3.1 Using and Expressing Measurements Do Now: Using prior knowledge in math, put the following numbers in scientific notation

Measurement Quantity that has both a number and unit 15 years old 32cm 100 degrees Celsius

Scientific Notation In chemistry, you maybe dealing with very large or very small numbers 602,000,000,000,000,000,000,000 hydrogen atoms Is the same as 6.02 x hydrogen atoms

Scientific notation is written as the product of two numbers, a coefficient and 10 raised to a power = 9.8 x (move the decimal to the first non zero digit) Moving decimal to left = positive exponent Moving decimal to the right = negative exponent

Try These Out Convert from standard notation to scientific notation

Accuracy, Precision and Error Accuracy- how close a measurement is to the true value Precision- how close a series of measurements are to each other

Error Accepted value- correct value of measurement based on reliable references (100°C boiling point of water) Experimental value- value measured in lab (suppose you measured 99.1°C as the boiling point)

Error= Experimental – accepted (can be a negative number) 99.1 – 100 = -0.9 error It is also useful to calculate percent error % error = (I error I / accepted value) x 100 % error = (I -0.9 I / 100 ) x 100 = 0.9% error

Try this out A student measures the depth of a swimming pool to be 2.04 meters. The accepted value is 2.00 meters. Calculate error and percent error of this student’s measurements.

Significant Figures Rounding with the last digit being an estimate Significant figures are important for increasing precision in measurements 0.8 < 0.77 < (from increasing precision)

Rules of Significant Figures 1. All digits 1-9 are significant – 123 – Zeros “sandwiched” between non zero digits are significant – 101 – – 101.5

Zeros trailing to the left of a nonzero digit are never significant (they are just place holders – – 0.15 Zeros trailing to the right of a nonzero digit depends on whether or not there is a decimal point – – yes those zeros are significant – 1400 – no those zeros are not significant

Try These Out How many significant figures are in the following A D. 13,000 B E C