Predict qualitatively whether the salts below dissolve to give solutions that are acidic, basic or neutral.
what is the rule for figuring this out?
a. KNO2 - basic
b. Ng(NO3)2 - neutral
c. NH4ClO2 - acidic
d. NaHCO3 - basic
To predict whether a salt will dissolve to give an acidic, basic, or neutral solution, you can use the concept of the ionization of water and the behavior of the constituent ions in solution. Here's a step-by-step approach:
1. Identify the ions that make up the salt:
For example, in the case of KNO2, the ions are K+ and NO2-.
2. Determine the behavior of each ion in water:
a. Cations (positively-charged ions): Most cations from alkali metals (Group 1) and alkaline earth metals (Group 2) do not exhibit acidic or basic properties. Therefore, they can generally be considered as neutral. In this case, K+ is from an alkali metal, so it is considered neutral.
b. Anions (negatively-charged ions): Some anions from weak acids tend to accept protons (H+ ions) from water, making the solution acidic. Examples include NO2- and ClO2-. Anions from strong acids, on the other hand, generally do not affect the pH, and the resulting salt solution is neutral. NaHCO3 contains HCO3- ion which is a weak base, therefore it makes the solution basic.
3. Combine the behaviors of the ions:
The overall effect on the pH of the salt solution depends on the behavior of both the cation and the anion. If the cation is neutral and the anion is basic or acidic, the solution will have a corresponding pH. If both the cation and anion are neutral, the solution will be neutral.
Based on this information, applying the above steps, we can predict the qualitative behavior of the salts given:
a. KNO2: The cation (K+) is neutral, and the anion (NO2-) is a weak base. Therefore, the salt will dissolve to give a basic solution.
b. Mg(NO3)2: Both the cation (Mg2+) and the anion (NO3-) are from strong acids/strong bases. Therefore, the salt will dissolve to give a neutral solution.
c. NH4ClO2: The cation (NH4+) is from a weak base, and the anion (ClO2-) is a weak acid. Hence, the salt will dissolve to give an acidic solution.
d. NaHCO3: The cation (Na+) is neutral, and the anion (HCO3-) is a weak base. As a result, the salt will dissolve to give a basic solution.
Remember, these predictions are based on general trends and assumptions, but there may be some exceptions depending on the specific properties of the ions involved.
I think the difficult way is to try to explain it on the basis of acidic or basic nature of the cation or anion; therefore, I don't think like that.
I write the hydrolysis of the salt (which isn't always correct BUT it gets the right answer) except in some special circumstances.
KNO2 + HOH ==> KOH + HNO2
Now look at the products. KOH is a STRONG base; HNO2 is a WEAK acid; therefore, KNO2 will be basic (from the strong base).
For cases where both the acid and base formed are strong, the salt is neutral.
For cases where both acid and base formed weak, it depends upon which is the stronger and Ka and Kb tables will help you decide. For the extra special case of NaHCO3, I remember (H^+) = sqrt(k1k2) which is about pH 8.3 or so.