Question

A student performs the following gravimetric analysis of iron ions in a water system:
Fe2+ (aq) + 2CO32- (aq) = FeCO3 (s)
If this student used excess carbonate and obtained the following data, what was the original concentration in moles/L) of Fe2+ in the water sample?
Total Volume of Solution: 100.00 mL
Mass of FeCO3 collected: 23.758 grams.

Answer 1

Answer on Question #55228 - Chemistry - General chemistry

Question:

A student performs the following gravimetric analysis of iron ions in a water system:

Fe²⁺ (aq) + 2CO₃²⁻ (aq) = FeCO₃ (s)

If this student used excess carbonate and obtained the following data, what was the original concentration in moles/L of Fe²⁺ in the water sample?

Total Volume of Solution: 100.00 mL

Mass of FeCO₃ collected: 23.758 grams.

Answer:

If student has used excess of carbonate, all the Fe²⁺ ions are precipitated in form of FeCO₃. It means that number of moles of obtained carbonate is equal to quantity of ions Fe²⁺.

$$n \left(\mathrm{Fe}^{2+}\right) = n \left(\mathrm{FeCO_3}\right) = m \left(\mathrm{FeCO_3}\right)/Mw\left(\mathrm{FeCO_3}\right)$$ $$c \left(\mathrm{Fe}^{2+}\right) = n \left(\mathrm{Fe}^{2+}\right)/V = m \left(\mathrm{FeCO_3}\right)/\left(Mw\left(\mathrm{FeCO_3}\right) \times V\right) = 23.758 \left(g\right)/\left(115.8539 \left(g/moles\right) \times 0.10000 \mathrm{~L}\right) = 2.0507 \mathrm{~moles/L}$$

Original concentration was 2.0507 moles/L

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