For which of following can the metal ions be separated from one another by adding solution of sodium hydroxide?
(a) cobalt nitrate and aluminum nitrate (b) barium nitrate and potassium chloride (c) magnesium nitrate and nickel nitrate (d) potassium nitrate and iron (II) nitrate
The answer is (d), but I don't know why. How would you figure out a question like this?
You must know the solubility rules for this.
a. NaOH added gives you Co(OH)2 and Al(OH)3. Both hydroxides are insoluble so they can't be separated that way.
b. Neither Ba(NO3)2 nor KCl form a ppt, both will be soluble and they can't be separated that way.
c. Both Mg(OH)2 and Ni(OH)2 are insoluble. Same reason as a.
d. KNO3 is soluble in the solution but Fe(NO3)2 forms Fe(OH)2 and it is ibsoluble. Easy to separate that one.
To determine which of the following pairs of metal ions can be separated from each other by adding a sodium hydroxide solution, you need to understand the concept of metal hydroxide precipitation reactions.
In a precipitation reaction, when a soluble salt reacts with a reagent to form an insoluble product (precipitate), a reaction occurs. In this case, metal hydroxides have limited solubility, and when they react with sodium hydroxide, they form insoluble metal hydroxide precipitates.
To figure out the answer, you need to know which of the metal hydroxide precipitates are insoluble. Here's how you can determine this:
1. Check the solubility rules:
You can refer to a solubility chart or solubility rules to determine the solubility of various metal hydroxides. In this case, you need to identify the metal ions in each of the given metal nitrates.
2. Identify the metal ions:
To do this, you can look at the anions in each of the given metal nitrates. For example:
- In cobalt nitrate (Co(NO3)2), the metal ion is cobalt (Co).
- In aluminum nitrate (Al(NO3)3), the metal ion is aluminum (Al).
- In barium nitrate (Ba(NO3)2), the metal ion is barium (Ba).
- In potassium chloride (KCl), the metal ion is potassium (K).
- In magnesium nitrate (Mg(NO3)2), the metal ion is magnesium (Mg).
- In nickel nitrate (Ni(NO3)2), the metal ion is nickel (Ni).
- In potassium nitrate (KNO3), the metal ion is potassium (K).
- In iron (II) nitrate [Fe(NO3)2], the metal ion is iron (Fe).
3. Determine the solubility of the metal hydroxides:
Using the solubility rules, you can determine if the metal hydroxide formed is soluble or insoluble. Generally, hydroxides of Group 1 metals (such as sodium and potassium) and ammonium are soluble, while hydroxides of most transition metals and Group 2 metals are insoluble.
Based on the rules, we can determine the solubility of the metal hydroxides:
- Cobalt hydroxide (Co(OH)2) is insoluble.
- Aluminum hydroxide (Al(OH)3) is insoluble.
- Barium hydroxide (Ba(OH)2) is soluble.
- Potassium hydroxide (KOH) is soluble.
- Magnesium hydroxide (Mg(OH)2) is insoluble.
- Nickel hydroxide (Ni(OH)2) is insoluble.
- Potassium hydroxide (KOH) is soluble.
- Iron (II) hydroxide [Fe(OH)2] is insoluble.
4. Compare the results:
From the above analysis, we can see that among the given options:
- Combining cobalt nitrate and aluminum nitrate will not lead to the separation of metal ions because both cobalt hydroxide and aluminum hydroxide are insoluble.
- Combining barium nitrate and potassium chloride will not lead to the separation of metal ions because both barium hydroxide and potassium hydroxide are soluble.
- Combining magnesium nitrate and nickel nitrate will not lead to the separation of metal ions because both magnesium hydroxide and nickel hydroxide are insoluble.
Finally, we find that combining potassium nitrate and iron (II) nitrate will lead to the separation of metal ions because while potassium hydroxide is soluble, iron (II) hydroxide is insoluble. Therefore, the correct answer is option (d) - potassium nitrate and iron (II) nitrate.