MEASUREMENT CALCULATIONS AND. Chapter 2 Chemistry I

Transcription

1 MEASUREMENT AND CALCULATIONS Chapter 2 Chemistry I

2 I. SCIENTIFIC METHOD

3 A. SCIENTIFIC METHOD: The Scientific Method is a logical approach to solving problems by observing and collecting data, formulating hypotheses, testing hypotheses, and formulating theories that are supported by data.

4 Identify the Problem Observe and Collect Data Form Hypothesis Experiment Analyze Data Draw Conclusions

5 B. STEPS OF THE SCIENTIFIC METHOD: 1. Identify the Problem: >What problem needs to be solved? >What question needs to be answered? *The problem will always be stated in the form of a question. *Example: Which type of soda will help radish seeds grow best?

6 B. STEPS OF THE SCIENTIFIC METHOD: 2. Observing/Collecting Information (Research): >Observing is the use of the senses to obtain information. >Data (information gained) may be: *Qualitative: (descriptive) *Quantitative: (numerical) >When studying data, scientists identify controlled conditions within which the experiment occurs, or a system.

7 DATA SYSTEM

8 B. STEPS OF THE SCIENTIFIC METHOD: 3. Formulating a Hypothesis: >Scientists make generalizations based on the data which are used to formulate a hypothesis, or testable statement. >Hypotheses are often If-then statements: *IF radish seeds are grown in Hawaiian Punch, THEN they will grow tallest.

9 HYPOTHESIS

10 B. STEPS OF THE SCIENTIFIC METHOD: 4. Design/Carry Out Experiments: >Testing a hypothesis requires experimentation that provides data to support or refute a hypothesis or theory. >In order for a test to be accurate, you must identify variables and use controls. >Controls: Experimental conditions that remain constant. >Variables: Experimental factors or conditions that are controlled or tested.

11 B. STEPS OF THE SCIENTIFIC METHOD: >Only one variable is changed at a time: >Independent variable (aka - manipulated variable): Variable that is changed >Ex: Type of Liquid (Coke, Sprite, etc) >Dependent Variable (aka - responding variable): Variable that is measured. >Ex: The height of the radish plant. >Constants: Variables that stay the same. >Ex: Same amount of liquid, same amount of light, same number of seeds, etc.

12 B. STEPS OF THE SCIENTIFIC METHOD: >Control: Sample treated exactly like the other experimental groups except the independent variable is not applied to it. >It is under normal conditions. >Ex: Radish plant is given water. >Number of trials: To make sure that you are getting valid results, you will need to repeat the experiment several times.

13 B. STEPS OF THE SCIENTIFIC METHOD: 5. Analyze Data: >Organize the data you collect from your experiment into graphs and charts. >Do not make conclusions at this step simply organize your findings. >Sample Data: Type of Liquid: Diet Coke Sprite Hawaiian Punch Water Plant Height (in cm) 5 cm 0 cm 10 cm 15 cm

14 B. STEPS OF THE SCIENTIFIC METHOD: 6. Draw Conclusions: >Does your data support your hypothesis? >Yes Repeat experiment to verify. >No Change Hypothesis and try again. >Why did you get these results? >What might have happened that could affect your results? >There are no wrong hypotheses! >There are only results that don t support your hypothesis. >Sample Conclusion: Hawaiian Punch is the best liquid for radish growth.

15 B. STEPS OF THE SCIENTIFIC METHOD: Theory: A hypothesis that has been repeatedly tested and is generally accepted as true. A theory can be disproven. Law: A repeatedly tested theory that has stood the test of time. Fact: Absolute Truth

16 B. STEPS OF THE SCIENTIFIC METHOD:

17 II. UNITS OF MEASUREMENT

18 Would you be breaking the speed limit in a 40 mi/hr zone if you were traveling at 60 km/hr? 1 km =.62 miles 60 km/hr = 37.2 mi/hr Nope not speeding!! Km/hr and mi/hr measure the same quantity using different units!

19 A. UNITS OF MEASUREMENT: >Measurements Represent Quantities: >A quantity is something that has magnitude, size or amount. Measurement Quantity >A teaspoon is a unit of measurement. >Volume is a quantity. >The choice of unit depends on the quantity being measured.

20 Why is it important to have a standard system of measurement?

21 B. SI MEASUREMENT: >Scientists all over the world have agreed on a single measurement system that uses prefix bases based on multiples of 10 and abbreviated SI. >SI has seven base units and most others are derived from these seven.

22 B. SI MEASUREMENT:

23 C. SI BASE UNITS: 1. Mass: A measure of the quantity of matter. SI Standard unit is the kilogram(kg). Different than weight weight is a measure of the gravitation pull on matter. Mass does not depend on gravity.

24 2. Length: C. SI BASE UNITS: A measure of distance that uses the meter as the SI Standard. The kilometer is used for longer distances and the centimeter is used for shorter distances.

25 C. SI BASE UNITS: 3. Temperature: Kelvin 4. Time: Second 5. Amount of Substance: Mole 6. Luminous Intensity: Candela 7. Electric Current: Ampere

26 D. DERIVED SI UNITS: >Combinations of SI Base units form derived units. > Some common derived units you have used before.

27 D. DERIVED SI UNITS: 1. Volume is the amount of space occupied by an object. >The derived unit is cubic meters, m 3. >The cubic cm, cm 3 or cc is often used. >The liter, L, an accepted non-si unit >1L = 1000cm 3 >1mL = 1 cm 3 = 1 g

28 Measuring Volume of Liquids always read the meniscus at eye level. (Visual Concept: 75023)

29 D. DERIVED SI UNITS: 2. Density is the ratio of mass to volume or mass divided by volume. >The derived unit is kilogram per cubic meter, kg/m 3 or g/cm 3 or g/ml. density = mass volume or D = m V >Density is a physical property of a substance and can be used to identify a substance.

30 >Density of Common Substances:

31 D. DERIVED SI UNITS: 3. Specific Gravity (SG): is the ratio of density of a substance to the density of a standard. >The standard for liquids and solids is water the density of water is 1.00g/mL or 1.00 g/cm 3. >The standard for gases is air the density of air is 1.29 g/l. >Specific gravity has no units.

32 D. DERIVED SI UNITS: Sample Problem: A sample of Aluminum metal has a mass of 8.4g. The volume of the same is 3.1cm 3. Calculate the density and specific gravity of Aluminum.

33 E. CONVERSION FACTORS: 1. Conversion Factor: Ratio derived from the equality between two different units that can be used to convert from one unit to the other. >Ex: Relationship between quarters and dollars. 4 quarters 1 dollar 1 1 dollar 4 quarters dollar 1 quarters 1 1 quarter 0.25 dollar 1

34 E. CONVERSION FACTORS: Conversion Factor (Visual Concept: 75025)

35 E. CONVERSION FACTORS: 2. Dimensional Analysis is a mathematical technique that allows you to use units to solve problems involving measurements. >Quantity Given x Conversion Factor = Quantity Sought >Example: Convert 12 dollars to quarters 12 dollars x conversion factor = # quarters 12 dollars x 4 quarters = 48 quarters 1 dollar

36 E. CONVERSION FACTORS: 3. You can derive a conversion factor if you know the relationship between the unit you have and the desired unit. > Conversion factor for inches and cm 1 inch = 2.54 cm 2.54 cm 1 inch

37 E. CONVERSION FACTORS: Sample Problem: Express a mass of grams in milligrams and then in kilograms.

38 III. SIGNIFICANT FIGURES

39 A. ACCURACY AND PRECISION: 1. Accuracy refers to the closeness of a measurement to the correct or accepted value of the measured quantity. 2. Precision refers to the closeness of a set of measurements of the same quantity made in the same way.

40 B. SIGNIFICANT FIGURES: 1. The accuracy of all measuring devices is limited, therefore the number of valid digits is also limited. 2. Valid digits are known as significant figures. 3. Significant figures in a measurement consist of all the digits known with certainty plus one final digit, which is somewhat uncertain or is estimated. 4. The term significant does not mean certain.

41 Significant Figures B. SIGNIFICANT FIGURES:

42 C. SIGNIFICANT FIGURES RULES: 1. Non-zero numbers (1 9) are ALWAYS significant. examples: In between zeros are ALWAYS significant. examples: Leading zeros are NEVER significant. examples: Trailing zeros are SOMETIMES significant. Zeros at the end and after a decimal are ALWAYS significant. examples: Zeros left of an understood decimal are NEVER significant. examples: *To avoid confusion use scientific notation: 3.00 X sig figs

43 C. SIGNIFICANT FIGURES RULES: >Unlimited Significant Figures: >Counting When you count the number of people in the room, there are exactly 24 not 24 ½ or 24.4 but exactly 24. You could write people. >Exactly Defined Quantities These are exact numbers. There are exactly 12 inches in 1 foot. If needed these can have unlimited significant figures.

44 C. SIGNIFICANT FIGURES RULES: Sample Problem: How many sig figs are in each of the following measurements? 28.6 g cm 910 m L kg

45 EVERY PROBLEM YOU DO THIS YEAR MUST HAVE THE CORRECT NUMBER OF SIG FIGS!!!

46 Your answer cannot be more precise than the least accurate of your measurements!

47 D. ROUNDING RULES FOR SIG FIGS: 1. Rounding Significant Figures: >Ex: You measure the area of a 7.7m x 5.4m floor and find it to be 41.58m 2. >Your answer is more precise than your measurements and therefore must be rounded.

48 D. ROUNDING RULES FOR SIG FIGS: 2. Addition and Subtraction with Sig Figs: >When adding or subtracting decimals, the answer must have the same number of digits to the right of the decimal point as there are in measurement having the fewest digits to the right of the decimal point. Ex: =

49 D. ROUNDING RULES FOR SIG FIGS: 3. Multiplication and Division with Sig Figs: >When multiplying and dividing the answer can have no more sig figs than the measurement with the fewest total number of sig figs. >In calculations, carry ALL digits to the end then determine sig figs. Ex: 7.7 x 5.4 =

50 D. MIXED OPERATIONS FOR SIG FIGS: 4. Showing all your work is necessary during this process. >Carry all digits to the end >Determine correct number of sig figs at the end. Work the following examples out. Show all your work. Carry all digits to the end, then we will watch a video that explains sig fig determination. 1. (2.8 x 4.532) = 2. ( ) / 9.3 =

51 IV. SCIENTIFIC NOTATION

52 A. SCIENTIFIC NOTATION: >In Chemistry, we use very large and very small numbers that are hard to keep track of when written normally instead we use Scientific Notation. >In scientific notation, numbers are written in the form M 10 n, where the factor M is the coefficient. >The coefficient is always a number greater than or equal to 1 but less than 10 >Move the decimal point four places to the right, and multiply the number by example: mm = mm

53 A. SCIENTIFIC NOTATION: >Determine M by moving the decimal point in the original number to the left or the right so that only one nonzero digit remains to the left of the decimal point. >Determine n by counting the number of places that you moved the decimal point. If you moved it to the left, n is positive. If you moved it to the right, n is negative.

54 B. PROPORTIONS: >Two quantities are directly proportional to each other if dividing one by the other gives a constant value >i.e. Both increasing or both decreasing. >Two quantities are inversely proportional to each other if dividing one by the other gives an opposite value. >i.e. If one is increasing the other decreases.

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