measurement Flashcards
uncertainty
def, calculation
= the doubt about the result of any measurement and its quantification
= (smallest division of measurement)/2
error
def, types
= the difference between the measured and true value of the thing being measured
systematic, random
systematic error
⇒ caused by instrumentation errors, methodology errors and personal errors
always either greater or lesser than the true value
random error
- ⇒ occur randomly and affect measurements in an unpredictable manner
- due to carelessness, lack of concentration, uncontrolled variables
- reduce the risk with repeating the measurements several times
- can be greater or lesser than the true value
percentage error
= (|literature value - experimental value|) : literature value = random error + systematic error
precision vs accuracy
precision ⇒ how close the measurements are to each other (affected by random error)
accuracy ⇒ how close a measurement is to the true value (affected by systematic error)
addition and subtraction with uncertainties
add uncertainties (ΔX)
multiplication and division with uncertainties
add relative uncertainties (δx = ΔX/X)
scientific notation
only positive numbers
1 < a < 10 × 10^y
rules for determining significant figures
- non-zero digits are always significant
- any zeros between two significant digits are significant
- a final zero or trailing zeros in the decimal portion are significant
addition and subtraction with significant figures
round the answer to the least number of decimal places of any number
multiplication and division with significant figures
least number of significant figures in any number of the problem determines the number of significant figures in the answer
interpolation vs extrapolation
interpolation ⇒ estimation of unknown values within the range of known data points (more reliable)
extrapolation ⇒ estimation of unknown values outside the range of known data points (less reliable)
reaction yield
- %yield = (experimental yield)/(theoretical yield)
- experimental yield ⇒ real amount of product (what we measure)
- theoretical yield ⇒ expected amount of product (what we calculate)
STP
- = standard temperature and pressure
- T = 0°C = 273 K
- P = 100 kPa
