0.212 g of magnesium were dissolved in hydrochloric acid and the volume of hydrogen collected
over water at 16degreeC and 750 mm pressure, was 213.5 ml. Calculate the eq. wt. of the metal.
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Answer:
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Given info : 0.212 g of magnesium were dissolved in hydrochloric acid and the volume of hydrogen collected over water at 16°C and 750 mm pressure, was 213.5 ml.
To find : equivalent weight of the metal is ...
solution : first find no of moles of HCl in the given reaction.
volume of hydrogen, V = 213.5 ml = 0.2135 L
temperature, T = 16°C = 273 + 16 = 289 K
pressure = 750 mm Hg = 750/760 atm = 0.987 atm
now using formula, PV = nRT
⇒n = PV/RT
= (0.987 atm × 0.2135 L)/(0.082 atm.L/mol/K × 289K)
= 0.00889207952 ≈ 0.009 mol
magnesium is combined with hydrochloric acid as
Mg + 2HCl ⇒MgCl₂ + H₂
here you see 2 moles of HCl is used to form 1 mole of hydrogen gas.
so, no of moles of HCl to form 0.009 mol hydrogen gas = 2 × 0.009 = 0.018 mol
from titration,
moles of HCl = equivalents of Metal
⇒0.018 = weight of metal/(equivalent weight of metal)
⇒equivalent weight of metal = 0.212g/0.018
= 11.778 g