Measurement Flashcards
What indicates an accurate measurement?
A low percent error value
- measured and true value is near from each other, indicating that their relative difference is low
What does highly precise measurement indicate?
It does not indicate accuracy. Precision mainly shows relationship between the measured values
What is a random error?
cannot be determined and corrected, it is an effect of uncontrolled variables
What is systematic error?
can be determined and corrected
flaw in experimental design /equipment
Which is an example of random error?
A. A chemical technician mistakenly prepared a different sample before running into an HPLC assay.
B. A 25-mL burette consistently delivers 24.98±0.03 mL.
C. An analytical balance consistently displayed 5.010 g upon weighing a 5.000-g calibrated weight material.
D. The reading of a gas sensor for a blank sample fluctuates from -0.009 to 0.002.
D. The reading of a gas sensor for a blank sample fluctuates from -0.009 to 0.002
It is a blank sample so it should not cause fluctuation. Causes of error from the other choices can be easily determined.
Which of the following has two significant figures after calculation?
A. (2.10 + 2.11)/2.0
B. 1000 x 2
C. 101 + 3.2 + 2.1
D. 4.75 / (2.50 – 0.11)
A.
2.10 + 2.11 leads to an answer with 3 significant figures. Dividing the answer (3 significant figures) by 2.0 (2 significant figures) leads to an answer with 2 significant figures according to the rules of significant figures for multiplication and division
Which of the following numbers has exactly 3 significant figures?
A. 1.00
B. 12.10
C. 120
D. 0.025
A. 1.00
The zeros at the right of a non-zero digit and at the right of the decimal point are significant. Thus, 1.00 has 3 significant figures. 120 and 0.025 both have 2 significant figures while 12.10 has 4 significant figures.
Which of the following is a unit for volume?
A. in3
B. m2
C. Pa
D. lb
Consider the formula for the volume of a box. V = l x w x h. Since each parameter is a measure of length, thus the unit must be that of length unit. Substituting this length unit to the formula gives us the cubic unit of length (V = u x u x u = u3). Thus, in3 is the correct answer.
