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Chemistry LibreTexts

Module 1 Practice

  • Page ID
    238013
  • 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)

     

    Measurement

    Exercise \(\PageIndex{1}\)

    What measurement should you record for the paper below using the ruler shown?

    PaperC10cmL2.jpg

    Hint

    The lines are every ten cm. You should record to the one cm.

    Answer

    17 cm. (If you put 16 cm or 18 cm, that is also acceptable.)

    Exercise \(\PageIndex{1}\)

    What mass should you record for the beaker using the balance below?

    DigitalBalanceB.jpg

    Answer

    75.090 g. Use all digits given by a digital instrument. Do not round off or add more.

    Exercise \(\PageIndex{1}\)

    What measurement should you put for the liquid level below:

    a) if you believe the liquid level is just below the line?

    b) if you believe the liquid level is right on the line?

    Remember to read the bottom of the meniscus (curve). The units are mL.

    Buret280.jpg

    Hint

    The lines are every 0.1 mL (even though numbers are every mL). You should record to the 0.01 mL.

    Answer a

    19.41 mL or 19.42 mL.

    Answer b

    19.40 mL (two past the decimal, just like answer a)

    Significant Digits

    Exercise \(\PageIndex{1}\)

    Tell the number of significant digits in each measurement.

    (a) 0.00760 kg

    (b) 470.80 mL

    (c) 80500 cm

    Answer (a)

    3 SD

    Answer (b)

    5 SD

    Answer (c)

    3 SD

    Exercise \(\PageIndex{1}\)

    Round each measurement to 4 significant digits.

    (d)  78043.7 m

    (e)  0.042268 km

    (f)  5.07038 g

    (g)  120.677 g

    Answer (d)

    78040 m

    Answer (e)

    0.04227 km

    Answer (f)

    5.070 g

    Answer (g)

    120.7 g

    Dimensional Analysis (conversions)

    Exercise \(\PageIndex{1}\)

    Convert  \(\dfrac{26.82 ft}{s}\) to \(\dfrac{mi}{h}\).  There are 5280 feet in a mile (defined, exact relationship).

    Answer

    \(\dfrac{18.29 mi}{h}\).

    Exercise \(\PageIndex{1}\)

    Given the relationships provided below, how many tablespoons (tbsp) are in 3.46 quarts (qt)?

    1 tbsp = 14.787 mL

    1 qt = 946.35 mL

    Answer

    221 tbsp

    Metric Conversions

    Exercise \(\PageIndex{1}\)

    How many \(\mu\)g are in 78.4 fg?

    Answer

    \(7.84\times 10^{-8} \mu g\)

    Exercise \(\PageIndex{1}\)

    How many mg are in 0.00567 Gg?

    Answer

    \(5.67\times 10^9 mg\) or 5,670,000,000 mg

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