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## PowerPoint Slideshow about 'Chemistry' - enrico

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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 #

Important Measurements

- Mass – measures quantity of matter
- Base unit (kg)
- Weight – measures force of gravity between 2 objects (earth and object being weighed)

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

- 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

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

4.72 km

4.72000 cm

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 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

- 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

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