Which of the following is a stronger lewis base: cyanide ion or dicarbide ion?
I'm assuming it is the dicarbide ion as it is more negatively charged and a compound consisting of 2 carbons is larger and therefore more likely to lose electrons than something consisting of carbon and nitrogen. I've extensively searched the internet looking for an answer and have yet to come across a definitive solution.
I looked, also, and didn't find an answer in print that answers the question in so many words ut I think you're right and for this reason.
If we look at the hydrolysis of each we have
CN^- + HOH ==> HCN + OH^-
Kb for CN^- = Kw/Ka for HCN. Ka for HCN is approx 10^-10 so Kb for CN is approx 1E-14/1E-10 = 1E-4.
For C2^2- + 2HOH ==> C2H2 + 2OH^-
Kb for (C2)^2 = Kw/Ka for HCCH. If you google acetylene you will find pKa of 25 for those H atoms so
Kb = 1E-14/1E-25 = 1E11 which makes Kb for (C2)2- much stronger than that for CN^-
Hope this helps.
To determine which molecule is a stronger Lewis base, we need to understand the Lewis acid-base theory and the factors that influence the strength of a Lewis base.
In the Lewis acid-base theory, a Lewis base is an electron pair donor, while a Lewis acid is an electron pair acceptor. A stronger Lewis base is one that is better able to donate electron pairs to form a coordinate bond with a Lewis acid.
In this case, we are comparing the cyanide ion (CN-) and the dicarbide ion (C₂²-). To evaluate their strengths as Lewis bases, we can consider the following factors:
1. Electron availability: The more electronegative an atom, the more it tends to attract electron density towards itself. In general, nitrogen (N) is more electronegative than carbon (C), which suggests that the cyanide ion (CN-) might have a greater electron density available for donation.
2. Size and charge: The larger the atom or ion, the more diffuse its electron cloud. Additionally, a higher charge increases the electron density and the likelihood of electron donation. In this case, the dicarbide ion (C₂²-) has a higher negative charge than the cyanide ion (CN-), which may make it a stronger Lewis base.
Considering these factors, it is reasonable to think that the dicarbide ion could be a stronger Lewis base. However, without specific experimental data or a reliable source discussing this specific comparison, it is difficult to determine the definitive answer.
When faced with questions regarding the relative strength of Lewis bases, it can be helpful to consider the molecular properties and trends, as well as consult reliable literature or textbooks for more specific information.