A pulverized rock sample believed to be pure calcium carbonate, CaCO3, is subjected to chemical analysis and found to contain 51.3% Ca, 7.7% C, and 41.0% O by mass. Why can't this rock sample be pure CaCO3?

Video transcript

everyone in this video, we're being asked if the sample of the rock is pure mgs oh four or given certain percentages of the sample. Alright, so let's go ahead and calculate the percent by mass of each element. And of course we need to know the molecular weight of our M g. S. 04. So the malacca, wait for that. So of M G. S. 04, that's going to be equal to 1 20.371 g Permal. So now we're first calculating for the element of magnesium. So the percent of magnesium, which is M. G. Well that equals to the molar mass of an element over the molar mass of our compound. So for the molar mass of our element which we can find on a pr tables is 24.305 g per mole. And then for our compound we just said it was mgs of four and the molar mass is 1 20.371 g per mole. Of course. Since we're finding percentage, we need to multiply this by 100% putting this in the calculator, I get the value of 20.19 and units. Well we don't have a unit. But we have this percentage. Alright, next one then would be the percent of sulfur. So percent of s. So the molecular mass molar mass of this element is 32.66 g per mole. Again divided by the molar mass of a compound which is again 20.371 g per mole. And all this is multiplied by 100%. To give us the value of 26.64%. Lastly calculated for the percentage of oxygen, The molar mass of this wall. We have actually in this compound for auction atoms, so we have four times. Each item is 16.0 g per mole. Okay, again, over the molar mass of a compound, which is again 1 20.371 g per mole offices multiplied by 100%. To give us 53.17%. We'll see then that the mass percent of each sample analyze isn't the same as the mass percentage of the pure MGs of four. Mass percent of the pure MGs of four components will be given to us. Here. We see that all of these values do not online and therefore we can say that the sample of rock isn't pure MGS 04 And that's going to be my final answer for this problem. Thank you all so much for watching