Measurements & Calculations Chapter 2 Chemistry Review

Scientific Method Logical approach Observe & collect data (research topic) Form hypothesis (a proposed explanation) Test hypothesis (set up & do experiment) Record & analyze data from experiment Summarize & make conclusions Modify, support, or reject hypothesis Communicate methods & results

Formulating Hypothesis Statement must be testable Can use “If…, then….” statement – If you use Dan’s SureFire Bait, then you’ll always catch premium bass. Can be worded as if it were a fact – Fisherman using Dan’s SureFire Bait catch more premium bass. – More premium bass are reeled in on Dan’s SureFire Bait.

Planning the Experiment Independent Variable (I.V.) – What is being tested; what’s different from control Dependent Variable (D.V.) – What is being measured as a result of I.V. Control group – Those not receiving/ treated with the I.V. – That to which the experimental group is compared Experimental group – Those receiving/ treated with the I.V. Constants – What is the same in both groups

Experimentation Contr ol group Bait of same appearance but not Dan’s Constants Same climate, place, time of day, boat/bank, user, rod & reel Experimental group Dan’s SureFire Bait (I.V.) average size Experimental vs. Control Results [# fish] (D.V)

From Hypothesis to Theory Hypothesis is supported by data Methods & Results are published Others test hypothesis & verify results Others relate their hypotheses to yours Others can build models & predict outcomes based on the collective hypotheses The scientific community adopts a new theory (or expands/ modifies existing one)

International System of Units Adopted in 1960 by the General Conference on Weights and Measures Has 7 base units – Length (m, meter); Mass (kg, kilogram); Time (s, second); Temperature (K, kelvin); Amount of substance (mol, mole); Electric current (A, ampere); Luminous intensity (cd, candela) All scientists understand & use same system

SI Prefixes tera-T giga-G mega- M kilo-k hecto- h dekada Base unit10 0 1

SI Prefixes, negative exponents Base unit deci-d centi-c milli-m micro-  nano-n pico-p femto-f

Derived Units Combinations of base units – Aream 2 – Densitykg/ m 3 ; g/cm 3 – Molar masskg/ mol; g/ mol – Energykg m 2 /sec 2 (J, joule) – Volumem 3 Liter = (10 cm) 3 = 1000 cm 3 = 1000 cc = 1000 mL

Conversion Factors Ratio derived from equality of 2 different units – 100 cm/ m; 1000 mm/ m;  m/ m – 10 2 x = 10 0 = 1 Just change sign of exponent – 1000 m/ km; m/ Mm – 10 3 m/ 10 3 m = 1; kilo = 10 3, M = 10 6 ; 10 6 / 10 6 = 1 Used in dimensional analysis to solve problem – How many mm are there in 2.3 km? – 2.3 km(1000 m/ km)(1000 mm/ m) = 2.3 x 10 6 mm

Accuracy vs. Precision Accuracy = close to accepted value Hits the bull’s-eye Percentage error % Error= (value experimental – value accepted )/ value accepted Some error always exists with measurements!!! Precision = close to one another’s values All hit same area but not necessarily the bull’s-eye

Significant Figures (S.F.) = All digits known + 1 final digit (estimated) Rules for S.F. – All digits 1 through 9 are S.F. (327) – All zeros between non-zero digits (30207) are S.F. – All zeros at the end of non-zero digits & right of the decimal point ( or ) are S.F. – All zeros after non-zero digits & before a decimal point ( ) are S.F.

Rounding Significant Figures Products or quotients can have no more S.F. than # of S.F. of what’s multiplied or divided Sums or differences can have no more decimal places than the least # of decimal places in the problem Rounding – Must round answer to correct # of S.F. – If the last digit is > 5, increase by 1 UNLESS THE 5 FOLLOWS AN EVEN NUMBER

Scientific Notation Written in the form of M x 10 n M = all significant figures n = can be a positive or negative # or zero (+n) = # is > 10; (-n) = # is between 0 & 1 When n = 0, # is between 1 & 10, not including 10 Rule of exponents 10 A x 10 B = 10 A+B 10 A / 10 B = 10 A-B

Proportionality Directly proportional x k = y, where k is a constant As x increases, y increases & vice versa (Pressure) (constant volume) = Temperature Indirectly proportional x y = k, where k is a constant As x increases, y decreases & vice versa (Pressure)(volume) = Constant Temperature