what.can be concluded about the properties of the elements that border the staircase on the periodic table of the elements
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Ответ:
These elements have properties of both metals and nonmetals
Ответ:
Explanation:
1) The lowering of the freezing point is a colligative property which means that it depends, and can be calculated from some contants of the pure solvent, and the number of solute particles dissolved.
ΔTf = m × Kf × iWhere, ΔTf is the reduction in the freezing point, m is the molality of the solution, Kf is the cryoscopic constant of the solvent, and i is the Van't Hoff factor.
2) Find the molality of each solution, m:
Formulae:moles of solute, n = mass in grams / molar mass
m = n / kg of solvent
(A) CuSO₄•5H₂O (M=250)
n = 20.0 g / 250 g/mol = 0.0800 molm = 0.0800 mol / 0.200 kg = 0.400 m(B) NiSO₄•6H₂O(M=263)
n = 20.0 g / 263 g/mol = 0.0760 molm = 0.0760 mol / 0.200 kg = 0.380 m(C) MgSO₄•7H₂O (M=246)
n = 20.0 g / 246 g/mol = 0.0813 molm = 0.0813 mol / 0.200 kg = 0.406 m(D) Na₂SO₄ • 10 H₂O (M = 286)
n = 20.0 g / 286 g/mol = 0.0699 molm = 0.0699 mol / 0.200 kg = 0.350 m3) Van't Hoff factor.
Since, all the solutes are ionic, you start assuming that they all dissociate 100%.
That means that:
Each unit of CuSO₄.5H₂O yields 2 ions in water ⇒ i = 2Each unit of NiSO₄. 6H₂O yileds 2 ions in water ⇒ i = 2Each unit of MgSO₄.7H₂O yields 2 ions in water ⇒ i = 2Each unit of Na₂SO₄.10H₂O yields 3 ions in water ⇒ i = 34) Comparison
Being Kf a constant for the four solutions (same solvent), you just must compare the product m × i
CuSO₄.5H₂O: 2 × 0.400 = 0.800NiSO₄. 6H₂O: 2 × 0.380 = 0.760MgSO₄.7H₂O: 2 × 0.406 = 0.812Na₂SO₄.10H₂O: 3 × 0.406 = 1.218As you see from above calculations, the dissociation factor defines the situation, and you can conclude that the last choice, i.e. the solution of Na₂SO₄ . 10H₂O, will have the greatest decrease of the freezing point, resulting in the lowest freezing point.