When blood is donated, sodium oxalate solution is used to precipitate Ca^2+, which triggers clot

When blood is donated, sodium oxalate solution is used to...

When blood is donated, sodium oxalate solution is used to precipitate $\mathrm{Ca}^{2+},$ which triggers clotting. A $104-\mathrm{mL}$ sample of blood contains $9.7 \times 10^{-5} \mathrm{g} \mathrm{Ca}^{2+} / \mathrm{mL}$ . A technologist treats the sample with 100.0 $\mathrm{mL}$ of 0.1550 $\mathrm{M} \mathrm{Na}_{2} \mathrm{C}_{2} \mathrm{O}_{4}$ . Calculate $\left[\mathrm{Ca}^{2+}\right]$ after the treatment. (See Appendix $\mathrm{C}$ for $K_{\mathrm{sp}}$ of $\mathrm{CaC}_{2} \mathrm{O}_{4} \cdot \mathrm{H}_{2} \mathrm{O} . )$

Key Concepts

Precipitation Reaction

This concept involves the formation of an insoluble solid (precipitate) when two soluble ionic compounds react in solution. In this context, calcium ions react with oxalate ions to form calcium oxalate, an insoluble salt. Understanding which ions combine to form a precipitate, and the conditions under which precipitation occurs, is key in applications like blood coagulation and various separation methods.

Solubility Product Constant (Ksp)

Ksp is the equilibrium constant for the dissolution of a sparingly soluble ionic compound. It quantifies the product of the concentrations of the ions at saturation, each raised to the power of its stoichiometric coefficient. This concept is crucial for determining the extent to which a compound dissolves under given conditions, and it allows one to calculate the residual concentration of ions in solution after precipitation.

Reaction Stoichiometry

Reaction stoichiometry focuses on the quantitative relationships between the amounts of reactants and products in a chemical reaction. In precipitation reactions, it is essential to use the stoichiometric ratios between the reacting ions to determine how much of one ion will react with another, which in turn affects the final concentrations of ions remaining in solution.

Dilution and Mixing Effects

When two solutions are combined, the total volume increases and the concentrations of all solutes are altered by dilution. This concept is important in calculating the final concentration of ions after mixing different solutions, especially when the initial volumes and concentrations of the reactants are known.

Transcript

00:01 So the chemical reaction is given here, and to determine the molarity of the calcium ions, it is necessary to use the solubility product constant.

00:12 To do so, we need to first know what the initial concentration of the ionic species are.

00:22 So to find moles of calcium 2 plus, what we do is we have 9 .0 .3 .5 .5 .5 .5 .5.

00:35 7 times 10 to the negative 5th and that's grams per milliliter okay and we have 104 millimeters of that and we don't need to convert this to liters because this is in milliliters here and so this will cancel out but we do in order to find the moles we do need to have one mole here and divide it by the mass of the calcium.

01:18 Okay, so that makes the grams cancel out there.

01:22 And this equals 2 .5 times 10 to the negative 4th moles.

01:33 Okay, now we need to find the moles of the c2o4 to minus.

01:46 And we have 100 milliliters.

01:49 This one we do need to convert to liters.

01:52 So we have one liter over a thousand milliliters, and that will cancel those out.

01:59 Okay.

02:02 And we have 0 .155 moles of this per liter.

02:12 So that makes the liters cancel out.

02:20 And this is for this is for the sodium along with the c2 .04.

02:32 Okay.

02:33 So what we need to do is we need to take.