Answer:
D. Na₃X
Explanation:
We have the neutral compound Ba₃(X)₂. <em>The total charge (zero) is equal to the sum of the charges of the ions times the number of ions in the molecule</em>.
3 × qBa + 2 × qX = 0
3 × (+2) + 2 × qX = 0
2 × qX = -6
qX = -3
If we have the cation Na⁺ and X³⁻, a neutral molecule would require 3 Na⁺ and 1 X³⁻. The resulting compound is Na₃X.
Answer is (b)
2,3,1 is the stoichiometry
The values in front of the elements are the stoichiometric values
(Since Al2Br6 has no value in front, it's considered 1)
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Explanation of the strategy: 1) calculate the mass of water and convert to number of moles, 2) convert the mass of anhydrous CuSO4 to moles, and, 3)calculate the mole ratio of water to CuSO4 anhydrous
1) Calculate the mass of water:
mass of water = mass of the hydrate CuSO4 - mass of the anhydrous compound
mass of water = 12.98 g - 9.70 g = 3.28g
2) Calculate the number of moles of water
number of moles = mass in grams / molar mass
molar mass of water = 18.01 g/mol
number of moles of water = 3.28 g / 18.01 g/mol = 0.182 mol
3) Calculate the number of moles of CuSO4 anhydrous
number of moles = mass in grams / molar mass
molar mass of Cu SO4 = 159.6 g/mol
number of moles of CuSO4 = 9.70g / 159.6 g/mol = 0.0608 moles
4) Calculate the ratio moles of water / moles of CuSO4
ratio = moles of water / moles of CuSO4 = 0.182 / 0.0608 = 2.99 ≈ 3
Therefore the molecular formula is CuSO4 . 3H2O
Name: copper(II) sulfate trihydrate.
