Chapter 2 Section 3 Flashcards
Accuracy
The closeness of measurements to the correct or accepted value of the quantity measured
Precision
The closeness of a set of measurements of the same quantity made in the same way
Measured values that are accurate are close to the
Accepted value
Measured values that are precise are close to
One another but not necessarily close to the accepted value
The accuracy of an individual value or if an average experimental value can be compared
Quantitatively with the correct or accepted value by calculating the percentage error
Percentage error is calculated by subtracting the
Accepted value from the experimental value, dividing the difference by the accepted value, and then multiplying by 100
Percentage error=
Experimental-accepted
———————-x 100
Accepted
In science for a reported measurement to be useful there must be some indication of
It’s reliability or uncertainty
Percentage error has a negative value of the accepted value is
Greater than the experimental value. The opposite is also true
The skill of the measured places
Limits on the reliability of the results
Conditions of measurement and the measuring instruments themselves place
Limits on precision
When you use a properly calibrated measuring device you can be almost certain of a
Particular number of digits in a reading
The hundredths place is somewhat
Uncertain but should not be left out because you have some indication of the values likely range
Thus the value would be estimated to the final
Questionable digit, possibly including a plus-or-minus value to express range
Measured values are reported in terms of
Significant figures
Significant figures in a measurement consist of all the
Digits known with certainty plus one final digit, which is somewhat uncertain or is estimated
Term significant does not mean
Certain
In any correctly reported measured value the final
Digit is significant but not certain
Insignificant numbers are
Never reported
The significance of zeros in a number depends on
Their location
Zeros appearing between nonzero digits are
Significant
Zeros at the end of a number and to the right of a decimal point are
Significant
Zeros at the end of a number but to the left of the decimal point
May or may not be significant
Zeros appearing in front of all nonzero digits are
Not significant
A decimal point placed after zeros indicated that they
Are significant
The answers given on a calculator can be
Derived results with more digits than are justified by the measurements
Answers have to be
Rounded off to make its degree of certainty match that in the original measurements
The extent of rounding required in a given Case depends on whether the numbers are
Being added, subtracted, multiplied, or divided
(Rounding rules) greater than 5
Increased by 1
(Rounding rules) less than 5
Stays the same
(Rounding rules) 5, followed by nonzero digits
Increases by 1
(Rounding rules) 5, not followed by nonzero digits, and preceded by an odd digit
Be increased by 1
(Rounding rules) 5, not followed by nonzero digits, and preceding significant digit is even
Stay the same
When adding or subtracting decimals the answer must have the same number of
Digits to the right of the decimal point as there are in the measurement with the fewest digit to the right of the decimal pt
When working with whole numbers the answer should be rounded so that the
Final significant digit is in the same place as the leftmost uncertain digit
For multiplication or division the answer can have no more significant figures than are in the
Measurement with the fewest number of significant figures
Conversion factors are typically
Exact
Because the conversion factor is considered exact the answer would not be
Rounded
Most exact conversion factors are
Derived, rather than measured, quantities
Counted numbers also product
Conversion factors of unlimited precision
In scientific notation numbers are written in the form
M x 10^n, where M is a whole number greater than or equal to one but less than 10 and n is a whole number
Wen numbers are written in scientific notation only the
Significant figures are shown
Determine M by moving the decimal point in the original number to the
Left/ right so that only one nonzero digit remains to the left of the decimal point
Determine n by counting the number of places that you moved the
Decimal point. If you moved it to the left, n is positive. The opposite is also tee
Addition and subtraction can be performed only if the by
Values have the same exponent (n factor)
If they don’t have the same n factor, adjustments must be made to the values so that
Their exponents are equal
The exponent of the answer can remain the same or it may then require adjustment if the
M factor of the answer has more than one digit to the left of the decimal point
Multiplication the M factors are
Multiplied and the exponents are added algebraically
Division the m factors are
Divided and exponent of denominator is subtracted from that of the numerator
The first step in solving a quantitiative word problem is to read the problem
Carefully at least twice and to analyze the information
Note any important descriptive terms that c
Clarify or add meaning
Identify and list data
Identify the unknown
Develop a plan for solving the problem that shows how
Info given is to be used to find the unknown
Decide which
Conversion factors
Mathematical formulas
Chemical principles you will need to solve the problem
The third step involved substituting
The data and necessary conversion factors into the plan you have developed
Computing
Calculate the answer
Cancel units
Round the result to the correct number of significant figures
Calculate your answer to determine whether it is reasonable
Check if units are correct
Make an estimate of expected answer and compare with actual result
Check order of magnitude
Ensure that answer has correct number of significant figures
Two quantities are directly proportional to each other if
Dividing one by the other gives a constant value
When 2 variables, x And y, are directly proportional the relationship. An be expressed as
y ∝ x.
y ∝ x.
Y is proportional to x
General equation for a directly proportions relationship between two variables
Y
- = k
X
K
Proportionally constant
Equation expresses that in a direct proportion ratio between 2 variables
Remains constant
Directly equation can be rearranged into
Y = kx
If 2 variables are directly proportional their graph is
A straight line that passes through the origin
Two quantities are inversely proportional to each other if their products are
Constant
Equation for inversely proportional equation
y ∝ 1
-
X
Equation thing for inversely means
Y is proportional to 1 divided by x
Equation can be rewritten as
K = xy
In this equation (inversely) if x increases, y must
Decrease by the same factor to keep the product constant
Inversely proportional graph produced a
Curve called a hyperbola
