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If 23 grams of sodium are used, how many grams of O2 are needed and how many grams of Na2O are formed?

Chemistry questions 4Na+2O2>>>>2Na2O

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Alejandro R. | Patient, supportive Tutor for High School/College Math & SciencePatient, supportive Tutor for High Schoo...
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So the reaction you wrote has a small typo. I believe it should be 4Na + O2 → 2Na2O. From the way you stated the question, you want to know how many grams of O2 are needed to fully react with 23 g of Na and how many grams of product form. To figure this out, you need to know that a mole of O2 weighs 32g, and convert 23 g Na to moles of Na using a periodic table. 
23g Na*(1/22.99 g mol-1) = 1 mol Na. 
1 mol Na*(1 mol O2/4 mol of Na)*(32 g O2/mol O2)= 8 g O2
So you need 8g O2 to fully combust 23g Na. You have a total mass on the reactants side of 31g, and the law of conservation of mass tells you that you form (in a perfect world) 31g of Na2O.