Unit 1

Types of Errors

Operator Ability – Differences in skill or attention to detail can lead to dramatically different results between different people.

Practice the techniques to improve accuracy.

a.k.a. User Error.

2) Measuring Device: A) Calibration (Scale of device) – Using a

measuring device that is to coarse or too fine

Can introduce errors due to estimation or compounding measurements.

Use the appropriate tool in order to reduce errors.

B) Bias of measuring device – Error that is reproducible and predictable. Alter by manipulating data.

Correct bias by adding, subtracting, multiplying, or dividing by a correction factor.

a.k.a. Systematic error. e.g. If a scale routinely measures 0.015 g

more than the actual amount, subtract 0.015 g from all of your measurements to “zero in” on the correct value – this must be explained in the reporting of your results.

3) Random Error – Error that cannot be predicted, reproduced, or otherwise accounted for.

Spillage is by far the most common form of random error.

Be careful with procedure to reduce this type of error.

Errors

# Error Description Type of Error

1A dirty stirring rod introduces a

contaminant into the reaction which increases the apparent result by 2%

2One lab partner reads the mass to be

5.873 g while the other lab partner reads the mass to be 5.9 g

3A procedure calls for 5.0 mL of HCl to

be added to the reaction. A 100 mL beaker is used to measure the 5 mL.

Errors II

4When drying, a small pocket of water is trapped in the crystals and adds an additional 5% to the mass.

5A technique routinely measures the density of known substances 1.28% higher than expected.

6A student records a length to be 4.25 cm but does not align the ruler with the very tip of the object.

7A procedure calls for 250 mL of water. A student uses a 25 mL graduated cylinder, filling it 10 times.

Errors III

8

A solution is boiled rapidly to dry the product. No lid is used on the beaker. After the experiment, little white dots can be seen on the lab bench.

9

Two students collide in the lab while one of the students is carrying her product. A small amount spills out of the container unnoticed.

10A filter paper rips slightly and some residue leaks into the filtrate.