00:01
Hi there.
00:02
In this question, we need to determine the empirical formula for a compound that contains potassium, hydrogen, phosphorus, and oxygen.
00:18
So the empirical formula is the formula that shows the elements in the compound in their smallest whole number ratio.
00:26
So that means we need the whole number ratio, and we need to express that in terms of the smallest whole number ratio.
00:36
So i'm just labeling those a, b, c, and d at this point.
00:40
So what we need to do is we need to find the ratio of these elements to each other in this compound.
00:45
And the way to do that is by determining the smallest whole number mole ratio.
00:51
So we are looking for a whole number mole ratio.
00:59
And we are given percentages by mass.
01:04
So remember when you have percentage composition, when it's percent by mass, that is the composition for any size sample.
01:12
And i am trying to get two moles.
01:15
So i need the mass of each of these so that i can convert to moles.
01:18
So to make life simple on myself, i am going to work with a 100 gram sample.
01:30
That way, converting these percent composition to mass to grams is going to be very easy because 28 .7 percent, phosphorus, or i'm sorry, potassium, is going to be 28 .7 percent.
01:48
Grams because 28 .7 % of 100 is 28 .7 grams of potassium.
01:55
The same is going to be true for the hydrogen.
01:58
1 .5 % is 1 .5 grams of hydrogen since we have a 100 gram sample.
02:07
The same is going to be true for the phosphorus and for the oxygen.
02:12
So 22 .8 grams phosphorus and finally 47 grams of oxygen.
02:23
Right.
02:24
Now that we have mass, it's a matter of converting each of these to moles.
02:29
We will do that by dividing by each one's molar mass in turn.
02:34
So for potassium, looking at the periodic table, there are 39 .10 grams of potassium and every mole of potassium.
02:44
This gives us 0 .734 moles of potassium.
02:52
Moving to the hydrogen.
02:54
Molar mass for hydrogen is 1 .008.
02:59
Grams of hydrogen and every mole of hydrogen.
03:04
Again, remember the molar masses come from the periodic table...