Standard Temperature and Pressure Example 1

Jules Bruno
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here in this example question. It says a sample of oxygen gas has a measured volume of 325 m. Els at STP. How many grams are present? All right, so here they're giving us volume in the forms of milliliters. An STP is giving us temperature plus pressure. We know from the ideal gas law with these values given to us or these variables given to us. The only thing that's missing is our moles. Because we have volume already. We have pressure and temperature and we always know what our is. So we're gonna divide op rt And when we do that, we're gonna get our moles. Moles here will equal pressure times volume over our Times team at STP. Our pressure is one atmosphere, our volume We just change middle leaders toe leaders. So 0.3 to 5 leaders, we have our our constant, which is 0.8 to 06 leaders times atmospheres over moles times K. Then remember, we're dealing with temperature at STP. We used the units off Kelvin, so that's to 73.15 Kelvin. So here Kelvin's council out leaders cancel out atmospheres cancel out and we'll be left with the moles off our oxygen gas. When we plugged that in, we get 0.1450 moles of But here the question is not asking us to determine the moles of oxygen gas, but instead the grams off oxygen gas. So we just need to do a simple conversion. We say that for every one mole of 02 it weighs g because there's two oxygen's those cancel out, but we get at the end is 0.464 g of CO. Two. Here are answer has three significant figures because the value of 3 has three significant figures as well. So just remember when we're faced a question like this, look and see what variables are given. Since we're dealing with the ideal gas law, we see that the value that's missing is moles. Then go for moles to grams to get your final answer