Why dil. sulphuric acid cannot be used instead of dil.hcl in lab preparation of carbon dioxide gas?
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Answer:
Mg will be the limiting reagent.
Explanation:
The balanced reaction is:
Mg + 2 HCl → MgCl₂ + H₂
By reaction stoichiometry (that is, the relationship between the amount of reagents and products in a chemical reaction), the following amounts of moles of each compound participate in the reaction:
- Mg: 1 mole
- HCl: 2 moles
- MgCl₂: 1 mole
- H₂: 1 mole
Being the molar mass of each compound:
- Mg: 24.3 g/mole
- HCl: 36.45 g/mole
- MgCl₂: 95.2 g/mole
- H₂: 2 g/mole
By reaction stoichiometry, the following mass quantities of each compound participate in the reaction:
- Mg: 1 mole* 24.3 g/mole= 24.3 g
- HCl: 2 moles* 36.45 g/mole= 72.9 g
- MgCl₂: 1 mole* 95.2 g/mole= 95.2 g
- H₂: 1 mole* 2 g/mole= 2 g
0.0350 g of Mg is reacted with 10.00 mL (equal to 0.01 L) of 6 M HCl.
Molarity being the number of moles of solute that are dissolved in a certain volume, expressed as:
in units
then, the number of moles of HCl that react is:
number of moles of HCl= 6 M*0.01 L
number of moles of HCl= 0.06 moles
Then you can apply the following rule of three: if by stoichiometry 2 moles of HCl react with 24.3 grams of Mg, 0.06 moles of HCl react with how much mass of Mg?
mass of Mg= 0.729 grams
But 0.729 grams of Mg are not available, 0.0350 grams are available. Since you have less mass than you need to react with 0.06 moles of HCl, <u><em>Mg will be the limiting reagent.</em></u>