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Chemistry LibreTexts

Module 6 Practice

  • Page ID
    237179
  • Theory and Law

    Exercise \(\PageIndex{1}\)

    Tell whether each statement is most similar to a hypothesis, observation, theory, or law.

    This box of cereal is less expensive than that one.

    Answer

    observation

    The larger the box of cereal, the lower the price per ounce is.

    Answer

    law

    If I buy the largest package of food I can eat before it goes stale, I will save money on groceries.

    Answer

    hypothesis

    The cost associated with packaging plays an important role in setting the price of groceries. For the size of the packaging, the cost does not increase proportionally to the volume. Therefore, the fraction of the price that is going towards packaging is smaller for larger sizes.

    Answer

    theory

    Extensive and Intensive Properties

    Exercise \(\PageIndex{1}\)

    Tell whether each is an extensive or intensive property.

    (a) length

    (b) mass

    (c) temperature

    (d) the weight of a piece of clay

    (e) the color of the clay

    (f) the price of a bunch of apples

    (g) the price per pound of the apples

    Answer (a)

    Extensive

    Answer (b)

    Extensive

    Answer (c)

    Intensive

    Answer (d)

    Extensive

    Answer (e)

    Intensive

    Answer (f)

    Extensive

    Answer (g)

    Intensive

    Exact and Measured Numbers

    Exercise \(\PageIndex{1}\)

    Tell whether each number represents an exact number or an uncertain, measured number.

    I have 12 coins.

    Answer

    Exact

    The total mass of my coins is 27.420 g.

    Answer

    Uncertain (measured)

    The average mass of each coin is therefore 2.2850 g per coin.

    Answer

    Uncertain (measured)

    One of the metals used to make the coins is nickel, which has a density of 8.908 g/cm3.

    Answer

    Uncertain (measured)

    The prefix "kilo" means 1000, so there are 1000 g in a kg.

    Answer

    Exact

    That means the total mass of my coins is 0.027420 kg.

    Answer

    Uncertain (measured)

    Precision and Accuracy

    Exercise \(\PageIndex{1}\)

    You used a calibration mass to test three balances. The mass is 25.000 g. Your results are below.

      Balance A Balance B Balance C
    Trial 1 24.81 g 24.97 g 24.57 g
    Trial 2 24.69 g 25.28 g 24.69 g
    Trial 3 24.93 g 24.93 g 24.63 g
    Trial 4 25.09 g 25.06 g 24.66 g
    Trial 5 25.33 g 25.11 g 24.55 g
    Average 24.97 g 25.07 g 24.62 g
    Standard Deviation 0.25 g 0.14 g 0.06 g

    Which balance is the most precise?

    Answer

    Balance C. (It has the lowest standard deviation. The trials are closest together.)

    Which balance is the least precise?

    Answer

    Balance A.

    Which balance is the most accurate?

    Answer

    Balance A. (The average value is closest to 25.000 g)

    Which balance is the least accurate?

    Answer

    Balance C.

    What is the percent error of balance B? (Use the average measurement to calculate.)

    Answer

    0.3 %.

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