the Use of a Dial-o-Gram^® Balance

Description

The use of a Dial-o-Gram^® balance is explained, including reading of the Vernier scale.

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• The Dial-o-Gram^® balance is commonly found in the high school laboratory. Reading the vernier scale is the feature of the balance with which students have the most difficulty. Most high school experiments require that the mass of samples be determined to +/- 0.01 gram. The vernier scale allows measurement to that sensitivity.
• The Dial-o-Gram^® balance has three major features. The double beam allows masses to be added in increments of 100 and 10 units. The dial allows addition of masses of up to 10 grams in 0.1 gram increments. The vernier scale fixed above the dial allows masses to be added in increments of 0.01 gram.
• To read the mass of an object, add the masses indicated on the two beams. Use the zero mark on the fixed vernier scale as a reference to read the additional mass to the tenth of a gram. Determine the mass to the hundredth of a gram by reading the value on the vernier scale that first coincides with a line on the dial.

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1. Demonstrate how to read a Dial-o-Gram^® balance using a demonstrator and the overhead projector. Practice reading the demonstrator scale several times.

   

2. The end of the movie displays slides of the balance scales. . Step through the slides reading each one and comparing your value with the proper reading.
3. Students should proceed to their lab stations and determine the mass of one or two common objects using the actual Dial-o-Gram^® balances.

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Name ___________________________ Class ________

Teacher__________________________

DoChem 013 The Use of a Dial-o-Gram^® Balance

1. The Dial-o-Gram^® balance is commonly found in the high school laboratory. Reading the vernier scale is the feature of the balance with which students have the most difficulty. Most high school experiments require that the mass of samples be determined to +/- 0.01 gram. The vernier scale allows measurement to that sensitivity.
2. The Dial-o-Gram^® balance has three major features. The double beam allows masses to be added in increments of 100 and 10 units. The dial allows addition of masses of up to 10 grams in 0.1 gram increments. The vernier scale fixed above the dial allows masses to be added in increments of 0.01 gram.
3. To read the mass of an object, add the masses indicated on the two beams. Use the zero mark on the fixed vernier scale as a reference to read the additional mass to the tenth of a gram. Determine the mass to the hundredth of a gram by reading the value on the vernier scale that first coincides with a line on the dial.
4. Watch the Movie. Read the vernier on each frame of the Movie. Record readings 13-16

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Purpose

To describe the use of a Dial-o-Gram^® balance.

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• 1 overhead projector
• 5 Dial-o-Gram^® balance
• 10 common objects to be "weighed"
• Dial-o-Gram^® transparency demonstrator:

  

• 1 brad
• scissors

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• The Dial-o-Gram^® transparency demonstrator must be constructed. Make a transparency copy of the demonstrator from the copy provided using an appropriate copying machine.
• Cut out the vernier dial.
• Place a cut-out of a dial next to the vernier scale so that the two zero marks coincide. Look at an actual Dial-o-Gram^® balance to check the placement.
• Use the transparent demonstrator in the classroom before the students practice on the actual Dial-o-Gram^® balances.
• Test tubes, graduated cylinders, coins, keys, chalk, etc. are examples or objects that may be used as samples to be weighed. Weigh some of these and record the weight so that they may be used as knowns.

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Teacher preparation: 30 minutes

Class Time: 20-30 minutes

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There are no unusual hazards in this experiment.

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No special precautions are required in this experiment. Follow routine laboratory precautions.

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Save the transparent demonstrator for future use.

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• The mass of an object is the sum of the masses indicated on the fixed and vernier scales. The mass of an object determined on a Dial-o-Gram^® balance can be reported to the nearest 0.01 g. The digit in the hundredth's place of a mass determined by using a Dial-o-Gram^® balance is the estimated digit.
• Discuss the sensitivity of the balance. Emphasize how important it is to record the mass of an object to the limit of the tolerance of the instrument used to measure its mass. Frequently, students will record a mass as 27.6 g when it would be far more appropriate to record 27.62 g.

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• balance
• Dial-o-gram^® balance
• vernier
• mass

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