Chapter 1:Chemistry & Measurement
Classification of Matter
Chemical Composition
pure substances: only one type of matter
definite composition
distinct properties
two categories of pure substances:
elements - cannot be broken down into simpler substances by chemical change
118 known; 112 named
compounds - 2 or more elements chemically combined (bonded together); have fixed composition
Law of Definite Proportions (Joseph Proust):
A specific compound must always be composed of the same proportion of its elements by mass.
mixtures:more than one type of mattermore than one substance physically combinedhave variable composition
homogeneous mixtures
heterogeneous mixtures
solids: rigidordered arrangement or particlesfixed volume and shapenot compressibleparticles very close together
liquids: fluid (flow) fixed volume but variable shape very slightly compressible short range order; short range motion
gases: fluidleast dense form of mattershape and volume are variablehighly compressible (lots of empty space)constant, random, chaotic motion
physical property or change:describes or involves only a change of phase
ex. sublimation of dry ice CO2 (s) ! CO2 (g)
chemical property or change:describes or involves change of chemical identity
ex. hydrogen combines with oxygen to form water
intensive property:independent of the amount of sample
ex. mp of water is 0oC (at 1 atm) density
molar mass
extensive property:depends on the size (extent) of the sample
ex. mass; volume; heat of combustion
Uncertainty in Measurements
Precision vs. Accuracy
How close are values to one another?
standard deviation
How close is your experimental value to the known value?
percent error
Uncertainty in Measurements
Significant Figures - all certain digits plus the first uncertain digit
How many significant figures do you record when making a measurement?
How many significant figures are in a number?
How many significant figures do you record in the answer to a calculation?
How many significant figures are in a given number?
1. Non-zero integers are always significant.
2a. Leading zeros are not significant;2b. Captive zeros are significant;2c. Trailing zeros may or may not be significant;
(trailing zeros are always significant if the number contains a decimal point)
2d. When in doubt, use scientific notation.
3. Exact numbers have an infinite number of significant figures.
examples: counting, definitions, integers
How many significant figures do you keep as an answer to a calculation?
1. Multiplication and Division:number of significant figures in the answer should be the same as the least number of significant figures in the data
2. Addition and Subtraction:number of decimal places in the answer should be the same as the least number of decimal places in the data
Dimensional Analysis and Unit Conversions
dimensional analysis - carry numbers and units through algebraic manipulations; treat the unit itself as an algebraic entity
ex. (2x)2 = 4x2; (4cm)2 = 16cm2
unit conversions - convert quantities from one unit scale to a different unit scale using one or more conversion factors
ex. 125.0 in = ??? cm
conversion factor - statement of equality between unit scales
ex. 1 in = 2.54 cm
Unit Conversions: Intrasystem Conversionsmetric system conversionsEnglish system conversions
examples:
54.5 ng = ________ pg
25.0 mi = ________ ft(1 mi = 5280 ft)
Unit Conversions: Intersystem Conversionsmetric " English system conversions
example:
115 mm = _______ ft(1 in = 2.54 cm)
Unit Conversions: Combined Unit Conversions
examples:
55 mi/h = ________ m/s(1 mi = 1.6093 km)
2580 cm2 = ________ m2
2580 cm2 = ________ in2
12.4 g/cm3 = ________ kg/m3
Density as a Conversion Factor:
density = mass/volume
examples:
Calculate the density of a liquid if a 43.7 g sample occupies a volume of 55.7 mL.
The density of an alloy is 6.286 g/cm3. Determine the mass of a spherical sample of this alloy if the sphere’s radius is 7.84 mm.
Temperature Conversions: Fahrenheit, Celsius, and Kelvin Temperature Scales