EXPERIMENT 6 Water in Hydrates MATERIALS AND EQUIPMENT ds fnely ground copperiID

Question

EXPERIMENT 6 Water in Hydrates MATERIALS AND EQUIPMENT ds fnely ground copperiID sulfate pentahydrate (Cuso, 3H,0), and unknown hydrate. It chloride test paper, dlay triangle, crucible and cover, 25 x 200 mm ignition test tube, watch glass. DISCUSSION Many salts form compounds in which a definite number of moles of water are combined with esch mole of the anhydrous salt. Such compounds are called hydrates. The water which is chemically combined in a hydrate is referred to as water of crystallization or water of hydration. The following are representative examples r two an Caso, . 2H20, CoC, . 6Hzo, Meso, . THao, Narco, . ?OHO In a hydrate the water molecules are distinet parts of the compound but are joined to it by bonds that are weaker than either those forming the anhydrous salt or those forming the water molecules. In the formula of a hydrate a dot is commonly used to separate the formula of the anhydrous salt from the number of molecules of water of crystallization. For example, the formula of calcium sulfate dihydrate is written Caso, 2H,0 rather than CasO,H Hydrated salts can usually be converted to the anhydrous form by careful heating Hydrated Salt Anhydrous salt + water are not Hydrated salts can be studied qualitatively and quantitatively. In the qualitative part of this experiment we will observe some of properties of the liquid (water) driven off by heating the sample. In the was in the hydrate by measuring the amount of water driven off by heating To make certain that all of the water in the original sample has been driven off, chemists t weight.S med, constant weight is essentially achieved when the sample is heated and weighed in sue- essive heatings until the weight differs by no more than 0.05 g. Thus, if the second weighing no more than 0.05 g less than the first heating, a third heating is not necessary because the mple has been heated to constant weight (almost). This is a very good reason to follow direc- use a technique known as teticulously when heating. If the sample is not heated long enough or at the correct all of the water may not be driven off completely in the first heating determin- amount of to constant weight. mass lost (water driven off) when a known mass of the hydrate is h Masslost )(100) Percentage water Massof sample

Explanation / Answer

A. Qualitative determination of water

1. First on heating it turns from blue to white and after cooling it turns into liquid with white powder in the bottom.

2. Answers for second questions will be same for CuSO4 and for Cobalt chloride it turns from sky blue to purple and then further purple to pink.

Part B can't be done as you know for this lab data is required.

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