Chapter 3 Convert Measurements to scientific notation. Distinguish among accuracy and precision. Determine the number of significant figures in a measurement and a calculated answer.

Measurement & Scientific Notation Please write the definitions from the book for the following vocabulary terms. Measurement (pg 63) Scientific notation (pg 63) Chemists use scientific notation because many times they encounter measurements that are very large or very small. For example, 1 gram of hydrogen = 602,000,000,000,000,000,000,000 hydrogen atoms. Or the mass of gold is 0.000 000 000 000 000 000 000 327 g. Instead chemists will say there are 6.02 x 1023 hydrogen atoms or the mass of 1 gold atom is 3.27 x 10-22 g. Measurement-a quantity that has both a number and a unit. Sci Notation-the given number is written as the product of 2 numbers: a coefficient and 10 raised to a power.

Accuracy, Precision Please answer this questions in your notes: How do you evaluate accuracy and precision (pg 64)? To evaluate accuracy, the measured value must be compared to the correct value. To evaluate precision, you must compare the values of two or more repeated measurements. A = good on both; b = poor accuracy, good precision; c = poor accuracy, poor precision For each target above, please describe the level of accuracy and precision.

Significant Figures Suppose you estimate a weight that is between 2.4 lb and 2.5 lb to be 2.46 lb. The first two digits (2 and 4) are known. The last digit (6) is an estimate and involves some uncertainty. All three digits convey useful information, however, and are called significant figures. The significant figures in a measurement include all of the digits that are known, plus a last digit that is estimated. Why must measurements be reported to the correct number of significant figures (pg 66 for the answer)? The significant figures in a measurement include all of the digits that are known, plus a last digit that is estimated.

Sig Figs Rules Print these off for the kids. Too much time wasted writing them.

Sig Figs Rules

Precision in Measurement How many sig figs are there in each? (1, 2, 3, respectively)

Practice A = 3 B = 5 C = 5 D = unlimited E = 4 F = 2 B = 2 C = 4 D = 4

Rounding & Scientific Notation In general, a calculated answer cannot be more precise than the least precise measurement from which it was calculated. The calculated value must be rounded to make it consistent with the measurements from which it was calculated. A = 8.71 x 10 to the 1 m B = 4.36 x 10 to the 8 m C = 1.55 x 10 to the -2 m D = 9.01 x 10 to the 3 m E = 1.78 x 10 to the -3 m F = 6.30 x 10 to the 2 m

Addition and Subtraction The answer to an addition or subtraction calculation should be rounded to the same number of decimal places (not digits) as the measurement with the least number of decimal places.

Multiplication and Division In calculations involving multiplication and division, you need to round the answer to the same number of significant figures as the measurement with the least number of significant figures. The position of the decimal point has nothing to do with the rounding process when multiplying and dividing measurements.

Section 2 A few reminders, mostly review Chapter 3 Section 2 A few reminders, mostly review

Common Chemical Measurements The five SI base units commonly used by chemists are the meter, the kilogram, the kelvin, the second, and the mole.

A Few Reminders: For the volume of liquids, 1 mL is the same as 1 cm3. Scientists commonly use two equivalent units of temperature, the degree Celsius and the kelvin. On the Celsius scale, the freezing point of water is 0°C and the boiling point is 100°C. On the Kelvin scale, the freezing point of water is 273.15 kelvins (K), and the boiling point is 373.15 K. The zero point on the Kelvin scale, 0 K, or absolute zero, is equal to 273.15 °C.

C to K, K to C Because one degree on the Celsius scale is equivalent to one kelvin on the Kelvin scale, converting from one temperature to another is easy. You simply add or subtract 273, as shown in the following equations.

Converting C  F and F  C °F = °C  x  9/5 + 32 °C = (°F  -  32)  x  5/9

The Mole A mole (mol) is 6.02 x 1023 representative particles of that substance and is the SI unit for measuring the amount of a substance. Avogadro’s number Representative particles refers to the species present in a substance: usually atoms, molecules, or formula units.

Representative Particles and Moles Substance Rep Particles Chem Formula In 1.00 mole Atomic nitrogen Atom N 6.02 x 1023 Nitrogen gas Molecule N2 Water H2O Calcium Ion Ion Ca2+ Calcium fluoride Formula Unit CaF2 Sucrose C12H22O11

Dimensional Analysis How many seconds are in 6 minutes? How many minutes in one week? How many student can do a lab if each needs 8.5 cm of magnesium ribbon and there are 570 cm of it? Convert .044 km to meters, 15 cm3 to liters. Use pg. 74 and 75 for help on the conversion charts. Convert 3.2 moles of CaCl2 to representative particles using your notes as help.