A 0.9030 gram sample of M(OH)2 was mixed with 20.00 mL of 2.000 M HCl and enough water added to make 100.0 mL of solution
M(OH)2(aq) + 2HCl(aq) 2H2O(l) + MCl2(aq)
A 10.00 mL aliquot of solution A was taken and titrated with 17.64 mL of 0.05121 M NaOH.
NaOH(aq) + HCl(aq) H2O(l) + NaCl(aq)
What is the metal, M? (Mg)
chemistry back titration question?
2017-11-28 7:19 pm
回答 (2)
2017-11-28 11:08 pm
Consider the titration of the excess HCl against NaOH :
NaOH(aq) + HCl(aq) → H₂O(l) + NaCl(aq)
Mole ratio of NaOH : HCl = 1 : 1
No. of moles of NaOH used in titration = (0.05152 mol/L) × (17.64/1000 L) = 0.0009088 mol
No. of moles of excess HCl in titration = 0.0009088 mol
No. of moles of excess HCl in the reaction mixture of M(OH)₂ and HCl = (0.0009088 mol) × (100/10) = 0.009088 mol
Consider the reaction of M(OH)₂ with HCl :
M(OH)₂(aq) + 2HCl(aq) → 2H₂O(l) + MCl₂(aq)
Mole ratio M(OH)₂ : HCl = 1 : 2
Total number of moles of HCl = (2.000 mol/L) × (20.00/1000 L) = 0.04000 mol
Number of moles of HCl reacted with M(OH)₂ = (0.04000 – 0.009088) mol = 0.03091 mol
Number of moles of M(OH)₂ reacted = (0.03091 mol) × (1/2) = 0.01546 mol
Molar mass of M(OH)₂ = (0.9030 g) / (0.01546 mol) = 58.4 g/mol
Molar mass of M = (58.4 – 16.0×2 - 1.0×2) g/mol = 24.4 g/mol
Atomic mass of M = 24.4
The atomic mass of M (24.4) is very close to that of Mg (24,3).
Hence, M is Mg.
NaOH(aq) + HCl(aq) → H₂O(l) + NaCl(aq)
Mole ratio of NaOH : HCl = 1 : 1
No. of moles of NaOH used in titration = (0.05152 mol/L) × (17.64/1000 L) = 0.0009088 mol
No. of moles of excess HCl in titration = 0.0009088 mol
No. of moles of excess HCl in the reaction mixture of M(OH)₂ and HCl = (0.0009088 mol) × (100/10) = 0.009088 mol
Consider the reaction of M(OH)₂ with HCl :
M(OH)₂(aq) + 2HCl(aq) → 2H₂O(l) + MCl₂(aq)
Mole ratio M(OH)₂ : HCl = 1 : 2
Total number of moles of HCl = (2.000 mol/L) × (20.00/1000 L) = 0.04000 mol
Number of moles of HCl reacted with M(OH)₂ = (0.04000 – 0.009088) mol = 0.03091 mol
Number of moles of M(OH)₂ reacted = (0.03091 mol) × (1/2) = 0.01546 mol
Molar mass of M(OH)₂ = (0.9030 g) / (0.01546 mol) = 58.4 g/mol
Molar mass of M = (58.4 – 16.0×2 - 1.0×2) g/mol = 24.4 g/mol
Atomic mass of M = 24.4
The atomic mass of M (24.4) is very close to that of Mg (24,3).
Hence, M is Mg.
2017-11-28 7:22 pm
HCDHIOSpo93r32=52
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