Each of the following solutions has a concentration of 0.1 mol/L. Compare the hydronium-ion concentration and pH in each pair, and explain why they are different.
a) H2SO4(aq) vs. H2SO3(aq)
b) H2S(aq) vs. NH3(aq)
To compare the hydronium-ion concentration and pH in each pair, we need to understand the chemical properties of the given solutions.
a) H2SO4(aq) vs. H2SO3(aq):
H2SO4 (sulfuric acid) is a strong acid, which means it dissociates completely in water to produce hydronium ions (H3O+). Since the concentration of H2SO4 is given as 0.1 mol/L, the concentration of H3O+ is also 0.1 mol/L.
H2SO3 (sulfurous acid), on the other hand, is a weak acid. It does not fully dissociate in water, and only a fraction of it dissociates to produce hydronium ions. Therefore, the concentration of H3O+ in H2SO3(aq) is less than 0.1 mol/L.
As a result, the hydronium-ion concentration in H2SO4(aq) is higher compared to H2SO3(aq), leading to a lower pH in H2SO4(aq) compared to H2SO3(aq). The high concentration of hydronium ions in H2SO4(aq) makes it highly acidic.
b) H2S(aq) vs. NH3(aq):
H2S (hydrogen sulfide) is a weak acid that partially dissociates in water to produce hydronium ions (H3O+) and sulfide ions (HS-). The concentration of H3O+ in H2S(aq) will depend on the extent of dissociation, which can be calculated using the acid dissociation constant.
NH3 (ammonia) is a weak base that reacts with water to produce hydroxide ions (OH-) and ammonium ions (NH4+). The concentration of hydroxide ions in NH3(aq) will depend on the extent of reaction with water, which can be calculated using the base dissociation constant.
Both H2S and NH3 are weak, but H2S is an acid while NH3 is a base.
Therefore, while H2S(aq) will have a higher concentration of hydronium ions (H3O+), NH3(aq) will have a higher concentration of hydroxide ions (OH-).
Since pH is a measure of the concentration of hydronium ions, H2S(aq) will have a lower pH compared to NH3(aq). The high concentration of hydronium ions in H2S(aq) indicates its acidic nature, whereas the presence of higher concentration of hydroxide ions in NH3(aq) makes it basic.
To compare the hydronium-ion concentration and pH in each pair of solutions, we need to understand the acid-base properties of the given compounds and compute the concentration of hydronium ions using the given concentration.
a) H2SO4(aq) vs. H2SO3(aq):
H2SO4 is a strong acid, while H2SO3 is a weak acid. In aqueous solutions, H2SO4 fully dissociates into H3O+ (hydronium) ions and HSO4- ions, whereas H2SO3 partially dissociates into H3O+ (hydronium) ions and HSO3- ions. Since H2SO4 is a strong acid, it produces a higher concentration of hydronium ions compared to H2SO3. Therefore, the hydronium-ion concentration and pH would be higher in the H2SO4 solution compared to the H2SO3 solution.
To calculate the hydronium-ion concentration, we can use the concentration of the solution (0.1 mol/L in both cases):
For H2SO4: Since it is a strong acid, it ionizes completely:
[H3O+] = 0.1 mol/L
For H2SO3: Since it is a weak acid, the degree of ionization is less than 100%. Assuming it ionizes to a small extent, let's say x:
[H3O+] = x mol/L
b) H2S(aq) vs. NH3(aq):
H2S is an acidic compound, while NH3 is a basic compound. In water, H2S undergoes partial dissociation, producing some H3O+ (hydronium) ions and HS- ions. On the other hand, NH3 acts as a weak base, accepting H3O+ ions and producing NH4+ ions. The equilibrium and the extent of ionization will determine the hydronium-ion concentration.
To compare their hydronium-ion concentration and pH, we need to know the equilibrium constants (Ka values) for these reactions. However, the question only provides their concentration. Therefore, we cannot definitively determine the exact hydronium-ion concentration or pH. However, we can still hypothesize the results based on the acid-base properties of H2S and NH3:
Since H2S is an acidic compound, it will produce a higher concentration of hydronium ions compared to NH3. Therefore, we would expect the hydronium-ion concentration and pH to be higher in the H2S solution compared to NH3. However, without additional information or equilibrium constants, we cannot calculate the exact values.
In summary, the difference in hydronium-ion concentration and pH in each pair of solutions is primarily due to the acid-base strength of the compounds involved. Stronger acids or acidic compounds will generally result in higher hydronium-ion concentrations and lower pH values compared to weaker acids or basic compounds.
a) H2SO4 is a strong acid (at least the first H is) and H2SO3 is a weak acid (both H are weak).
The H3O^+ of H2SO4 is essentially the molarity. For H2SO3, you must set up an ICE chart from
H2SO3 ==> H^+ + HSO3^-
and solve for H^+
For H2S,
H2S ==> H^+ + HS^-
Set up ICE chart and solve for H^+.
For NH3,
NH3 + HOH ==> NH4^+ + OH^-
Set up ICE chart and solve for OH^- and convert to pH.
There isn't anything difficult about this question but it's a lot of leg work to get it done.
Post your work if you get stuck.