Chemistry in Our Lives. Chemistry and Chemicals

Transcription

1 Chemistry in Our Lives Chemistry and Chemicals

2 What is chemistry? Chemistry is the study of substances in terms of Composition Structure Properties Reactions What a material it made of How the elementary particles are put together; atoms and molecules The characteristics of the material How it behave with other substances

3 Chemical reactions happen when a car is started fertilizer is added to help plants grow food is digested electricity is produced from burning natural gas rust is formed on iron nails

4 Everything in our lives from materials to life involve chemistry metal alloys chemically treated water plastics and polymers drugs foods fertilizers and pesticides living beings

5 Chemicals in Toothpaste

6 The Scientific Method The scientific method is the process used to explain observations in nature. The method involves: making observations forming a hypothesis doing experiments to test the hypothesis

7 Everyday Scientific Thinking Observation: The sound from a CD in a CD player skips. Hypothesis 1: The CD or player is faulty. Experiment 1: When the CD is replaced with another one, the sound from the second CD is OK. Hypothesis 2: The original CD has a defect. Experiment 2: When the original CD is played in another player, the sound still skips. Theory: The experimental results suggest that the original CD has a defect.

8 Units of Measurement

9 In chemistry or in medicine: quantities are measured experiments are performed results are often calculated We often use numbers to report measurements, and our results are usually compared to standards.

10 In a measurement of the thickness of the skin fold at the waist, calipers are used. A measuring tool is used to compare some dimension of an object to a standard.

11 In every measurement, a number must be followed by a unit to have any meaning. Observe the following examples of measurements: Number and Unit 35 m (meter) measure of length 0.25 L (liter) measure of volume 225 lb (pound) measure of? 3.4 h (hour) measure of time Does anyone know what the units associated with blood pressure are?

12 The Metric System The metric system is the standard system of measurement units are based on the number 10 used in most of the world used everywhere by scientists

13 Length is measured using a meter stick uses the unit meter

14 The unit of an inch is equal to exactly 2.54 centimeters in the metric system 1 in. = 2.54 cm

15 Volume is the space occupied by a substance the unit of volume is the liter (L) in the metric system 1 L = 1.06 qt

16 The mass of an object is a measure of the quantity of material it contains the unit gram (g) or kilogram (1000 g) is used What is the difference between mass and weight? Weight is the result of the action of gravity on mass. Your weight on the moon would be a lot less even though your mass would remain the same Despite this important difference, we will use these two terms interchangeably

17 The temperature indicates how hot or cold a substance is the Celsius ( C) scale is used in the metric system the Kelvin (K) scale is also used 18 C is 64 F on this thermometer On the C scale, the melting point of ice is 0 C and boiling point of water is 100 C What is heat or cold? What does temperature really measure?

18 Time measurement the unit second (s) is used in the metric system. Time is based on an atomic clock that uses a frequency emitted by cesium atoms

19 Scientific notation is used to write very large or very small numbers the width of a human hair ( m) is written 8 x 10-6 m a large number such as s is written 4.5 x 10 6 s

20 Scientific Notation A number in scientific notation contains a coefficient and a power of 10. coefficient power of ten coefficient power of ten 1.5 x x 10-4 To write a number in scientific notation, the decimal point is usually but not necessarily placed after the first digit. The spaces moved are shown as a power of ten = 5.2 x = 3.78 x spaces left 3 spaces right

21 10-3 /10 5 = 10-3 *10 5 = = =

22 Measurements What is the length of this piece of wood? What is the first digit? Any uncertainty in the digit? 4 What is the second digit? Any uncertainty in this digit? 4.5 What is the third digit? Any uncertainty in this digit? 4.56 Definition of a significant figure: Significant digits include all digits with no uncertainty plus one estimation

23 . l8.... l.... l9.... l.... l10.. cm What is the length of the red line? 1) 9.38 cm 2) 9.39 cm 3) 9.40 cm 9.38, or 9.39, 9.40 is less likely

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25 Measurement cm 5.6 ft m in 1200 m Number of Significant Figures

26 A. Exact numbers are obtained by 1. counting 2. definition; they are known exactly B. Measured numbers are obtained by 3. using some measuring tool; they have some associated uncertainty

27 Classify each of the following as exact (E) or measured (M) numbers. Explain your answer. A. Gold melts at 1064 C. B. 1 yard = 3 feet C. The diameter of a red blood cell is 6 x 10-4 cm. D. There are 6 hats on the shelf. E. The atom sodium has 11 protons and 12 neutrons.

28 Significant Figures In calculations: Answers must have the same number of significant figures as the measured numbers. Calculator answers must often be rounded off. Rounding rules are used to obtain the correct number of significant figures.

29 Rounding Off When the first digit dropped is 4 or less, the retained numbers remain the same. To round to 3 significant figures drop the digits 32 = 45.8 When the first digit dropped is 5 or greater, the last retained digit is increased by 1. To round to 2 significant figures drop the digits 884 = 2.5 (increase by 0.1) To round to 3 significant figures 2.49

30 Multiplication and Division When multiplying or dividing use the same number of significant figures (SF) as the measurement with the fewest significant figures Example: x = = 5.3 4SFs 2SFs calculator 2SFs

31 Addition and Subtraction Keep as many significant figure as the number of fewest digits after the decimal

32 For each calculation, round the answer to give the correct number of decimal places if all numbers are measured numbers A = 1) 257 2) ) B = 1) ) ) 40.7

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35 An equality states the same measurement in two different units can be written using the relationships between two metric units Example: 1 meter is the same as 100 cm and 1000 mm. 1 m = 100 cm 1 m = 1000 mm 1m/100cm = 1; 1m/1000mm = 1 1 = 100cm/1m; 1 = 1000mm/1m

36 volume has the dimensions of length cubed

37 Several equalities can be written for mass 1 kg = 1000 g 1 g = 1000 mg 1 mg = g

38 Some Common Equalities

39 An injured person loses 0.30 pints of blood. How many milliliters of blood would that be? 0.30pt*1qt/2pt = 0.15qt; 0.15qt*946mL/qt = ml; 140 ml 0.30pt*2pt/1qt = 0.60pt 2 /qt

40 If a person weighs 200 pounds, how many kiograms does the person weight? 200 lb*1 kg/2.2 lb = 90.9 kg 200 lb*2.2 lb/1 kg = 440 lb 2 /kg

41 If the thickness of the skin fold at the waist indicates an 11% body fat, how much fat is in a person with a mass of 86 kg? 11 % fat means 11kg/100kg body weight 86 kg x 11 kg fat = 9.5 kg of fat 100 kg

42 Density Density compares the mass of an object to its volume is the mass of a substance divided by its volume Density expression: D = mass = g or g volume ml cm3 = g/cm3

43 Osmium is a very dense metal. What is its density in g/cm 3 if 50.0 g of osmium has a volume of 2.22 cm 3? 1) 2.25 g/cm 3 2) 22.5 g/cm 3 3) 111 g/cm 3

44 The density of the zinc object can be calculated from its mass and volume. d = 68.6g/( )mL; 68.6g/9.5 ml d = 7.2 g/ml