CaCO3 + 2HCl ==> CaCl2 + H2O + CO2
11.2 L CO2 (atSTP) = 11.2/22.4 = 0.5 mol.
1 mole CO2 in the reaction = 1 mole CaCO3 initially; therefore, 0.5 mole CO2 means you started with 0.5 mol CaCO3.
grams = moles x molar mass = ??
Since the marble is only 95% pure, you must start with a little more marble or
??g CaCO3 calculated/0.95 = xx.
Here is a worked example of a stoichiometry problem.
http://www.jiskha.com/science/chemistry/stoichiometry.html
calculate the amount of 95% marble required to obtain 11.2Litres OF CARBON DIOXIDE
3 answers
You should calculate fully and try to be a little more understanble
CaCO3→CaO+CO2CaCO3→CaO+CO2
Given volume of CO2" role="presentation" style="box-sizing: border-box; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.2px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; CO2CO2 = 11.2 litres
Molar volume at STP = 22.4 litres
1 mole CO2 in the reaction = 1 mole CaCO3No. of moles of CO2 = frac11.222.4=0.5moles" role="presentation" style="box-sizing: border-box; display: table-cell !important; line-height: 0; text-indent: 0px; text-align: center; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.36px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 20.935em; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; width: 10000em; position: relative;">1 mole CO2 in the reaction = 1 mole CaCO3No. of moles of CO2 = frac11.222.4=0.5moles1 mole CO2 in the reaction = 1 mole CaCO3No. of moles of CO2 = frac11.222.4=0.5moles
1 mole  rmCO2" role="presentation" style="box-sizing: border-box; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.2px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;"> rmCO2 rmCO2 in the reaction = 1 mole CaCO_3
Therefore, 0.5 mole CO2 means 0.5 mol CaCO3 has reacted in the above reaction.
No. of grams of CaCO3=no. of moles of CaCO3×molar mass of CaCO3=0.5×100=50g" role="presentation" style="box-sizing: border-box; display: table-cell !important; line-height: 0; text-indent: 0px; text-align: center; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.36px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 31.886em; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; width: 10000em; position: relative;">No. of grams of CaCO3=no. of moles of CaCO3×molar mass of CaCO3=0.5×100=50gNo. of grams of CaCO3=no. of moles of CaCO3×molar mass of CaCO3=0.5×100=50g
Since the marble is only 95% pure,
Amount of marbleCaCO3=500.95=52.63g" role="presentation" style="box-sizing: border-box; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.2px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CaCO3=500.95=52.63g
Given volume of CO2" role="presentation" style="box-sizing: border-box; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.2px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; CO2CO2 = 11.2 litres
Molar volume at STP = 22.4 litres
1 mole CO2 in the reaction = 1 mole CaCO3No. of moles of CO2 = frac11.222.4=0.5moles" role="presentation" style="box-sizing: border-box; display: table-cell !important; line-height: 0; text-indent: 0px; text-align: center; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.36px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 20.935em; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; width: 10000em; position: relative;">1 mole CO2 in the reaction = 1 mole CaCO3No. of moles of CO2 = frac11.222.4=0.5moles1 mole CO2 in the reaction = 1 mole CaCO3No. of moles of CO2 = frac11.222.4=0.5moles
1 mole  rmCO2" role="presentation" style="box-sizing: border-box; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.2px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;"> rmCO2 rmCO2 in the reaction = 1 mole CaCO_3
Therefore, 0.5 mole CO2 means 0.5 mol CaCO3 has reacted in the above reaction.
No. of grams of CaCO3=no. of moles of CaCO3×molar mass of CaCO3=0.5×100=50g" role="presentation" style="box-sizing: border-box; display: table-cell !important; line-height: 0; text-indent: 0px; text-align: center; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.36px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 31.886em; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; width: 10000em; position: relative;">No. of grams of CaCO3=no. of moles of CaCO3×molar mass of CaCO3=0.5×100=50gNo. of grams of CaCO3=no. of moles of CaCO3×molar mass of CaCO3=0.5×100=50g
Since the marble is only 95% pure,
Amount of marbleCaCO3=500.95=52.63g" role="presentation" style="box-sizing: border-box; display: inline-block; line-height: 0; text-indent: 0px; text-align: left; text-transform: none; font-style: normal; font-weight: normal; font-size: 19.2px; letter-spacing: normal; overflow-wrap: normal; word-spacing: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CaCO3=500.95=52.63g