![]() What would happen if a bell jar was lowered over the burning candle blocking off the supply of oxygen? You know that oxygen is needed for the combustion of candle wax, so when the oxygen inside the bell jar is used up, the candle will go out. The photo on the opposite page shows the combustion of a candle using the oxygen in the surrounding air. Vocabulary stoichiometry mole ratio Were you surprised when, in doing the DISCOVERY LAB, you saw the purple color of potassium permanganate disappear as you added sodium hydrogen sulfite? If you concluded that the potassium permanganate had been used up and the reaction had stopped, you are right. Determine the mole ratios from a balanced chemical equation. Section 1.1 What is stoichiometry? Objectives Identify the quantitative relationships in a balanced chemical equation. Analysis What evidence do you have that a reaction occurred? Would anything more have happened if you continued to add NaHSO 3 solution to the beaker? Explain. Record the total volume of the NaHSO 3 solution you used to cause the beaker s contents to become colorless. ![]() Slowly add additional 5.0-mL portions of the NaHSO 3 solution until the KMnO 4 solution turns colorless. Add 5.0 ml of 0.01M sodium hydrogen sulfite solution (NaHSO 3 ) to the potassium permanganate solution while stirring. Measure 5.0 ml of 0.01M potassium permanganate solution (KMnO 4 ) and pour it into a 100-mL beaker. What evidence can you observe that a reaction takes place? Safety Precautions Materials 10-mL graduated cylinder 100-mL beaker stirring rod 0.01M potassium permanganate (KMnO 4 ) 0.01M sodium hydrogen sulfite (NaHSO 3 ) Procedure 1. 35 Chapter 1ΔΆ DISCOVERY LAB Observing a Chemical Reaction Reactants are consumed in a chemical reaction as products are produced. The candle will continue to burn as long as oxygen and candle wax are present. Visit the Chemistry Web site at to find links to stoichiometry. Why It s Important The cost of the things you buy is lower because chemists use stoichiometric calculations to increase efficiency in laboratories, decrease waste in manufacturing, and produce products more quickly. You will determine the percent yield of a chemical reaction. You will identify the limiting reactant in a chemical reaction. You will calculate the number of moles and the mass of a reactant or product when given the number of moles or the mass of another reactant or product. 1 CHAPTER 1 Stoichiometry What You ll Learn You will write mole ratios from balanced chemical equations.
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