EXPERIMENT XX Solutions

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EXPERIMENT XX

Measurements

Materials and Equipment: Digital balance (0.01g precision); thermometer; 150mL and 250mL beakers; Teaspoon; 1 Cup Measuring Cup; Coffee Mug; 10mL and 100mL graduated cylinders; watch glass; marble.

Introduction

In this experiment we will become familiar with several instruments. Every instrument has some level of uncertainty, in other words, no measuring devise is perfect or exact. The smaller the increments of the measuring device, that is, the smaller the spaces between the actual markings (lines, tick marks) on the device, the closer the observer is able to determine the quantity being measured to its true value. The procedure used to report non-digital instrument readings is as follows: 1. Determine the size of the increments (spaces) on the measuring device (For example, 0.1cm, or 1mL). 2. Record your reading as a numerical value including one decimal place further to the right of the incremental value (For example, if the increment is 0.1cm, a one-tenth increment, you must record your reading as a numerical value that includes a digit or zero in the hundredths place). Examples of how to read non-digital volumetric, temperature, and length measuring instruments are provided below. For a digital measurement, record all the digits and zeros displayed.    The number of significant figures in your measurement is based off of the accuracy of the instrument.  The more significant figures, the more accurate the measurement is.

Mass (weight) measurements in this lab are recorded to the 0.01g (hundredth of a gram) or 0.001g (thousandth of a gram), depending on the precision of the digital balance used.

Volumetric measurements in this lab are made in graduated cylinders.  Most of liquids we use are water (aqueous) solutions. The curved surface (curve “pointing” downward) that you observe when reading the volume contained in a graduated cylinder is called the meniscus.  Observe the meniscus at eye level to read the volume correctly.  In the 10mL graduated cylinder, the increments (spaces) are 0.1mL. In the 100mL graduated cylinder, the increments are 1mL. An example reading technique is shown in Figure 2-1.

Figure 2-1

Temperature measurements in this lab are recorded using a thermometer with increments of 1oC. Example temperature readings are shown in Figure 2-2.

Figure 2-2

Length measurements in this lab are recorded using printed metric rulers (below) with different size increments. On Ruler A, (Figure 2-3) the increments are 1cm.  On Ruler B, (Figure 2-3) the increments are 0.1cm.  On Ruler A, an example length might be estimated as 12.5cm. However, on Ruler B, the same example length might be estimated as 12.55cm because Ruler B has smaller increments.

Figure 2-3

 

Density

One distinguishing physical property of matter is density. Each pure substance has its own density. Therefore, density can be used to help identify the substance. In words, density is the ratio of a substance’s mass to the volume occupied by that mass. Mathematically, with density, d, mass, m, and volume, V,

 

d = _m_

V

 

 

In this lab, you will measure mass in grams, g, and volume in milliliters, mL. Therefore, the units of density will be, in words, grams per milliliter, or in symbols, g/mL or _g_ .

mL

Liquid volumes are easily measured by means of graduated cylinders. However, solids, unless precisely machined, for example, have volumes that are difficult to determine by direct measurement with a ruler or other similar instrument. The volume of irregularly shaped solids that do not dissolve (for example, rocks, pieces of metal) may be measured by the volume of a liquid that the solid displaces when the solid is completely submerged. If a graduated cylinder is partially filled with water and an insoluble solid is carefully submerged in the water, the water level will rise. The volume of the solid is the difference between the water levels before and after the solid is added.

 

In this lab, you will determine the density of water and the density of a metal slug.

 

Procedure

 

Part A: Measuring Length

  1. Measure the diameter of a watch glass using Ruler A (Figure 2-3).
  2. Record the measurement on your report.
  3. Measure the diameter of the same watch glass using
  4. Ruler B (Figure 2-3). Record the measurement on your report.

 

 

 

 

 

Part B: Measuring Mass

 

Digital balances are sensitive. Proceed carefully. Be sure the balance is energized. The display should read “0.00 g.” If it does not, press the “TARE” key (the one with T/0) and wait a few seconds.  Place the item to be weighed on the balance pan and read the digital display.  The digital display represents the mass of the item in grams.  Remember that all the decimal places shown on the display are to be recorded.

 

  1. Use a digital balance to determine the mass of a 100mL beaker.
  2. Record the mass.
  3. Using a 100mL graduated cylinder, pour about 20mL of tap water into the same beaker. (See NOTE at the end of this paragraph.)
  4. Determine the combined mass of the beaker and water.
  5. Record the combined mass.
  6. Calculate the mass of the water. Record the result.

 

**(NOTE: When you read an instruction about a volume that states “about” or “approximately,” there is no need to go through the careful procedure described in the introduction to this lab. Unless your instructor tells you otherwise, use the “plus or minus 10%” rule. For example, for “about 20mL of tap water,” obtain between 18mL and 22mL of tap water.)

Part C: Measuring Volume

  1. Pour 1 Teaspoon of water in the 10 mL graduated cylinder.
  2. Record the volume of the water in the 10 mL cylinder.
  3. Pour 1/3 cup of water in the 100 mL graduated cylinder.
  4. Record the volume of the water in the 100 mL cylinder.

 

Part D: Measuring Temperature

  1. Fill a 250mL beaker about halfway with tap water.
  2. Use a thermometer to record the temperature.
  3. Using a microwave proof glass (such as a coffee mug), heat 1 cup of water to boiling.
  4. Carefully remove the water from the microwave and use a thermometer to record the temperature of the water.

 

Part E: Measuring the Density of a Liquid

  1. Dry a 10mL graduated cylinder, weigh it, and record its mass.
  2. Put about 9mL of deionized water into the cylinder and carefully record the volume of the water. (Refer to the introduction.)
  3. Weigh the cylinder with the water and record the combined mass.
  4. Calculate the mass of the water.
  5. Calculate the density of the water.

Part F: Measuring the Density of a Solid

  1. Weigh the marble and record its mass.
  2. Fill a 100mL graduated cylinder about halfway with tap water.
  3. Read and record this initial volume of water following the rules.
  4. Tilting the graduated cylinder at an angle without spilling the water, carefully slide the marble down the cylinder without splashing water up along the sides.
  5. Read and record this final volume of water.
  6. Calculate the volume of the marble and its density and record both values on your report.

 

                                                          Name__________________________

                                                          Section_______Date______________

Report for Experiment 2                  Instructor_______________________

 

Measurements

 

Part A: Measuring Length

 

Diameter of watch glass using Ruler A                      __________________________

 

Diameter of watch glass using Ruler B                      __________________________

 

 

Part B: Measuring Mass

 

Mass of 100mL beaker                                               __________________________

 

Mass of 100mL beaker with water                             __________________________

 

Mass of water                                                             __________________________

(show calculation)

Part C: Measuring Volume

 

Volume of water in 10mL cylinder                            __________________________

 

Volume of water in 100mL cylinder                          __________________________

 

 

 

Part D: Measuring Temperature

 

Temperature of cold water                                         __________________________

 

Temperature of boiling water                                     __________________________

 

Part E: Measuring the Density of a Liquid

 

Mass of cylinder                                                        __________________________

 

Mass of cylinder with water                                       __________________________

 

Mass of water                                                             __________________________

(show calculation)

 

Volume of water                                                         __________________________

 

Density of water                                                         __________________________

(show calculation)

 

 

Part F: Measuring the Density of a Solid

 

Mass of marble                                                           _________________________

 

Initial volume of water                                               __________________________

 

Final volume of water                                                 __________________________

 

Volume of marble                                                       __________________________

(show calculation)

 

Density of marble                                                       __________________________

(show calculation)

 

 

POST LAB QUESTIONS
  1. Determine the number of significant figures in each of the following measurements:

 

  1. 35s ___________ 1.05cm __________

 

  1. 89g ___________ f. 10.5mL __________

 

  1. 012g ___________ g. 10.00mL __________

 

  1. 0cm ___________ h.  -40.0oC __________

 

  1. Perform the following calculations; apply sig. fig. and round off rules:

 

  1. 6g + 50.05g + 50.432g  =

 

  1. 77mL – 23.4mL  =

 

  1. (41.5cm)(0.4cm)  =

 

  1. 8 mm3 / 25.4 mm  =

 

  1. Convert 37.6oC to Fahrenheit. (Remember: In the formula for converting between Fahrenheit and Celsius, the “32” and “1.8” are exact numbers.)
  2. Convert 112oF to Celsius.
  3. What is the mass of a liquid that has a volume of 50.0mL and a density of 2.40g/mL?
  4. Calculate the volume, in milliliters, of a solid that has a density of 7.142g/cm3 and a mass of 232.51g. (HINT: 1cm3 = 1mL exactly)
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