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A 3.7gm sample of copper (ii) carbonate is added to 25cm3
 of 2.0moldm3 hydrochloric acid. Which volume of gas is produced under room conditions?
A) 0.56dm3
B) 0.72dm3
C) 1.20dm3
D) 2.40dm3

Answer
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Hint: The amount of product produce when two or more reactant take part in a chemical reaction is decided by the limiting reagent
A limiting reagent is that reactant which is present in the least amount among all reactants and thus it will decide what will be the end point of the reaction and also will be used to calculate the amount of product that is formed in the chemical reaction.
Formula used:
moles=givenweightMolecularweight
M=nV
Here M is the molarity of the compound
And n is the number of moles present in a volume V

Complete step by step solution:
 In the given question copper (ii) carbonate is added to hydrochloric acid and the reaction will be as follows:
CuCO3+2HClCuCl2+CO2+H2O
As the given question provides the given weight of copper (ii) carbonate as 3.7gm we can calculate its moles using the formula given below
moles=givenweightMolecularweight
Using molecular weight of copper (ii) carbonate as 123.5
We get moles of CuCO3 =3.7123.5
=0.03
Now to calculate the moles of hydrochloric acid using the formula of
M=nV
Here M is the molarity of the compound
And n is the number of moles present in a volume V
Now as given the volume of Hydrochloric acid is 25cm3 and
The molarity of hydrochloric acid is given as 2.0moldm3
Hence after converting volume given in cm3 into dm3 (using 1cm3=103dm3) we can calculate the moles of Hydrochloric acid using the above formula as follow:
2=n25×103
n=2×25×103=0.05
As we can see that the number of moles of hydrochloric acid comes less than the moles of
 Copper (ii) carbonate it will act as a limiting reagent
As we can see that two moles of hydrochloric acid are forming one mole of CO2
Hence 0.05 moles of hydrochloric acid will form 0.052 moles of CO2
At room conditions one of mole has volume 22.4dm3
Then 0.052 moles of CO2 will have
Volume =0.052×22.4
=0.56dm3
Hence option ’A’ is the correct solution for the given question.

Note:
A limiting reagent gets completely consumed during a chemical reaction and will always decide the end point of the chemical reaction even though the other reactants have not been reduced by a small amount.
Also, the other reactants are known as excess reagents.