State whether each of the following aqueous solutions would be acidic, basic, or neutral. Include appropriate net-ionic equations to show why a given solution is acidic or basic.
a) NaNO3
b)KC6H5CO2
c)50:50 mixture of C6H5CO2H+KC6H5CO2
d)(CH3NH3)Cl
e)50:50 mixture of CH3NH2+(CH3NH3)Cl
f)50:50 mixture of 0.1M NaBr +0.1M HBr
-How can you tell which substance receives the H+ or not? and which one is neutral?
The correct answer to your question is that you must recognize the kind of solution you have. Sometimes that is easier said than done, especially until you get some practice at it. Practice makes perfect.
1. If it is a salt (a,b,d), the Bronsted-Lowry Theory tells you. In the case of NaNO3, neither Na+ nor NO3- is hydrolyzed; therefore, NaNO3 is neutral in water solution. For b (potassium benzoate), the benzoate ion is hydrolyzed, the K+ is not, so the benzoate takes the H+ and releases OH- and the solution is basic. (But see below for what I use.)
2. For solution that are not salts but are mixtures, such as c, e, and f, use of the Henderson-Hasselbalch equation will tell you. (But see below to see how I do it.)
Frankly, for salts, I use another approach. It will be frowned on by your teacher, I'm sure, but it works every time. For NaNO3,
NaNO3 + HOH ==> NaOH + HNO3.
The reaction actually does not take place BUT you can use it to answer the question of acidity or basicity. NaOH is a strong base. HNO3 is a strong acid. Therefore, the salt is neutral in water. What about KC6H5CO2?
C6H5COOK + HOH ==> C6H5COOH + KOH
C6H5COOH is a weak acid. You can find it listed in Ka tables. KOH is a strong base. In water, solution, the salt is basic (because of the strong base part). etc. I will leave d for you.
For c, the H-H equation is
pH = pKa + log (base/acid).
pH = look up the value of Ka (and convert to pKa) or pKa C6H5COOH and substitute for pKa in the equation. Then substitute into the log part. A 50:50 mixture means base and acid or equal so base/acid = 1 and log 1 = 0; therefore, pH = pKa and you will know acid or base for the solution.
Be sure to follow up if some of this is murky.
What do I do for mixtures? If it is a mixture of weak acid and its salt the solution will be acidic. If it is a mixture of a weak base and its salt, the solution will be basic.
Thank you so much!
a) NaNO3: NaNO3 dissociates into Na+ and NO3- ions in water. Both Na+ and NO3- ions are spectator ions that do not participate in the acidity/basicity of the solution. Therefore, NaNO3 is neutral.
Net-ionic equation: There is no net-ionic equation since there is no reaction taking place.
b) KC6H5CO2: KC6H5CO2 dissociates into K+ and C6H5CO2- ions in water. The C6H5CO2- ion is the conjugate base of a weak acid (C6H5CO2H), which can accept protons (H+ ions) from water. Thus, the solution is basic.
Net-ionic equation: C6H5CO2- + H2O → C6H5CO2H + OH-
c) 50:50 mixture of C6H5CO2H + KC6H5CO2: This mixture consists of an acidic component (C6H5CO2H) and its conjugate base (C6H5CO2-) from KC6H5CO2. Since the acidic and basic components are in equal concentrations, the solution is neutral.
Net-ionic equation: There is no net-ionic equation since there is no reaction taking place.
d) (CH3NH3)Cl: (CH3NH3)Cl dissociates into (CH3NH3)+ and Cl- ions in water. The (CH3NH3)+ ion is the conjugate acid of a weak base (CH3NH2), which can donate protons (H+ ions) to water. Thus, the solution is acidic.
Net-ionic equation: (CH3NH3)+ + H2O → CH3NH2 + H3O+
e) 50:50 mixture of CH3NH2 + (CH3NH3)Cl: This mixture consists of a basic component (CH3NH2) and its conjugate acid (CH3NH3+) from (CH3NH3)Cl. Since the basic and acidic components are in equal concentrations, the solution is neutral.
Net-ionic equation: There is no net-ionic equation since there is no reaction taking place.
f) 50:50 mixture of 0.1M NaBr + 0.1M HBr: Both NaBr and HBr dissociate into their respective ions when dissolved in water. The bromide ion (Br-) from NaBr and HBr is a spectator ion and does not participate in the acidity/basicity. HBr is a strong acid that fully dissociates, resulting in a high concentration of H+ ions. Therefore, the solution is acidic.
Net-ionic equation: H+ + H2O → H3O+
In general, an acidic substance donates protons (H+ ions) to water, resulting in an increase in H+ concentration. A basic substance accepts protons (H+ ions) from water, resulting in an increase in OH- concentration. A neutral substance does not significantly donate or accept protons, resulting in an equal concentration of H+ and OH- ions.
To determine whether a given aqueous solution is acidic, basic, or neutral, we need to consider the nature of the ions present in the solution and their interaction with water.
a) NaNO3:
NaNO3 is a salt composed of sodium ions (Na+) and nitrate ions (NO3-). Both sodium ions and nitrate ions do not react with water to produce H+ or OH- ions. Therefore, when NaNO3 is dissolved in water, it remains as Na+ and NO3- ions. Since there is no production of H+ or OH- ions, the solution is neutral. The net-ionic equation is: N/A (no reaction).
b) KC6H5CO2:
KC6H5CO2 is a salt composed of potassium ions (K+) and benzoate ions (C6H5CO2-). Similar to the previous case, neither potassium ions nor benzoate ions react with water to produce H+ or OH- ions. Consequently, the solution is neutral. The net-ionic equation is: N/A (no reaction).
c) 50:50 mixture of C6H5CO2H + KC6H5CO2:
This mixture contains equal amounts of benzoic acid (C6H5CO2H) and potassium benzoate (KC6H5CO2). Benzoic acid is a weak acid, and when it dissolves in water, it donates a proton (H+) to water, producing hydronium ions (H3O+) and benzoate ions (C6H5CO2-). Conversely, potassium benzoate dissociates into potassium ions (K+) and benzoate ions (C6H5CO2-). The presence of hydronium ions (H3O+) makes the solution acidic. The net-ionic equation for the acidic reaction is: C6H5CO2H + H2O → H3O+ + C6H5CO2-
d) (CH3NH3)Cl:
(CH3NH3)Cl contains the cation methylammonium (CH3NH3+) and the anion chloride (Cl-). Methylammonium is a weak base, and when it reacts with water, it accepts a proton (H+) from water, producing hydronium ions (H3O+) and methylamine (CH3NH2). Consequently, the solution is acidic. The net-ionic equation for the acidic reaction is: CH3NH3+ + H2O → CH3NH2 + H3O+
e) 50:50 mixture of CH3NH2 + (CH3NH3)Cl:
This mixture contains equal amounts of methylamine (CH3NH2) and methylammonium chloride [(CH3NH3)Cl]. Methylamine is a weak base and donates a lone pair of electrons, reacting with hydronium ions (H3O+), which are produced from the reaction of methylammonium cation [(CH3NH3)+] with water. This reaction forms methylammonium chloride and water. Consequently, the solution is basic. The net-ionic equation for the basic reaction is: CH3NH2 + H3O+ → (CH3NH3)+ + H2O
f) 50:50 mixture of 0.1M NaBr + 0.1M HBr:
This mixture contains sodium bromide (NaBr) and hydrobromic acid (HBr). Hydrobromic acid (HBr) is a strong acid, which, when dissolved in water, dissociates completely, producing hydronium ions (H3O+) and bromide ions (Br-). Sodium bromide (NaBr) is a salt composed of sodium ions (Na+) and bromide ions (Br-). Since hydronium ions (H3O+) are present, the solution is acidic. The net-ionic equation for the acidic reaction is: HBr + H2O → H3O+ + Br-.
Overall, to determine whether a substance receives the H+ or not and whether a solution is acidic, basic, or neutral, one needs to consider the nature of the ions present and their ability to interact with water. Strong acids and bases fully dissociate to form H+ and OH- ions, respectively, while weak acids and bases only partially dissociate.