Like always, begin with a balanced chemical equation for this decomposition reaction

#"CaCO"_text(3(s>) stackrel(color(red)(Delta)color(white)(aa))(->) "CaO"_text((s>) + "CO"_text(2(g>)# #uarr#

Notice that you have actually #1:1# mole ratios throughout the board. One mole the calcium carbonate will certainly decompose to type one mole the calcium oxide and also one mole of carbon dioxide.

Keep this in mind.

Now, because you didn"t provide information around the temperature and pressure in ~ which the oxygen gas is gift collected, I"ll assume the you"re in ~ STP, Standard Pressure and Temperature.

You are watching: Calcium carbonate s calcium oxide s carbon dioxide g

Under STP condittions, which are characterized as a pressure of #"100 kPa"# and also a temperature of #0^
"C"#, one mole of any ideal gas is well-known to occupy #"22.7 L"# - this is recognized as the molar volume of a gas in ~ STP.

This means that you can use the volume of carbon dioxide to figure out how many moles that oxygen were developed by the reaction

#6.72 color(red)(cancel(color(black)("L"))) * overbrace("1 mole O"_2/(22.7color(red)(cancel(color(black)("L")))))^(color(purple)("molar volume the a gas")) = "0.2960 mole CO"_2#

Now go ago to the mole ratio that exists between calcium carbonate and carbon dioxide. If the reaction produced #0.2960# mole of carbon dioxide, climate it must have consumed #0.2960# moles of calcium carbonate.

Use calcium carbonate"s molar mass to discover how many grams of calcium carbonate would certainly contain this many moles

#0.2960 color(red)(cancel(color(black)("moles CaCO"_3))) * "100.1 g"/(1color(red)(cancel(color(black)("mole CaCO"_3)))) = "29.63 g"#

Now, you recognize that your initial sample contained #20%# impurities. This is indistinguishable to saying the it contained #80%# calcium carbonate.

If the is the case, then the initial mass of the sample was

#29.63 color(red)(cancel(color(black)("g CaCO"_3))) * overbrace("100 g sample"/(80color(red)(cancel(color(black)("g CaCO"_3)))))^(color(purple)(=80%"CaCO"_3)) = color(green)("37 g")#

I"ll leave the price rounded to two sig figs.

See more: Great Warriors Of India - 12 Greatest Kings And Warriors In Indian History

SIDE NOTE Make sure to use the value of the molar volume of a gas in ~ STP given to you. Usually, that value is #"22.4 L"#, so if that"s what friend have, simply redo the calculations by replacing #"22.7 L"# with her value.