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3.3.1: Practice Classifying Change

  • Page ID
    236034
  • Exercise \(\PageIndex{1}\)

    Classify each of the following as a chemical or physical change.

    a)  You let salt water evaporate to leave salt behind.

    b)  You dilute juice with water because it is too sweet.

    c)  Starch gets broken down by saliva enzymes into simpler sugars.

    Answer a

    physical change (liquid water and salt becomes gaseous water and salt, no change in substance identity)

    Answer b

    physical change (water and juice components becomes more water with juice components, no change in substance identity)

    Answer c

    chemical change (starch becomes glucose.  Try leaving some bread or cracker in your mouth for a while and see if you taste the sweetness!)

    Classify each of the following as a chemical or physical change.

    d)  A solid piece of dry ice becomes gas.

    e)  You stir some table sugar into water to dissolve it.

    f)  A piece of lead melts at 327.5 °C.

    Answer d

    physical change (sublimation)

    Answer e

    physical change (you still have sugar and water, just mixed)

    Answer f

    physical change (melting)

    Classify each of the following as a chemical or physical change.

    g)  You drop a piece of zinc metal into acid and it bubbles, tarnishes, and starts to disappear.

    h)  Apple juice ferments to become hard cider.

    i)  You add more water to a 15% glucose solution until you have a 10% glucose solution.

    Answer g

    chemical change (zinc metal is becoming zinc ion and hydrogen gas:  zinc ion is soluble in water and hydrogen bubbles away)

    Answer h

    chemical change (the sugars are being digested, ethanol is being produced:  change in substance identity)

    Answer i

    physical change (still is water and glucose, no change in substance identity)

     

     

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