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Significant Figures - Introduction

Significant Figures - Introduction. 0. 1. 2. 3. 4. 5. 6. Using the scale below, measure and write down how long the arrow is. There is a level of uncertainty in our measurement. We can only reliably write two numbers: 3.8.

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Significant Figures - Introduction

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  1. Significant Figures - Introduction 0 1 2 3 4 5 6 Using the scale below, measure and write down how long the arrow is. There is a level of uncertainty in our measurement. We can only reliably write two numbers: 3.8 The level of uncertainty in a measurement is given by the number of significant figures.

  2. Rules for Significant Figures A trailing zero is significant: 4.130 4 significant figures A zero within a number is significant: 35.06 4 significant figures A zero before a digit is not significant: 0.082 2 significant figures A number ending in zero with no decimal point, as in 20, is ambiguous. 1 or 2 significant figures

  3. Calculations using Significant Figures Multiplication and division: The number of significant figures is determined after all the calculations and is equal to the smallest number of sig figs in the original numbers. Example 4.135 x 2.4 = 9.924 But we can only use 2 sig figs = 9.9 cm2 4.135 cm x 2.4 cm = Round 9.924 to 9.9

  4. Calculations using Sig. Figs. Addition and Subtraction After finishing the calculation, the number of sig figs after the decimal point must be equal to the number of sig figs in the least well known original number Example But the decimal that is uncertain (least well known) is the first decimal place 2 4.5 -1.258 3.242 4.5 mm - 1.258 mm = So round 3.242 to 3.2 4.5 mm - 1.258 mm = 3.2 mm

  5. Physical or Chemical Physical Change - the compound undergoes a change without losing its identity Freezing, melting, evaporation, condensation Chemical Change - the compound reacts with another substance and loses its identity to become a new substance Burning gasoline, Baking a cake

  6. Properties of Matter Pure Substance - a pure substance can undergo physical changes without losing its identity Element - cannot be decomposed by chemical means. Compound - composed of elements in a fixed ratio that can be decomposed into simpler pure substances by chemical means Figure 1.10 Analysis of the composition of matter.

  7. Mixtures - consisting of two or more pure substances Homogeneous - uniform distribution throughout Heterogeneous - not evenly distributed throughout Properties of Matter Figure 1.10 Analysis of the composition of matter.

  8. Fundamental Properties of Matter Mass - the measure of the quantity of matter (in kg) different than weight - the response of mass to gravity Think of yourself on the moon vs. on Earth Volume - amount of space that a sample occupies (in L)

  9. Answer: Density. Density (d) = mass (g)/ volume (cm3 or mL) When something is less dense than water, it floats. Q: Metal sinks in water, but a boat, made out of metal, floats. How can this be? Aluminum boat mass = 5.35 x103 g Volume of empty Boat = 1.8 x 104 mL Density = 5.35 x 103g/1.8 x 104 mL = 0.29 g/mL Because a boat is mostly hollow, its density is less than water so it floats.

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