Introduction


 * INTRODUCTION - Draft**

When substances change from one solid phase into another the change is accompanied by absorption or release of heat. The temperature at which such a change takes place is called the transition temperature. This change can be thought of as a change from one compound to another. In this experiment, the compounds used are hydrates, meaning they contain water (h20) in their chemical formulas. When these hydrates are heated (change in temperature), the water will evaporate and thus the compounds will no longer be hydrates.

There are various methods used to measure a substance's transition temperature. Some use complicated spectroscopes, while others use a series of standardized tests to determine the temperature at which the substance will change state.

For the purposes of this experiment, we will attempt to find the transition temperatures of 3 compounds, Sodium Thiosulphate Penta Hydrate, Sodium Sulfate Decahydrate, and Sodium Acetate Dehydrate. The results of our experiments will likely not be 100% accurate, due to the constraints on available equipment, as well as the limited intelligence we possess on this topic.

Transition Temperature  When substances change from one solid phase into another the change is accompanied by absorption or release of heat. The temperature at which such a change takes place is called the transition temperature. This change can be thought of as a change from one compound to another. In this experiment, the compounds used are hydrates, meaning they contain water ( **  H2O  **) in their chemical formulas. When these hydrates are heated (change in temperature), the water will evaporate and thus the compounds will no longer be hydrates.  In this experiment, an attempt will be made to find the transition temperature of 3 specific compounds. This will be done by weighing the compounds at various temperatures. When the mass of the compounds remains the same(stabilizes), it means all the water in the compound has been evaporated, meaning it is no longer a hydrate. Therefore, the temperature at which the mass stabilizes is the transition temperature. Hydrates Hydrates are compounds where molecules of water are involved with an ionic compound. They are formed when ionic compound are formed in water and then isolated as solids. As a result, water is trapped in the compound. Hydrates are written with a dot between the ionic compound and the amount of water molecules involved with the compound. This indicates the number of water molecules per one molecule of the ionic compound. Though water is involved in the chemical formula, this does not indicate that the substance is wet. In fact, many hydrates have dry appearance and touch. When water is removed from the hydrates, one is left with the anhydrous compound. The mass of the anhydrous compound and water removed must equal the original mass of the hydrate. The solids used for this experiment are Sodium Thiosulphate Penta Hydrate (Na2S2O3∙** 5H20), Sodium Sulphate Decahydrate (Na **2** SO **4∙** 10H2O) and **Sodium Acetate Dehydrate (NaCH3COOH). However, Sodium Acetate Dehydrate will be replaced with Sodium Acetate Trihydrate which, when dehydrated, forms Sodium Acetate Dehydrate.

1. http://science.jrank.org/pages/2335/Electrical-Resistance.html 2. http://www.howstuffworks.com/question610.htm

- Kam, Lowell

Hey everyone: Kam and I were talking and we're going to do our intro in 2 parts. One on transition temperature itself and one on hydrates. should we talk about each solid separately? LOWELL

 EDITING

When substances change from one solid phase into another the change is accompanied by absorption or release of heat. The temperature at which such a change takes place is called the transition temperature. This change can be thought of as a change from one compound to another. In this experiment, the compounds used are hydrates(meaning they contain water ( H2O  ) in their chemical formulas) or dehydrates(meaning they do no contain water in their chemical formulas). Hydrates are formed when ionic compounds are formed in water and then isolated as solids, therefore the water remains trapped in the compound. Dehydrates or anhydrous compounds are formed when water is removed from a hydrate. The mass of a anhydrous compound must be equal to the mass of the original hydrate. When these hydrates are heated (change in temperature), the water will evaporate and thus the compounds will no longer be hydrates. When water vapour is added to the dehydrates, the dehydrates absorb the water vapour to form a hydrate.  In this experiment, an attempt will be made to find the transition temperature of 3 specific compounds: Sodium Thiosulphate Penta Hydrate, Sodium Sulphate Decahydrate and Sodium Acetate Dehydrate. To determine the transition temperatures of the hydrates, the experiment will be done by weighing the compounds at various temperatures. When the mass of the compounds remains the same(stabilizes), it means all the water in the compound has been evaporated, meaning it is no longer a hydrate. Therefore, the temperature at which the mass stabilizes is the transition temperature. To determine the transition temperature of the dehydrates, water in the form of water vapour is added and the temperature at which the dehydrates becomes hydrates is detected. -Kristie

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