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Chemistry. Study of matter and the changes it undergoes. Measuring and Calculating. SI System Qualitative vs Quantitative Qual – describes a property w/o measuring it Quant – measurement with a #. Metric System. Prefixes – Kilo hecta deka base deci centi milli

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chemistry

Chemistry

Study of matter and the changes it undergoes

measuring and calculating
Measuring and Calculating
  • SI System
    • Qualitative vs Quantitative
      • Qual – describes a property w/o measuring it
      • Quant – measurement with a #
metric system
Metric System
  • Prefixes –

Kilo hecta deka base deci centi milli

System is based on the power of 10

important measurements
Important Measurements
  • Mass – measures quantity of matter
    • Base unit (kg)
  • Weight – measures force of gravity between 2 objects (earth and object being weighed)
base units
Base Units

Length – m

Time – s

Mass – kg

Temperature - K

accuracy vs precision
Accuracy vs. Precision

Accuracy – how close a measurement is to the true or accepted value

Precision – how close a set of measurements are to EACH OTHER

****Think dart board!!!

significant figures
Significant Figures
  • Digits that occupy places for which an actual measurement was made
    • Includes one uncertain or estimated digit
    • # of sig figs depends on the instrument doing the measuring!!!
sig fig rules
Sig Fig Rules
  • Digits other than zero are always significant

96g

61.4g

3253.854 cm

sig fig rules1
Sig Fig Rules

2) One or more final zeros used after the decimal are always significant

4.72 km

4.72000 cm

sig fig rules2
Sig Fig Rules

3) Zeros between 2 other sig figs are always significant

5.029 m

306 km

sig fig rules3
Sig Fig Rules

4) Zeros as placeholders are not significant

7000 g

0.000783 g

calculating with sig figs
Calculating with Sig Figs
  • What happens to the # of sig figs when we add or multiply #’s????

Ex: length = 2.02 cm

Width = 1.63 cm

Height = 3.2 cm

V = l x w h

V = 10.53632 cm 3

** Do we really need all these decimal places???

multiplying and dividing
Multiplying and Dividing
  • Multiplying or dividing - # of sig figs is the same as the measurement having the least # of sig figs
    • So in the above example answer would be = 10.8 cm 3

Ex: Area = l x w

l = 1.1 cm w = 2.38 cm

A = l x w = 2.38 x 2.618

A =

adding or subtracting
Adding or Subtracting
  • Round the answer so that it has the same # of decimal places as the measurement having the least # of decimal places

Ex: 5.43 cm

2.6 cm

+ 1.57 cm

9.60 cm = 9.6 cm

density
Density
  • Mass per unit volume

D = m

V

Units = g/ml OR g/cm 3

percent error
Percent Error

% Error = accepted value – experimental value x 100

accepted value

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