Name. Academic Chemistry Measurement and Calculations. Notes. Measurement cincochem.pbworks.com 1

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1 Name Academic Chemistry Measurement and Calculations Notes Measurement cincochem.pbworks.com 1

2 Academic Chemistry SIGNIFICANT FIGURES Unit 1 Significant figures are the digits in a measurement that you can prove are true on a measuring device plus one unknown, or uncertain digit that you estimate. When any measurement falls BETWEEN 2 lines on a measuring device, then you WILL estimate the final digit. This is the digit. When a measurement falls on a line, your doubtful digit is zero (in the above graphic, 43.0 ml). For example, a ruler: We can estimate that the measurement is 3.7 cm. We are certain of the first digit, the 3, but we are not certain of the second digit, the.7. Therefore the.7 is our doubtful digit. Given a measurement, we can COUNT how many significant figures are present in that number. This is important, because in science, our work is only as good as our measurements. Pacific Ocean Is a decimal Absent or Present? Atlantic Ocean How to determine number of significant figures in a measurement. 2 cincochem.pbworks.com Measurement

3 Academic Chemistry SIGNIFICANT FIGURES Determine if the decimal is Absent or Present. Atlantic decimal is Absent. Begin counting on the Atlantic side (the right). From RIGHT of the number, find the first non-zero digit and count Right to Left until you reach the end of the number. Ex: 6050 sig figs Ex: 6051 sig figs Pacific decimal is Present. Begin counting on the Pacific side (the left). From LEFT of the number, find the first non-zero digit and count Left to Right until you reach the end of the number. Ex: sig figs Ex: sig figs Practice How many significant figures? Term Non-zero digit any number other than zero. Measurement cincochem.pbworks.com 3

4 OPERATIONS with SIGFIGS Academic Chemistry Adding/Subtracting arrange numbers in a. Line up the. Omit any digits to the right of a column that contains a doubtful digit (think place value). Units must match! Practice: 2.43 cm cm m m 87 ml ml Multiplying/Dividing the number of sigfigs in your product or quotient is the same as the number in the operation with the sigfigs. When using a calculator, round to the sigfig needed. Units must stay in the place they are located in the operation! Practice: 5.12 m x 223 m = g x 2.00 g = 4 cincochem.pbworks.com Measurement

5 Academic Chemistry OPERATIONS with SIGFIGS m 0.52 s = Combining Operations First, observe the order of operations ( ) when considering sigfigs. For each step, you must determine sigfigs, then use that result in the next step of the operation. Keep track of the units. Practice: (2.3 cm cm) x 38.2 cm 62.2 kg 2.0 kg kg Note: PEMDAS perform operations in this order. 1. Parenthesis 2. Exponent 3. Multiply 4. Divide 5. Add 6. Subtract Measurement cincochem.pbworks.com 5

6 SCIENTIFIC NOTATION Academic Chemistry Scientific notation is used to express very large and very small numbers. Often in science we measure and count extremely small and large numbers. Scientific notation makes our work easier (promise!). *The number of sig figs does not change when converting to or from scientific notation. General formula: The coefficient (number in front) is always between 1 and 10. For very large numbers (greater than 10), n is positive. For very small numbers (less than 1), n is negative. To convert TO scientific notation from ordinary notation: 1. Move the decimal point one digit at a time so the coefficient is between 1 and Count how many places you moved the decimal point. 3. This will be the exponent, or n. 4. For large numbers, n is positive 5. For small numbers, n is negative. Practice: 91.4 m = m = 6,378,000 m = 34,071,000 m = 6 cincochem.pbworks.com Measurement

7 Academic Chemistry SCIENTIFIC NOTATION To convert FROM scientific notation to ordinary notation, move the decimal point the number of places signified by the exponent n. For a positive n, move the decimal to the right to make the number large. For a negative n, move the decimal to the left to make the number smaller. No decimal present = an implied decimal after the ones place. Practice: 4 x 10 7 m = 2 x 10-3 m = 1.8 x 10 3 m = x 10 4 m = 7.1 x 10-2 m = x 10-3 m = cm = 31,580,000 s = km = 7.8 x 10 5 mm = Term Ordinary notation a method of expressing numerical values in which the entire number is expressed in the notation. Measurement cincochem.pbworks.com 7

8 Metric System Academic Chemistry Scientists use the metric system to make measurements in the lab. Measurement Basic Unit Mass Volume Length/Distance KING HENRY DIED BY drinking chocolate milk Basic Unit Very large measurement (move decimal left) Very small measurement (move decimal right) Use the Stair Step method to make the following metric conversions. Examples: 47 g = kg 500 mm = cm km = m cl = L Practice: 1) 500 g = kg 2) ml = cl 3) kg = mg 4) 20.0 m = mm 8 cincochem.pbworks.com Measurement

9 Academic Chemistry Metric Conversion Help Sheets Unit 1 Measurement cincochem.pbworks.com 9

10 Academic Chemistry Metric Conversion Help Sheets Unit 1 10 cincochem.pbworks.com Measurement