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August 31, 2014

Homework Help: chemistry

Posted by sarah on Thursday, March 1, 2007 at 12:30pm.

i need to deduce the type of bonding that holds sodium cyanide together
and write a balanced equation for sodium cyanide dissolving in water

any help would be appreciated

sarah

Na^+ + :C:::N:^-
Na to CN bond is ionic (more or less).
C-N bond is covalent.
NaCN + HOH ==> NaOH + HCN.
The Na is not involved. The net ionic equation is
CN^- + HOH ==> HCN + OH^-

thank you very much for getting back to me but i'm more confused now
how do you get the balanced chemical equation NaOH + HCN
i also need to state whether it is covelent or ionic the text i have worked from doesn't say which is involved in these bonds it just wants one or the other
i'm beginning to think i should have chosen a different subject.


I have the same question. I took write a balanced equation for the reaction that occurs when sodium cyanide dissolves in water as a separate question, to the type of bonding.

Read the beginning of the question about the chemicals that will give you some clues about answering it.


The electronegativity of C is 2.55 on a chart I have and the EN of Na is 0.9. The difference is 1.65 which is VERY close to a 50% covalent-50% ionic bond. Technically we would call this a covalent bond. USUALLY when a question asks about a bond in a molecule the bond between the cation and the anion is the one the focus on. Since I don't know your text or your prof's views, I don't know which answer to give. Polar covalent would be my best answer if we ignore the bond for the anion which is the CN^- ion. And the break even point for covalent/ionic character is also murcky; i.e., some use 1.7, some 1.9, and some 2.1. To add confusion, some call the bond ionic if it is more than 50% ionic and they call it covalent if it is more than 50% covalent and don't quibble about polar covalent. Your job is to take all of this information in and answer according to your notes and your text's views. As for the equation, NaCN is the salt of a strong base (NaOH) and a weak acid (HCN). When NaCN is placed in water, it hydrolyzes (reacts with) water. Actually, the Na^+ doesn't react; only the CN^- does. The net ionic equation for the hydrolysis of CN^- is
CN^- + HOH ==> HCN + OH^-.

CN^- is a stronger Bronsted-Lowry base than water; therefore, it pulls a H^+ away from HOH to form HCN. The OH^- remains. That means that a solution of NaCN is basic BECAUSE OH^- are produced. You can even calculate the ionization constant for CN^- as a base. It is Kw for water/Ka for HCN.

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