Finding the Ratio of Moles of Reactants in a Chemical Equation

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Finding the Ratio of Moles of Reactants in a Chemical Reaction

Purpose: The goal of the lab is to determine the mole ratio of two reactants in a chemical reaction (AgNO3 and K2CrO4). However, the formulas for the products are unknown.


When determining the molar ratio of a chemical equation, usually the formulas of the reactants and the products are known. With that information, it is particularly easy to determine the ratio. However, since the products and the formulas for the products are unknown, another property of the reaction must be analyzed to find the ratio. This property depends on the amount of the product formed or on the amount of reactant that remains. Properties may include the color intensity due to the product, the mass of the precipitate that forms, or the volume of a gas evolved.

In this experiment, the method of continuous variations will be used to determine the mole ratio of two reactants. With this method, the total number of moles of reactants is kept constant for the series of measurements. The property that is going to be measured is the change in temperature. The temperature change, or the heat produced, will be directly proportional to the amount of reaction occurs and to the total extent of it. The optimum ratio, which is the ratio of the reactants in the balanced chemical reaction, will form the greatest amount of product, or generate the most heat, and will be key to determining the molar ratio. Corrosive liquids, which burn the skin, will be used in the experiment. When this liquid reacts with acid, a toxic gas will formed. Keep away from the gas and protect your skin and clothing. Work in a fume hood or well-ventilated lab. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

The molar ratio of the reactants is the ultimate goal of the lab. In order to achieve that, secondary observations on...
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