unit topic: introduction to chemistry: laboratory safety, scientific method, & measurements

Unit Topic: Introduction to Chemistry: Laboratory Safety,

Scientific Method, & Measurements

SOL CH.1 a-jPages: 7-31, 63-93, and R56-R77

Lab Safety packets

Virginia Standard of Learning: CH.1 a-jThe student will investigate and understand that experiments in which variables are measured, analyzed, and evaluated, produce observations and verifiable data.Key Concepts:a. designated laboratory techniquesb. safe use of chemicals and equipment;c. proper response to emergency situations.d. manipulation of multiple variables with repeated trials;e. accurate recording, organizing, and analysis of data through repeated trials.f. mathematical and procedural error analysis;g. mathematical manipulations including SI units, scientific notation, linear notation, linear equations, graphing, ratio and proportion, significant digits, and dimensional analysis);h. the use of appropriate technology including computers, graphing calculators, and probeware for gathering data and communicating results; and using simulations to model conceptsi. construction and defense of a scientific viewpoint; andj. the use of current applications to reinforce chemistry concepts.

Anticipated Learning Objectives for this unit

What is Chemistry?

It is the study of matter and all the changes it undergoes.

Matter is any substance that has mass and volume. Mass- is the amount of material within a

substance. Volume- the amount of space an object occupies.

Is Air considered matter?? PROVE IT

Chemistry• Is important to:

– Archaeologist – unusual levels of iridium (Ir) and niobium (Nb) in core samples of rocks helped Luis Alvarez solve the problem of disappearing dinosaurs.

– Historian – lead (Pb) poisoning was a contribution to decline of Roman empire. Romans enjoyed drinking a sweetened syrup (sapa) which was prepared by boiling down grape juice in lead lined pots. The lead acetate (PbCH3CO2) produced as juice is boiled down is one of the reason for sapa’s sweetness.

– Psychologist – studies of inmate in Stateville Prison in Illinois links low levels of cobalt (Co) with violent behavior.

SCIENTIFIC MEASUREMENT

Always contains a number and unit. Most common measurements are mass,

temperature, length, and volume. Different instruments are used to take

measurements. Reading these instruments correctly are EXTREMELY IMPORTANT.

Scientific Measurement Significant Figures

1. Nonzero digits are always significant2. Zeros between non-zero figures are

significant.3. Zeros used as a place holder are necessary

but not significant.4. Zeros following a non-zero figure and have a

decimal point in the number are significant.Now let’s do some practice problems.

Assuming that the measurement was recorded correctly…

Scientific Measurement Significant Figures (Practice Problems)

1. 4261 ml

2. 207.32 g

3. 0.58 cm

4. 230 mol

5. 3.200 m

6. 0.00691 g/ml

7. 20.0 cm3

8. 0.04500 kg

Now let’s try some on your own!

Scientific Measurement Significant Figures -Calculations

1. When adding or subtracting measured quantities the answer should contain only as many decimal places as the least number in the problem.

2. When multiplying or dividing measured quantities the answer should contain only as many significant figures as the least number in the problem.

Now let’s do some practice problems.

Scientific Measurement Significant Figures Practice Problems

For each problem explain how to properly round the answer.

1. 5.27 ml + 83.5 ml =2. 18.362 g / 9.6 ml =3. 71.548 g – 70.882 g =4. 21.62 cm x 1.43 cm = 5. 6.725 g / (25.82 ml – 21.4 ml) =


Scientific Measurement Scientific Notation

Very large and very small numbers are expressed in scientific notation.

In scientific notation the number is written as the product of two numbers The coefficient -must be greater than or equal to 1 or

less than 10. The exponent (10 raised to a power) equal to the

number of places that the decimal is moved to the left or right.

Numbers less than one will have a negative exponent. Numbers greater than one will have a positive exponent.



Write down the number of significant figures and convert to scientific notation.

1. 84,000 m = 5. 0.0000320 m =

2. 0.00736 m= 6. 5406 m =

3. 950400 m= 7. 0.04800 =

4. 700.10 m= 8. 0.9100 m =



Multiplication and Division To multiply numbers written in scientific notation,

multiply the coefficients and add the exponents. To divide numbers written in scientific notation divide

the coefficients and subtract the exponent in the denominator from the exponent in the numerator.

Addition and Subtraction If you want to add or subtract numbers expressed in

scientific notation and you are not using a calculator, then the exponents must be the same.


Directions: Solve each problem, and express your answer in correct scientific notation.

1. (8.0 x 10-2) x (7.0 x 10-5)=

2. (7.1 x 10-2) + (5 x 10-3)=

3. (4.8 x 103) / (2.4 x105)=

4. (6.3 x 103) - (4.5x 102)= Now let’s try some on your

own!

SCIENTIFIC MEASUREMENTDENSITY

Density is ratio of mass and volume of an object. The density of an object is inversely related to

temperature (as temperature increases density decreases when mass is kept constant.

Density = mass / volume (must memorize)

Density Practice Problems

Complete the following density problems. Show all required work and make sure final answer has the correct number of sig. figs.

1. What is the mass of an object that has a density of 12.3 g/cm3 and a volume of 6.8 cm3?

2. An new substance was found to have a mass of .850 g and a volume of 3.66 cm3. What is the density of this new substance?

3. What is the volume of an object with a mass of 300. g and density of 56.7 g/mL?


Scientific Measurement Measuring with SI Units

International System of Units (abbreviated SI) was established in 1960.

There are seven SI base units. All other units of measurement are derived from these seven units.

Easier to use than English system because it is based on powers of ten


Seven base units in the metric system.


•Metric prefixes are used to increase or decrease the value of a base unit. - Kilo (k) is used to increase the value of the base unit.

- Deci-(d), centi-(c), milli-(m) are used to decrease the value of the base unit.

Common metric conversion factors (Must memorize)1000 m = 1 km10dm =1 m These values will work for all base units 100 cm = 1m Ex: 1000g = 1 kg1000 mm = 1m

Metris (SI) prefixesMemorize all prefixes from giga to pico

Measurement Dimensional Analysis

Dimensional Analysis (unit factor method) - A method used convert from system of units to another. Conversion (unit) factor are necessary for dimensional analysis

problems. (Ex: 1000 g =kg)

• General Dimensional Analysis FormulaGiven x unit

factorVolume Conversions Factors

1000 L = 1m3 1000 mL = 1L 1cm3 = 1mL

Non-metric Conversion Factors

12 in = 1ft 5280 ft = 1 mile 2.54 cm = 1 inch

LET’S DO SOME PRACTICE PROBLEMS :)

Metric/Metric Conversion Problem Problem # 1 How many meters are in 12.8 cm?

Step 1: Identify the known and unknown informationKnown 12.8 cm =

Unknown ? m 12.8cm = ? mStep2: Write out the conversion factor 100 cm =1 mStep 3: Use the known information and conversion factor to convert to

unknown unit. Place the known unit in the denominator and the unknown unit in the numerator.

12.8 cm 1 m = 12.8 m = .128 m 100 cm 100

English/metric Conversion ProblemProblem 2: How many inches are in 48.9 ft?

Step 1: Known 48.9 ft Unknown ?inches

48.9 ft=? inchesStep 2: What is the conversion factor?

1 ft = 12 inchesStep 3: Set-up the problem to solve the unknown.48.9 ft 12 inches = 48.9 x 12 inches = 586.8 inches

=587 in. 1ft Now let’s try some on your own!

remember final answer must have correct unit and sig fig.

Dimensional Analysis

Directions: Perform the following conversions using dimensional analysis. Make sure your final answer has correct sig. fig. and units

1. How many weeks in 6.3 years?Answer: 330 weeks

2. Convert 45 m to kilometers.Answer: 0.045 km

3. Calculate the number of days in 1800 h.Answer: 75 days

4. How many inches long is a 100. yd football field? (3ft = 1 yd)Answer: 3.60 x103 inches

5. Convert 8.5 dm to mm.Answer: 850 mm

6. A spider travels 115 inches in 1 min (speed = 115 in/min). What is the speed of the spider in miles/hour? (5280 ft = 1mi)

Answer: 1.06 mi/ hr

Unit Topic: Introduction to Chemistry: Laboratory Safety,

Scientific Method, & Measurements

SOL CH.1 a-jPages: 7-31, 63-93, and R56-R77

Lab Safety packets

Virginia Standard of Learning: CH.1 a-jThe student will investigate and understand that experiments in which variables are measured, analyzed, and evaluated, produce observations and verifiable data.Key Concepts:a. designated laboratory techniquesb. safe use of chemicals and equipment;c. proper response to emergency situations.d. manipulation of multiple variables with repeated trials;e. accurate recording, organizing, and analysis of data through repeated trials.f. mathematical and procedural error analysis;g. mathematical manipulations including SI units, scientific notation, linear notation, linear equations, graphing, ratio and proportion, significant digits, and dimensional analysis);h. the use of appropriate technology including computers, graphing calculators, and probeware for gathering data and communicating results; and using simulations to model conceptsi. construction and defense of a scientific viewpoint; andj. the use of current applications to reinforce chemistry concepts.

Anticipated Learning Objectives for this unit

How to read a graduated cylinder

Scientific Measurement Taking Measurements -Scaled Instruments

Scaled instrument -instruments has numbered lines to determine measurement Graduated cylinders shows each

line (scale). This instrument is accurate to ones

place, therefore estimated digit should be in tenth place.

For scaled instruments the estimated digit must be determined by YOU.

Liquid volume is 43.0 ml not 43 ml. The zero, in tenth place, is the estimated digit.

Scientific Measurement Taking Measurements - Digital Display

Digital display -measurement is displayed electronically by machine Electronic thermometer is an

example of a instrument that uses digital display.

The last digit in these types of instruments is the estimated digit and is always supplied.

The 6 in the tenth place in the estimated digit.

32.6 oC is the correct reading.

Scientific Measurement

All measurements have some degree of uncertainty. WHY?????

When measurements are recorded CORRECTLY it must be written with a digit of uncertainty (estimated digit) and a unit.

Last digit in ANY measurement is the digit of uncertainty (estimated digit).

Scientific Measurement Accuracy and Precision

All measurements should have accuracy and precision.

Accuracy - how close the measured value is to the the true (accepted) value.

Precision- how close a series of measurements are two each other.

Scientific Measurement Accuracy and Precision

Look at the dart board drawings and determine the accuracy and precision of each.

#1

#2

#3

#4

Scientific MeasurementPercent Error

An individual measurement can be accurate or inaccurate.

Percent error is used to calculate how far the experimental value is from the accepted value.


Scientific MeasurementPercent Error Practice Problems

1. Working in the laboratory, a student find the density of a piece of pure aluminum to be 2.85 g/cm3. The accepted value for the density of aluminum is 2.699 g/cm3. What is the student's percent error?

2. A student experimentally determines the specific heat of water to be 4.29 J/g x Co. He then looks up the specific heat of water on a reference table and finds that is is 4.18 J/g x Co. What is his percent error?

3. A student takes an object with an accepted mass of 200.00 grams and masses it on his own balance. He records the mass of the object as 196.5 g. What is his percent error?


Scientific MeasurementGraphing

1. Assign Variables To The Proper Axis

• A graph relates two variables from an experiment. One of the variables is changed in order to study how it affects the other variable.

• The independent variable and it’s values are plotted on the ‘x’ or horizontal axis.

• The dependent variable and it’s values are plotted on the ‘y’ or vertical axis.


2. Set-up the scales/label axis

Each axis must have a numbered scale to show the values of each variable.

The scale should begin with a number slightly less than the lowest value and extend to a number slightly more than the greatest value and designed to occupy the majority of the paper.

The scale must be uniform. That is each block on the graph must represent the same amount as any other block of that scale.

Scales do not necessarily need to begin at zero. The two scales do not necessarily need to match.

Each axis must have a label which states the variable which is plotted on the axis.

Each axis must indicate the unit used to measure the variable.


5. Plot and Connect The Points

Use a small uniform dot to plot each point in it’s proper position.

How the points are connected depends upon what kind of data was collected.

Discrete data (counted items) are usually bar graphs or pie charts.

Continuous data (measured quantities) are connected by a

smooth line which may be straight or curved. The line

does not need to touch each circle as it only shows the trend in the data.

Each graph should have a title placed near the top of the paper. It should be informative. That means that it should relate to the reader information about the experiment that is not part of the graph without the title.

unit topic: introduction to chemistry: laboratory safety, scientific method, & measurements

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