Unit 1: Introduction to Chemistry

Transcription

1 Unit 1: Introduction to Chemistry

2 I. Observations vs. Inferences Observation: information you gather using your five senses ***You will NEVER use taste in class! o Describes facts Examples You see the plant is green You feel the solution is warm You see it is raining outside You hear the alarm is beeping

3 Inference: a possible or explanation conclusion based on observations o cannot be directly observed using the 5 senses. Examples The plant is green so it must be healthy The solution is warm so there must have been a chemical reaction The street is wet so it must have rained The alarm is beeping there may be a fire Observations are what you see, feel, hear, taste, or smell. Inferences are what you think!

4 Practice 1. Identify the following as an observation (O) or inference (I). O a. The mineral on the table is clear and smooth. I b. The caterpillar did not eat the moth because it is not a carnivore. O c. The container is filled to the 350 ml mark with water. I d. The plant on the left is growing faster because it is watered more.

5 2. Look at the picture below. Read the statement and decide if it is an observation (O) or an inference (I). *Hint: ask yourself, does this statement describe information gathered from using the 5 senses? I a. The plant has roots. b. The plant uses water. I c. The plant has flowers. O O d. The plant is in a pot. e. The plant grew from a seed. I

6 3. Look at the picture below. Write two observations and two inferences. Observation Inference

7 II. The Scientific Method What is the Scientific Method? The Scientific Method: a series of steps used to help. answer a question or solve a problem o There are 6 steps 1. State the problem What do you want to know or explain? Use observations you ve made to come up with a topic/problem you want to investigate. This is usually written in question form Background research 2. Use all available resources to collect data on the topic i.e. experts, textbooks, journal articles,online databases, etc. Form a hypothesis 3. What do you think will happen? Based on your research, predict the answer to your question or the outcome of the experiment.

8 4. Run the experiment Follow the steps in your procedure to perform your experiments and test your hypothesis. Record data and observations! Analyze the data 5. Examine all the data collected from the experiment. Tables and graphs are used to organize the data State your conclusion 6. Based on the analysis of the data, draw a conclusion about your hypothesis. Does the data support your hypothesis? If the data does not support the hypothesis, there may be an error in the experiment or the hypothesis is wrong. You cannot change data scientists must be unbiased. o Note: In reality, due to the ever-changing nature of science, there is more than one correct scientific method ; scientists do not always follow these exact steps. These six steps are more like common guidelines that scientists follow when looking to answer a question or solve a problem.

9 Parts of an Experiment Experiment: an organized series of steps for testing a hypothesis Main parts of an experiment: o Hypothesis: an educated guess or prediction based on observations and previous knowledge. Typically uses If then format Example: If caffeine is added to plant seeds, then they will grow faster

10 o information Data: collected in an experiment Two types: 1. Quantitative: deals with measured o Can be think! **Quantitative Quantity numbers amount Examples: Length, Height, Area, Time, Temperature 2. Qualitative: deals with observed descriptions o Can be but not measured **Qualitative Quality Examples: Colors, Smells, Tastes, Appearance

11 Practice Identify the following data as qualitative or quantitative. Circle the correct answer. 1.The baby weighs 20 pounds Qualitative Quantitative 2.Ms. Marble is annoyed Qualitative Quantitative 3.The solution is purple Qualitative Quantitative 4.Ms. Marble has $1,000,000 Qualitative Quantitative 5.There are ten boys in the class Qualitative Quantitative

12 o Experimental Group: the group that receives the treatment - the test group The variable that is being tested is manipulated/changed in this group Independent Variable the factor that is changed in the experiment. The variable I change. Dependent Variable the variable that depends on the independent variable. This is the data collected. Constants factors that throughout remain the same the entire experiment. Only test one variable at a time! *the independent variable is the cause, the dependent variable is the effect*

13 o Control Group: the group that doesn t receive the treatment The standard of comparison important in order to compare results of the variable being tested Exposed to the same conditions as the experimental group except for the variable being tested

14 Practice 1. SpongeBob noticed that his favorite pants were not as clean as they used to be. His friend Sandy told him that he should try using Clean-O detergent, a new brand of laundry soap she found at Sail- Mart. SpongeBob made sure to wash one pair of pants in plain water and another pair in water with the Clean-O detergent. After washing both pairs of pants a total of three times, the pants washed in the Clean-O detergent did not appear to be any cleaner than the pants washed in plain water. a. What was the problem SpongeBob wanted to investigate? Does using clean-o detergent clean his pants better than plain water? b. What is the independent variable? Laundry soap c. What is the dependent variable? How clean his pants get d. What should Sponge Bob s conclusion be? Using clean-o does not make his pants more clean

15 2. We want to test if fertilizer helps plants. One plant is given fertilizer, while the other plant is not. Both plants are the same type, given the same size planter, the same amount of light, and the same amount of water. After letting both plants grow for one week, we observe that the plant given the fertilizer has grown taller. Identify the following: Experimental Group: Plant given fertilizer Independent Variable: Fertilizer Dependent Variable: Plant growth Control Group: Plant without fertilizer Constants: plant type, size of planter, amount of light/water, length of experiment

16 III. Data Representation - Graphs Graphing is used by scientists to display the data that is collected during a controlled experiment. In science, a graph is most commonly used. The graph should contain 4 major parts: the title, the independent variable, the dependent variable, and the scales for each variable. title line 1. : this shows what the graph is about. A basic title follows the following format: the effect of (the independent variable) on (the dependent variable) independent 2. Variable: this is the factor that is controlled or manipulated by the experimenter. This variable should be placed on the horizontal or x-axis and should be labeled with a name and units

17 Last step: Always round up to a number that is convenient. For example, if you get 18.7 as your value for each square on the x-axis, that rounds up to 19 but 20 is much easier to work with. dependent 3. Variable: this is the variable that changes in response to the independent variable. It is the result of what happens because of the independent variable. This variable is placed on the y or vertical axis and should be labeled with a name and units 4. The Scales for each Variable: the scales are the numbers on the axes that guide where you plot your points. Scales must be evenly spaced, consistent, and carefully selected so that the data fills up the whole graph. It is very common for students to guess the scale but there is a better way! Highest X Value = value for each square on x-axis Number of lines Highest Y Value = value for each square on y-axis Number of lines

18 When completing a graph, remember STALK! S -- T -- A -- L -- K -- Scale Title Axis Labels Key

19 Example ph of water Number of tadpoles

20 *Hint in a data table, the variable that goes on the x axis (the independent variable) is typically on the ; left the variable that goes on the y-axis (the dependent variable) is typically on the. right Just think of it as alphabetical order! Questions 1.What is the independent variable? ph of water 2.What is the dependent variable? Number of tadpoles 3.What is one conclusion you can make from this data? he # of tadpoles is greatest around a ph of 6.5-7

21 Sometimes, a graph may contain two sets of data. If that is the case, you will need to make a key to label which line is which. Example Day Plant height without fertilizer (cm) Plant height with fertilizer (cm)

22 Questions 1.Which is the control group? How do you know? Plants without fertilizer didn t receive the treatment 2.Which is the experimental group? How do you know? Plants with fertilizer did receive the treatment 3.What is one conclusion you can make from this data? Plants that received fertilizer grew taller than the plants that didn t

23 IV. Measurement 1. Distance (length, width, height) What do you want to measure? Distance Definition Tool Basic Metric Unit and Abbreviation Amount of space between 2 points Ruler, meter Meter stick, (m) measuring tape Unit Abbreviations mm = millimeter km = kilometer cm = centimeter m = meter How much does each one equal? 1 m = mm m = cm km= m 1000

24 2. Volume What do you want to measure? Volume Definition Tool Basic Metric Unit and Abbreviation Amount of space a substance takes up Liquids graduated cylinder Solids - ruler Liquids milliliter (ml) Solids cubic centimeters (cm 3 ) Unit Abbreviations ml = milliliter kl = kiloliter cl = centiliter L = liter How much does each one equal? 1 L = ml L = cl kl= L 1000 What do you notice about these units and the units for distance? The prefixes and relationships between prefixes are the same. Only the base unit changes

25 Finding Volume: There are three ways to find the volume of different objects: 1)Calculate the volume of solid cubes or rectangular objects using a formula 2)Measure the volume of liquids using a graduated cylinder 3)Develop a procedure to calculate the volume of oddly shaped objects Hint!!!! Volume is a 3 DIMENSIONAL measurement. Your units will be ml for liquids and oddly shaped objects and a length measurement cubed (cm 3, m 3, mm 3 ) for cubic solids. 1mL = 1 cm 3

26 1) Calculate Volume: Cubes and Rectangular Prisms In order to calculate the volume of a cube or rectangular prism, you will use the following formula. Find the volume of this box by using the length, width, and height measured for you: L = 6cm H = 3cm W =1cm 6cm 1cm 3cm 18cm 3 Example: A textbook has the following dimensions Length = 28cm Height= 3cm Width= 22cm What is its volume? 1848cm 3

27 2) Measure Volume: Liquids In order to measure liquids, it is necessary to use a graduated cylinder, beaker or flask. Practice measuring liquids by looking at the pictures: a. Find the meniscus (the upside down bubble). Draw an arrow to the bottom of the meniscus in each drawing. b. Read the line closest to the bottom of the meniscus. Record your answer in ml. 43 ml 35 ml 52.8 ml

28 3) Develop a Procedure of Volume: Oddly Shaped Objects How can you find the volume of strangely shaped objects? After watching the demonstration, write a procedure explaining how you will find the volume of oddly shaped objects using only a graduated cylinder: 1. Gather material: graduated cylinder (or something that measures volume), water, and object 2. Measure out a few ml of water in graduated cylinder. Record initial volume Place object in graduated cylinder and see how much the water level rises. Record final volume Subtract the initial volume from the final volume the difference is the object s volume This procedure for finding the volume of oddly shaped objects is called. water displacement

29 3. Mass What do you want to measure? Mass Definition Tool Basic Metric Unit and Abbreviation Amount of matter (atoms and molecules) in an object Scale or balance Grams (g) Unit Abbreviations mg = milligram kg = kilogram cg = centigram g = gram How much does each one equal? 1 g = mg g = cg kg= g 1000 Again, notice the prefixes and relationships are the same as distance and volume! Only the base unit changed! Finding Mass: When finding the mass of an object using a balance, make sure the balance is zeroed and in the correct! units

30 4. Temperature What do you want to measure? Temperature Definition Tool Basic Metric Unit and Abbreviation Hotness/coldn ess of a sample The average kinetic energy of molecules in a substance thermometer Celsius ( C) There are three units of temperature: Fahrenheit ( F), Celsius ( C), and Kelvin (K). Although we are used to using, Fahrenheit in science we typically use Celsius and. Kelvin

31 Match the correct label with the diagram below: Room Temperature Freezing Point of Water Boiling Point of Water Body Temperature

32 As mentioned before, in science temperature is measured in Celsius or Kelvin. Often times, it is necessary to convert between the two. Looking at the picture above, what do you predict the equation is to convert Celsius to Kelvin? K = C Using algebra, this equation can also be written to convert the other way, from Kelvin to Celsius: C = K - 273

33 Practice Record the following temperatures and convert them to Kelvin. Note, the thermometers are in degrees Celsius. Temperature in C = 17 Temperature in C = Temperature in K = Temperature in K =

34 Metric Conversions In the metric system, we can make smaller or larger units by adding a prefix. To convert from a larger unit to a smaller unit or vice versa, all you have to do is move the! decimal point Unit (or base unit) can be grams, liters, meters, etc. It is whatever you are measuring without a prefix

35 Practice 1. Convert 18mL to liters L 2. Convert 300km to meters 300,000 m 3. Convert 450mg to grams 0.45 g 4. Convert 20km to cm 2,000,000 cm

36 V. Percent Error T

37 Examples: 1.Michael Scott measured the piece of paper to be 24 cm long. It was actually 20 cm long. What is the percent error? 2.The mass of a rock was measured by a student and determined to be 325 grams. The actual mass of the rock was 330 grams. Calculate the percent error in the student's measurement of the rock's mass. 3.In an experiment, the density of copper is determined to be 9.45 g/ml. The accepted value for the density of copper is g/ml. Find the percent error.

38 VI. Density Density: How much matter (atoms and molecules) is packed in an object or in other words, how much mass is located in a specific volume of space. The units for density are g/ml or g/cm 3 Equation see Table : T **Remember 1 ml = 1 cm 3

39 Practice 1. Find the density of a liquid with a mass of 10 grams and a volume of 10cm 3 2. If you have a lead ball with a mass of 450 g and a density of 45 g/cm 3, what is the volume? 3. Helium has a density of g/l. If you have 1000 L of helium, what would its mass be?

40 4. A rock has a mass of 120.5g. It is put into ml of water and the water rises to ml. Find the density of this rock. 5. What is the density of an unknown block having a mass of 972.3g and dimensions of 4.57cm by cm by 11.28cm?

41 The density of a specific substance does not change at a given temperature. For example, the density of pure water is always. 1 g/ml o Because of this fact, density can be used to identify substances. Example: A person brings in what he thinks to be a gold ring to a jewelry store. The ring has a mass of 4.5 g and a volume of cm 3. He knows the density of gold is 19.3 g/cm 3. Is this a gold ring? How do you know?