Chemistry The Importance in Measurement

What type of Measurement are made in Chemistry? 1.Qualitative Measurements Descriptive, non-numerical formDescriptive, non-numerical form Color, shape, size, feelings, textureColor, shape, size, feelings, textureExample: The basketball is round and brown. 2.Quantitative Measurements Definite form with numbers AND unitsDefinite form with numbers AND units Mass, volume, temperature, etc.Mass, volume, temperature, etc.Example: The basketball has a diameter of 31 cm and a pressure of 12 lbs/in 2.

In science, we deal with some very LARGE numbers: 1 mole = In science, we deal with some very SMALL numbers: Mass of an electron = kg Scientific Notation

Imagine the difficulty of calculating the mass of 1 mole of electrons! kg x x ???????????????????????????????????

Scientific Notation: A method of representing very large or very small numbers in the form: M x 10 n M x 10 n  M is a number between 1 and 10  n is an integer  # of times to move the decimal  If n is negative, the number is really small  If n is positive, the number is really large.

Step #1: Insert an understood decimal point. Step #2: Decide where the decimal must end up so that one number is to its left up so that one number is to its left Step #3: Count how many places you bounce the decimal point the decimal point Step #4: Re-write in the form M x 10 n

2.5 x 10 9 The exponent is the number of places we moved the decimal. Since it was a large number, the exponent is positive.

Step #2: Decide where the decimal must end up so that one number is to its left up so that one number is to its left Step #3: Count how many places you bounce the decimal point the decimal point Step #4: Re-write in the form M x 10 n 12345

5.79 x The exponent is negative because the number we started with was less than 1.

PERFORMING CALCULATIONS IN SCIENTIFIC NOTATION ADDITION AND SUBTRACTION

4 x x 10 6 IF the exponents are the same: 1. add or subtract the numbers in front 2. bring the exponent down unchanged. 7 x 10 6

4 x x 10 6 The same holds true for subtraction in scientific notation. 1 x 10 6

4 x x 10 5 If the exponents are NOT the same, we must move a decimal to make them the same.

4.00 x x 10 5 Student A 40.0 x x 10 5  Is this good scientific notation? NO! = x 10 6 To avoid this problem, move the decimal on the smaller number!

4.00 x x 10 5 Student B.30 x x 10 6  Is this good scientific notation? YES!

A Problem for you… 2.37 x x 10 -4

2.37 x x Solution… x x x 10 -4

PERFORMING CALCULATIONS IN SCIENTIFIC NOTATION MULTIPLICATION AND DIVISION

4 x 10 6 x 3 x 10 6 IF the problem is multiplication: 1. Multiply the numbers as usual 2. add the exponent. 12 x 10 12

24 x x 10 6 IF the problem is division: 1. Divide the numbers as usual 2. subtract the exponents: numerator - denominator 8 x 10 3

Calculate the following answer: kg kg ______ x ??????????????????????????????????? 9.1 x x 6.02 x x x kg

Practice Problems # x x x x x x x x 10 -9

Practice Problems # x 10 6 / 2 x x 10 8 x 5 x x 10 3 / 2 x x 10 7 x 4 x 10 -9

Precision and 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

Percent Error Accepted Value – Correct value based on reliable references. Example: Boiling Point of water is 100°C Experimental Value – Value measure in lab. Example: Boiling Point measured in lab reads 99.1°C Percent Error = x 100 | experimental value – accepted value | accepted value |99.1 – 100| x x 100 = 0.9% error Errors less than 5-10% is acceptable!

International System of Units (SI)

The Fundamental SI Units (le Système International, SI) QuantitySI Base UnitSymbolOther Symbols Lengthmeterm Volumecubic meterm3m3 liter (L) Masskilogramkm Density grams / cubic centimeter g/cm 3 grams / milliliter (g/mL) TemperaturekelvinKdegree Celcius (°C) Timeseconds PressurepascalPaatmosphere (atm) EnergyjouleJcalorie (cal) Amt of Subs.molemol

Prefixes in Measurements PrefixSymbolFactor Scientific Notation mega-M kilo-k deci-d1 / centi-c1 / milli-m1 / micro-μ1 / nano-n1 / pico-p1 /

Units of Length UnitSymbolRelationshipExample Kilometerkm1 km = 10 3 mLength of 5 city blocks Metermbase unitHeight of door knob Decimeterdm10 1 dm = 1 mDiameter of orange Centimetercm10 2 cm = 1 mWidth of button Millimetermm10 3 mm = 1 mThickness of dime Micrometerμmμm10 6 μm = 1 mDiameter of a bacteria Nanometernm10 9 nm = 1 mThickness of an RNA

Units of Volume UnitSymbolRelationshipExample LiterLbase unitQuart of Milk MillitermL10 3 mL = 1 L20 drops of water Cubic Centimeter cm 3 1 cm 3 = 1 mLcube of sugar MicroliterμLμL10 6 μL = 1 Lcrystal of table salt

Units of Mass UnitSymbolRelationshipExample Kilogramkg base unit 1 kg = 10 3 g small textbook Gramg1 g = kgdollar bill Milligrammg10 3 mg = 1 gten grains of salt Microgramμgμg10 6 μg = 1 g particle of baking powder