A crystalline salt on being rendered anhydrous loses 45.6% of it's weight. The composition of anhydrous salt is Al - 10.5%, K - 15.1%, S - 24.8%, O - 49.6%, Calculate the molecular formula of anhydrous and crystalline salt
Answers
Answer:
An empirical formula of hydrated salt will be
Explanation:
The molecular masses of Aluminium, potassium, Sulphur and Iodide are 27 g/mol, 39 g/mol, 32 g/mol and 127 g/mol respectively.
The %age composition of an anhydrous saltwill be :
Aluminium = 10.5%
Potassium = 15.1%
Sulphur = 24.8%
Iodide = 49.6%.
Hence, 100 g of an anhydrous salt includes :
10.5 g = Aluminium
15.1 g = Potassium
24.8 g = Sulphur
49.6 g = Iodide.
10.5 g Aluminium will correspond to 10.527 = 0.39 moles
15.1 g potassium will correspond to 15.139 = 0.39 moles
24.8 g Sulphur will correspond to 24.832 = 0.775 moles
49.6 g Iodide will correspond to 49.6127 = 0.39 moles
Hence, the ratio of the no. of moles of Al: K :S: I will be:
0.39 : 0.39 : 0.775 : 0.39
Then, we divide this by 0.39
Then,
Al:K:S:I
1:1:2:1.
The empirical formula of an anhydrous salt will be KAlS2I.
Formula mass= 39+27+32+32+127= 257g/mol.
Formula wt. of hydrated salt will be= 100100−45.6×257=472.
Mass of water of crystalline salt= 472−257=215g.
21518=12 water molecules.
An empirical formula of hydrated salt will be KAlS2I.12H2O.
Answer:
Explanation:
On heating the crystalline salt, it loses its water and become anhydrous. The weight lost in this manner is that of water which according to question forms 45.6% of total weight of crystalline salt. Hence rest of salt 54.4% is that of anhydrous salt.
Let us consider 100 grams (54.4%) of anhydrous salt.
Total mass of crystalline salt = 100/0.544 = 183.82 grams
mass of water = 183.82 - 100 = 83.82 grams
The composition of the salt is;
Aluminum = 10.5 grams = 10.5/27 = 0.38 moles
Potassium = 15.1 grams = 15.1/39 = 0.38 moles
Sulphur = 24.8 grams = 24.8/32 = 0.775 moles
Oxygen = 49.6 grams = 49.6/16 = 3.1 moles
Water = 83.82 grams = 83.82/18 = 4.65 moles
Hence the empirical formula of anhydrous and crystalline salt:
Al₀.₃₈K₀.₃₈S₀.₇₇₅O₃.₁ and Al₀.₃₈K₀.₄₈S₀.₇₇₅O₁.₅₅4.65H₂O respectively.
Dividing whole terms by 0.38 and rounding off to nearest digit,we get.
AlKS₂O₈ and AlKS₂O₈ 11.92 H₂O
Formula of anhydrous salt = KAlS₂O₈
Formula of crystalline salt = KAlS₂O₈ 12 H₂O