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Chapter 2

Chapter 2. Matter and Change. Scientific Method. Most scientific advances result from carefully planned investigations Often called scientific method The scientific method is used as a guideline for scientists to structure their investigations .

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Chapter 2

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  1. Chapter 2 Matter and Change

  2. Scientific Method • Most scientific advances result from carefully planned investigations • Often called scientific method • The scientific method is used as a guideline for scientists to structure their investigations. • It’s a logical approach to solving problems that is based on common sense • There are several stages to the method

  3. Scientific Method • Observing and Collecting Data • Observing is the use of the senses to obtain information • Often means making measurements or collecting data • Data may be quantitative (numerical) or qualitative (descriptive) • Penny weighs 1.1g is quantitative • Sky is blue is qualitative • Experimenting involves carrying out a procedure under controlled conditions to make observations and collect data

  4. Scientific Method SYSTEM • Chemists study the effects of change on matter of a system • A system is the area of focus during an experiment • In a rxn, the beaker and its contents are the system

  5. Scientific Method • Formulating Hypotheses • Scientists strive to find relationships and patterns in their collected data • Scientists organize their data in tables and charts • Scientists analyze their data using statistics and mathematical techniques, often using graphs and computers • Scientists use generalizations about the data to formulate a hypothesis • A hypothesis is a testable statement

  6. Scientific Method • Serves as a basis of making predictions and for carrying out further experiments • Usually written as an “if – then” statement • Must make an educated guess • Scientists use generalizations about the data to formulate a hypothesis • A hypothesis is a testable statement

  7. Scientific Method • Testing Hypotheses • Proposed hypotheses are tested through experimentation • The goal during testing is to support or refute the current hypotheses • If hypothesis is refuted the generalizations that lead to the hypothesis are discarded or modified

  8. Scientific Method • Theorizing • When a hypothesis has been tested and found favorable, scientists try to explain the phenomena by constructing a model • A model is an attempted explanation of how events occurand how data or events are related • May be visual, verbal, or mathematical • If a model explains many events it may become a theory

  9. Scientific Method • If a model explains many events it may become a theory • A theory is a broad generalization that explains a body of facts or phenomena • Theories are accepted only if they can predict the results of many different experiments

  10. Units of Measurement • Measurementsprovide quantitative information, but represent more than numbers. • Suppose a chef were to write a recipe listing measurements such as: • 1 salt • 3 sugar • and 2 flour • Cooks could not use the recipe as is • need to know whether the number 3 represented teaspoons or cups

  11. Units of Measurement • Measurements represent quantitieswith dimension. • Which have magnitude, size, or amount • For instance 3 teaspoons is a measurement of the dimension volume and the quantity of 3 of them. • Nearly every measurement includes a number and a unit • The choice of unit depends entirely on the quantity and dimension being measured

  12. Units of Measurement • Units of measurement compare what is to be measured with a previously defined length, weight, volume, etc. • Think about this – if someone said that it is 50 paces from here to the water fountain • Is everyone’s pace the same? • For a measurement to be interpretable it must be a standard or defined measure • For instance: yard, Liter, teaspoon, mole, pound

  13. Units of Measurement: SI Base Units • Scientists eventually agreed on a single measurement system called Le Système International d’Unités. (AKA… SI Base Units) • The SI system was adopted in 1960 by the General Conference on Weights & Measures • It became the standard system of measures with each defined by a consistent, measure-able standard • Objects or natural phenomena that are of constant value, easily preserved, reproducible, and practical in size

  14. Units of Measurement: Prefixes • These base units can represent larger or smaller quantities by adding a metric prefix • Prefixes added to the SI Base Units are used as multipliers to represent a small piece of the base unit or a series of the base units • For ex. centi- is 1/100 of the base unit, therefore, 40 centimeters is 40/100 or .40of a meter • Or kilo- is 1000 of the base units, therefore, 40 kilometers is equivalent to 40,000 meters.

  15. Your Turn… Place a >, <, or = sign in between the two measurements… > 60 centimeters ___ 60 millimeters < 10 milligrams ___ 10 Megameters = 20 decisecond ___ 0.20 decasecond > 15 hectoampere ___ .15 kiloampere

  16. Units of Measurement: Derived Units • Many SI units are combinations of the quantities called derived units • A set of SI Base units multiplied or divided by each other create a unit set that represent useful measures. • E.g. volume is a unit that represents the amount of space an object occupies in 3-dimensions and can have units of m•m•m or m3 • Prefixes can also be added to enhance derived units (cm2 and mm2)

  17. Units of Measurement: Density • A key physical property of any substance and a derived unit is density • Density is a measure of how much stuff is packed in a given volume • The more closely packed the particles the higher the density. • Density is temperature dependent • The density of water at 0˚C is 0.999 g/cm3, but the density of water at 100˚C is 0.0958 g/cm3

  18. Units of Measurement: Density • Density is a ratio of mass and volume and is an intensive property • It doesn’t matter how much of the substance is present the density of that substance is consistent at a given temp. • Density is a property that can help to identify a substance

  19. Units of Measurement: Density • The density of any substance can be measured and calculated by dividing the mass of the substance by its volume • Any mass unit (g, kg, lb, oz, etc.)/any volume unit (L, ml, m3, km3, fl oz, etc) is a density. • At a constant temperature the density ratio is a constant • Density can be used to calculate the volume of a substance given any mass, or vice versa. • Just be sure the units are consistent

  20. Density Calculations: Example 1 Let’s say a 10 cm3 piece of lead, has a mass of 114 g. What is the density of the piece of Lead? Analyze: look for given units and decide on units of the result Volume: 10 cm3 mass: 114 g density: ___ g/cm3 Brainstorm: use clues provided by the desired units to decide on calculation Density is the ratio of the mass and volume and a ratio implies division

  21. Density Calculations: Example 1 Calculate: perform the task mapped out in brainstorm Mass 114 g ________ ______ Density: = Volume 10 cm3 Density = 11.4 g/cm3 Defend: is this an acceptable result? The unit structure makes sense. The mass is heavy for a relatively small volume. If we compare the result to the list earlier it is comparable. Evaluate: what did we learn? Given a mass and a volume of the same substance we can find the ratio of the 2 to measure a property that can be used to identify the substance.

  22. Density Calculations: Example 2 What is the volume of a sample of liquid Mercury that has a mass of 762 dg, given that the density of mercury is 13.6 g/ml? Analyze: Volume: ____ ml mass: 762 dg density: 13.6 g/ml Brainstorm: We have to pay attention to the units…dg for the given mass and g for the given density. Since we want ml as the desired unit, we need to divide out the mass. This can only be done with like units…so we must convert 1st, then calculate vol.

  23. Density Calculations: Example 2 Calculate: Convert… 1 dg = 0.1 g 76.2 g = [(0.1)762] 762 dg = 76.2 g M ______ Volume Calculation: ____ 13.6 g/ml = D = V V Vol = 5.6 ml Defend: Since the mass units divided out we end up with a volume unit (ml). If we take our mass and divide it by the obtained vol. we end up with the density. Evaluate: We can check our work by taking our result and dividing it to get the density. We can use any mass & the density to predict the volume or vice versa.

  24. Your Turn… A material will float on the surface of a liquid if the material has a density less than that of the liquid. Given that the density of water is approximately 1.0 g/ml, will a cube with a side 58.2 cm in length and weighing 158.8 kg float or sink when put in water? (1 ml = 1 cm3) The density of pure silver is 10.5 g/cm3. If 5.25 g of pure silver pellets is added to a graduated cylinder containing 11.2 ml of water, to what volume level will the water in the cylinder rise? 1) D = .81 g/ml so it will float 2) New vol = 11.7 ml

  25. Units of Measurement: Unit Conversion • If you consider any number of everyday situations, you will realize that any quantity can be expressed in several different measures. • For example the same amount of money can be measured in more than one way: 1dollar=4quarters=10dimes=20nickles=100pennies • These are all expressions, or measurements, of the same amount of money

  26. Units of Measurement: Unit Conversion • Whenever 2 measurements are equivalent, a ratio of the 2 can be formed, which can be used to convert from one unit to the other • Consider a ruler 1 ft = 12 in • Since 1 ft and 12 in are equivalent measures of the same length, we can convert any number of inches into the equivalent number of feet or vice versa with the ratios: 12in 1ft Ratio used to convert feet to inches Ratio used to convert inches to feet or 1ft 12in

  27. Units of Measurement: Unit Conversion • A ratio of equivalent measurements, such as 12in/1ft or 1ft/12in, is called a conversion factor • In a conversion factor, the measurement in the numerator is equal to the measurement in the denominator • When a measurement is multiplied by a conversion factor, the numerical value is changed, but the actual size of the quantity measured remains the same. • The key is the equality to connect the units

  28. Units of Measurement: Unit Conversion • One of the best methods for solving conversion problems is a technique called dimensional analysis. • A technique that uses multiplication of ratios to convert from one unit to another • The best way to describe this technique is to apply it in practice

  29. Unit Conversion: Example 1 Your school club has sold 600 tickets to a chili-supper fundraising event, and you have volunteered to make the chili. You have a chili recipe that serves ten people. The recipe calls for 2 tspns of chili powder. How much chili powder do you need for 600 servings?

  30. Units of Measurement: Unit Conversion • Conversions are often accomplished through multiple steps. • The table of equalities shown earlier can lead to the connections that can stepwise lead to the desired unit. • You must have a connection between 2 equal measures to convert from one unit to another

  31. Unit Conversion: Example 2 How many inches there are in 2.65 miles?

  32. Unit Conversion: Example 3 World Record Holder Usain Bolt can run 100 meters in 9.69 seconds, how fast is that in miles per hour?

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