Question

2 K2Cr₂O₇ (aq) + 8 H₂SO₄ (aq) + 3 C₂H₄OH (aq) --> 2 Cr₂(SO₄)₃ (aq) + 2 K₂SO₄ (aq) + 3 CH₃COOH (aq) + 11 H₂O (l)

The above reaction is what occurs in a breathalyzer test. The ethanol (MM = 46.08 g/mol) reacts with the dichromate ion in potassium dichromate (MM = 294.20 g/mol) to produce the green chromate ion in chromium sulfate (MM = 392.21 g/mol). The sample is analyzed in a hand-held spectrophotometer, and the amount of light transmitted is converted into an electrical signal. The signal is then converted to an absorbance value which is proportional to the amount of ethanol in a sample.

Calculate the grams of chromium sulfate formed from 0.0250 g ethanol.

Answer 1

To calculate the grams of chromium sulfate formed from 0.0250 g of ethanol, you need to determine the mole ratio between ethanol and chromium sulfate in the balanced equation. Using the mole ratio and the molar mass of ethanol and chromium sulfate, the calculation is done. The result is approximately 0.1416 g of chromium sulfate formed.

Step-by-step explanation:

To calculate the grams of chromium sulfate formed from 0.0250 g of ethanol, we first need to determine the mole ratio between ethanol and chromium sulfate in the balanced equation. From the equation, we see that 3 moles of ethanol react with 2 moles of chromium sulfate. Using the molar mass of ethanol (C2H5OH) which is approximately 46.08 g/mol, we can calculate the number of moles of ethanol present in 0.0250 g. This is done by dividing the mass by the molar mass:

Moles of ethanol = mass of ethanol / molar mass of ethanol = 0.0250 g / 46.08 g/mol = 0.000542 mol
Now, using the mole ratio from the balanced equation, we can calculate the moles of chromium sulfate formed. Moles of chromium sulfate = Moles of ethanol x (2 moles of chromium sulfate / 3 moles of ethanol) = 0.000542 mol x (2 mol / 3 mol) = 0.000361 mol

Finally, to calculate the grams of chromium sulfate formed, we can use the molar mass of chromium sulfate (Cr2(SO4)3) which is approximately 392.164 g/mol.

Grams of chromium sulfate formed = Moles of chromium sulfate x molar mass of chromium sulfate = 0.000361 mol x 392.164 g/mol = 0.1416 g