MEASUREMENT SIGNIFICANT FIGURES, ACCURACY, GLASSWARE, SCIENTIFIC NOTATION, DENSITY AND FACTOR LABEL METHOD

Where do I round to when taking measurements? In measuring you can only guess one digit past what you can actually read on the instrument. The measurement is between 44 and 45 so we can estimate 44.5 as an answer.

Types of measurements in chemistry

Temperature is a measurement of the average kinetic energy of the particles in a sample of material. Temperature is not a form of energy. (4.2b) Two temperature scales used in chemistry are Celsius and Absolute The unit of temperature in the Celsius scale is the degree (ºC) The unit of temperature on the Absolute scale is the Kelvin (K) J Deutsch 2003

To convert between absolute and Celsius temperature scales use K=ºC+273 J Deutsch 2003

Melting Point The temperature at which a liquid and a solid are in equilibrium The melting point for ice is 0ºC The melting point of a substance is the same as its freezing point J Deutsch 2003

Boiling Point The temperature that a substance will boil Going from liquid to gas For water it is 100 degrees celcius

Regents Question: 06/03 #41 þ See Table S The freezing point of bromine is (1) 539°C (2) –539°C (3) 7°C (4) –7°C See Table S Melting point is the same as freezing point Convert K to C (K=C+273) þ J Deutsch 2003

Dimensional Analysis Solving problems in chemistry requires careful manipulation of numbers and their associated units, a method known as dimensional analysis.

Another way to show dimensional Analysis 5.25 g 1 mL = 4.47 mL 1.23 g

Scientific Notation

WHAT IS A SIGNIFICANT FIGURE? Significant figures are all the digits in a measurement that are known with certainty plus a last digit that must be estimated. 12/1/2018

WHICH NUMBERS ARE SIGNIFICANT? For the purposes of significant figures there are two major categories Nonzero digits: 1,2,3,4,5,6,7,8,9 Zero digits: 12/1/2018

Now you try How many significant digits in each of the following: 12 apples 3000 m 69 people 12/1/2018

BEFORE YOU CAN CRUNCH You must know which digits are significant Because they are going to control the number of digits in a calculated figure 12/1/2018

ADDITION AND SUBTRACTION The answer has the same number of decimal places as the least precise measurement used in the calculation. 12.11 18.0  Limiting term has one decimal place 1.013 31.123 Corrected to 31.1 (one decimal place) The correct result is 31.1, since 18.0 has only one decimal place. 12/1/2018

MULTIPLICATION AND DIVISION An answer has the same number of significant figures as the number in the least precise measurement used in the calculation. 36 cm x 1.03 cm = 37.08 cm2 36 is the least precise measurement with 2 significant figures. Therefore the answer can have only 2 significant figures The answer is 37 cm2 12/1/2018

Now you try 0.356 kg x 1.5 m 1.234 g + 0.67 g + 13.2 g 101 g / 0.33 mL 15.27 s – 3.695 s 12/1/2018

Answers 0.356 kg x 1.5 m = 0. 53 kgm 1.234 g + 0.67 g + 13.2 g = 15.1 g 101 g / 0.33 mL = 310 g/mL 15.27 s – 3.695 s = 11.58 s 12/1/2018