. A 0.428-gram sample of a mixture of the solids, KCl and KClO3, is heated. If 80.7 mL of oxygen gas is collected over water at 18.0 oC and 100.8 kPa, calculate the mass percentage of KClO3 in the mixture. (PH2O at 18.0 oC = 15.5 torr
To calculate the mass percentage of KClO3 in the mixture, you need to determine how much oxygen gas is produced from the decomposition of KClO3 and then compare it to the total mass of the mixture.
Here's how you can approach this problem:
1. Convert the pressure of water vapor collected (PH2O) from torr to atm, since the pressure of oxygen is given in atm. 1 atm = 760 torr, so PH2O in atm = 15.5 torr / 760 torr.
2. Use the ideal gas law, PV = nRT, to calculate the number of moles of oxygen gas (n) collected over water. Rearrange the formula to solve for n: n = PV / RT, where P is the pressure of oxygen gas, V is the volume of gas collected, R is the ideal gas constant (0.0821 L·atm/mol·K), and T is the temperature in Kelvin.
Convert the given volume of oxygen gas (80.7 mL) to liters by dividing by 1000 since 1 L = 1000 mL.
Convert the given temperature of 18.0 oC to Kelvin by adding 273.15.
Substituting the values, you can find the number of moles of oxygen gas.
3. Write and balance the chemical equation for the decomposition of KClO3. It decomposes into KCl and oxygen gas.
2KClO3 → 2KCl + 3O2
4. Calculate the molar ratio between KClO3 and O2. Compare the coefficients in the balanced equation to determine the ratio. In this case, for every 2 moles of KClO3 that decompose, 3 moles of O2 are produced.
5. Use the mole ratio between KClO3 and O2 to calculate the number of moles of KClO3 that decomposed. Multiply the number of moles of O2 calculated in step 2 by the mole ratio.
6. Finally, calculate the mass percentage of KClO3 in the mixture. Divide the mass of KClO3 decomposed (in grams) by the initial mass of the mixture (0.428 grams) and multiply by 100 to obtain the mass percentage.
By following these steps, you will be able to determine the mass percentage of KClO3 in the mixture.
I assume that 18.0 is 18mm Hg.
2KClO3 ==> 2KCl + 3O2
Calculate mols O2 from PV = nRT
Since the pressure is listed in kPa and the vapor pressure in mm Hg you must convert one of them. I would convert 18.0 mm to kPa.
18.0 mm Hg x (1 atm/760 mm Hg) x (101.325 kPa/1 atm) = 2.399 kPa.
Ptotal = 100.8 = pO2 + pH2O
pH2O = 2.399. Solve for pO2 and substitute that for P in PV = nRT
You know V(in L), R(8.314) and T (in kelvin).
mols O2 x (2 mol KClO3/3 mols O2) = mols KClO3.
g KClO3 = mols KClO3 x molar mass KClO3
%KClO3 = (g KClO3/mass sample)*100 = ?