Learn the toughest concepts covered in your Analytical Chemistry class with step-by-step video tutorials and practice problems.

Experimental Error

**Uncertainty** can be thought of as the range (+/-) that is associated with any given value.

1

Types of Uncertainty

1m

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2

Types of Uncertainty

2m

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3

Problem

Calculate the absolute uncertainty from the given problem.

6.77 (± 5.6%)

A

0.38

B

0.056

C

0.83

D

0.038

4

Propagation of Uncertainty

2m

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5

Propagation of Uncertainty

3m

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6

Propagation of Uncertainty

4m

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7

Propagation of Uncertainty Calculations

3m

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8

Problem

Determine the absolute and relative uncertainty to the following addition and subtraction problem.

8.88 (± 0.03) - 3.29 (± 0.10) + 6.43 (± 0.001)

A

0.1 absolute; 0.012 relative

B

0.1 absolute; 0.010 relative

C

0.1 absolute; 0.008 relative

D

0.01 absolute; 0.0012 relative

9

Propagation of Uncertainty Calculations

5m

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10

Problem

Determine the absolute and relative uncertainty to the following multiplication and division problem.

1.12(±0.01) x 0.546 (±0.01) / 3.12(±0.02) x 1.12 (0.03)

A

0.003 absolute; 0.01 relative

B

0.03 absolute; 0.006 relative

C

0.006 absolute; 0.03 relative

D

0.006 absolute; 0.01 relative

11

Propagation of Uncertainty Calculations

6m

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12

Problem

Based on the previous example calculate the molarity value for each student if they dissolve 0.300 (± 0.03) moles of analyte.

A

1.5 ± 0.2 M for both

B

1.5 ± 0.2 M for student A and 1.5 ± 0.1 M for student B

C

1.5 ± 0.1 M for student A and 1.5 ± 0.2 M for student B

D

1.5 ± 0.04 M for student A and 1.5 ± 0.01 M for student B

13

Propagation of Uncertainty Calculations 4

3m

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14

Propagation of Uncertainty Calculations 4

3m

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15

Problem

I am making a 0.1 M KCl (molar mass 74.551) solution for an experiment. To measure the mass of the KCl, I will use an analytical balance that is only accurate to ± 0.01 g. I place a piece of paper on the balance and set the tare to read 0.00. I then put the KCl on the balance until it reads 6.79 g. What is the uncertainty in this mass?

A

0.010 g

B

0.014 g

C

0.0002 g

D

0.020 g

16

Problem

The volume of the solution I am making is 2.5 L. To measure this volume I will use a large graduated cylinder that can measure volume to ± 10 mL. What is the absolute uncertainty in my concentration?

A

0.0001 M

B

0.0100 M

C

0.4499 M

D

0.0002 M