Is each of the following salts acidic, basic or neutral in aqueous solution? Use

Question

Is each of the following salts acidic, basic or neutral in aqueous solution? Use appropriate equations to explain why for each please. a) NH4Cl b) NaClO4 c) NaNO2

Explanation / Answer

are solutions of the following salts acidic, basic, or neutral? for those that are not neutral, write balanced equations for the reactions causing the solution to be acidic or basic a) KCl b) NH4C2H3O2 c)CH3NH3Cl d)KF e)NH4F f)CH3NH3CN Acid and base strength is really a touchy subject, because it tends to be relative. However, here are a few guidelines for you. Strong acids are HClO4, HI, HBr, HCl, H2SO4, and HNO3. (HF is not a strong acid because F is too electronegative and doesn't like to give up its proton.) Strong bases are any group 1 element with OH attached, and usually only Ba in group 2 with OH attached. The key to figuring out this question is to know also that the salts from strong acids and bases tend to form neutral solutions. (Think of them cancelling each other out.) For example, in a), take KCl. K is in group 1, so it is what is called the conjugate of a strong base (that is, KOH is a strong base). Cl is the conjugate of a strong acid (HCl). Thus, this salt will form a neutral solution when mixed with water. (In these problems, assume mixing with water, and always split the water into H+ and OH-.) In this line of reasoning, though, there is some conflict, since according to Chang's Chemistry text, all conjugates of Group 1 and 2 except Be with strong acid conjugates will form neutral salts. Any strong base conjugate with a weak acid conjugate will form a basic solution, and any strong acid conjugate with a weak base conjugate will form an acidic solution. The hard part is knowing where to split these salts to see what they form. a) KCl ---> K+ and Cl- (strong base is KOH, strong acid is HCl, so neutral). b) NH4C2H3O2 ---> NH4+ is a strong base conjugate, just trust me..., and C2H3O2 is sorta nebulous, but not in the list of strong acids so.... predict basic solution. Balanced rxn would be: NH4C2H3O2 + H2O ---> (NH4)+(OH)- + (H)+(C2H3O2)- (I'm just showing the ionic charges so you can tell how they go together... you don't have to put them in your balanced equation Another way to write these is NH4C2H3O2 + H2O ---> NH4+(aq) + C2H3O2-(aq) the (aq) means aqueous and means it is dissolved in water. Both are perfectly acceptable. c)CH3NH3Cl + H2O ---> CH3NH3-(aq) + Cl-(aq)... since HCl is a strong acid, then predict this one to be acidic. d)KF.... since KOH is strong base (K is in group 1) and HF is not a strong acid, then predict basic solution. KF + H2O ---> K+(aq) + F-(aq) e) NH4F... NH4+ and HF are both weak, so neutral (again, the NH4+ thing is just something I learned from experience, hard to explain) f) CH3NH3CN is probably a neutral solution, because the NH3 part of CH3NH3 is a weak base, and HCN (the acid formed from H and CN) is not in our strong acid list, so.... (although CH3NH3 is an organic molecule, and there are some extra effects to consider, but that may be beyond the scope of this problem.)

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