FLIMINARY EXERCISES PR Experiment 7 Hydrates and the Determination of the Formul
ID: 1033477 • Letter: F
Question
FLIMINARY EXERCISES PR Experiment 7 Hydrates and the Determination of the Formula of a Hydrate uld you test a colorless crystalline compound to determine if it was a hydrate? crystalline compound, when heated in an open test tube, produced several A sample of a ts of water on the cool upper region of the tube. The residue dissolved in water llow-brown solution, while the original compound formed a colorless solution 2. forming a yellow-er Why should you conclude that the compound is not a true hydrate? . What is the meaning of the numeral represented by X in the general formula for a hydrate, salt XH,0? 4. Cobalt'(I) chloride is commonly obtained from chemical supply houses as a hydrate with the formula CoCl2.6 H20. An analysis showed that 25.0 g of this hydrate contains 11.3 g of water. What is the percent water by weight in this hydrate? Please show your calculations below Percent water =Explanation / Answer
[1] Anhydrous and hydrous compounds have distint physical, chemical and structural properties. usually the hydrates are colored compounds and have distinct color than the non-hydrated compound.
So, if a colorless crystalline compound changes, changes its color when it is crystalised in presence of water, then it is a hydrate otherwise not. Sometimes even the small amount of water is sufficient to observe the color change (for example CuSO4, CaCl2 etc.).
[2] A true hydrate regains its color (color in hydrous form) once it is in contact with water. But here color of anhydrous compound in water (colorless) is different from the color of hydrous compound in water (yellow-brown). Hence, it not a true hydrate.
[3] In a general hydrate salt.X H2O, X represents number of water molecules per formula unit of salt.
[4] Given, 25 g of CoCl2.6H2O contains 11.3 g of water
therefore, 100 g of CoCl2.6H2O will have (11.3/25)*100 = 45.2 g of water.
well, percentage is defined as parts in 100. Thus, % of water in CoCl2.6H2O is 45.2%
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