How many moles of potassium Chlorate would decompose on heating to give 60cm^3 of oxygen at 25 degrees Celsius and 1atm?

1 Answer
May 2, 2018

The mass of #"KClO"_3# would be 0.2 g.

Explanation:

There are four steps involved in this stoichiometry problem:

  1. Write the balanced chemical equation
  2. Calculate the moles of #"O"_2#
  3. Calculate the moles of #"KClO"_3#
  4. Calculate the mass of #"KClO"_3#

Step 1. Write the balanced chemical equation.

#M_r:color(white)(m) 122.55#
#color(white)(mmm)"2KClO"_3 →"2KCl" + "3O"_2#

Step 2. Calculate the moles of #"O"_2#

For this calculation, we can use Ideal Gas Law:

#color(blue)(barul|stackrel(" ")( pV = nRT)|)#

We can rearrange this formula to give

#n = (pV)/(RT)#

#p = "1 atm"#
#V = "60 cm"^3#
#"R" = "0.082 06 dm"^3color(white)(l)"atm·K"^"-1""mol"^"-1"#
#T = "(25 + 273.15) K = 298.15 K"#

#n= (1 color(red)(cancel(color(black)("atm"))) × 0.060 color(red)(cancel(color(black)("dm"^3))))/( "0.082 06" color(red)(cancel(color(black)("dm"^3color(white)(l)"atm·K"^"-1")))"mol"^"-1" × 298.15 color(red)(cancel(color(black)("K")))) = "0.0025 mol"#

Step 3. Calculate the moles of #"KClO"_3#

#"Moles of KClO"_3 = 0.0025 color(red)(cancel(color(black)("mol O"_2))) × ("2 mol KClO"_3)/(3 color(red)(cancel(color(black)("mol O"_2)))) = "0.0016 mol KClO"_3#

Step 4. Calculate the mass of #"KClO"_3#

#"Mass of KClO"_3 = 0.0016color(red)(cancel(color(black)("mol KClO"_3))) × ("122.55 g KClO"_3)/(1color(red)(cancel(color(black)("mol KClO"_3)))) = "0.2 g KClO"_3#

Note: The answer can have only one significant figure because that is all you gave for the pressure.

Here's a useful video on volume-mass conversions.