Scientific Measurement

Nature of Measurement Examples: Measurements are fundamental to the experimental sciences. Important to make measurements Important to decide whether a measurement is correct Measurement - quantitative observation consisting of 2 parts Part 1 - number Part 2 - scale (unit) Examples: 20 grams 6.63 x 1034 atoms

Precision & Accuracy Accuracy refers to the agreement of a particular value with the true value. Precision refers to the degree of agreement among several measurements made in the same manner. Neither accurate nor precise Precise but not accurate Precise AND accurate

Uncertainty in Measurement A measurement always has some degree of uncertainty. A digit that must be estimated is called uncertain.

Why Is there Uncertainty? Measurements are performed with instruments. No instrument can read to an infinite number of decimal places Which of these balances has the greatest uncertainty in measurement?

Reading the Meniscus Always read volume from the bottom of the meniscus. The meniscus is the curved surface of a liquid in a narrow cylindrical container.

Measuring Volume Determine the volume contained in a graduated cylinder by reading the bottom of the meniscus at eye level. Read the volume using all certain digits and one uncertain digit. Certain digits are determined from the calibration marks on the cylinder. The uncertain digit (the last digit of the reading) is estimated.

Use the graduations to find all certain digits There are two unlabeled graduations below the meniscus, and each graduation represents 1 mL, so the certain digits of the reading are… 52 mL.

Estimate the uncertain digit and take a reading The meniscus is about eight tenths of the way to the next graduation, so the final digit in the reading is… 0.8 mL The volume in the graduated cylinder is 52.8 mL.

10 mL Graduate What is the volume of liquid in the graduate? 6 _ . _ _ mL 6 2

25mL graduated cylinder _ _ . _ _ mL 1 1 5 1 What is the volume of liquid in the graduate? _ _ . _ _ mL 1 1 5 1

The cylinder contains: Self Test Examine the meniscus below and determine the volume of liquid contained in the graduated cylinder. The cylinder contains: 7 _ _ . _ mL 6

The Thermometer Read the scale on the thermometer at eye level. Read the temperature by using all certain digits and one uncertain digit. Certain digits are determined from the calibration marks on the thermometer. The uncertain digit (the last digit of the reading) is estimated.

Do not allow the tip to touch the walls or the bottom of the flask. If the thermometer bulb touches the flask, the temperature of the glass will be measured instead of the temperature of the solution. Readings may be incorrect, particularly if the flask is on a hotplate or in an ice bath.

Reading the Thermometer Determine the readings as shown below on Celsius thermometers: _ _ . _ C 8 7 5 _ _ . _ C 3 5

Determining Mass 1. Place object on pan 2. Move riders along beam, starting with the largest, until the pointer is at the zero mark

Check to see that the balance scale is at zero

1 1 4 ? ? ? _ _ _ . _ _ _ Read Mass

1 1 4 4 9 7 _ _ _ . _ _ _ Read Mass More Closely

The Fundamental SI Units (ie: Système International, SI) Physical Quantity Name Abbreviation Mass kilogram kg Length meter m Time second s Temperature Kelvin K Amount of Substance (1 mol = 6.02x1023) mole mol

BASE UNIT SI Prefix Abbr Exp Meaning Equality mega M 106 kilo k 103 1 million x larger 1,000,000 base unit = 1 M_ kilo k 103 1,000 times larger 1,000 base unit = 1 k_ deca da 10 10 times larger 10 base unit = 1 D_ BASE UNIT (meters, grams, liters, etc.) 1 1 base unit deci d 10-1 1/10 1 base unit = 10 d_ centi c 10-2 1/100 1 base unit = 100 c_ milli m 10-3 1/1,000 1 base unit = 1,000 m_ micro  10-6 1/million 1 base unit = 1,000,000 _ nano n 10-9 1/billion 1,000,000,000 n_ pico p 10-12 1/trillion 1,000,000,000,000 p_

Y Z E P T G M k h da d c m µ n p f a z y FACTOR ...or in full ... or in words SI PREFIX SI SYMBOL 1,0E+24 1,0E+21 1,0E+18 1,0E+15 1,0E+12 1,0E+9 1,0E+6 1,0E+3 1,0E+2 1,0E+1 1,0E-1 1,0E-2 1,0E-3 1,0E-6 1,0E-9 1,0E-12 1,0E-15 1,0E-18 1,0E-21 1,0E-24 1 000 000 000 000 000 000 000 000 1 000 000 000 000 000 000 000 1 000 000 000 000 000 000 1 000 000 000 000 000 1 000 000 000 000 1 000 000 000 1 000 000 1 000 100 10 0,1 0,01 0,001 0,000 001 0,000 000 001 0,000 000 000 001 0,000 000 000 000 001 0,000 000 000 000 000 001 0,000 000 000 000 000 000 001 0,000 000 000 000 000 000 000 001 septillion sextillion quintillion quadrillion trillion billion million thousand hundred ten tenth hundredth thousandth millionth billionth trillionth quadrillionth quintillionth sextillionth septillionth yotta- zetta- exa- peta- tera- giga- mega- kilo- hecto- deca- deci- centi- milli- micro- nano- pico- femto- atto- zepto- yocto- Y Z E P T G M k h da d c m µ n p f a z y

SI Basic Units & Quantities Length = meter (m) Volume = volume of 1m x 1m x 1m cube = 1 m3 More convenient = liter (L) 1 cm3 = 1 mL 10 drops H2O ≈ 1 mL Mass = kilogram (kg) Defined as the mass of 1 L of H2O @ 4ºC weight is a force that measures the pull on a given mass by gravity

SI Basic Units & Quantities Temperature = Celsius (°C) - Water freezes @ 0 °C Water boils @ 100 °C Kelvin (K) - the absolute scale Don’t use the degree symbol Water freezes @ 273 K Water boils @ 373 K K = °C + 273 °C = K - 273

Practice Simple Conversions 5m to cm 2.3 cm to mm 87mm to cm 935 mm to m