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Calculate the $\mathrm{pH}$ of a solution that is $1.00 \mathrm{M} \mathrm{HCN}$ and $1.00 M$ HF. Compare the concentration (in molarity) of the $\mathrm{CN}^{-}$ ion in this solution with that in a 1.00 $M$ HCN solution. Comment on the difference.

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Chemistry 102

Chapter 15

Acids and Bases

Liquids

Carleton College

Rice University

University of Maryland - University College

Lectures

03:07

A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, a liquid is one of the four fundamental states of matter (the others being solid, gas and plasma). A liquid is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular bonds. Water is, by far, the most common liquid on Earth. Like a gas, a liquid is able to flow and take the shape of a container. Most liquids resist compression, although others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly constant density. A distinctive property of the liquid state is surface tension, leading to wetting phenomena.

04:38

A liquid is a state of matter in which a substance changes its shape easily and takes the form of its container, and in which the substance retains a constant volume independent of pressure. As a result of this, a liquid does not maintain a definite shape, and its volume is variable. The characteristic properties of a liquid are surface tension, viscosity, and capillarity. The liquid state has a definite volume, but it also has a definite surface. The volume is uniform throughout the whole of the liquid. Solids have a fixed shape and a definite volume, but they do not have a definite surface. The volume of a solid does not vary, but the volume of a liquid may vary.

08:49

Calculate the $\mathrm{pH…

02:30

Calculate the pH of a solu…

01:26

Calculate the $\mathrm{pH}…

02:59

Explain how to calculate t…

00:32

01:05

04:26

Calculate the concentratio…

And this question we've been given to us HF end. It's the end and we've been asked to determine ph in the first part of the question and concentrations of see and I am. So this information that that we've been given here, we have our HF being the stronger acids. So it means the ph is largely determined by the organization of hmm cause remember ph is equal to negative law concentration of the H plus I. And this concentration of H plus ions will be coming from the organization of these assets that is H. F. Ionizing to form H plants minus and at C. N. Ionizing to form a blast end. See in my so we are saying if this is remember the stronger the asset, the more iron is in solution. So we are looking at the hydrogen ions which then gives us a measure of the ph. So the strongest asset, which one which is H. F. We're saying this is what data mines our ph because it is the one that lionizes and gives most of the hydrogen iron. That gives wise a certain ph. So what we're going to do here, we're just going to be focusing on H. F. Because it is the strongest to us. Yes, ph will be largely due to the concentration of hmm. So what we have here is we want to determine their ph using this formula. What we're going to have is we have HF edge to all Ionizing to form H. three or blast and if we know some may just like this S. H. F. In ionizing to form H blast. And if so what we're going to hear is we want the concentrations and equilibrium and the initial concentration we have one. And before the organization process that we won't be having any of these. So if this decreases by X. Looking at these documentary coefficients where we have one more of these, if this decreases by X, it means this will increase by X. And this will also increase by So what this means is Equilibrium. The concentration of H. F. is one -X. And that of the hydrogen ions is and that of the florida irons is also equal to. So what we can do here to determine his expertise is to use the acid equilibrium constant K. Which we know to be equal to 7.1 by 10 to the power negative for So this is equal to the concentration of H plus multiplied by the concentration of f minus divided by the concentration of and all of this will be happening at equilibrium. And we have already determined the expressions for these species equals so this is equal to him. X multiplied by X Divided by one -X. So all we have to do is to solve for X. So our x here is going to be equal to 0.0 cool seven. Remember we are after the concentration of H plus for us to then determine VP and the concentration of H plus at equilibrium is called to X. So this is equal to the concentration of mm. Therefore the ph is called negative block 0.02. Uh huh. So the ph This is equal to 1.57. Now going on at CNN is a very weak asset. So its equilibrium Concentration of 8cm Will still be approximately equal to the initial concentration of one. Therefore the concentration of CN if we are to use the K. A. Which is equal to the concentration of H. Plus, multiplied by the concentration of the science at Hiram divided by the concentration of its cm. What's going to happen is we have this being equal to 4.9 x 10 to the power negative 10. So we are saying this concentration of C. N. This is going to be equal to concentration of CN. Of at C. N. Times the K. A. Divided by the concentration of H. And we already have the concentration of H plus Which is 0.0 blue salmon. So the concentration of design and I am this is going to be 1.8 x 10. to the power negative. Yeah. Now moving on, determine for another concentration we have at CNN is going to form H plus and CN minus. So the initial concentration is one And we have 00. And if this decreases by X. This is going to increase by X. And this is going to increase by X. So at equilibrium we have 1 -6. We have X. And as we have another X. Here. So Kay So we're going to have our K. A. or 4.9 by 10 to the power to man being equal, Multiplied by X, divided by one -X. So if we solve for X, X is going to be equal to 2.2 by 10 to the power negative five M. Which is also equal to the concentration of CN minus I am. So the concentration of CN if we are to just analyze these results, concentration of CNN It is greater in one M. It's the end compared to one M home. It's the end slash one in all. Thanks. Yeah so we've got more sign it irons in this solution than in second solution. And according to lisa Talia's principle the high H plus ions from this equilibrium a shift equilibrium to the left, decreasing the ionization of it's the end. So at the end of the day the etc. And equilibrium shifts from the right to the left, decreasing the organization of H C. N. And as a result we have a lower concentration of CN ions in a solution when we have yeah that solution, what we're trying to say here is we have at CNN ionizing and solution to form H plus and see in my so for this one 2nd system We also have H. F. That is ionizing to form H plus and see anymore. So what is happening now to this equilibrium? If we add we are acting H plus ions. So it's going to accept. Set this initial or the first equilibrium according to the data, we're now adding more eggplants. So this equilibrium will shift towards the direction that is consuming the excess H plus iron. And this direction is to the left. So if we are shifting towards the left, it means we are having more of at CNN and we are having less, etc. So that's why we are saying the concentration of CN minus ions is larger when we don't have any HF. Because the presence of HF is causing the shifting of the SCN equilibrium to the left, minimizing the organization of a CN and resulting in a lower concentration. See in solution.

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