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minutes of videosCommon brass is a copper and zinc alloy containing 37.0% zinc by mass and having a density of 8.48 g/cm^{3}. A fitting composed of common brass has a total volume of 112.5 cm^{3}. How many atoms (copper and zinc) does the fitting contain?

Hey guys, in this question we're talking about a brass fitting, now brass is just an alloy meaning it's made up of 2 different or maybe more than 2 different elements or metals combined together, in this case we're talking about brass, brass is just copper and zinc combined together they tell us in this question that we have a fitting that's brass and 37 percent of it is Zinc and so the remaining percentage would have to be of course copper so we do 100-37 and that would give me 63 percent and that would represent the copper.

Now if you're going to want me to figure out the amount of atoms of copper and zinc from the information given so they tell me that the density of this fitting is 8.48 grams per 1 centimeters cubed and we're told that the told that the total volume is 112.5 centimeters cubed, so we should realize that if we take this volume and multiply it times the density that would give me the overall mass so we have 112.5 centimeter cubed we're going to multiply it times the density so 8.48 grams for every 1 centimeter cubed so my total mass is going to be 954 grams, now out of this 954 grams 37 percent of it is Zinc 63 percent of it is Copper so we're going to say we have....we can't use percentages we have use the decimal form so you divide these by 100 to get their decimal forms so if we do 954 grams times 0.37 that's going to give me the grams of zinc and all we have to do now is change grams into moles so 1 mole of Zinc is equal to 65.39 grams of Zinc, grams of Zinc cancel out now we have moles 1 mole of zinc is equal to AvogadroÕs number in terms of atoms, so moles cancel out now we have atoms so that's going to be 3.25x10^24 Zinc atoms and then here 954 grams times 0.63 gives me 601.02 grams of copper, we could have also done 954 minus the mass of Zinc and the remained would have given me the same exact answer.

Here do the same exact thing you just have to change this into atoms so it's basically the same to set up except the mass is different since we're dealing with a different element, grams cancel out again now we have moles and all we have to do now is change moles into atoms so moles cancel out now we have atoms so at the end what we're going to get of this is 5.70x10^24 copper atoms. So those would be the to answer that would give us the atoms that we're looking for.

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