In a .1M aq. soln of NaCN, how would you determine the major species (other than water)? And how would you determine the pH (not exact pH, I just want to know how to know if it is acidic ie. <7, etc).
Thanks in advance
Wouldn't litmus paper or litmus solution determine if the pH is acidic or basic? The pH is approximately 11.
For the species, the fact that it is basic will tell you OH^- is one major specie. Addition of AgNO3 will tell you CN is there but that isn't a definitive test for CN^-. A flame test is far too sensitive but it will tell you Na^+ is a major specie.
Well I'm not actually making it in a lab...I just don't fully understand the concept of this
The concept is to make you think!
To determine the major species in a 0.1 M aqueous solution of NaCN (sodium cyanide), you need to consider the dissociation of NaCN in water. NaCN is an ionic compound that dissociates into sodium ions (Na+) and cyanide ions (CN-) in water. Therefore, the major species in the solution are Na+ and CN- ions.
To determine if the solution is acidic or basic (alkaline), you need to consider the behavior of the CN- ion, which can act as a weak base in water. CN- can react with water to form OH- ions, which makes the solution basic.
The CN- ion can also react with H+ ions (from the auto-ionization of water) to form HCN (hydrogen cyanide) gas. The HCN gas, being a weak acid, contributes to the acidity of the solution.
Now, to determine the pH of the solution, you need to know the concentration of H+ ions. In a 0.1 M aqueous solution of NaCN, you can assume that the concentration of CN- is approximately 0.1 M.
However, the concentration of H+ ions is not provided. To determine whether the solution is acidic (pH < 7), basic (pH > 7), or neutral (pH = 7), you need to know the concentration of H+ ions.
If the concentration of H+ ions is higher than the concentration of OH- ions, the solution will be acidic (pH < 7). If the concentration of H+ ions is lower than the concentration of OH- ions, the solution will be basic (pH > 7). If the concentrations are approximately equal, the solution will be neutral (pH = 7).
To determine the exact pH of the solution, you would need to measure the concentration of H+ ions using a pH meter or perform calculations based on the equilibrium constants of the relevant chemical reactions.