pH of Strong Acids and Bases - Video Tutorials & Practice Problems
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1
concept
Strong Acids and Bases
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2m
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Recall that strong acids and strong bases completely ionized in water. And because of this fact, we can say here that the concentration of H plus ions and the concentration of oh minus ions are equal to the concentration of strong acids and bases respectively. So what exactly do I mean by this? Well, here, if we take a look, we have 0.25 molar of hydrochloric acid, a strong acid when it ionizes, it ionizes 100% into these two ions. That would mean that the concentration of the acid is the same concentration as my ions. So this would still be 0.25 molar and 0.25 molar. So the concentration of HCL is equivalent to 0.25 molar for H plus for strong bases, they completely ionize as well. They would uh make 100% of calcium ion and two hydroxide ions here. So here we'd have 1.2 molar of calcium ions. But with the hydroxide ion, we have to take into account that it's not just one hydroxide ion being produced but two, what effect does this have on the concentration? Well, we'd say the real concentration of hydroxide ions will be 1.2 molar, the original molarity times two because we make 20 minus ions. So the complete concentration of hydroxide ion in this case will be 2.4 molarity. Now, I also recall that strong base uh bases may contain the following ions for a strong base. The four basic anions are hydroxide ions which we saw up above but also hydride ion amide ion and oxide ion. We're gonna say when it comes to calculations dealing with Ph or POH, we're gonna treat the concentration of oh minus ions as being the same as the concentration of hydride ions amide ions and oxide ions. In addition to this, remember the formulas that are connected to Ph and POH remember that Ph plus POH equal 14. If we know the H plus concentration that allows us to find Ph since it's the negative log of H plus, if we know the Ph, then we know what H plus concentration is because H plus equals 10 to the negative Ph POH equals negative log of oh minus concentration. And if you know POH itself, you'll remember oh minus concentration equals 10 to the negative POH.
2
example
pH of Strong Acids and Bases Example
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1m
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If the concentration of barium hydride solution is 0.398 molar, calculate its POH. Now, barium hydride represents a strong base. Remember strong base is completely ionize into ions. So here we form one barium barium ion plus two hydride ions. The concentration of the of the strong base is 0.398 molar because we produce two Clyro ions, it'd be two times 0.398 molar to get its real concentration. When we do that, we get 0.796 molar at the concentration of our hydride ion. Now remember that the concentration of hydride ion is equal to the concentration of your hydroxide ion. This is important because now that we know the concentration of hydroxide ion, we can find the POH eoh itself equals negative log of oh minus concentration. So plug in the 0.796. And when we do that, we're gonna get as our answer 0.0991 as the POH of our barium hydride solution.
3
Problem
Problem
An aqueous solution of HBrO4 has a pH of 4.34. Find the molar concentration of HBrO4 solution.
A
4.6 × 10−19 M
B
2.6 × 10−6 M
C
2.2 × 10−10 M
D
4.6 × 10−5 M
4
Problem
Problem
Calculate the pH of a 25 mL of 5.45 × 10−2 M LiOH solution.
A
1.264
B
12.736
C
0.338
D
11.134
5
Problem
Problem
HI is a strong acid (Ka = 3.2 × 109). Calculate [H+], [OH−], pH and pOH of a 7.1 × 10−2 M HI solution.
A
[H+] = 7.1 × 10−2 M [OH−] = 1.4 × 10−13 M pH = 1.15 pOH = 12.85
B
[H+] = 7.1 × 10−2 M [OH−] = 1.4 × 10−13 M pH = 8.50 pOH = 5.50
C
[H+] = 7.1 × 10−2 M [OH−] = 7.1 × 10−16 M pH = 1.15 pOH = 15.15
D
[H+] = 7.1 × 10−2 M [OH−] = 7.1 × 10−12 M pH = 1.15 pOH = 11.15
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