Posted by **smartypants** on Saturday, April 21, 2007 at 11:37pm.

How many grams of KCl are produced by the thermal decomposition of KClO3 that produces 25mL of O2 at 25 degrees and at 1 atm?

A)0.0508

B)0.0762

C)0.0835

D)0.125

what is the anwser and what equation would i use to get the anwser?

Write the balanced equation for the decomposition of KClO3.

2KClO3 ==> 2KCl + 3O2.

2. Use PV = nRT to calculate mols of O2 at the conditions given. Don't forget to change 25 C to K. 273 + C = K.

3. Use the equation to convert mols O2 to mols KCl.

4. Convert mols KCl to grams KCl.

mols KCl x molar mass KCl = g KCl.

Post your work if you get stuck.

PV/RT=n

(1atm X .o25L)/ (0.080257 X 298) =

0.00104558 mol O2

Mol O2 converted to Mol KCl =

0.00104558 mol O2 X 3 mol O2/2 molKCl=

0.001568mol KCl

multiplied by 74.551 = 0.116

im stuck

Mol O2 converted to Mol KCl =

0.00104558 mol O2 X 3 mol O2/2 molKCl=

0.001568mol KCl

**This step is not right. 0.00104 x (2 mol KCl/3 mol O2)= mols KCl. Then multiply by 75.55 and you will be ok. Note that mols KCl = mols O2 x (2molKCl/3mol O2)---note that mol O2 in the numerator cancels with mol O2 in the denominator and leaves mols KCl as the unit we want in the numerator. Your factor is the reciprocal of that and gives units that don't make sense; i.e., mols O2 x 3mol O2/2 mol KCl = (mols O2)^2/mol KCl. You can ALWAYS know which way to place the conversion factor if you look at the units. ALWAYS works. **
multiplied by 74.551 = 0.116

im stuck

OMG you are so right i see what i was doing wrong thank you so much ok i got

0.0528

should i mark the first anwser choice since it is the closet?

Check you arithmetic.

I get 0.001022 x 2/3 x 74.55 = 0.0508 g

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