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Sun 10 Sep, 2006 10:39 pm
A sample of 0.370 mol of a metal oxide (M2O3) weighs 55.45 g. How many grams of O are in the sample?
Metal hydrides react with water to form hydrogen gas as shown for Sr,
SrH2(s) + 2H2O(l) => Sr(OH)2(s) + 2H2(g)
Calculate the mass of hydrogen gas that can be prepared from 91.2 g SrH2 and excess water.
Elemental sulfur occurs as octatomic molecules, S8. What mass of fluorine gas, F2, is needed for complete reaction with 38.5 g sulfur to form sulfur hexafluoride?
To answer all of these questions, you need to undersnand the relationship between moles and weight. Take the first problem for example. To find the weight of one mole of M2O3, you would add all the atomic weights for the components. 2 * M + 3 * 16 with 16 being the atomic weight of O. In this case, all you need to know is that you have .37 moles of M2O3 and that each mole of M2O3 has 16*3 or 48 grams of Oxygen. You should be able to take it from here.
For the second one, you need the number of moles of SrH2. Find the atomic weights for Sr and H and compute the weight for SrH2. Divide that into 91.2 and that is how many moles you have. From the reaction, for each mole of SrH2, you can get two moles of H2. The atomic weight of H2 is 2, so now you can find the total mass.
The concept is the same for number 3.
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