7. Gases
Gas Stoichiometry
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So here it says, what mass of silver oxide is produced when 384 milliliters of oxygen gas at 736 millimeters of mercury and 25 degrees celsius is reacted with excess solid silver. Alright. So step 1 is we need to map out the portion of the stoichiometric chart you will use. They're giving us within this question the volume of the gas, the pressure of the gas, and its temperature. So we know with that information we can find the moles of our gas because moles equals pressure times volume divided by r t. First, we need to convert our pressure into atmospheres. Remember, 1 atmosphere is 760 torres or 760 millimeters of mercury. Millimeters of mercury cancel out and when we do that we get 0.9684 atmospheres. Then we are going to take the volume which is 0.384 liters. You're going to divide that by the r constant. And then remember you add 273.15 to get 298.15 kelvin from the temperature. This information here, what is it doing? It's converting the given quantity that we have, these amounts, into our moles of given. So when I plug all this in, my moles of given for oxygen gas comes out to be 0.015 199 moles of oxygen gas. Now that we have moles of given, we go to step 3. We do a mole to mole comparison to convert moles of given into the moles of our unknown. So we're gonna say here, moles of oxygen go on the bottom. Our unknown is what we're being asked to find, which is our silver oxide. At this point, we need to do a mole to mole comparison, which says that for every one mole of oxygen gas we have 2 moles of silver oxide. So moles of oxygen gas cancel out and now we have moles of silver oxide. Now step 4, if necessary, convert the moles of unknown into the final desired units. Alright. They're not asking us for moles of silver oxide so I'm just continuing onward till we get grams of silver oxide. So for every one mole of silver oxide, the mass of 2 silvers and one oxygen has a combined mass of 231 0.7 grams of silver oxide. Moles of silver oxide cancel out and now I have my final answer of silver oxide. So that comes out to be 7.0 grams of silver oxide. Here our answer has 2 significant figures because 25 has 2 significant figures. Here we didn't have to do step 5 because in step 5 it says recall, if you calculate more than one final amount then you must compare them to determine the theoretical yield. Here we are only given amounts for oxygen gas. So step 5 isn't necessary. Now if you don't remember the whole concept of theoretical yield, make sure you go back and take a look at my topic videos on theoretical yield. What does it mean and how does it relate to stoichiometry is explained in those series of videos. Alright. So now that we've gotten our answer, this is the approach we need to take when it comes to gas stoichiometry.
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