Honors Chemistry. Measurement. Alchemy. How do you picture a chemist?. What is chemistry? . Chemistry is the study of all things and the changes they can undergo. Chemistry is called a central science because it overlaps so many sciences.
Honors Chemistry Measurement
What is chemistry? • Chemistry is the study of all things and the changes they can undergo. • Chemistry is called a central science because it overlaps so many sciences. • Chemical – is any substance with a definite composition.
Chemists use the scientific method as a systematic approach to gather knowledge. • Observation • Question • Hypothesis • Experiment • Conclusion • All hypotheses must be testable in order to be a valid hypothesis.
Types of Observations • Qualitative: Describes something using the 5 senses • Quantitative: Uses numbers in the description • Quantity – something that has magnitude, size, or amount. • Unit – a quantity adopted as a standard of measurement
Experiment • Natural Law – Describes how nature behaves • Theory – Explains why nature behaves the way it does • A theory and a hypothesis are both explanations, but a theory is an explanation formed after much experimentation.
Variables in a Experiment • Independent Variable - You control • Dependent Variable – Variable factor – what is being tested • Experimental Control – Factor that remains constant for comparison
Factors in an Experiment • Independent:most regular variable – goes on the X-axis • Dependent:what you are testing – goes on the Y-axis • Experimental Control:part of the experiment that stays the same. Dependent variable “Y” axis Independent variable “X” axis
Measurement in Chemistry Measurement is a key ingredient in ALL sciences, especially chemistry. • Scientific Notation • Accuracy and Precision • Significant Figures • Measurement Devices • Metric System • Dimensional Analysis
Scientific Notation is a shorthand way of expressing a number.Consists of two factors: • Coefficient - a number between 1 and 10 (only 1 digit to the LEFT of the decimal point) • Base - a power of 10 “power of 10” shows the number of 10’s that are to be multiplied together • Examples on the number line: 1x102 4x101 1x100 1x10-10 1x10-1
Small Numbers Negative Numbers Large Numbers 1x10-10 1x10-1 1x102 0 4x101 1x100
Adding and Subtracting(without calculator) • Exponents must be the same • If number gets bigger, exponent gets smaller • If number gets smaller, exponent gets larger (8 x 10-2) + (3 x 10-4) - (2 x 10-3) (80 x 10-3) + (0.3 x 10-3) – (2 x 10-3) = 78.3 x 10-3 = 7.83 x 10-2
Multiplication(without calculator) • Multiply number and add exponents (base 10 remains the same) (6 x 10-6)(8 x 103) = 48 x 10-3 4.8 x 10-2 (6 x 10-3)2 = 36 x 10-6 = 3.6 x 10-5
Division(without calculator) • Divide number and subtract exponents (base 10 remains the same) (7.2 x 10-8)÷(8 x 10-5) = 0.9 x 10-3 9 x 10-4
Cube Root • Make number a whole number, take cube root of number, multiply exponent by 1/3. (2.7 x 10-8)1/3 = (27 x 10-9)1/3 = 3 x 10-3
Square Root • Make number a whole number, take square root of number, multiply exponent by ½. (1.44 x 10-6)1/2 = (144 x 10-8)1/2 = 12 x 10-4 = 1.2 x 10-3
1st Commandment of Chemistry: KNOW THY CALCULATOR! Find the “EE” key – it may be a 2nd function! If you have a graphing calculator look for the following keys: Find the (-) key.
Find the “Exp” or “x10x” 1st Law of Chemistry: Know Thy Calculator! Look at the calculator that is similar to yours… Find the “(-)” or the “+/-” key.
Uncertainty in Measurement • Measurements are uncertain because: • 1) Instruments are not free from error. • 2) Measuring involves some estimation. • Precision –when the instrument gives you about the same results under similar conditions. The smaller the increments of measurement an instrument has, the more precise it can be. • Accuracy – when the experimental value is close to the actual value. • % Error = experimental– acceptedvalue x 100 accepted value
What is the goal for a game of darts? Hitting the Bulls Eye!
Label the following data as accurate, precise, neither, or both. • 1) 200g, 1g, 40g • Neither • 2) 78g, 80g, 79g • Precise • 3) 16g, 14g, 17g • Accurate and Precise
How to use a graduated cylinder Read the meniscus
How to use a graduated cylinder 36.4 mL 19.0 mL 6.25 mL
Length - Rulers 3.7 3.6 3.63
Temperature 21.8 21.68
How to read a triple beam balance 28.570 g Ohaus Triple Beam Balance Tutorial Reading A Triple Beam Balance Tutorial
How to read a triple beam balance 109.076 g Ohaus Triple Beam Balance Tutorial Reading A Triple Beam Balance Tutorial
Significant Figures and Digits • A prescribed decimal that determines the amount of rounding off to be done base on the precision of the experiment. • ALWAYS ESTIMATE 1 DIGIT MORE THAN THE INSTRUMENT MEASURES. • Significant digits include measured digits and the estimated digit. • Exact Numbers – Do not involve estimation • ex. 12 in = 1 ft
VI. Significant Digits • Use Atlantic-Pacific Rule – imagine a US map decimal point decimal point Pacific Atlantic resent bsent
2 significant digits 1100 4 significant digits 1100. 8 significant digits 11.010000 2 significant digits 0.025 5 significant digits 0.00035000 1,000,100 5 significant digits Decimal Absent Start counting with the 1st nonzero digit and count all the rest. Decimal Present Start counting with the 1st nonzero digit and count all the rest.
Significant Digits in Addition and Subtraction • Add or subtract numbers • Answer can only be as exact as the least exact number. (Look at the decimal place) • Ex. 4.1 cm + 0.07cm • 4.17 cm • 4.2 cm
Significant Digits and Multiplication and Division • Multiply and Divide the numbers. • Round answer to the same number of significant digits as the number with the fewest significant digits. • Ex. 7.079 cm / 0.535 cm • 13.2317757 • 13.2
Atmospheric pressure is measured with a barometer. This is a glass tube sealed at one end and filled with Hg.
Using a Manometera device used to measure pressure • Reading a Manometer • Barometer containing Hg
Temperature ConversionsCelsius and Kelvin • K = °C + 273 • °C = K - 273 • Zero Point on Kelvin Scale – Absolute Zero • 0 K and -273 °C • Kinetic energy is energy of motion. Temperature is a measure of kinetic energy. Since the temperature at absolute zero is a true zero, there is no particle motion Therefore, nothing can exist at absolute zero.
Measurements: basic to all sciences & all are comparisons to a standard • English – still used in US • Metric – devised in the late 1700’s in France • SI – Le SystèmeInternationaled’Unités • Modern metric system (1960) • Based on 7 base units • Base units are modified by prefixes
SI Base Units meter (m) • Length • Mass (SI standard unit) • Time • Temperature • Amount of a substance mole (mol) • Electric current ampere (A) • Luminous intensity candela (cd) kilogram (kg) second (s) Kelvin (K)
The Meter • The original standard for the meter was kept in a safe in France. • The meter stick is a replica of that standard. • A meter is made up of 100 centimeters and 1000 millimeters. • Lasers are now used to determine the standard for a meter.
Mass is the amount of matter in an object. 1 cm3 of water = 1 gram. The standard kilogram is kept under lock and key in Washington, DC and other cities around the world. The Gram
Derived Units • Area: 2-D • L x W (m2) • Volume: 3-D • Solid - L x W x H (m3) • Liquid or irregular shaped object - graduated cylinder (L or cm3) • Density • mass/volume (kg/m3)
The Liter • The liter is 1000 mL • 10cm x 10cm x 10cm • 1 liter= 1000 cm3 = 1 dm3 • 1 milliliter = 1 cm3 = 1 cc = 20 drops =
Conversions between units • Factor-label method or dimensional analysis – based on using unit equalities 60 s = 1 min 60 s OR 1 min 1 min 60 s