Introduction to Chemistry Part 2 Significant Figures (aka- “sig figs”) Density Calculations

Two step unit conversions If you do not have a conversion factor between the given unit and the one you are looking for, you must do two conversions. Example- How many milliliters are in 0.005 kiloliters?

Practice 1) 254 mm =____________km 2) 0.004 kg = ___________mg 3) 46 cL = _____________ kL 4) 675 km = ____________ cm 5) 0.072 kL = ___________mL 6) 97.8 mg = _____________kg 7) 1.88 ms = ______________ cs 8) 6.48 cm = _____________mm 9) 14.72 kL = ____________ mL 10) 25 mm = ______________cm ** All of the given units and all of the units I asked for have a prefix… that means it is a two step problem! Convert to the base unit first!!!!

Significant Figures Sig Fig Rules All non-zeros are significant. All zeros in-between significant numbers are significant. Zeros to the right of a decimal after a whole number (greater than or equal to one) are significant. Zeros to the right of a decimal after a significant number are significant   Examples (underlined are significant) 123= 3 sig figs 320= 2 sig figs 10003= 5 sig figs 10050= 4 sig figs 40.07= 4 sig figs 1.00000= 6 sig figs 0.0005= 1 sig fig (not a whole number)   0.07000= 4 sig figs 6.0500= 5 sig figs

Sig Fig Practice 1234 9.0x10-3 0.00390 0.023 9.010x10-2 8120 890 0.00030 7.991x10-10 91010 1020010 72 9010.0 780. 1090.0010 1000 0.00120 918.010 3.4x104 0.0001

Accuracy is how close a measured value is to the actual (true) value. Accuracy vs Precision Accuracy Accuracy is how close a measured value is to the actual (true) value. Precision Precision is how close the measured values are to each other.

Rounding to the correct number of sig figs Express the following using 3 sig figs 600 48000 326451 0.000004555 3995 0.09965

Multiplying / Dividing / Trigonometric Functions a) First perform all the operations, even if changing from one formula to another. b) Round off the result so that it has the same number of sig figs as the least of all those used         in your calculation. Example: (2.5 m) x (2.01 m) x (2.755 m) = 13.843875 m Answer = 14 m3     (2 sig figs)

Addition / Subtraction When measurements are added or subtracted, the answer can contain no more decimal places than the least accurate measurement. Example: 153. ml + 1.8 ml + 9.16 ml = 163.96 ml Answer = 164 ml

Density Mass per unit volume How far apart the molecules are m V D =

Density Example Problem What is the volume of 325 g of metal with a density of 9.0 g/cm3?