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# Chemistry - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about ' Chemistry' - enrico

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### Chemistry

Study of matter and the changes it undergoes

• SI System

• Qualitative vs Quantitative

• Qual – describes a property w/o measuring it

• Quant – measurement with a #

• Prefixes –

Kilo hecta deka base deci centi milli

System is based on the power of 10

• Mass – measures quantity of matter

• Base unit (kg)

• Weight – measures force of gravity between 2 objects (earth and object being weighed)

Length – m

Time – s

Mass – kg

Temperature - K

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!!!

• 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!!!

• Digits other than zero are always significant

96g

61.4g

3253.854 cm

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

4.72 km

4.72000 cm

3) Zeros between 2 other sig figs are always significant

5.029 m

306 km

4) Zeros as placeholders are not significant

7000 g

0.000783 g

• 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 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 =

• 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

• Mass per unit volume

D = m

V

Units = g/ml OR g/cm 3

% Error = accepted value – experimental value x 100

accepted value