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# Precision Lab. Question: What is the density of 2 unknown liquids, and how precise are the measurements used to make the calculations?

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Introduction

IB # 000345-153

Measuring Precision in Liquid Measurements

IB Physics SL Lab

9-03-11

IB Physics SL

Question: What is the density of 2 unknown liquids, and how precise are the measurements used to make the calculations?

Introduction:

Background Information: The density of a liquid, ρ, is calculated by dividing mass by volume, m/v. This quantity, thus, is a measurement of the mass of an object per cubic unit. Precision can be defined as the accuracy of a measurement when compared to other measurements, not necessarily accurate when compared to the theoretical measurement.  In other words, all measurements made are within error range of each other, and are thus qualified as being precise.

Materials:

• 2 unknown liquids: one blue and one green.
• A liquid of known density: ethyl alcohol.
• A 100 mL graduated cylinder
• A balance
• 2 250 mL beakers

Middle

19.51

20

21.33

21.44

26.36

30

31.73

31.12

35.50

40

41.93

42.00

45.07

50

52.62

52.53

53.14 Density:

Liquid A: 52.62/ 50  =  1.0524

Liquid B: 52.53/49.9 =  1.0527

Isopropol alcohol = 45.07/50 = .9014

Slope:

Slope of Liquid A: 1.062 Equation: Y = 1.062*X

Slope of Liquid B: 1.0426 Equation: Y = 1.0426*X

Slope of Isopropol Alcohol: .877 Equation: Y= .877*X

Conclusion

The water measurements can be used as an indicator of accuracy and precision because water’s density is 1 mg/ mL, and thus you can determine how close your measurements are to the known value. They can also be used to determine precision, as each water subset should have the same density, so if the densities you measure are close to each other, then you are fairly precise. Based on their measurements, my groups was fairly precise in our measurement.

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