Acetic acid has a Ka of 1.8 * 10-5. Three acetic acid/acetate buffer solutions, A, B, and C, were made using varying concentrations: acetic acid ten times greater than acetate, acetate ten times greater than acetic acid, and acetate=acetic acid.
Match each buffer to the expected pH. pH = 3.74 ; pH = 4.74 ; pH = 5.74
Part B: How many grams of dry NH4Cl need to be added to 2.30 L of a 0.600 M solution of ammonia, NH3, to prepare a buffer solution that has a pH of 8.71? Kb for ammonia is 1.8 * 10-5.
Express your answer with the appropriate units.
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Ответ:
A) acetic acid ten times greater than acetate pH = 3.74
B) acetate ten times greater than acetic acid pH = 5.74
C) For solution 3: acetate=acetic acid pH = 4.74
Mass NH4Cl = 40.30 grams
Explanation:
Step 1: Data given
Ka is: 1.8 * 10^-5
Solution 1: acetic acid ten times greater than acetate
Solution 2: acetate ten times greater than acetic acid
Solution 3: acetate=acetic acid
Step 2: The pH formula
pH = pKa + log[CH3COO-]/[CH3COOH]
For solution 1: acetic acid ten times greater than acetate this means ) [[CH3COO-]/[CH3COOH]) has a value of 1/10
pH = pKa + log[CH3COO-]/[CH3COOH]
pH = -log(1.8*10^-5) + log(1/10)
pH = 4.74 -1
pH = 3.74
For solution 2: acetate ten times greater than acetic acid
pH = pKa + log[CH3COO-]/[CH3COOH]
pH = -log(1.8*10^-5) + log(10)
pH = 4.74 + 1
pH = 5.74
For solution 3: acetate=acetic acid
pH = pKa + log[CH3COO-]/[CH3COOH]
pH = -log(1.8*10^-5) + log(1)
pH = 4.74 + 0
pH = 4.74
Part B: Calculate molarity
pOH = pKb + log [H
5.29= -log (1.8*10^-5) + log [BH+]/[0.600 M]
5.29 = 4.744 + log [BH+]/[0.600 M]
0.546 = [BH+]/0.600
[BH+] = 0.3276 M
Moles NH4+ = 0.3276 M * 2.30 L
Moles NH4+ = 0.75348 moles
Moles NH4Cl = 0.75348 moles
Mass NH4Cl = 0.75348 moles * 53.49 g/mol
Mass NH4Cl = 40.30 grams
Ответ:
46.80 ml
Explanation:
V1 =50ml
T1 =313K°
T2 = 293K°
V2 =?
V1/T1 =V2/T2
V2=V1*T2/T1
V2=50*293/313
46.80ml