8. Will a solution of NHaF be acidic, basic, or neutral? Ka for NH\' = 5.5 x 10-
ID: 1037885 • Letter: 8
Question
8. Will a solution of NHaF be acidic, basic, or neutral? Ka for NH' = 5.5 x 10-10. Kb for F-1.4 x 10-11. (a) Acidic because NHa is a stronger acid than F is a base. (b) Acidic because NHs is a weaker acid than F- is a base. (c) Basic because NHs is a stronger acid than F- is a base (d) Basic because NHs is a weaker acid than F is a base. (e) Neutral because the ratio of acid to base is 1:1. If it takes 50 mL of 0.5 M KOH solution to completely neutralize 125 mL of sulfuric acid solution (H2SO4), what is the concentration of the HaSOs solution? 9. 10. Explain the difference between an endpoint and equivalence point in a titration.Explanation / Answer
8. Answer is a
NH4+ is a strong acid as its conjugate base NH3 is a weak base. While F- is a weak base while its conjugate acid HF is a pretty strong acid.
As a thumb rule, if Ka>Kb, then the solution will be acidic while if Ka<Kb, then it will be basic. If Ka = Kb, then the solution is neutral.
This also means NH4+ will hydrolyze more quickly as it is a strong acid.
9. For a neutralization reaction, the final solution should have a pH of Exactly 7 at 298 K (standard temperature)
So, Number of equivalents of the base X Number of moles of the base = Number of equivalents of acid X Number of moles of acid
No of equivalents of the base ( KOH gives just one pair of OH- ions on hydrolyzation ) = 1
No of equivalents of the acid (H2SO4 gives two H+ ions on hydrolyzation) = 2
Putting all the values into our equation:
Since number of moles = molarity X volume
The equation becomes:
No of eq. of KOH X Molarity X volume = No of eq of H2SO4 X Molarity X volume
Let the concentration of H2SO4 required = y mL
1 X 0.5 M X 0.05 L = 2 X y X 0.125 L
0.025 = 0.25 X y
which gives,
y = 0.1 M
Concentration of H2SO4 solution = 0.1 M
10. The equivalence point is the exact point in a titration when moles of one titrant equal the moles of the analyte in the sample. Another definition can be that it is the point at which the added titrant is chemically equivalent completely to the analyte in the sample. This is the point where the chemical reaction is completed stoichiometrically.
The endpoint is the point where the system changes when the moles of the reacting titrant exceed the moles of the substance being titrated. This can be seen as a sharp change in pH, a surge of voltage, a change in the color of the indicator, etc
For ex. when you add phenolphthalein indicator to titrate HCl with NaOH, there is a color change that is permanent to the solution (i.e. a permanent pink coloration in the solution) when there's an excess of NaOH.
In this case, equivalence point will be when all the HCl in the reaction vessel will be neutralized by the NaOH. At this point, the pH of the medium is neutral.
The endpoint is when the solution starts turning pink due to an excess of NaOH in the reaction vessel,
Thus, it can be said that equivalence point comes before endpoint in a titration.
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