![]() The only way to be certain that a chemical reaction has taken place is to test the composition of the substances after the change has taken place, to see if they are different from the starting substances. Adding a more hydrochloric acid will produce a blue solution containing mainly CoCl 4 2, while adding water will restore the pink colour. ![]() A violet-coloured solution should be formed. The melting of a solid absorbs energy, while the condensation of a gas releases energy. Make the pink cobalt chloride solution up to 100 cm 3 with 60 cm 3 concentrated hydrochloric acid from a measuring cylinder. Physical changes also involve a transfer of energy. Mix 0.1 M sodium carbonate (Na2CO3) and 6 M hydrochloric acid (HCl) solutions. While energy changes are a potential sign of a chemical reaction, care must be taken to ensure that a chemical reaction is indeed taking place. Mix 0.1 M sodium chloride (NaCl) and 0.1 M silver nitrate (AgNO3) solutions. When zinc reacts with hydrochloric acid, the test tube becomes very warm as energy is released during the reaction. ![]() What can the student conclude about the unknown 2. The student then adds a clear, colorless solution of an unknown metal to hydrochoric acid solution and the result is clear and colorless. ![]() lead(II) nitrate and lithium bromide 2. A student adds silver nitrate solution to hydrochloric acid solution and obtains a white precipitate. \): A yellow precipitate of solid lead (II) iodide forms immediately when solutions of lead (II) nitrate and potassium iodide are mixed. (Credit: Paige Powers (Flickr: paigggeyy) Source: (opens in new window) License: CC by 2.0(opens in new window))Īll chemical changes involve a transfer of energy. Which of the following reactions will produce a precipitate a. ![]()
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