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 mLMass of FeCO3 collected: 23.758 grams.Is this how you would solve it change 100 ml to .1 liters. 115.853x = 23.758 x .1 = .02 liters

Answer 1

Answer on Question #55230 - 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. Is this how you would solve it change 100 ml to .1 liters. 115.853x = 23.758 x .1 = .02 liters

Answer:

Not actually.

First of all in this calculation you have to pay significant attention to significant figures.

When you are transforming units, the result is as following

100.00 mL = 0.10000 L (5 significant figures)

m = 23.758 g (5 significant figures)

You have to use the scientific way of thinking — calculate the quantity of substance and then concentration

$$n \left(\mathrm{Fe}^{2+}\right) = n \left(\mathrm{FeCO}_{3}\right) = m \left(\mathrm{FeCO}_{3}\right) / M w \left(\mathrm{FeCO}_{3}\right)$$ $$M w \left(\mathrm{FeCO}_{3}\right) = 115.8539 \text{ (7 significant figures)}$$ $$n \left(\mathrm{Fe}^{2+}\right) = 23.758 / 115.8538 = 0.20507 \text{ moles (5 significant figures)}$$ $$c \left(\mathrm{Fe}^{2+}\right) = n \left(\mathrm{Fe}^{2+}\right) / V = 0.20507 / 0.10000 = 2.0507 \text{ moles/L (5 significant figures)}$$

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