TRUE OR FALSE?
1) A solution that is made out of 1.00mol/L ammonia and 0.50mol/L of ammonium chloride is a basic buffer.
2) The pH at the equivalence point of a weak base with a strong acid is expected to be less than 7 because the acid that is added is very strong
3) The pH of a buffer solution made out of 0.20mol/L hydrofluoric acid and 0.30mol/L sodiumfluoride is the same as a buffer solution that is made out of 0.10mol/L of acetic acid and 0.15mol/L of sodium acetate.
4) One cannot prepare a buffer from a strong acid and its conjugated base, because a conjugated base of a strong acid cannot buffer; meaning cannot react in the reverse direction of the acid dissociation.
5) The pH at the equivalence point of a weak base with a strong acid is expected to be less than 7 because of the presentce of the conjugated acid in the water.
6) You cannot prepare a buffer from nitric acid and sodium nitrate, but you can make one from nitrous acid and potassium nitrite
7) A solution that is made out of 1.00mol/L ammonia and 0.05mol/L of ammonium chloide can act as a basic buffer.
8) You cannot prepare a buffer with a pH of 11.5 with trimethylamine and trimethylammonium chloride
9) The capacity of a buffer solution made out of 0.20mol/L hydrofluoric acid and 0.30mol/L sodiumfluoride is the higher than that of a buffer solution made out of 0.10mol/L of hydrofluoric acid and 0.15mol/L of sodiumfluoride. But the pH of the two buffers solutions is the same.
I thought it was: true, false, false, true, true true, true, false, false, but it was not the good answer. I've been stuck on this for a looong time, help please!
1) A solution that is made out of 1.00mol/L ammonia and 0.50mol/L of ammonium chloride is a basic buffer.
pH = pKa + log(base/acid)
pH = 9.25 + log(1.00/0.5)
pH = 9.55
basic.
2) The pH at the equivalence point of a weak base with a strong acid is expected to be less than 7 because the acid that is added is very strong
WB/SA = say NH4Cl. That will be acidic because the NH4^+ is hydrolyzed to produce H3O^+
NH4^+ + H2O ==> H3O^+ + NH3
It is acidic but and I even agree to some extent with the strong acid part but I would count it false because I think they want the answer of the hydrolysis of NH4^+.
3) The pH of a buffer solution made out of 0.20mol/L hydrofluoric acid and 0.30mol/L sodiumfluoride is the same as a buffer solution that is made out of 0.10mol/L of acetic acid and 0.15mol/L of sodium acetate.
HF:
pH = 3.14 + log(0.3/0.2) = 3.33
HAc:
pH = 4.75 + log(0.15/0.1) = 4.93
false
I don't know why the conjugate base can't react (for example Cl^- can react with Ag^+ to form AgCl);however I would go the statement as true.
Your other answers look ok to me also; I suspect the outlier may be those where part of the statement is true and part is not true and we must make a guess as to which is right. Sorry I'm not of more help.
Let's go through each statement one by one and determine whether it is true or false, along with an explanation for each.
1) A solution that is made out of 1.00mol/L ammonia and 0.50mol/L of ammonium chloride is a basic buffer.
True. A buffer solution typically consists of a weak acid and its conjugate base (or a weak base and its conjugate acid), present in approximately equal concentrations. In this case, ammonia (NH3) acts as the weak base and ammonium chloride (NH4Cl) acts as the conjugate acid. Since the concentration of base (ammonia) is higher than the concentration of acid (ammonium chloride), this solution will act as a basic buffer.
2) The pH at the equivalence point of a weak base with a strong acid is expected to be less than 7 because the acid that is added is very strong.
True. The equivalence point occurs when stoichiometrically equivalent amounts of acid and base have reacted with each other. In the case of a weak base with a strong acid, the acid is completely dissociated, resulting in a higher concentration of H+ ions in the solution. This higher concentration of H+ ions leads to a lower pH, which is less than 7.
3) The pH of a buffer solution made out of 0.20mol/L hydrofluoric acid and 0.30mol/L sodium fluoride is the same as a buffer solution that is made out of 0.10mol/L of acetic acid and 0.15mol/L of sodium acetate.
False. The pH of a buffer solution depends on the equilibrium constant of the acid-base pair and the concentrations of the acid and the conjugate base. The pH of a hydrofluoric acid/sodium fluoride buffer will not be the same as an acetic acid/sodium acetate buffer due to differences in their equilibrium constants and concentrations.
4) One cannot prepare a buffer from a strong acid and its conjugated base, because a conjugated base of a strong acid cannot buffer; meaning cannot react in the reverse direction of the acid dissociation.
True. A buffer system requires the presence of a weak acid and its conjugate base (or a weak base and its conjugate acid). The conjugate base of a strong acid, however, is fully dissociated and cannot act as a buffer because it cannot react in the reverse direction of the acid dissociation.
5) The pH at the equivalence point of a weak base with a strong acid is expected to be less than 7 because of the presence of the conjugated acid in the water.
False. The pH at the equivalence point of a weak base with a strong acid is less than 7 not because of the presence of the conjugated acid in the water but because the acid is strong and completely dissociated, resulting in excess H+ ions in solution, which lowers the pH.
6) You cannot prepare a buffer from nitric acid and sodium nitrate, but you can make one from nitrous acid and potassium nitrite.
True. Nitric acid (HNO3) is a strong acid and its conjugate base, nitrate (NO3-), is fully dissociated. Therefore, nitric acid and sodium nitrate cannot form a buffer. On the other hand, nitrous acid (HNO2) is a weak acid and its conjugate base, nitrite (NO2-), can react reversibly to maintain a buffer solution when combined with a suitable salt, such as potassium nitrite.
7) A solution that is made out of 1.00mol/L ammonia and 0.05mol/L of ammonium chloride can act as a basic buffer.
False. To act as a buffer, the concentrations of the weak base and its conjugate acid should be approximately equal. In this case, the concentration of ammonia (weak base) is much higher than the concentration of ammonium chloride (conjugate acid), so it will not effectively act as a buffer.
8) You cannot prepare a buffer with a pH of 11.5 with trimethylamine and trimethylammonium chloride.
True. The pH of a buffer solution is determined by the equilibrium constant of the acid-base pair and the concentrations of the acid and the conjugate base. For a buffer solution to have a pH of 11.5, the equilibrium constant and the ratio of base to acid concentrations need to be appropriate. However, trimethylamine (CH3N) is a weak base with a pKa around 9.8, so it would be challenging to achieve a pH of 11.5 even with appropriate concentrations.
9) The capacity of a buffer solution made out of 0.20mol/L hydrofluoric acid and 0.30mol/L sodium fluoride is higher than that of a buffer solution made out of 0.10mol/L of hydrofluoric acid and 0.15mol/L of sodium fluoride. But the pH of the two buffer solutions is the same.
False. The capacity of a buffer solution depends on the concentrations of the acid and the conjugate base. In this case, the higher concentrations of hydrofluoric acid (HF) and sodium fluoride (NaF) in the first buffer solution suggest that it has a higher buffer capacity than the second buffer solution. However, the pH of the two buffer solutions may or may not be the same, as it depends on the equilibrium constant and the acid-base pair.
Based on your answers, it seems that your initial assumptions for some of the statements were incorrect. The correct answers are as follows:
1) True
2) True
3) False
4) True
5) False
6) True
7) False
8) True
9) False