Presentation on theme: "Chemistry and Chemicals"— Presentation transcript:
1 Chemistry and Chemicals Chemistry in Our LivesChemistry and Chemicals
2 What is chemistry? Chemistry is the study of substances in terms of Composition What a material it made ofStructure How the elementary particles are put togetherProperties The characteristics of the materialReactions How it behave with other substances
3 Chemical reactions happen when a car is startedtarnish is removed from silverfertilizer is added to help plants growfood is digestedelectricity is produced from burning natural gasrust is formed on iron nails
4 Everything in our lives from materials to life involve chemistry glass (SiO2)nmetal alloyschemically treated waterplastics and polymersbaking soda, NaHCO3foodsfertilizers and pesticidesliving beings
6 The Scientific MethodThe scientific method is the process used to explain observations in nature.The method involves:making observationsforming a hypothesisdoing 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.
9 In chemistry:quantities are measuredexperiments are performedresults are calculateduse numbers to report measurements,results are 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 tocompare some dimensionof 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 Unitm (meter)L (liter)lb (pound)h (hour)
12 The Metric System (SI)The metric system and SI (international system) arerelated decimal systems based on 10used in most of the worldused everywhere by scientists
13 Lengthis measured using a meter stickuses the unit meter(m) in both the metric and SI systems
14 The unit of an inchis equal to exactly2.54 centimeters inthe metric system1 in. = 2.54 cm
15 Volumeis the space occupiedby a substancethe unit of volume is the liter (L) in the metric system1 L = 1.06 qt
16 is a measure of the quantity of material it contains The mass of an objectis a measure of the quantity of material it containsthe unit gram (g) or kilogram (1000 g) is usedWhat 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 sameDespite this important difference, we will use these two terms interchangeably
17 indicates how hot or cold a substance is The temperatureindicates how hot or cold a substance isthe Celsius (C) scale is used in the metric systemthe Kelvin (K) scale is also used18 °C is 64 °F on this thermometerOn the C scale, the melting point of ice is 0 C and boiling point of water is 100 CWhat is heat or cold? What does temperature really measure?
18 Time measurementthe 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 notationis used to write very large or very small numbersthe width of a human hair ( m) is written8 x 10-6 ma large number such as s is written4.5 x 106 s
20 Scientific NotationA number in scientific notation contains a coefficient and a power of 10.coefficient power of ten coefficient power of tenx xTo write a number in scientific notation, the decimal point is placed after the first digit.The spaces moved are shown as a power of ten.= x = x 10-34 spaces left spaces right
22 Measurements Definition of a significant figure: What is the length of this piece of wood?What is the first digit? Any uncertainty in the digit?4What is the second digit? Any uncertainty in this digit?4.5What is the third digit? Any uncertainty in this digit?4.56Definition of a significant figure:Significant digits include all digits with no uncertainty plus one estimation
23 What is the length of the red line? . l l l l l cmWhat is the length of the red line?1) cm2) cm3) cm9.38, or 9.39, 9.40 is less likely
25 Number of Significant Figures Measurement38.15 cm5.6 ftmin1200 m42522
26 A. Exact numbers are obtained by 2. counting3. definitionB. Measured numbers are obtained by1. using some measuring tool
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 feetC. __ 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 OffWhen the first digit dropped is 4 or less, the retained numbers remain the same.To round to 3 significant figuresdrop the digits 32 = 45.8When the first digit dropped is 5 or greater,the last retained digit is increased by 1.To round to 2 significant figuresdrop the digits 884 = 2.5 (increase by 0.1)
30 Multiplication and Division When multiplying or dividing usethe same number of significant figures (SF) as the measurement with the fewest significant figuresExample:x = =4SFs SFs calculator SFs
31 Addition and Subtraction When adding or subtracting, usethe same number of decimal places as the measurement with the fewest decimal placesone decimal placetwo decimal places26.54 calculated answerfinal answer (with one decimal place)
32 For each calculation, round the answer to give the correct number of decimal places.A =1) 2572)3)B – 18.2 =1)2)3) 40.7
35 1m/100cm = 1; 1m/1000mm = 1 1 = 100cm/1m; 1 = 1000mm/1m An equality states the same measurement in two different unitscan be written using the relationships between two metric unitsExample: 1 meter is the same as 100 cm and 1000 mm.1 m = cm1 m = mm1m/100cm = 1; m/1000mm = 11 = 100cm/1m; = 1000mm/1m
39 An injured person loses 0. 30 pints of blood 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; mL0.30pt*2pt/1qt = 0.60pt2/qt
40 If a person weighs 200 pounds, how many kiograms does the person weight? 200 lb*1 kg/2.2 lb = 90.9 kg200 lb*2.2 lb/1 kg = 440 lb2/kg
41 If the thickness of the skin fold at the waist indicates an 11% body fat, howmuch fat is in a person with a massof 86 kg?11 % fat means 11kg/100kg body weight86 kg x kg fat = 9.5 kg of fat100 kg
42 Density Density compares the mass of an object to its volume is the mass of a substance divided by its volumeDensity expression:D = mass = g or g = g/cm3volume mL cm3
43 Osmium is a very dense metal. What is its density in g/cm3 if 50 Osmium is a very dense metal. What is its density in g/cm3 if 50.0 g of osmium has a volume of 2.22 cm3?1) g/cm32) g/cm33) 111 g/cm3
44 The density of the zinc object can be calculated from its mass and volume. d = 68.6g/( )mL; g/9.5 mLd = 7.2 g/mL