How many grams of NaCN would you need to dissolve in enough water to make exactly 250 mL of solu

step 1 Hello, and let's do another pretty challenging problem. And this problem is going to look at rel

How many grams of NaCN would you need to dissolve in enough...

Key Concepts

pH and pOH Relationship

This concept involves understanding that pH and pOH are directly related by the equation pH + pOH = 14, which allows one to convert a given pH value into the corresponding hydroxide ion concentration. This is fundamental when dealing with solutions where the basicity or acidity needs to be quantified.

Salt Hydrolysis

Salt hydrolysis refers to the reaction of a salt with water to produce a solution that is either acidic or basic. In the context of salts derived from weak acids or bases, the ion (in this case, the anion) can react with water to generate hydroxide or hydronium ions, thus affecting the pH of the solution. Understanding this process is key to predicting and controlling the pH of a solution.

Equilibrium Constants in Weak Base Reactions

When a salt undergoes hydrolysis, the reaction typically reaches an equilibrium that is characterized by a base dissociation constant (Kb). This constant expresses the extent to which the anion reacts with water to form hydroxide ions. Mastery of using Kb in equilibrium expressions is essential for calculating concentrations of species in the solution, which directly ties into achieving a specific pH.

Molarity and Mass Calculations

This concept involves converting between moles and grams using molar mass, as well as calculating the molarity of the solution based on the number of moles of solute and the volume of the solution. It is a critical skill for preparing solutions with precise compositions, ensuring that the desired pH and ion concentrations are achieved in the final mixture.

Transcript

00:01 Hello, and let's do another pretty challenging problem.

00:05 And this problem is going to look at relationships for ph, solution prep, salts, et cetera, et cetera.

00:12 Okay, we are asked to solve for how many grams of sodium cyanide would we need to dissolve in water if we wanted to make 250 milliliters, which of course is 0 .250 .0.

00:29 I get rid of that zero because that's not significant.

00:32 I don't think, no, 250 liters of a solution that has a ph of 10 .00.

00:47 Okay, so this has a ph of 10 .00.

00:52 And we're not really dealing with an acid here, so we were going to have to be looking up what our original concentrations are and figuring out all of our initials and changes.

01:09 We're going to write out our chemical equation first.

01:14 And our chemical equation, i think i'll just go ahead and go to a new page, so i have plenty of room, is c -n, cyanide ion.

01:28 Of course, water is always involved in these aqueous things.

01:34 And my products are going to be h -c -n and o -h -minus.

01:47 Okay, there we go.

01:50 And we're going to do an ice table, and this is going to be our x.

01:58 Don't consider water, and we know that these are zero.

02:02 We know that these are going to be plus x, x and x.

02:08 I guess they're not going to be x.

02:09 Excuse me.

02:10 I've got my ph here.

02:14 So i know that the ph, i'll write this down here, i might have to erase this.