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# 205Lab5Template - Laboratory 5 Decomposition of Compounds...

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Laboratory 5 Decomposition of Compounds and Determination of Percent by Mass Name: AZIZAH AHMAD Partner: NORKHAIRIN YUSUF Section Section 40, Monday 2 PM Performed: 06 October, 2008 Submitted: 13 October, 2003 Laboratory Instructor: HONGMEI YUAN Your Signature _________________________________ 1

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Purpose The purpose of this lab was to decompose a compound and determine the mass percent of water in the compound. Introduction In this experiment, a compound was separated into its elements and ions through heating process. One category of compounds binds water molecules when formed and they lose water molecules easily upon heating. These are called hydrates and have formulas recognized by a number of water molecules placed after the compound’s formula, separated by a dot. CuSO 4 . 5H 2 O copper(II) sulfate pentahydrate (5 waters) CuSO 4 . 5H 2 O (s) + heat ° CuSO 4(s) + 5 H 2 O (g) The non-hydrated salt is called an anhydrous salt. Very often, there is a distinct difference between the two compounds especially in the form of color before and after being heated. If the formula of the hydrate is known, the percent by mass of water can be calculated directly: ___total mass of water___ x 100 = % water (by mass) total mass of hydrated salt Some compounds also decompose by losing gases upon heating and this may be only have less obvious change. Sometimes we do not know the products, but we can still experimentally report the percent decomposition: ________total mass loss_______ x 100 = % decomposition total mass of starting compound Experimental PART A : PERCENT WATER IN A HYDRATED SALT 1. 2 crucibles with cover were obtained with distilled water and dried. The ring stand, iron ring, clay triangle and burner was set up. 2. Crucible was placed on the triangle and the mass was measured with cover on. Then, one gram of hydrated salt was placed on the crucible and measured the mass again. This step was repeated by using the second crucible.
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