what is the total mass of kno3 that must be dissolved in 50 This is a topic that many people are looking for. amritsang.org is a channel providing useful information about learning, life, digital marketing and online courses …. it will help you have an overview and solid multi-faceted knowledge . Today, amritsang.org would like to introduce to you How to Calculate Mass Needed to Make a Solution. Following along are instructions in the video below:
s it going guys in this video. Were gonna go over the problem types types that ask what mass is needed to make a solution with a certain molarity. Just before we jump into the problems.
I just want to go over some of these definitions. Again solutions are just homogeneous mixtures of a solute distributed through a solvent and a solute is whats being dissolved. Its usually like a powder like a solid or something like that and then the solvent is whats doing the dissolving.
The universal solvent being water and thats what youre going to find. Most frequently in these types of problems so without further ado. Ill just jump into the first one calculate the mass of the tax potassium.
Nitrate which is needed to prepare 100ml of 85. Molar solution in water so first of all what is potassium nitrate. Sometimes you will have these problems that are going to require you to know and they might not they might not tell you what it is which is going to be unfortunate.
But what i like to do is if you if its an element just write it out and whatever in charge is associated if it has one and then. Nitrate we know is going to be no3 minus. And luckily this worked out because its a plus 1 and a minus 1.
We dont have to do anything special. Were just gonna put them next to each other. And thats what its going to be now.
Kno3 i pre calculated the molar mass to be 1011 grams. Per mole. So well have that ready to go for later.
And then we can kind of jump right in so essentially what we would do in the previous types of problems where were looking for meat. Were trying to solve for for the molarity. We can still use that molarity equation.
Which is going to be the moles of solute. Which in this case is going to be the potassium nitrate per liters of solution. And what are we looking for here.
So if we can find the moles then we can work backwards and find the grams using that typical equation that we use so for this we can kind of plug in what we have we have zero point five zero m. Is going to be equal to the moles of solute over what we have for our liters. Which is going to be 100 ml and were just going to convert that into liters because its very important for any molarity that its divided by liters as opposed to.
Ml so from. Here we can just multiply both sides by 01. And what were gonna get there is that r and a solute should be 005.
Moles and now from there we can work backwards so we know how many moles of kno3 we have so 005. Moles of kno3 and then were going to plug that into what we have for its molar mass. So we have moles on top.
We need moles on bottom to cancel. K and. O3 one mole is equal to 100 and 11.
Grams. Of kno3 and then that should give us the final. Answer so were gonna have there is the 05.
Times. One on one and we have five point zero five five grams of k. And o3 and that is going to be how many grams.
It takes to make that solution to make that much of that solution so yeah. Its basically how how these are done i will just move on now to the next one. Alright so we have a two molar solution is made with 64.
Liters of h2o and nacl how much nacl was added to the h2o to make this solution so first of all nacl. We know what that is and it has a molar mass. Which i looked at before is fifty eight point four four grams per mole and well have that ready to go for when you need it now we have our molarity equation is moles of solute per liter of solution and we know we have six point four liters and now we just need our and enough solute and we also have one molarity.
Whoops i should have plug that in so we have 20. M. Is equal to and solute over six point four.
And we can just do times six point four times six point four and were going to get twelve point eight. So we n of solute equals. Twelve point eight now we can just solve it so we have twelve point eight moles of nacl times.
Well use that molar mass. We have one mole on the bottom because we want moles to cancel nacl and then we have fifty eight point forty four grams of nacl and from there we can just solve that so we have twelve point eight times. Fifty eight point four four.
Were going to get seven forty eight point zero three two and we can round that to seven forty eight grams of nacl. So that is the mass of nacl thats required to make six point four liters of a two molar solution. Now well just move on to the last one here.
Okay. A solution is made by dissolving 19 grams. Of kcl and 10 grams of naoh and water how much water must be used to make the solution.
30 kcl by mass and then what is the solutions resulting molarity. So thats kind of a bonus question. There and the the mass percentage is kind of just something i wanted to cover.
But didnt necessarily want to dedicate an entire video to but for those of you that might not know or just you know to move on with the video here mass percentage is going to be equal to the individual mass over the total mass and then times 100. Thats pretty straight forward. I mean.
Thats obviously how youd find the percentage of just about anything you know how well you did in an exam for instance you just divide what you got by the total amount of points. But anyway. We can just kind of move forward with that so here we have 30.
Its going to equal. What we have is our 19 grams. Of kcl over x grams.
Because we dont exactly know x. 100. So.
What is our x grams. What were looking for is essentially we need to know how much water was used in order to add that to these two. Masses.
Here so another. Way we can set this up is 03. 0.
Is equal to 19 grams. Of kcl x grams. And then we can multiply both sides.
By x were going to get. 03. X so 03.
0. X. Is going to be equal to.
19 and then we can divide both sides by 03. 0. And were going to get sixty three point three three repeating.
Grams. And thats going to be the total mass. So now we just got this number and we have this number so we can find the mass percentage and then well know how much water was needed in order to do this so from there.
We can take make a quick calculation for the m total. Thats going to be sixty three point three three minus nineteen and then minus 10. Which is the naoh and were just subtracting those right off in order to figure out how much water.
We have so we have thirty four point three three grams of h2o and now from there we can figure out okay. So the first question how much water must be used to make the solution thirty percent. We know that answer thats right here now the next thing.
Its asking is what is the solutions resulting molarity so back to the beginning. We have molarity is going to equal and a solute per per liters of solution now we have lets see here so it basically one way that we can do this like i think that if this is a problem i threw together so its not going to make perfect sense. But one table that would probably be required a table could give us the h2o.
Grams. That would result in liters so the grams to liters. I mean you could do it like if you had like a home kitchen scale or something like that but basically.
Its just going to be h2o. Grams. Divided by a thousand.
Its going to roughly equal one litre of h2o and from there we can take what we got for our thirty four point three three and were going to divide that so what were going to take is thirty four point three three divide. It by a thousand is going to equal zero point zero three four three three liters of h2 oil and thats what were going to plug right onto the bottom there. But the important thing is we need to solve for the moles of solute in order to find that were going to actually need to do two separate equations one for each of these so were gonna have up top 19 grams.
Kcl. Times. One mole and the molar mass is going to be seventy four point five five grams.
And that is going to equal okay. So first we have on the top zero point two five four eight six and were just going to do that make that many numbers because of how how many significant figures. We have for the water.
We want it to be roughly accurate and you know if we rounded that to you know just 03. It wouldnt really make as much sense. Thats going to be moles of kcl and were gonna do the same thing for the na o h.
So naoh times. We ate one mole and anyway. Its gonna be the 41 zero grams.
And thats just okay zero point two five zero zero whatever moles of naoh cool. So now what were gonna do is were gonna take the sum of these two and thats gonna be our solute. So what do we have here zero point five oh.
Four eight six is going to be our total moles of solute sorry thats getting kind of messy and then were gonna divide that by our leaders of solute of solutions. Sorry so which is going to be zero point zero three four three three liters of h2o and okay. So i think with the theoretical solution.
Molarity is gonna be 14 point 7 1. Molar. Its gonna be the result sorry about that so yeah like i said this this isnt kind of you wouldnt normally have that there.
But if you did and youd get the table and everything. Its kind of just good to be able to take one problem and then be able to solve whatever else you can out of it i think and it kind of you know one more thing to add on to the question. So yeah.
This is the you know the basis of how you know youre gonna calculate the mass and again heres the definitions again and yeah. I hope this helped someone .
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