Sodium chlorate decomposes into sodium chloride and oxygen gas as seen in the equation below.

Question

­­2NaClO_3­ -->  2NaCl +3O₂

How many grams of NaClO_3­ were needed to produce 3 grams of O₂? Round your answer to the nearest whole number.

Round your answer to the whole number. If your answer is a whole number like 4, report the answer as 4.0

Use the following molar masses. If you do not use these masses, the computer will mark your answer incorrect.:

Element	Molar Mass
Sodium	23
Chlorine	35.5
Copper	63.5
Oxygen	16

Answer 1

We can solve this problem without even worrying about pesky molar mass conversions! Since we have the ratios of the substances' molar masses, we can just calculate using those. We know that our end product has 3 grams of oxygen; our equation shows that the end product has 3O₂ after decomposition, so we can compare how much oxygen we actually have to how much 3O₂ would weigh if we had whole moles of substance.

3O₂ would be six moles, and weigh 96 grams. Since we only actually have 3 grams, we know that we are working with 3 / 96 = 1/32 of a mole per substance. Now, we look at the equation again, and multiply the ratio of each substance by 1/32, and then by the molar weight. All that's left is finding the weight of the Sodium and the Chlorine, both of which are prevalent in a ratio of 2, so we take 2/32=1/16 of each substance and multiply by their molar weights; 23/16 grams of Sodium, and 35.5/16 grams of Chlorine. Adding those together, we have 58.5/16 grams, which we can round to 64/16, or 4. Adding those 4 grams to the 3 grams of oxygen that the problem gives us, we have seven grams of Sodium Chlorate necessary to give us 3 grams of oxygen post-decomposition.