A 20.0-mL sample of 0.200 M HBr solution is titrated with
0.200 ...

Question

A 20.0-mL sample of 0.200 M HBr solution is titrated with 
0.200 M NaOH solution. Calculate the pH of the solution 
after the following volumes of base have been added: 
(e) 35.0 mL.

Accepted Answer

Hello everyone today. We are being given the following problem 0.350 molar of potassium hydroxide is used to titrate. A 25 millimeter sample of 250.35 Mueller hydrogen chloride. What is the ph after 40 ml of the base is added. So first you want to make note of what we have. We have hydrogen chloride hcl which is a strong acid. And we also have potassium hydroxide which is a strong base. Mhm. Our next goal is to find out how many moles of each of acid and base that we have. So to find the number of moles of our acid. We're gonna take, the moles of acid is to go to our polarity. So 0.3 50. And that's going to be moles over leader since that's what charity is. And we're gonna go ahead and multiply that and convert that into miller. We're gonna get rid of our milliliters and use this conversion factor that one leader equals 1000 militia leaders. We're then going to try to get rid of these milliliters. Finally, by multiplying by that 25 mL that we have before. And so our units are going to cancel out. We're going to be left with 8.75 times 10 to the negative third moles of H. C. L. Or hydrogen chloride. We're gonna do the same procedure for our base potassium hydroxide. We're gonna use our 0.35 moles per liter which is the polarity of the base. We're gonna use this conversion factor that one leader is equal to 1000 ml. And then we're gonna multiply that by the 40 ml that we have that we added in the problem. So we're gonna have our unit's canceled out. And we're gonna be left with 0.014 moles of potassium hydroxide. Notice that the moles of our base is greater than the number of moles for our acid, meaning that this solution is basic. So the solution is basic. So what we're gonna do is we're gonna take how many moles of our base? We have .014 moles and subtract that by the number of assets that we have 0.75 times 10 to the negative third moles. That's going to give us 5.25 times 10 to the negative third. And we are then going to calculate our total volume, so our total volume Which will equal the 25 ml that we initially had. And the 40 ml that we added, giving us 65 million liters. And so finally, not finally, but almost To the end, our concentration of hydroxide ions is going to be 5.25 times 10 to the negative third moles that we had originally. We're gonna go ahead and multiply this or divide this by the leaders to find the polarity. And so we want to use the conversion factor that one leader, 0 to 1000 mL. And we want to multiply this by the total number or the total volume that we have. And so once our units Are going to cancel out, we are going to be left with 0.0808 polarity. Our last and final step is to calculate the P O. H. Since we have the concentration of hydroxide islands. And that is simply negative log times the concentration of hydroxide ions, which when we plug that into our calculator from the previous section, we get the negative log we get the negative log 0.0808 Polarity, which is 1.927. And so the question asked about ph ph is simply 14 minus the P. O. H. And in this case we have 14 minus R. P O H, which is 1.927. Giving us a final ph of 12.907. As our answer, I hope this helped. And until next time.

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