Chem P1 Mcq Help thread

[Symzyx]

help me with this please~

17 A piece of rock has a mass of 2.00g. It contains calcium carbonate, but no other basic substances. It neutralises exactly 36.0cm3 of 0.500moldm–3 hydrochloric acid. What is the percentage of calcium carbonate in the 2.00g piece of rock? A 22.5% B 45.0% C 72.0% D 90.1%

 

[techgeek]

help me with this please~

17 A piece of rock has a mass of 2.00g. It contains calcium carbonate, but no other basic substances. It neutralises exactly 36.0cm3 of 0.500moldm–3 hydrochloric acid. What is the percentage of calcium carbonate in the 2.00g piece of rock? A 22.5% B 45.0% C 72.0% D 90.1%

First we write down the balanced equation so we can know the ratio of moles of calcium carbonate to moles of hydrochloric acid:
CaCO3 + 2 HCl >>> CaCl2 +CO2 + H2O
Now find the number of moles of Hcl:
36 cm3 is 0.036 dm3
so no. of mol = 0.036 x 0.5 = 0.018 mol
since 2 mol of hcl react with one mol of CaCO3.
No. of mol of CaCo3 that reacted (from the 2-gm-rock) = 0.018/2 = 0.009 mol
mass in gm = 0.009 x 100 (Mr of CaCO3)
= 0.9 g
now find % age of total: 0.9/2.0 x 100
= 45%
so B is the answer