A few questions for some master of the MCAT

[going2breakdown]

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1. Here it says a 1M solution of NaOH has a pH of 14. How do I know that, i.e. how do you calculate the pH of a 1M solution of NaOH?

2. How do I figure out the oxidation state of carbon in CN minus ?

 

[maybemed2013]

1. You find pH through this formula---pH = 14 + log [NaOH] log [1] is zero so the pH is 14.
2. Carbon has a positive 4 charge and N has a negative 5 so the net charge is -1.

 

[going2breakdown]

1. You find pH through this formula---pH = 14 + log [NaOH] log [1] is zero so the pH is 14.
2. Carbon has a positive 4 charge and N has a negative 5 so the net charge is -1.

...The first part I get. However, it says the answer for the Oxidation state of C is +2 in cyanide.

 

[solitarius]

A few things:

1. Hydroxide is a strong base with 100% dissociation. Thus, pOH = [OH] = starting [NaOH] = 1 M. 1 = 1 x 10^0; therefore, pOH = 0 and pH = 14.

2. Be careful about oxidation state vs. formal charge. Formal charge of C would be -1 and N = 0 based on the Lewis structure :C=N:. For oxidation state, N's higher electronegativity dictates the relationship. N typically has a -3. Since the molecule has a -1, C must equal +2 to balance out.