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