Chem& 140
General Chemistry Prep w/Lab

Lab Exercise: The Metric System

Purpose
This laboratory will give you practice in measuring and performing calculations using the metric system.

Introduction
Background material for this exercise can be found on pages 19–29, and 34–37, of your text.

Measuring Length

  1. Estimate the following lengths in the specified units and then measure the item (You will not be graded on your estimates.) Be sure to use the correct significant figures.

    EstimateActual
    a. Width of this lab sheet (centimeters)______________
    b. Length of this lab sheet (centimeters)______________
    c. Width of the lab bench (meters)______________
    d. Length of the lab bench (meters)______________
    e. Your height (meters)______________

  2. Determine the number of centimeters in an inch as follows:

    1. Measure the width of these lab directions in inches: __________

    2. Divide the width of the page in centimeters by the width of the page in inches: _______

    3. This gives the number of centimeters in an inch. According to your textbook, what is this value? _______

  3. Measure the following distances on the line in millimeters, to the nearest 0.10 mm, then calculate the other values.

    A B C
    |___________|_______________________|

    Distancemmcmdmm
    AB____________________________
    BC____________________________
    AC____________________________

Measuring Volume

  1. Volume of a Liquid: The graduated cylinder is a typical container used to measure the volume of liquids in the lab. To read a graduated cylinder, set the cylinder on a level surface and bring your eye even with the liquid level. Most liquids form a curve that goes down in the center of the cylinder. This curve is called the meniscus. Read the level of the liquid at the lowest point of the meniscus. Several graduated cylinders have been placed at the front of the lab. Read the volume of liquid in each to the nearest mL.

    Cylinder A_______ mL
    Cylinder B_______ mL
    Cylinder C_______ mL

  2. Volume of a Rectangular Solid: The volume of a rectangular solid may be obtained by multiplying the width times the length times the height. If the unit of length for each dimension is centimeters, the unit of volume is cubic centimeters (cm3 or cc). You should also know that 1 cm3 = 1 mL. Obtain a rectangular block from the lab cart. Measure the length, width, and height, and then calculate the volume in cm3. You will need to read your ruler to the nearest tenth of a centimeter to obtain an accurate calculation.

    Block #Length (cm)Width (cm)Height (cm)Volume (units?)
    ________________________________

    Check your answer with your instructor.

  3. Volume of a Cylindrical Object: The formula for obtaining the volume of a cylindrical object is pr2h where p = 3.14, r = the radius of the cylinder and h = height of the cylinder. Obtain a wooden cylinder from the lab cart. Measure the height and radius (best obtained by measuring the diameter and dividing by 2) and calculate the volume in cm3. You will need to read your ruler to the nearest tenth of a centimeter to do an accurate calculation.

    Cylinder #Radius (cm)Height (cm)Volume (units?)
    ____________________________

    Check your answer with your instructor.

  4. Volume by displacement: Obtain a metal cylinder from the lab cart. Place about 50 mL of water in your 100 mL graduated cylinder. Read the volume of water to the nearest 0.1 mL.

    Carefully tilt the graduated cylinder and gently slide the metal down the side of the cylinder. Record the volume. The difference between the initial and final volumes is the volume of the cylinder.

    Cylinder # _______ Volume of the cylinder _______ mL

Measuring Mass

  1. Determine the mass of a numbered cylinder to the nearest 0.01 g.

    Cylinder #Mass (g)
    ______________

    Check your answer with your instructor.

  2. Estimate the mass of the following items in the specified units and then measure them. (You will not be graded on your estimates.) Be sure to use the correct significant figures.

    EstimateActual
    a. Lab Scoop (grams)______________
    b. 10 mL graduated cylinder (grams)______________
    c. 100 mL beaker (grams)______________

Density of Unknown Samples

The density of a substance tells us the mass of a certain volume of that material. The formula is:

Density = mass/volume

If mass is measured in grams, and the volume in milliliters, density then has the units of grams per milliliter, g/mL.

  1. Determine the density of a liquid.
    1. Weigh a clean, dry 100 mL graduated cylinder. _______ g
    2. Pour about 30 mL of an unknown liquid into the graduated cylinder. Read the volume to the nearest tenth of a milliliter. _______ mL
    3. Weigh the graduated cylinder containing the unknown liquid. _______ g
    4. Determine the mass of the unknown liquid. _______ g
    5. Calculate the density of the unknown liquid. _______ g/mL
  2. Determine the density of a solid.
    1. Weigh (exactly) about 20 grams of an irregularly shaped solid. _______ g
    2. Fill a 100 mL graduated cylinder to about the 50 mL mark with water. Record the actual volume to the nearest tenth of a milliliter. _______ mL
    3. Carefully add all of your solid to the graduated cylinder to determine its volume by displacement, just as you did earlier with the metal cylinder. Again be sure that all measurements are to the nearest tenth of a milliliter. The total volume is _______ mL
    4. Determine the volume of your solid. _______ mL
    5. Calculate the density of your solid. _______ g/mL
  3. Calculation of the percent error. Obtain the accepted densities for both the unknown liquid and solid from your instructor, and then calculate the percent error for each density determination by using the following formula:

    Percent Error =(Experimental Value – Accepted Value)
    Accepted Value     		x 100%

    Note: The (Experimental Value – Accepted Value) can be written as (Accepted Value – Experimental Value) since the difference is always expressed as a positive number.


    Return to the Laboratory Experiments Schedule

    Copyright © 1999–2009 • Green River Community College
    Chemistry Department, All Rights Reserved
     Last Revised: 9/9/9