(Ksp of AgI = 8.3 X 10?¹? ; Kf of Ag(CN)?? = 1.0 x 10²¹) 5....

(Ksp of AgI = 8.3 X 10?¹? ; Kf of Ag(CN)?? = 1.0 x 10²¹) 5. Acid-base titration is commonly used to determine the molarity of acid and base solution in laboratory. In most cases, indicator is used to identify the titration end point. However, to choose a right indicator requires some calculations before doing the actual titration. Now, assume that you are about to titrate 50 mL of 0.20 M nitrous acid with 0.10 M NaOH (HNO?, Ka = 4.0 x 10??). (1) What is the pH value of the nitrous acid solution before addition of NaOH? a. 0.70 b. 2.05 c. 3.40 d. 4.10 e. None of the above (2) After addition of 20 mL of NaOH, what is the pH value of the solution? a. 0.80 b. 0.96 c. 2.80 d. 3.50 e. None of the above (3) What is the pH value of the solution at the equivalence point? a. 7.00 b. 8.11 c. 8.35 d. 10.60 e. None of the above (4) What is the pH value of the solution when 110 mL of NaOH is added? a. 10.60 b. 11.80 c. 11.96 d. 13.00 e. None of the above (5) Which indicator is the most suitable indicator for this titration experiment? a. Indicator A: Ka = 1.0 x 10?² b. Indicator B: Ka = 1.0 x 10?? c. Indicator C: Ka = 1.0 x 10?? d. Indicator C: Ka = 1.0 x 10??

Transcript

00:01 Question or the first part here is about what it would be the ph of just the nitrous acid solution before any sodium hydroxide is added so we are given the k -a here and i'm hoping that i was able to read this correctly it's if not then just adjust your answers accordingly but this is the process so ka equals the concentration of the hydrogen ion squared over the concentration of the acid.

00:33 And so we know our ka is 4 .0 times 10 to the negative fourth.

00:38 We're looking for this hydrogen ion concentration, and the concentration of our acid is 0 .20.

00:46 So when we plug that in, give us an h -plus concentration equal to 0 .008 -9.

00:59 And then to find the ph, it's the negative log of that.

01:03 So ph would equal 2 .05.

01:16 Questions choice b.

01:21 When we add 20 milliliters of the base, we are in the buffer zone.

01:25 How do we know that? if i take the malaria of the acid times of the malarity of the base, excuse me, malaria times the volume of the acid equal and set it equal to malaria of the base times the volume of the base, we would find our equivalence points of 0 .2 times, 50 divided by 0 .1 is going to be 100.

01:44 So our equivalent point isn't until 100 milliliters.

01:48 Equivalence point is 100 milliliters.

01:53 So at 20 milliliters, we're in that buffer zone.

01:57 And there's only one equation that you need to use, ka times our acid info over our base info.

02:05 Okay, so we know our ka is 4 .0 times 10 to the negative fourth.

02:11 We know that if we take 50 times 0 .2, that we would have 10 millimoles of just this acid at the start.

02:20 We have none of the base.

02:21 We're going to add base, so we put a plus on the bottom and a minus on the top.

02:26 So now we'll take our 20 times the 0 .1, and that gives us 2.

02:32 So we will have 8 divided by 2, 8 divided by 2 times 4 times 10 to the negative 4.

02:40 And that's going to give us an h plus concentration equal to 0 .0016 molar.

02:48 And then we take the negative log of that to get our ph.

02:52 So now our ph is going to be 2 .80.

02:59 Question or c.

03:01 Let's look at this.

03:02 At the equivalence point, that means we have our equal moles of our acid and our base.

03:08 And so they are going to complete.

03:10 Cancel each other out and all we will have in solution then is our salt this salt that we have made now this is a basic salt because it comes from a strong base sodium hydroxide and a weak acid nitrous acid and strong always wins so that means we're going to need our kb so let's go ahead and get that kb so we take one times 10 to the negative 14th divided by four times times 10 to the negative 4th, and that's 2 .5 times 10 to the negative 11.

03:46 Okay, so the first thing we need to do is figure out the concentration of that base...

Question

Please give Ace some feedback