Unit 1 Tools of Chemistry. Objective: To understand the fundamentals used throughout a study of chemistry

Transcription

1 Unit 1 Tools of Chemistry Objective: To understand the fundamentals used throughout a study of chemistry

2 Learning Goals O I can describe the scientific method. O I can determine whether a hypothesis is valid. O I can create a valid hypothesis. O I can convert numbers into and out of scientific notation. O I can convert values in the metric system. O I can determine the number of significant figures in a value. O I can round to the appropriate number of sig figs. O I can calculate the density, mass, and volume of a substance given two of those values. O I can convert between different measurements. O I can differentiate between physical and chemical properties and changes of a substance. O I can evaluate measurements based on accuracy and precision. O I can determine the percent error of a value.

3 What is Chemistry? O The study of matter and it s changes O Matter all the stuff around you O The stuff that makes up the universe O Example changes digesting food, make synthetic fabrics, burning fuel, producing medicines

4 How do we study Chemistry? O The Scientific Method a system of making questions, developing explanations, and testing those explanations against the reality of the natural world O OR: an organized system helping to explain the world around us

5 The Scientific Method The Steps 1. Identify and state the problem or question 2. Gather information and collect data 3. Make a hypothesis about the problem 1. A tentative, reasonable, TESTABLE explanation of the facts 4. Experiment! 1. Test whether or not your hypothesis is correct 5. Collect and analyze your data 6. Make a conclusion 1. Did your problem get solved or question answered? 1. If not repeat the steps

6 The Scientific Method Hypothesis, Theory, or Law O Hypothesis a possible explanation or guess at the solution to your problem based on observation O O IE: The sun caused the paint to fade more on the west side vs. the north side of the house. What you think might happen in your experiment? O Theory summarizes a hypothesis or group of hypotheses that have been supported with repeated testing. O O Are accepted as true when there is no evidence to refute it NOT fact IE: Darwin s Theory of Evolution, Einstein s Theory of Relativity O Law a generalization of a body of observations O O O There are no exceptions in a scientific law when it is made IE: Newton s Laws of Motion, Ideal Gas Laws Do not explain why, they just say what occurs

7 The Scientific Method Moving from Hypothesis to Theory 1. Identify the Problem 2. Collect Data 3. Hypothesis 4. Experiment 5. Analyze Data 6. Make Conclusions Hypothesis Theory

8 Warm Up O SpongeBob loves to garden and wants to grow lots of pink flowers for his pal Sandy. He bought a special Flower Power fertilizer to see if will help plants produce more flowers. He plants two plants of the same size in separate containers with the same amount of potting soil. He places one plant in a sunny window and waters it every day with fertilized water. He places the other plant on a shelf in a closet and waters it with plain water every other day. O What did SpongeBob do wrong in this experiment? Explain. O What should SpongeBob do to test the effectiveness of Flower Power fertilizer? Write an experiment.

9 Tools of Chemistry Scientific Notation O A way for people to deal with very large and very small numbers O Eliminates the need to count zeros O Takes the form of M x 10 n O 1 M > 10 O n = # of decimal places O If n is positive, the number is greater than one and the decimals need to move to the right O If n is negative, the number is less than one and the decimals need to move to the left

10 Scientific Notation O From Scientific Notation to Standard O 1. Determine M O 2. Determine n and which direction O Example: 1.2 x 10 5 O M = 1.2 O n = 5 O So, move the decimal 5 digits to the right O120000

11 Scientific Notation O From Standard to Scientific Notation O 1. Determine M (drop all zeros and make the number between 1 and 10) O 2. Determine the number of decimals places you moved (this is n) O Example: O M = 4.5 O n = -5 O 4.5 x 10-5

12 Scientific Notation O Practice O Convert the following into Scientific Notation: 1) 98,500,000 = 2) 64,100,000,000 = 3) = 4) = O Answers x x x x 10-4

13 Scientific Notation O Convert the following to standard x 10 9 = x 10-3 = x = x 10-5 = O Answers 1. 8,900,000, ,800,000,

14 Tools of Chemistry Significant Figures O Science uses lots of measurements and thus lots of numbers O Types of Numbers O Counting numbers numbers without partial units, cannot be broken up O Ie: 6 shirts, 5 boys, 17 chickens O Defined numbers pre-calculated and/or memorized conversion factors in the form of fractions O Ie: 12inches in 1 foot = 1/3 yard O Measured Numbers numbers with measured units (99% of what is used in chemistry) O Ie:1.25cm, 5.79mm

15 Determine the Significant Figures in Numbers O Significant figures digits for which actual measurement took place, includes one estimated digit O Counting and Defined numbers an infinite number of sig figs O Measured Numbers O Digits 1-9 ALWAYS count O Zeros SOMETIMES count

16 Determine the Significant Figures in Numbers O Zeros O Leading zeros never count O sig figs O sig figs O Middle Zero always count O sig figs O sig figs O Trailing zeros Count IF AND ONLY IF a decimal point is present somewhere in the number O sig figs O sig figs O sig figs O sig figs

17 Sig Fig Practice O Type of Number? people gram tbsp in 1 cup 4. 6 cans 5. 4 qrts in l gallon 6. 3 feet in 1 yard in cm O Answers 1. Counting 2. Measured 3. Defined 4. Counting 5. Defined 6. Defined 7. Measured 8. Measured

18 Sig Fig Practice O Type of Zero and Number of Sig Figs cm cm g x 10-3 mg mL cm L O Answers 1. Leading, 2 2. Trailing, 3 3. Middle/trailing, 6 4. Trailing, 4 5. Middle, 4 6. Leading, 2 7. Trailing, 3

19 Sig Figs in Calculations O Addition and Subtration O Answer goes by the least number of sig figs in the given numbers O Multiplication and Division O Answer goes by the number of sig figs O Examples O 12.0cm cm = O =14.45cm O 14.5cm O 111cm x 22cm = O = 2442cm O 2440cm

20 Warm Up O Convert the following into scientific notation: O Convert the following into standard notation x x x x 10 4 O Round the following to 3 sig figs: x

21 Warm Up O Round the following to three sig figs

22 Tools in Chemistry Metric Measurement O Metric is the standard measurement system in chemistry (and the only one we ll use) O SI unit (Standard Internation Unit) O Time: s seconds O Length: m meter O Mass: kg kilogram O Volume: m 3 meters cubed (rarely used) O Temperature: K Kelvin O Also KNOW: C Celcius

23 Metric prefixes Prefix Symbol Meaning Multiplier Multiplier Mega M Million 1,000,000 1 x Kilo k Thousand 1,000 1 x 10 3 Hecto h Hundred x 10 2 Deka da Ten 10 1 x 10 1 Base unit (Suffix gram, meter, liter) Deci d Tenth x 10-1 Centi c Hundreth x 10-2 Milli m Thousandth x Micro μ Millionth x Nano n Billionth x Pico p Trillionth x 10-12

24 Converting Between Units 1. Start with what you are given 2. Place the unit you want to convert to on the top of the next section and where you are converting from on the bottom 3. Set the larger unit equal to 1 1. The farther up the list the larger the unit 4. Set the smaller unit equal to 1with x number of zeros 1. X = The number of steps between the units 5. Multiply across the top and bottom 6. Divide the two answers 5cm = km 5cm 1 km cm = = 5 km = 5 x 10-5 km

25 Conversion Practice 1. How many grams are in 4kg? 2. How many millimeters are in 2 meters? 3. The name equivalent of 0.001m is what?

26 Warm Up O Convert the following: (Show your work) O 1.25mm = dam O 150cL = nl O 458kg = g O 879.0µm = dm

27 Derived Units O Units that are made when two other units are put together O Ie: miles per gallon O Types: O Volume 1mL = 1cm 3 O Density O Mass/volume = g/cm 3 or g/ml

28 Density O O O O O How much matter (stuff) in a certain volume of a substance O Ie: marshmallows are less dense, than lead O More gaps between the matter Density = mass/volume O D = m/v Densities for solids are reported in grams per cm 3, ml, or L Densities for liquids are reported in grams per ml or cm 3 O 1mL = 1cm 3 The density of water is 1.00g/mL. O You can quickly approximate the mass of water or something in water when the volume is known O Ice floats b/c it has a density less than 1.00g/mL

29 Examples O A gold colored ring has a mass of 18.9grams and a volume of 1.12mL. What is its density? O What volume would a gram sample of air occupy if the density of air is 1.29g/L? O Pumice is volcanic rock that contains many trapped air bubbles. A 225 gram sample occupied 236.6mL. Will pumice float on water? O A cup of sugar has a volume of 237mL. What is the mass of the cup of sugar if the density is 1.59g/mL?

30 Warm Up O If the density of a gas is 0.24g/cm 3 and occupies a space of 250mL, what is the mass of the gas? O If a marshmallow has a mass of 15.24g and a volume of 150.0mL, what is the density of the marshmallow?

31 Chemistry Tools Dimensional Analysis O In science, sometimes we need to convert from a given unit into desired units O Dimensional Analysis is just a fancy (and MUCH) easier way to set up this conversion O Same process as when we converted metric units O Uses conversion factors O Ratio of two equivalent quantities using different units O 1 hr = 60 min or 1 hour/60min or 60min/1hr

32 Conversion Factors O Length O 1inch (in) = 2.54cm O 1foot (ft) = 12 in O 1 yard (yd) = 3ft O 1mile (mi) = 1,760yd O 1mile = 1.609km O 1mile = 5,280 O Time O 1minute (min) = 60 seconds (s) O 1 hour (hr) = 60 min O 1 day = 24 hr O 1year (yr) = 365 days O Volume O 1 cup (c) = 16tbsp. O 1pint (pt) = 2c O 1quart (qt) = 2pt O 1gallon (gal) = 4qt O 1gal = 3.78L O Mass O 1 pound (lb) = 16 ounces (oz) O 1oz = 28.35grams O 2.2lb = 1kg O 1ton = 2,000lb

33 Steps O Place the given quantity on the top of the ladder O Place the unit you want to convert to on the top and the unit you want on the bottom O What is the conversion factor between the two units? O Cross out the units that cancel O Multiply across the top and bottom O Divide the top from the bottom 2.5 hours =? minutes 2.5 hr 60 min 1 hr = = 150 min 1 = 150 min

34 Helpful Hints O Figure out what unit(s) you are converting to and from O Write them down O Set up the problem using your units first O Don t forget, you can do this in several steps, if you don t have a conversion factor between two units find a unit they have in common O If the units don t cancel and leave you with your desired unit, something is wrong

35 Practice 1. If your heart beats at a rate of 72 beats per minute, how many times will your heart beat each year? 2. Basketball player Shaquille O Neal weighs 310pounds. What is his weight (mass) in kilograms? 3. How many days would it take you to count 200,000 items assuming you count one item every second, without stopping? 4. Since 5280ft = 1 mile, and 12in = 1ft, how many inches are in 3.5miles?

36 Evaluating Measurement O Percent Error how far away from the accepted value O %error = accepted value experimental value x 100 accepted value O Qualitative Measurement a description without any measurement tools O Color, shape, texture, etc O Quantitative Measurement a description of an object with numbers using units O Length, density, mass, etc O Something you can place on a graph

37 Evaluating Measurement O Accuracy the Closeness of a quantitative measurement to its accepted value O Precision the closeness of a set of values in relationship to each other

38 Uncertainty in Measurement O Using Sig Figs, sometimes accuracy and precision are lost O IE: two population signs say the follow O Littleton Population 784 O Largeton Population 6100 O Which of these is a more precise reporting of the population based on sig figs? O The same rules apply to measurement in chemistry O You need to measure in the number of sig figs the tool is graduated in plus one estimated unit

39 Uncertainty in Measurement O To determine the estimated digit O When measuring and the measurement isn t directly on a line, you must round to the next closest significant figure O This means you must determine what the increments stand for and what the next increment will tell you

40 Measurement Uncertainty O When measuring volume, you eye level should be looking squarely at the bottom of the meniscus O The crescent shaped liquid surface caused by the attraction of the liquid to the container

41 Chemistry Basics Physical & Chemical O Physical Properties properties of an object that can be changes WITHOUT changing the objects chemical components O Temperature, state, length, mass, volume, pressure, velocity, area, color, texture O Physical Change an alteration of a substance that DOES NOT change into something new O Heating, shaping, cutting, changing state,

42 Chemistry Basics Physical & Chemical O Chemical Properties describe the ability of an object to undergo a chemical change (rxn) forming something completely new O Reactivity, toxicity, preferred type of chemical bonds, oxidation state, flammability O Chemical Changes reactions (this is the fun lab work of actually changing an object into something new) O Digestion, combustion, explosions, O Clues to a chemical change: color change, productions of a new substance (solid, liquid or gas), energy absorbed or released, not easily reversed