Objectives: * 1. Define significant digits. * 2. Explain how to determine which digits in measurement are significant. * 3. Convert measurements in to scientific notation. Key Terms: significant digit, percent error, density

* The purpose of significant digits is to limit the amount of uncertainty in the data you display. The measured and the estimated digits of a measurement are considered significant. (If you look at the picture the significant digits would be read as 26.45g measured,.05 estimated) The estimated digit adds to the accuracy of the measurement

* When making measurements in science it is important to write down all of the digits that a device can give you and one estimated digit. Remember that measurements are never completely accurate for the following two reasons : * measuring equipment is never completely free of flaws * measurements always involve some degree of estimation Note: * Electronic devices take care of estimation for you and record the last digit as the estimated digit.

When recording the measurement of a piece of scientific equipment try following the following steps: 1) determine the scale increments… ea. graduation is 10ml 2) record the real measurement… 110ml 3) estimate the distance traveled toward the next real measurement… half way is ~5ml 4) record your measurement using the real and estimated digits… 115ml

* Rule #1: Trailing zeros without a decimal are NEVER significant (13000… only the 13 are significant) * Rule #2: Leading zeros are NEVER significant (0.0027… only the 27 are significant) * Zeros that simply hold places are not significant * Rule #3: Trailing zeros after a decimal are ALWAYS significant ( … are all significant and add to the precision of the measurement) * Rule #4: Zeros found between numbers are ALWAYS significant (987001… all numbers are significant)

* The measurement with the smallest amount of significant digits determines the significant digits of the answer Example: g x 45.2g = ? 1) determine the operand with the smallest amount of significant digits (0.3287… 4 sig digits & 45.2 … 3 sig digits) 2) perform the operation on your calculator and round to the correct amount of digits g x 45.2g = g (too many digits) 14.9g (rounded to 3 sig digits)

* The total cannot be more accurate than the least accurate measurement. This time the amount of significant digits of each number does not matter. The quantity with the least digits to the right of the decimal point determines the accuracy of the answer Example: 125.5kg kg + 2.1kg = ? 1) determine the precision of your least accurate measurement. (125.5kg and 2.1kg are both accurate to the tenths place while 52.68kg is accurate to the hundredths place) 2) perform the operation 125.5kg kg + 2.1kg = kg (too precise!) 180.3kg (precise to the tenths place)

* When doing combinations of addition/subtraction and multiplication/division, each step determines its significant digits. The digits in the end answer are determined by the last operation performed. Example: 1250cal – ( cal/52.69cal) = ? 1250cal – (4.445cal) = (parenthesis 1 st … answer has 4 sig digits) 1250cal – (4.445cal) = cal (too precise!) 1250cal (accurate to the tens place)

* Scientific notation is a way that scientists make incredibly large numbers used in science easier to work with. There are 602,000,000,000,000,000,000,000 atoms in a mole of a substance. It is much easier to use the answer as 6.02 x Rules: * 1) The answer must be in the form of a real number followed by a decimal point while retaining the correct amount of significant digits. * 2) If the magnitude of the number is to be reduced the exponent will be positive. Example: = x 10 5 (the exponent is equal to the number of times that the decimal point was moved) * 3) If the magnitude of the number is to be increased the exponent will be negative. Example: = 5.01 x 10 -3

* Percent error calculations are used to compare test results to a known accepted quantity. The formula is as follows: Percent error = ((measured value - accepted value) / accepted value ) * 100% * Note: The result can be positive or negative but the answer is always represented as the absolute value Example: The accepted mass of an object is 5.00g. When you measure it on your digital scale the reading shows 5.02g. What is the percent error of your measurement? (5.02g – 5.00g) / 5.00g = or 0.4%