Lecture 2

Question 1

Sensitivity

Answer 1

• minimum amount of X needed to record a positive result

Question 2

Specificity

Answer 2

• a positive result only comes from a truly positive sample

Question 3

Random Error

Answer 3

• new error introduced with each measurement
• variability present
• not reproducible

Question 4

Systematic Error

Answer 4

• error that is consistently present
• result is always the same
• consistent
• reproducible

Question 5

Accuracy

Answer 5

• how close a recorded value is to the true value

- a single measurement

Question 6

Precision

Answer 6

• how reliably you can measure a value
• multiple measurements
• clustered together with similar results

Question 7

Significant Figures

Answer 7

• many measurements have a set level of precision/accuracy

- round the correct sig figs at end of all calculations

Question 8

Units of Measurements

Answer 8

• when a value requires the use of scientific notation it common to change the unit of measurement

Question 9

pH Meter

Answer 9

• fragile glass probe permeable to H+
• current produced by probe is compared against standards to report pH value
• probe rinsed and stored in solution between uses (KCl or acidic buffer)

Question 10

pH Meter Random Error

Answer 10

• taking measurement before things have adequately mixed
• taking reading too early
• contamination

Question 11

pH Meter Systematic Error

Answer 11

• calibrated incorrectly

Question 12

Scale

Answer 12

• primarily used to weigh chemicals for making lab solutions

- scale must be tared/zeroed with empty container to obtain accurate measurements

Question 13

Scale Errors

Answer 13

• systematic: not zeroing off

- random: accidentally place extra sheet

Question 14

Vortex Mixer

Answer 14

• used to mix small quantities of solutions
• setting for mixing speed and continuous or touch operation
• may be invaluable to mix some solutions and damaging to others

Question 15

Stir Plate

Answer 15

• Teflon coated magnets placed in solution
• magnet in base with adjustable spin speed
• sometimes coupled with a heating element to aid in dissolving solutes

Question 16

Pipettes

Answer 16

• graduated plastic or glass tubes
• bulbs draw solution in to be measured and dispensed
• volumetric: measure one volume
• graduated: lines along length to determine volume