing with So it's the moles of the solute the substance that is dissolved divided by the leaders of solution or the total amount of mixture that you have So at its simplest You would have a problem That looks something This one question number one what is the molarity of of a solution that contains 4.53 moles of lithium nitrate in 2.85 liters of solution in This question we have moles and leaders and if we look back at our equation, that's exactly what we need moles of solute in this case lithium nitrate and leaders of solution So all we got to do is substitute and solve for this one molarity capital M Equals moles of solute divided by leaders of Solution so that would be the 4.53 on top and the 2.85 on the bottom Let me punch this in my calculator real quick 4.53 divided by 2.85 is 1.589 Around that 1. 5.9 fills up the calculator display So we're gonna round remember the test you're taking a multiple choice as long as you're close enough you'll get it Unit wise we just put that capital M there because that's how we abbreviate molarity And it's always good to write down the formula of your compound This is lithium Nitrate lithium is li Nitrate a te means polyatomic ion Ate and I te are the endings we put on polyatomic ions. So I look at my table of polyatomic ions. That's no three Now let the ends are group one. So it is a plus one oxidation number nitrates in that table of polyatomic ions This says it's negative one oxidation number plus one minus one those cancel out. So there are no subscripts And the formula is li no three Now that's the straightforward application That's one where you don't have to do too much thinking too much work to get it done as we know Chemistry is never that easy. There's always some kind of other work We have to do and that's where a problem like this comes into play There's plenty to do in this one like figure out formulas calculate formula masses do mole mass conversions Do metric conversions this single question here test at least five different concepts that we covered in chemistry So you've got to know all five concepts to get to the right answer You got to know all five concepts on a multiple-choice test to even get any credit This is the difference. It says grams here and because it says grams. I don't have what I need for my equation I need moles and liters. So I got to get that grams converted into moles And that's where most of the work in this problem comes in I'm doing osmium three fluoride Osmium is OS that's its symbol from the periodic table the Roman numeral three is its oxidation number Fluoride ends in IDE IDE tells me just a plain old non-metal. It's fluorine And fluorine isn't group 17 group 17 has a negative one oxidation number So the three comes over here and the one goes over there OS F3 Now that we have a formula we need to do a formula mass There is one osmium in this particular formula one ninety point two three and you know, you're doing multiple-choice tests here So really do you need the decimal place values on that? I'd say not You know, you get it close enough. You'll be able to pick what the right answer is and pretty much every question So we can just leave this as a whole number if we want to fluorine There's three of those and each one is 19 so three times 19 It's 57 Add them up and we get 247 grams That is the molar mass or formula mass of osmium three Fluoride if you have any issues with that go back look through my video history. You'll find a video on doing Formula masses watch that and go through to get Any problems with the formula go back and find the formulas for iota compounds thing and Watch it Now with this number we can write an equivalence one mole Osmium fluoride is equal to 247 Grams of osmium three fluoride Now we'll use that to convert these grams into moles So we always start our equation with the number that we're given times in a fraction bar and Then we're going to put grams on the bottom and the reason we're doing that is because we're starting off with grams Whatever you're starting off with here has to go on the bottom The other number the one mole goes on top Ignore the one because it doesn't do anything mathematically the 247 is on the bottom. So we'll divide by that 214.2 divided by 247 Calculator spits out a big old number point eight six seven two zero six four seven seven seven We're going to round that to point eight seven And that's the moles that we need to do our molarity calculation Now this one's got even more work in it because this one I haven't given you liters of solution. I've given you milliliters of solution So you're gonna have to convert that as well both numbers in this question have to be converted into the correct units for our equation Because our equation is very specific Our equation says I have to have moles of solute I gave you grams so we did that conversion And it says leaders of solution. So I gave you milliliters. We got to convert it to liters King Henry died by drinking chocolate milk kilo hectodeca base desi seni mille I gave you a milli We need base unit one two three places to the left so I take 67.3 One two three places over Fill the empty place value with a zero. So it is point zero six seven three liters Now to do the final calculation molarity equals mole solute Over liters Solution so moles of solute is that number zero point eight seven Leaders solution is that number zero point six seven three Divide them out point eight seven divided by point six seven three Is one point three There you have it We want to put that formula on there. So we know what we're talking about osf three You never want to put a solution up without the chemicals name or at least formula on it. So there you go Molarity one of the most important concepts in the unit. I'd see you can almost count on that having Some question one or two on the final exam