Percent Composition By Mass Part 1
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Percent Composition By Mass Part 1

October 14, 2019


If you’re struggling with percent
composition, I’ll show you that it really only takes three simple steps. Hello
everyone, I’m Melissa Maribel your personal tutor and in this example we
are calculating percent composition of each element in the compound of
potassium oxide or K2O. Here’s the general formula for percent composition
by mass on top we have the mass of the element divided by the mass of the
compound all multiplied by 100. We will apply this formula to find the percent
composition of potassium and this is what we’ll use. Step 1: Find the total
mass of the element. Using our periodic table we’ll find the molar mass of
potassium and since there’s a two subscript in K2O
we must multiply 2 times the molar mass of potassium and we get 78.20. Step two: Find the total mass of the compound. To find the total
mass of the compound we need to find each individual mass of each element and
add them together. So we already found potassium we now need oxygens mass so
looking at our periodic table oxygens mass is 16.00, so we will
add the total mass of each element together to get our total mass of the
compound which is this. Step 3: Plug everything into the formula so we’ll
plug in the total mass of potassium and the total mass of the compound and then
make sure to divide first then multiply the answer by 100 and we’ll round to
four sig figs to get this for our percent composition of potassium but we
still need oxygens percent composition. So let’s set that up for oxygen we
previously found the total mass of the compound we also know the total mass of
oxygen is 16.00, now let’s divide both of those values and then
multiply by 100 and we will get our percent composition of oxygen rounded to
four sig figs. So here are the percent compositions of each element. If you’re
up for a little bit of a challenge then this other video
is for you and remember stay determined you can do this!

Only registered users can comment.

  1. Thank you! My chem teacher was making this percent composition diff but when i watched your vid this %comp become easyyyyyyyyy

  2. If when both of the percentages are added up and they don’t equal 100, does it mean it’s wrong? And plus do we have to round? Thx love ur vids‼️‼️‼️

  3. Very nice video but can you use these in a real equation lol? Like a reactant and product equation. I can’t find a video that teaches it well

  4. Ughh, you make me so motivated to keep on pushing forward in Chemistry this semester!! God Bless you so much Melissa, I appreciate you! <3 <3

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