Question

Given the following recipe:

H2SO4 = 0.00200 mol/L Solution equilibrated with an excess of CaCO3(s) (calcite). The Ksp of calcite is 10-8.35
i) List the species present at equilibrium and find n equations for your n unknowns. (Hints: find out what carbonate does on your pKa chart.)
ii) You will have one "b" expression for each "non-simple" mole balance equation and one more for the charge balance equation. Write these down.
iii) Choose one parameter to guess in each "b" expression (for example, for the b expression from your charge balance, you will choose pH, which gives you the parameter[H+])
iv) Write down the list of equations you will use in Excel to calculate the concentrations of all of your species (remember that you will only use equilibrium expressions and simple mole balance equations to derive these equations; you will not use the equations you are using as your "b" expressions).

Answer 1

The equation for the dissociation of CaCO3(s) into calcium ions and carbonate ions is CaCO3(s) → Ca²+(aq) + CO3²−(aq). The Ksp of calcium carbonate is 4.5 × 10−⁹. At equilibrium, there are three species present: Ca²+, CO3²−, and HCO3−.

Step-by-step explanation:

The equation for the dissociation of CaCO3(s) into calcium ions and carbonate ions is: CaCO3(s) → Ca²+ (aq) + CO3²−(aq). The equilibrium concentrations of each ion are equal to s, which represents the molar solubility of CaCO3. The Ksp of calcium carbonate is 4.5 × 10−⁹.

Using a pKa chart, we can find that carbonate acts as a base and forms bicarbonate ions when dissolved in water. Therefore, at equilibrium, we have Ca²+, CO3²−, and HCO3− ions present. These ions can be represented by three equations: CaCO3(s) → Ca²+ + CO3²−, CO3²− + H2O → HCO3− + OH−, and H2O → H+ + OH−.

To calculate the concentrations of all species, we can use the solubility product expression for calcium carbonate and the equilibrium expressions for the bicarbonate and hydroxide ions. We can also use mole balance equations and charge balance equation to derive the necessary equations.