Lesson 2.1

Measurements in Analytical Chemistry

Unit

type of dimension used as a basis of comparison

Number

specifies how many/how much

Significant figures

• include all of the digits that are known and a last digit that is estimated.

• Measurements must always be reported to the correct number of ____ because calculated answers often depend on the number of significant figures in the values used in the calculation.

Non-zero

• Every ____ in a reported measurement is assumed to be significant.

• Rule #1

Between

• Zeros appearing ___ nonzero digits are significant.

• Rule #2

Placeholders

• Leftmost zeros appearing in front of nonzero digits are not significant. They are ___. By writing the measurements in scientific notation, you can eliminate such placeholding zeros.

• Rule #3

End & right

• Zeros at the ___ of a number and to the ___ of a decimal point are always significant.

• Rule #4

Rightmost end

• Zeros at the ____ of a measurement that lie to the left of an understood decimal point are not significant if they serve as a placeholder.

• Rule #5

Significant

• Trailing zeros in a whole number with the decimal shown are ____

• Rule #6

Counted quantities and defined quantities

There are two situations in which numbers have an unlimited number of significant figures:

N

For a number in scientific notation: (N x 10x), all digits comprising ___ ARE significant by the first 6 rules; "10" and "x" are NOT significant.

Addition or subtraction

The answer to an ____ or ___ problem should be rounded to the same number of decimal places (not digits) as the measurement with the least number of decimal places.

Least

The answer to an addition or a subtraction problem should be rounded to the same number of decimal places (not digits) as the measurement with the ___ number of decimal places.

Fewest

For multiplication and division, we round the answer to the same number of significant figures as the measurement with the ____ number of significant figures.

Multiplication and division

For ____ and ____ , we round the answer to the same number of significant figures as the measurement with the fewest number of significant figures.

Common exponent

When working with scientific notation, first convert each measurement to a ____ before determining the number of significant figures.

Mass

is an unchanging measure of the quantity of matter in an object.

Weight

is the force of attraction between an object and its surroundings, principally Earth.

Mole/ mol

is the SI unit for the amount of a chemical substance. It is always associated with specific microscopic entities such as atoms, molecules, ions, electrons, other particles, or specified groups of such particles as represented by a chemical formula.