WEBVTT
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when we're converting between given quantities of measurement describing amounts
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of substances it's helpful to draw out a roadmap were
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planned to know which conversion to use when. So
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if, for example, we're starting off with a
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given quantity of Yuri's in this case 8.35 moules of
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copper, one carbonate. Okay, and we want
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to know the mass equivalent or how many grams to
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go between moles and mass. The relationship that we
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use is the molar mass, and we find the
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molar mass by using the formula of the compound and
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the periodic table. So to figure out what copper
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carbonate is copper is See you in the room.
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Number one indicates it's got a charge plus one.
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The carbonate ion is CEO three tu minus. So
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to make it a neutral ionic compound, the formula
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is see you too, CEO three. And then
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using our periodic table, we find the molar.
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Mass. One mole is equal to the mass of
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copper from the periodic table times two so two times
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63 0.5 46 plus the massive carbon 12.11 plus three
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times the mass of oxygen. So these numbers here
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have all come from the periodic table is the atomic
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mass of each element. And so when we multiply
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and add them together, one mole of copper Kirk
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Copper carbonate has a molar mass of 187 0.10 grams
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. So using this relationship, the molar mass.
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If we have 8.35 moles, we can change it
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to grams by multiplying by the molar mass. So
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we multiply 8.35 times 187.10 or a molar mass of
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a total mass of 1.56 times 10 to the third
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grams. So 8.35 moles is equal to 1.56 times
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10 to the third cramps. Another example. We
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might be given molecules instead of molds when we have
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molecules. The relationship that we used to change two
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moles is Allah God rose number because that tells us
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that in every mole there are 6.2 times 10 to
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the 23rd molecules. And then if we want to
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go from molecules two grams after we changed two moles
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, we again use our molar mass. So in
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this case, We're talking about a compound called Die
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Nitrogen hence oxide. So to find the molar mass
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of die nitrogen pent oxide, we find the formula
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. We know that it has nitrogen and the dye
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means there are two. It has oxygen and the
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pent means five. So I have n 205 So
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we confined our Moeller Mass just like we did above
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by multiplying two times the molar mass of nitrogen were
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14 point 007 plus five times the molar mass of
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oxygen 15.999 We're one more is equivalent to 108 0.1
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grams. This is a two step problem where we
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first start off with our molecules. We changed two
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moles using of a god rose number one more is
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equal to 6.2 times 10 to the 23rd molecules.
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And then we changed two grams using our Mueller Mass
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. We're one more has a mass of 108.1 grams
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, so multiplying 4.4 times 10 to the 20 times
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108.1 women dividing by 6.2 times 10 to the 23rd
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gives us the answer of 0.0 7 to 5 grams
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. You may be given a mass to start with
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and then find quantities and moles, formula units and
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then even smaller descriptions based on what the chemical formula
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is. So if we have 78.9 grams of a
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compound called sodium per chlorate, we can find how
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many moles this is equivalent to and again grams to
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moles. We use the molar mass. We confined
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on a smaller level. How Maney formula units this
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is equivalent to, and a formula unit is just
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the smallest unit of an Ionic compound. So again
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, we use Allah God Rose number. So before
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we start converting, we need to figure out what
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sodium per chlorate is. Sodium is an eye on
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an A plus. The per chlorate ion is C
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L 04 with an overall minus one charge. So
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the formula is N a. C l 04 and
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the molar mass is equal to the mass of sodium
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plus the massive chlorine plus four oxygen's or 122.44 grams
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so I can convert from my given grams, two
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moles because I want it in moles I divide by
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the Moeller math. So 78.9 divided by 100 and
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22.44 in this equals 0.644 moles find the equivalent and
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formula units. I take my number of moles and
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I multiply by Abu God Rose number So this equals
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3.88 times 10 to the 23rd formula units Ah,
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an a c l o For we can use that
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information to break it down even further If I want
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to know how maney sodium ions there are for every
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formula unit of an a c l 04 there is
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one sodium ion. So if I have 3.88 times
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10 to the 23rd formula unit, I will also
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have the same amount of sodium ion. Similarly,
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for every formula unit, I have one per chlorate
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ion. So I should also have 3.88 times 10
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to the 23rd quarry. I am for every same
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quantity of formula units. If I want to know
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how many chlorine atoms, if I look at the
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formula here in this formula for every one of these
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, there's one chlorine Adam. So if I have
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3.88 times 10 to the 23rd formula units, I
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should have the same amount of chlorine atoms or 3.88
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times 10 to the 23rd Chlorine atoms. If,
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however, I ask how maney oxygen atoms are,
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you can see that in one formula unit there are
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four oxygen atoms. So that means that there will
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be four times as many oxygen atoms in the given
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quantity. Okay, who are 1.55 times 10 to
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the 24 atoms of oxygen.