Problem: When 0.84 g of ZnCl2 is dissolved in 245 mL of 0.150 M NaCN, what are [Zn2+], [Zn(CN)4 2−], and [CN−] [Kf of Zn(CN)4 2− = 4.2×1019]?

FREE Expert Solution

We’re being asked to determine [Zn2+], [Zn(CN)42−], and [CN] when 0.84 g of ZnCl2 is dissolved in 245 mL of 0.150 M NaCN


Since the compounds are ionic compounds, they form ions when dissociating in water

The dissociation of ZnCl2 and NaCN in water are as follows:

ZnCl2  Zn2+(aq) + 2 Cl(aq)

NaCN  Na+(aq) + CN(aq)


When Zn2+ and CN are mixed, the complex [Zn(CN)42–] is formed:

Zn2+(aq) + 4 CN(aq)  Zn(CN)42–


The equilibrium constant for this is called the formation constant (Kf) and is associated with the formation of a compound from two ions. Kf is also the opposite of Ksp.


The Kf expression for this is:

Kf = [products][reactants]=[Zn(CN)42-][Zn2+][CN-]4

Note that each concentration is raised by the stoichiometric coefficient: 

[Zn2+] and [Zn(CN)42–] are raised to 1 while [CN] is raised to 4.


We need to do the following for this problem:

Step 1: Calculate the molarity of Zn2+ and CN.
Step 2: Construct an ICE table for the reaction.
Step 3: Calculate the equilibrium concentrations.

79% (226 ratings)
Problem Details

When 0.84 g of ZnCl2 is dissolved in 245 mL of 0.150 M NaCN, what are [Zn2+], [Zn(CN)4 2−], and [CN] [Kf of Zn(CN)4 2− = 4.2×1019]?

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Formation Constant concept. If you need more Formation Constant practice, you can also practice Formation Constant practice problems .

What professor is this problem relevant for?

Based on our data, we think this problem is relevant for Professor Selampinar's class at UCONN.

What textbook is this problem found in?

Our data indicates that this problem or a close variation was asked in . You can also practice practice problems .