how did they find these answers (note that last one is wrong) For a solution equ
ID: 853863 • Letter: H
Question
how did they find these answers (note that last one is wrong)
For a solution equimolar in HCN and NaCN, which statement is false? what combination of substances will give a buffered solution that has a pH of 5. 05? (Assume each pair of substances is dissolved in 5. 0 L of water. ) A weak acid, HF, is in solution with dissolved sodium fluoride, NaF. If HCl is added, which ion will react with the extra hydrogen ions from the HCl to keep the pH from changing? You have a 250. 0-mL sample of 1. 00 M acetic acid =(ka 1. 8 times 10-5). Calculate the pH after adding 0. 0040 mol HCl to 1. 0 liter of the best buffer. Consider the titration of 300. 0 mL of 0. 450 M NH? =(kn = 1. 8 times 10-5) with 0. 450 M HNO^. How many milliliters of 0. 450MHN03are required to reach the stoichiometric point of the reaction?Explanation / Answer
1. Due to common ion effect the dissociation of HCN is diminished .
2. pOH = pKb + log [salt / base]
pOH = 8.75 + log [1.5 / 1]
pOH = 8.75 + 0.176 = 8.926
Thus pH = 14- 8.926 = 5.07
3. F- ion, as reaction with flouride ion will decrease their conc and hence increase the dissociation of HF.
4.pH = pKa + log [salt / acid]
On adding HCl in the buffer the conc of salt will decrease due to reaction of acetate ions with H+ (From HCL) and conc of acid will increase by the same amount (0.004 moles)
Therefore pH = 4.75 = log [1-.004 / 1+.004] = 4.72
5. N1V1= N2V2 (milliequivalents of base is equal to that of acid at stoichiometric point aka equivalence point.)
So
0.450 X 300 = 0.450 X xmL
Thus volume of Acid = 300 mL = 3 X 102
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