Chapter 1 Topics Dr. Ali Bumajdad The Scientific Method Units, Prefix, and Unit Conversion Accuracy, Precision and Significant Figure Temperature Scales Density Matter, Mixtures and separation methods Physical and Chemical change Extensive and Intensive properties Introduction
The Scientific method: Overall philosophy of approach to the study of nature. observation Law Statements of fact often in equation form Hypotheses tentative explanation of experiments results Theory tested explanation of experiments results quantitative numbers concentration qualitative no numbers 2Na + Cl 2 2NaCl Note that theory is not fact and it could be wrong but we need to proof it. The Scientific method
SI-Derived Unit Area = m 2 Volume = m 3 Speed = m/s Unit conversion Usually we use 1)Factor-label method : units undergo the same kind of mathematical operation as numbers 2) Conversion Factor: a fraction that we use to change the units
Accuracy, Precision and Significant Figure Accuracy – how close a measurement is to the true value : A -TRUE Precision – how close a set of measurements are to each other P - EACH accurate & precise but not accurate & not precise
1 L = 1000 mL e.g. How many mL are in 1.63 L? 1L 1000 mL 1.63 L x = 1630 mL e.g. The speed of sound in air is about 343 m/s. What is this speed in miles per hour? 1 mi = 1609 m 1 min = 60 s 1 hour = 60 min meters to miles seconds to hours
Sig. Fig. 1) Nonzero digits always count as S. F. 2) Zeros between nonzero always count as S.F. 3) Zeros to the left of the first nonzero digit not count as S.F. 4) Zeros at right end of numbers significant only if there is a decimal point 5) For and , the no. of S. F. in the result = the least no. of S. F. used in the operation 6) For + and -, the no. of decimal places in the result = the least no. of decimal places in the operation 7) If the first digit after the S. F. is < 5, drop the digits that follow the S.F. numbers. 8) If the first digit after the S. F. is ≥ 5, drop the digits that follow the S.F. numbers and add 1 to the last digit 9) Exact numbers ( numbers contain no uncertainty) are not considered in the calculating of S. F. Sig. Fig. = important numbers important numbers = all the number I am sure about it + one estimated number
e.g. How many significant figures are in each of the following measurements? 24 mL2 significant figures 3001 g 4 significant figures 0.0320 m 3 3 significant figures 6.4 x 10 4 molecules 2 significant figures 560 kg2 significant figures
e.g. Addition or Subtraction 89.332 1.1??+ 90.432 round off to 90.4 One decimal place (one significant figure after decimal point) 3.70?? -2.9133 0.7867 two decimal places round off to 0.79 Multiplication or Division 4.51 x 3.6666 = 16.536366= 16.5 6.8 ÷ 112.04 = 0.0606926= 0.061
e.g. Exact Numbers Numbers from definitions or numbers of objects are considered to have an infinite number of significant figures e.g. The average of three measured lengths; 6.64, 6.68 and 6.70? 6.64 + 6.68 + 6.70 3 20.02 = 6.673 Because 3 is an exact number Sa Ex. 1.4: Write the answer with te correct Sig. Fig. a) (1.05 × 10 -3 ) ⁄ 6.135 = 1.71149 × 10 -4 = 1.71 × 10-4 b) 21 – 13.8 = 7.2 = 7 C) P V/T, where P = 2.560, T= 275.15, V = 8.8 = 0.0818753 = 8.2 × 10 -2 3
Temperature Scales T K = T C + 273.15 T C = T K – 273.15 T C = (T F – 32) 5 9 T F = (T C 9 ) + 32 5
e.g. Convert 172.9 0 F to degrees Celsius. T C = 78.28 0 C Sa. Ex. 1.12 Liquid nitrogen boil at 77 K convert to Fahrenheit. T F = -321 0 F
Density SI derived unit for density is kg/m 3 1 g/cm 3 = 1 g/mL = 1000 kg/m 3 density = mass volume d = m V e.g. A piece of platinum metal with a density of 21.5 g/cm 3 has a volume of 4.49 cm 3. What is its mass? d = m V m = d x V = 21.5 g/cm 3 x 4.49 cm 3 = 96.5 g
Matter, Mixtures and Separation methods A Matter any thing occupies a space and has a mass Three States solid liquid gas
mixture composition is constant mixture composition not constant substance with constant composition that can be broken down into elements by chemical process OR Two or more different atoms bind together by a chemical bond substance that can not be decompose into simpler form by chemical or physical change What is the different between element and atom?
1. Homogenous mixture – composition of the mixture is the same throughout. 2. Heterogeneous mixture – composition is not uniform throughout. soft drink, milk, solder cement, iron filings in sand A mixture is a combination of two or more substances in which the substances retain their distinct identities.
Physical methods can be used to separate a mixture into its pure components.
A physical change does not alter the composition or identity of a substance. A chemical change alters the composition or identity of the substance(s) involved. ice melting sugar dissolving in water hydrogen burns in air to form water Physical and Chemical change
An extensive property of a material depends upon how much matter is is being considered. An intensive property of a material does not depend upon how much matter is is being considered. mass length volume density temperature color Extensive and Intensive properties