Prelab 399R

Prelab 399R - c A solid formed It is insoluble d The change...

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KEY to PRELAB 399: Detecting Signs of Chemical Change NOTE: sections in italics are provided as additional information only and are not deemed to be part of the “correct” answer for the purposes of correcting your pre-lab assignment. 1. All of the 1M solutions (HCl, NH 3 , NaOH) are toxic and corrosive. Further, both hydrochloric acid and sodium hydroxide can cause burns upon contact with skin. However, you may not notice the reaction with your skin immediately. If you think that you have gotten either of these chemicals on your skin, go to the sink and rinse the area thoroughly (30 seconds is NOT long enough), and then rinse for two minutes more to make sure that you have gotten ALL of the chemical off. 2. a. The color of the solution changed, but it remained transparent. b. The reaction mixture’s temperature dropped. Heat was absorbed during the reaction.
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Unformatted text preview: c. A solid formed. It is insoluble. d. The change involved a change in the appearance of the substance, but it did not change its chemical composition. 3. a. Physical change Water vapor (gas state) comes in contact with the cooler glass surface and releases energy to the glass. As it loses energy, it changes from the gas to the liquid state and turns into water droplets. This is a change in the state of matter (phase change), the chemical composition is not changed. b. Chemical change The addition of the lemon juice (acidic) causes a reaction with the substance responsible for the color of the tea. c. Physical change The addition of water dilutes the tea, so the observed color change is due to a change in concentration, not a chemical reaction....
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