Chemistry Day 39 Friday, December 14 th Monday, December 17 th, 2018
Do-Now: Reactions Quiz Do-Now 1. Write down today s FLT 2. Copy: KCl + H 2 O à? 3. Identify the type of reaction in #2. 4. Predict the product(s) in #2. Show all work. 5. Balance the equation in #2. Show all work. 6. What is 466.034160 rounded to the nearest a. Hundredths b. Tenths c. Ones d. Tens e. Hundreds Take out your planner and ToC
FLT I will be able to determine the number of significant figures in a measurement by completing Sig Figs Notes Standard HS-PS1-7: Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction
Scientific Measurement
Measurements
Measurements We often take measurements in chemistry labs
Measurements Are our measurements accurate? This depends on: The reliability of the measuring instrument the care with which it is read this is determined by YOU!
Video Notes Measurements Write down four facts or examples from the video clip
Accuracy vs. Precision
Accuracy, Precision, and Error It is necessary to make good, reliable measurements in the lab Accuracy how close a measurement is to the true value Precision how close the measurements are to each other (reproducibility)
Precision and Accuracy Neither accurate nor precise Precise, but not accurate Precise AND accurate
Sig Figs
Significant Figures in Measurements Significant figures = all known digits plus one estimated digit Measurements must be reported to the correct number of significant figures.
Significant Figures in Measurements If you don t use the correct sig figs, your answer is incorrect L
Rules for Sig Figs
Rules for Counting Sig Figs -Nonzero digits are always significant Ex/ 3456 4 sig figs
Rules for Counting Sig Figs -Leading zeroes are NOT significant Ex/ 0.0486 3 sig figs
Rules for Counting Sig Figs -Zeroes in between significant digits are also significant Ex/ 16.07 4 sig figs
Rules for Counting Sig Figs Trailing zeroes are significant only if a decimal point is present Ex/ 9.300 4 sig figs Ex/ 0.03010 4 sig figs
Rules for Counting Significant Figures Counted items & defined quantities have unlimited sig figs Counted items 23 people, or 425 thumbtacks Exactly defined quantities 60 minutes = 1 hour
1 M < 10 M x 10 n n is an integer
Pair-Share-Respond How many significant figures in the following? 1.0070 m à 5 sig figs 17.10 kg à 4 sig figs 100,890 L à 5 sig figs 3.29 x 10 3 s à 3 sig figs 0.0054 cm à 2 sig figs 3,200,000 ml à 2 sig figs 5 dogs à unlimited This is a counted value
Significant Figures in Calculations In general a calculated answer cannot be more precise than the least precise measurement from which it was calculated. Ever heard that a chain is only as strong as the weakest link? Sometimes, calculated values need to be rounded off.
Rounding Calculated Answers 1. Determine how many sig figs are needed 2. Round your answer to the correct number of sig figs
Rounding Calculated Answers + and - Round to the number with the fewest decimal places Ex/12.25 m + 349.0 m + 8.24 m 369.5 m
Rounding Calculated Answers and Round answer to the smallest # of sig figs present Ex/ 6.38 x 2.0 = 12.76 à 13 (2 sig figs) Ex/2.10 meters x 0.7 meters = 1 m 2
Pair-Share-Respond Calculation Calculator says: Answer 3.24 m x 7.0 m 22.68 m 2 23 m 2 100.0 g 23.7 cm 3 4.219409283 g/cm 3 4.22 g/cm 3 0.02 cm x 2.371 cm 0.04742 cm 2 0.05 cm 2 710 m 3.0 s 236.6666667 m/s 240 m/s 1818.2 lb x 3.23 ft 5872.786 lb ft 5870 lb ft 1.030 g x 2.87 ml 2.9561 gml 2.96 gml
Scientific Notation Review
Overview How wide is our universe? 210,000,000,000,000,000,000,000 miles That s 22 zeroes When numbers are this large, it is easier to write them in scientific notation à 2.1 x 10 23 miles
1 M < 10 M x 10 n n is an integer
Overview Rules: 1. Move decimal pt. after the first nonzero digit, and include all significant digits 2. Count how many places you moved the decimal à that is your exponent 3. Moved left à positive exponent. Moved right à negative exponent. 4. Write as M 10 n
Overview 210,000,000,000,000,000,000,000 miles Place the decimal point after the first digit Between the 2 and the 1 2.10,000,000,000,000,000,000,000.
Overview 2.10,000,000,000,000,000,000,000. Count how many places your decimal moved 23 I moved my decimal left, so my exponent is Positive 23 The answer in scientific notation is 2.1 x 10 23
Examples
Examples 1) 0.0000000902 Where would the decimal go to make the number be between 1 and 10? 9.02 The decimal was moved how many places? 8 I moved right, so my exponent is negative 9.02 x 10-8
Try These: Write in sci notation 1) 28750.9 2) 4,580,000 3) 0.00018
Try These: Write in decimal form 4) 3.2 10 5 5) 4.76 10-6 6) 10.14 10 13
Try These: Write in sci notation 7) 531.42 x 10 5 8) 234.6 x 10 9 9) 0.0642 x 10 4
Chemistry Day 40 Tuesday, December 18 th Wednesday, December 19 th, 2018
Do-Now: Lab Day Do-Now 1. Write down today s FLT 2. Distinguish between a physical and chemical change 3. What are our five signs of a chemical change? 4. What is meant by the term precipitate? 5. List at least 5 important things to remember in the lab. These can include safety rules, how to dress, and how to clean after. Take out your planner and ToC
Chemistry Day 41 Thursday, December 20 th Friday, December 21 st, 2018
Do-Now: Unit Conversion CN 1. Write down today s FLT 2. How many sig figs in a. 123 b. 9.80000 c. 98,000 3. Calculate 22.4 m x 11.3 m x 5.2 m 4. Write in scientific notation: a. 50,100,000 b. 0.0015 5. Fold or draw a margin under your do-now Take out your planner and ToC
Scientific Measurement
Units
Units We use units to express our measurements
Units The International System of Units (AKA Metric system) is a standard system Common base units in chemistry: Length: Meter (m) Mass: Gram (g) Temperature: Kelvin (K) Time: Second (s) Amount: Mole (mol) Energy: Joule (J) Volume: Liter (L) or cm 3
Units Non-SI units (Liter, Celsius) and derived units (miles/hour, grams/ml) are sometimes also used
The Fundamental SI Units (Le Système International, SI) Physical Quantity Name Abbreviation Length Meter m Mass Kilogram kg Temperature Kelvin K Time Second s Amount of substance Mole mol Not commonly used in chemistry: Luminous intensity Candela cd Electric current Ampere A
Conversions
Conversion Factors In the SI system, base units are used and can be easily converted since they are factors of 10 Example: 1000 mm = 10 3 mm = 1 m 100 cg = 10 2 cg = 1 g
SI Prefixes
Recall: Conversion Factors First: Write what you start with Second: Draw a conversion factor (ratio) this is called dimensional analysis
SI Prefixes See Page 130
Conversion Factors We can represent these same units in conversion factors Example: 10 3 ml = 1 L
Conversion Factors These conversion factors are defined, and have unlimited significant figures. Do not use to determine the number of sig figs in your final answer. Only use given measurements.
Ex 1/ Write the two possible conversion factors for kilograms and grams
Ex 2/ Write the two possible conversion factors for centimeters and meters
Converting Between Units We can multiply by the number one creatively to change the units. Ex 3/ Convert 13 inches to yards We know that 36 inches = 1 yard. 1 yard = 1 36 inches 13 inches x 1 yard = 36 inches
What are they good for? We can multiply by a conversion factor to change the units. Problem: 13 inches is how many yards? Known: 36 inches = 1 yard. 1 yard = 1 36 inches 13 inches x 1 yard = 0.36 yards 36 inches
Ex 4/ Convert 12.0 inches to cm ( 1 inch = 2.54 cm) How long is this in meters?
Conversion Factors Complex Conversions involve multiple conversion factors Ex 5: Express 750 dg in kilograms
Conversion Factors Complex Conversions Ex 6: Express 9.7 kg in centigrams
Other Calculations
Conversion Factors Complex units are those that are expressed as a ratio of two units: Speed might be meters/hour Ex 7/ Change 15 meters/hour to units of centimeters/second
Density Which is heavier- a pound of lead or a pound of feathers? Most people will answer lead, but the weight is exactly the same They are normally thinking about equal volumes of the two
Density Density = mass/volume Common units are: g/ml, or possibly g/cm 3, (or g/l for gas) Density is a physical property, and does not depend upon sample size
Try This One: Ex 8/ A penny has a mass of 3.1 g and a volume of 0.35 cm 3. Calculate its density.
Density What happens to the density as the temperature of an object increases? Mass remains the same Most substances increase in volume as temperature increases Thus, density generally decreases as the temperature increases
Density Water is an important exception to the previous statement. Over certain temperatures, the volume of water increases as the temperature decreases (Do you want your water pipes to freeze in the winter?) Does ice float in liquid water? Why?