If 267 mL of O2, measured at STP, are obtained by the decomposition of the KClO3 in a 3.33 g mixture of KCl and KClO3, 2KClO3(s) --> 2KCl(s) + 3O2
What is the percent by mass of KClO3 in the mixture?
Given that 1 mole of any gas occupies 22.4 litres at STP you can calculate the number of moles of O2 in 267 ml, (F moles)
2KClO3(s) --> 2KCl(s) + 3O2
tells you that 3 moles of O2 came from 2 moles of KClO3, therefore you can work out how many moles of KClO3 would be needed to yield F moles of O2
number of moles of KClO3
=Fx2/3
Calcluate the molar mass of KClO3, M.
Thus the mass of KClO3 needed is
(Fx2xM/3) g
Hence the percentage of KClO3 in the mixture is
Fx2xMx100%/(3x3.33)
To find the percent by mass of KClO3 in the mixture, you need to calculate the amount of KClO3 present in the 3.33 g mixture.
1. Determine the molar mass of KClO3:
The molar mass of KClO3 is the sum of the atomic masses of each element in its chemical formula. In this case, K (potassium) has a molar mass of 39.10 g/mol, Cl (chlorine) has a molar mass of 35.45 g/mol, and O (oxygen) has a molar mass of 16.00 g/mol. So, the molar mass of KClO3 is:
39.10 g/mol (K) + 35.45 g/mol (Cl) + (3 * 16.00 g/mol (O)) = 122.55 g/mol
2. Calculate the moles of KClO3 in the mixture:
Use the molar mass of KClO3 to convert the mass of the mixture (3.33 g) to moles:
moles of KClO3 = 3.33 g / 122.55 g/mol = 0.0271 mol
3. Use the balanced chemical equation to determine the molar ratio between KClO3 and O2:
From the balanced equation, 2 moles of KClO3 will produce 3 moles of O2.
4. Calculate the moles of O2 produced:
Since the volume of O2 is given as 267 mL, and the equation is balanced such that 2 moles of KClO3 produce 3 moles of O2, we can use the following conversion factors:
1 mole = 22.4 L at STP (Standard Temperature and Pressure)
Convert mL to L: 267 mL * (1 L / 1000 mL) = 0.267 L
Convert L to moles of O2: 0.267 L * (1 mole / 22.4 L) = 0.0119 mol
5. Calculate the moles of KClO3 in the mixture:
Since 2 moles of KClO3 produce 3 moles of O2, we can calculate the moles of KClO3 by multiplying the moles of O2 by the ratio of KClO3 to O2:
moles of KClO3 = 0.0119 mol * (2/3) = 0.0079 mol
6. Calculate the mass percent of KClO3 in the mixture:
Mass percent = (mass of KClO3 / mass of mixture) * 100%
mass of KClO3 = moles of KClO3 * molar mass of KClO3
mass of KClO3 = 0.0079 mol * 122.55 g/mol = 0.965 g
mass percent of KClO3 = (0.965 g / 3.33 g) * 100% = 29.01%
Therefore, the percent by mass of KClO3 in the mixture is approximately 29.01%.