The Nature of Science The Nature of Science

Objective 1 Objective 1

Science vs. TechnologyScience vs. Technology

Science is the Science is the knowledge gained knowledge gained from from experimentation.experimentation.

Newton’s Laws Newton’s Laws Theory of Relativity Theory of Relativity Ohm’s Law Ohm’s Law Human Genome Human Genome

Project Project

Technology is the Technology is the use of science use of science knowledge to knowledge to make things.make things.

Calculators & Calculators & computers computers

Atomic Energy Atomic Energy Electric motors Electric motors Gene therapy Gene therapy Antibiotics Antibiotics

A Brief History of Science A Brief History of Science

Ancient Greek and Ancient Greek and Roman philosophers Roman philosophers began observing and began observing and recording their recording their observations of the observations of the world around them. world around them.

They tried to propose They tried to propose how and why these how and why these things occurred. things occurred.

These observations led to more These observations led to more questions . . . questions . . .

Which led to Which led to proposed proposed answers, answers,

now called now called hypothesehypothese

s.s.

Use of the Scientific MethodUse of the Scientific Method

Formal Formal experimentation experimentation follows the steps of follows the steps of the scientific method.the scientific method.

Many discoveries in Many discoveries in science were not science were not made using the made using the scientific method, but scientific method, but this method was used this method was used to confirm those to confirm those discoveries.discoveries.

How do scientists find How do scientists find answers to answers to questions?questions?

Scientific MethodScientific Method

What if the data doesn’t What if the data doesn’t support the hypothesis? support the hypothesis?

Some very important discoveries occurred when the Some very important discoveries occurred when the scientist was actually looking for something else. For scientist was actually looking for something else. For example, the discovery of some antibiotics. example, the discovery of some antibiotics.

Validating Scientific ClaimsValidating Scientific Claims

Weigh the Weigh the evidence!!!evidence!!!

Be careful what you Be careful what you conclude!!!conclude!!!

There are a lot of There are a lot of false claims out false claims out there!!!there!!!

Which question is valid in testing this hypothesis? Which question is valid in testing this hypothesis?

F F Do most other scientists agree with the Do most other scientists agree with the hypothesis?hypothesis?

GG Could abiotic processes account for the carbon Could abiotic processes account for the carbon dioxide?dioxide?

H H What is the percent of argon compared to What is the percent of argon compared to carbon dioxide in the Martian atmosphere?carbon dioxide in the Martian atmosphere?

J J Have the scientist’s other predictions about Have the scientist’s other predictions about Mars been validated? Mars been validated?

A scientist has hypothesized that theA scientist has hypothesized that theexistence of life on Mars is likely existence of life on Mars is likely becausebecauseMars’s atmosphere is 95% carbon Mars’s atmosphere is 95% carbon dioxide.dioxide.

Which question is valid in Which question is valid in testing this hypothesis?testing this hypothesis?

F F Do most other Do most other scientists agree with scientists agree with the hypothesis?the hypothesis?

GG Could abiotic Could abiotic processes account processes account for the carbon for the carbon dioxide?dioxide?

H H What is the percent What is the percent of argon compared to of argon compared to carbon dioxide in the carbon dioxide in the Martian atmosphere?Martian atmosphere?

J J Have the scientist’s Have the scientist’s other predictions other predictions about Mars been about Mars been validated? validated?

When testing an hypothesis, there should be only one variable changed at a time.

If this is not possible, then all possible reasons for an

outcome need to be considered.

In this case, carbon dioxide can be produced by chemical reactions other than cellular respiration, which is a biotic

process. That is why answer G is the best answer.

When analyzing When analyzing data . . .data . . . Compare the data trend Compare the data trend

to the hypothesis. to the hypothesis. Does the data agree? Does the data agree? Does it show the Does it show the

opposite? opposite? Could there be another Could there be another

reason that the trend reason that the trend agrees with the agrees with the hypothesis? Did all hypothesis? Did all other factors get other factors get controlled? controlled?

Scientific TheoryScientific Theory Based upon Based upon

experimental data. experimental data. A broad principle of A broad principle of

nature that has been nature that has been supported over time.supported over time.

Confirmed by repeated Confirmed by repeated experiments.experiments.

May be modified as new May be modified as new information is gathered. information is gathered.

Scientific LawScientific Law

Conclusions about relationships in Conclusions about relationships in nature that presently have no nature that presently have no exceptions. exceptions.

Scientists work to understand why Scientists work to understand why these relationships exist. these relationships exist.

The smell of an The smell of an ammonia solutionammonia solution used to clean a floor can quickly be used to clean a floor can quickly be detected throughout a house. detected throughout a house. Scientists explain this phenomenon Scientists explain this phenomenon by theorizing that gas molecules by theorizing that gas molecules from the ammonia are in from the ammonia are in continuous random high-speed continuous random high-speed motion, drifting rapidly and motion, drifting rapidly and permeating the air. permeating the air.

Which statement best demonstrates Which statement best demonstrates the strength of this theory?the strength of this theory?

And your choices are . . .And your choices are . . . AA Scientists have observed tiny smoke Scientists have observed tiny smoke

particles moved by unseen particles in particles moved by unseen particles in a rapid, irregular fashion.a rapid, irregular fashion.

B B Scientists have unanimously agreed on Scientists have unanimously agreed on this theory since Thomas Graham’s this theory since Thomas Graham’s experiments in the 1820s.experiments in the 1820s.

C C The possibility of another theory being The possibility of another theory being formed to explain the phenomenon as formed to explain the phenomenon as well is very remote.well is very remote.

D D Reason, as opposed to Reason, as opposed to experimentation, is superior to any experimentation, is superior to any explanation found through chemical explanation found through chemical testing. testing.

AA Scientists have Scientists have observed tiny smoke observed tiny smoke particles moved by particles moved by unseen particles in a unseen particles in a rapid, irregular fashion.rapid, irregular fashion.

B B Scientists have Scientists have unanimously agreed on unanimously agreed on this theory since this theory since Thomas Graham’s Thomas Graham’s experiments in the experiments in the 1820s.1820s.

C C The possibility of The possibility of another theory being another theory being formed to explain the formed to explain the phenomenon as well is phenomenon as well is very remote.very remote.

D D Reason, as opposed to Reason, as opposed to experimentation, is experimentation, is superior to any superior to any explanation found explanation found through chemical through chemical testing. testing.

A compares the A compares the ammonia movement to ammonia movement to something known. A is something known. A is good evidence! good evidence!

B, I don’t think so, it B, I don’t think so, it takes hundreds of years takes hundreds of years for scientists to agree on for scientists to agree on any theory. any theory.

C, Other theories are C, Other theories are proposed all the time, so proposed all the time, so throw this one out. throw this one out.

D, Experimentation is D, Experimentation is always the preferred always the preferred method, so this one is method, so this one is out, too. out, too.

Therefore, you were Therefore, you were right! It is A! right! It is A!

Experimental DesignExperimental Design

Define the problem. Define the problem. Make a testable Make a testable

hypothesis. hypothesis. Define the variables, Define the variables,

independent, independent, dependent and dependent and controlled. controlled.

Determine Determine appropriate sample appropriate sample size. size.

Run the experiment.Run the experiment.

F F Combine the hypotheses so they give valid predictions Combine the hypotheses so they give valid predictions of the acetone’s behaviorof the acetone’s behavior

G G Conduct a study of original papers describing the Conduct a study of original papers describing the experiments leading to acetone’s discoveryexperiments leading to acetone’s discovery

HH Perform an experiment that attempts to identify the gas Perform an experiment that attempts to identify the gas above the open beakerabove the open beaker

J J Ask a classmate’s opinion about the chemical and Ask a classmate’s opinion about the chemical and physical properties of acetone physical properties of acetone

Two science students discovered that the mass of a sample of acetone in an open beaker decreased within a few minutes. One student hypothesized that the acetone reacted with oxygen to form a gaseous compound that escaped. The other student believed that the acetone evaporated into the air. What should the students do to test these hypotheses?

Let’s look at each answer . . Let’s look at each answer . . ..

F F Combine the Combine the hypotheses so hypotheses so they give valid they give valid predictions of the predictions of the acetone’s behavioracetone’s behavior

This would require This would require testing for a testing for a chemical reaction chemical reaction AND the presence AND the presence of acetone above of acetone above the beaker. the beaker.

T O O M A N Y T O O M A N Y

V A R I A B L E SV A R I A B L E S

G G Conduct a study Conduct a study of original papers of original papers describing the describing the experiments experiments leading to leading to acetone’s acetone’s discoverydiscovery

This may tell us a This may tell us a lot about acetone, lot about acetone, but it will not but it will not answer our answer our question. We still question. We still won’t know if it won’t know if it evaporated or not.evaporated or not.

Your classmates’ opinions Your classmates’ opinions although they may be smart although they may be smart won’t answer the question won’t answer the question either. Throw out J.either. Throw out J.

HH Perform an Perform an experiment that experiment that attempts to attempts to identify the gas identify the gas above the open above the open beakerbeaker

This looks like our best This looks like our best answer, it involves answer, it involves actually trying to actually trying to identify the gas identify the gas above the beaker, above the beaker, which will tell us if it which will tell us if it is still acetone. If it is still acetone. If it is, then it is, then it evaporated.evaporated.

VariablesVariables – – MIXMIX

MManipulated or anipulated or IIndependent ndependent

Variable is the Variable is the one you are one you are

changing and is changing and is first in a data first in a data

table and plotted table and plotted on the on the XX-axis of -axis of

the graph. the graph.

VariablesVariables - - DRYDRY

DDependent or ependent or RResponding esponding variable is second column in a variable is second column in a

data table, and plotted on the data table, and plotted on the YY--axis of a graph. axis of a graph.

An advertisement claims that patients can be cured of the common cold in 48 hours by vitamin C tablets with secret mineral supplements. In a scientific experiment to test these claims, which data can be considered irrelevant?

A The amount of vitamin C in each tabletB The severity of the patients’ cold symptomsC The chemical formula for vitamin CD The amount of time before symptoms improve

What doesn’t matter to the What doesn’t matter to the test?test?

A A The amount of vitamin C in each tablet The amount of vitamin C in each tablet This should be a controlled variable! This should be a controlled variable!

B B The severity of the patients’ cold symptoms The severity of the patients’ cold symptoms This would be very hard to control, but a large experimental This would be very hard to control, but a large experimental

group should allow for differencesgroup should allow for differences

CC The chemical formula for vitamin C The chemical formula for vitamin C Compound formulas NEVER change so this is our Compound formulas NEVER change so this is our

answer. It is irrelevant!!! answer. It is irrelevant!!!

D D The amount of time before symptoms improve The amount of time before symptoms improve This is what we are testing, it is most relevant. This is what we are testing, it is most relevant.

What is the independent What is the independent variable in the vitamin C variable in the vitamin C

experiment? experiment?

The amount of vitamin C!The amount of vitamin C!

What is/are the dependent What is/are the dependent variables in the Vitamin C variables in the Vitamin C

experiment?experiment?

How long it takes for the symptoms How long it takes for the symptoms to improve!to improve!

Possible ResultsPossible Results

Vitamin C

012345678

100 mg 500 mg 1000 mg

Vitamin C

A A ControlControl vs. vs. Controlled Controlled VariablesVariables

ControlControl or control group is one that or control group is one that participates in the experiment participates in the experiment without the change being tested. without the change being tested. (Receives a placebo, or grown under (Receives a placebo, or grown under the same conditions.) the same conditions.)

Controlled VariablesControlled Variables are the other are the other factors in an experiment that might factors in an experiment that might affect the results. (Amount of water, affect the results. (Amount of water, sunlight, strength of the drug, food.) sunlight, strength of the drug, food.)

The table shows times required for water to evaporate from identical containers. Which of these is the best question to ask before developing a reasonable hypothesis to explain the data?

What do you know? Identical What do you know? Identical containers, and same volume of containers, and same volume of

water.water.FF Why does a lower Why does a lower

temperature slow the temperature slow the rate of evaporation?rate of evaporation?

G G What is the boiling point What is the boiling point of the water after both of the water after both samples are heated?samples are heated?

H H Why does water exist as Why does water exist as a solid at -15°C and as a a solid at -15°C and as a liquid at 25°C?liquid at 25°C?

J J How does the rate of How does the rate of evaporation change evaporation change when a different when a different container is used?container is used?

J is out since the J is out since the containers are identical. containers are identical.

H has nothing to do with H has nothing to do with the rate of evaporation the rate of evaporation so it is out so it is out

G is out, because the G is out, because the boiling point of a boiling point of a substance is a physical substance is a physical property that can identify property that can identify a substance, so it is out a substance, so it is out

That leaves F, which asks That leaves F, which asks about temperature and a about temperature and a rate “slow”. rate “slow”.

What variable(s) were What variable(s) were controlled?controlled?

Container type/sizeContainer type/size

Amount of waterAmount of water

Data Collection and Sample Data Collection and Sample SizeSize

The larger the The larger the amount of data amount of data collected, collected,

The larger the The larger the sample size, sample size,

The more times the The more times the experiment is experiment is repeated, repeated,

The more valid are The more valid are the results. the results.

ValidityValidity

Does the Does the experiment experiment measure measure what it what it claims to claims to measure?measure?

An herbal company advertises that its product will help people lose weight if they take a tablespoon of the product with a glass of water at bedtime each night. Weight loss is guaranteed if a person does not eat for at least 3 hours before bedtime, gets moderate exercise, and drinks 8 glasses of water each day. Why is the company’s claim difficult to verify?

F The company has yet to disclose the identity of its special herb.

G Numerous uncontrolled variables are involved in evaluating results.

H Fasting lessens the absorption rate of the herb.

J The advertisement lacks data from before and after the weight loss.

True, but you wouldn’t expect them to.

True, and also correct!!

Not eating before bedtime is recommended for all weight loss programs, and it takes several hours to digest and absorb anything you take so this statement is invalid

True, but still doesn’t control any of the other factors.

Analysis of the Data Analysis of the Data

Data tables, flow charts and graphs present Data tables, flow charts and graphs present the information collected during an the information collected during an experiment. experiment.

What the data shows, any trend in information What the data shows, any trend in information is explained in the analysis of data. is explained in the analysis of data.

An environmental-science company measured the ozone pollutant levels at two different locations in a metropolitan area. Which statement is best supported by these data?

Look for the unsafe levels and where and when they occur.

Both occurred on 7/15 at a Both occurred on 7/15 at a temperature of 38 temperature of 38 ooC, so . . C, so . .

A A Lower fuel efficiency and northerly winds Lower fuel efficiency and northerly winds in the winter increase ozone pollution the in the winter increase ozone pollution the most.most.

B B Northwest winds in the spring transport Northwest winds in the spring transport ozone pollution into the metropolitan area.ozone pollution into the metropolitan area.

CC High summer temperatures and southerly High summer temperatures and southerly winds contribute to high levels of ozone.winds contribute to high levels of ozone.

D D Heavy use of automobiles changes ozone Heavy use of automobiles changes ozone levels the most.levels the most.

This is true, however not supported by the data in the table since both downtown and northwest areas had increases.

winterspring

Data Presentation and Data Presentation and AnalysisAnalysis

Data tables are lists Data tables are lists of information that of information that may or may not may or may not show a relationship. show a relationship.

Graphs are pictorial Graphs are pictorial representations of representations of information to aid in information to aid in seeing any relation seeing any relation between them. between them.

Data Tables Data Tables

The first column is usually the independent The first column is usually the independent variable, or what was being changed. variable, or what was being changed.

Other columns are counts or measurements Other columns are counts or measurements that were taken at each change.that were taken at each change.

The table shows environmental The table shows environmental factors and soybean production factors and soybean production for three regions. for three regions.

Which of the following Which of the following probably accounts for the probably accounts for the decrease in soybean yield in decrease in soybean yield in Region 1?Region 1?

FF High levels of ozone damaged the High levels of ozone damaged the soybean plants, decreasing the average soybean plants, decreasing the average yield.yield.

G G Low rainfall amounts failed to meet the Low rainfall amounts failed to meet the plants’ moisture needs and inhibited growth.plants’ moisture needs and inhibited growth.

H H Poor mineral levels found in the soil in Poor mineral levels found in the soil in that region limited the soybean harvest.that region limited the soybean harvest.

J J Higher-than-normal rainfall increased pest Higher-than-normal rainfall increased pest activity, decreasing the average yield.activity, decreasing the average yield.

What do you have to know?What do you have to know?

11stst you really only have two choices, you really only have two choices, decreased rainfall, or Odecreased rainfall, or O33 level. level.

Since the rainfall did not decrease Since the rainfall did not decrease consistently (it actually increased in consistently (it actually increased in 1999) that would not be a good answer. 1999) that would not be a good answer.

Therefore, it must be the OTherefore, it must be the O33, which is , which is the chemical formula for ozone. the chemical formula for ozone.

Answer? Answer? F

Reading Graphs Reading Graphs Always read the Always read the

title. title. Read the x- & y-Read the x- & y-

axis labels & axis labels & UNITS. UNITS.

What is What is happening?happening?

As the pressure of As the pressure of oxygen increases, oxygen increases, the % saturation is the % saturation is

increased. increased.

Graph Types – Pie and BarGraph Types – Pie and Bar

Pie Graphs are used to show parts of a whole and percent distributions.

Bar Graphs show noncontinuous data such as number of males and females in each science class with different hair colors.

Graphs – Line or CurvesGraphs – Line or Curves

Line GraphsLine Graphs show show continuous data continuous data like distance vs. like distance vs. time, time, acceleration, or acceleration, or change over change over time.time.

Data Trends Data Trends

DirectDirect relationship relationship means as one means as one variable variable changes, the changes, the other other changes in changes in the same the same way. way.

Other Data Trends Other Data Trends

InverseInverse – when one – when one goes up the other goes up the other one goes down or one goes down or as one goes down as one goes down the other goes up. the other goes up.

ExponentialExponential – – typical of typical of uncontrolled growth uncontrolled growth of a population, is a of a population, is a J-shaped curveJ-shaped curve

Which graph best shows the Which graph best shows the comparison of the elements to the comparison of the elements to the

total composition of the copper ore?total composition of the copper ore?

This is noncontinuous data (not time or temperature or increasing forces) and it is in percentages. D is a pie graph which shows percentage parts of the whole!

Drawing conclusionsDrawing conclusions

Not getting the results expected, or Not getting the results expected, or predicted often provides more predicted often provides more information than getting what you information than getting what you expected.expected.

Ernest Rutherford did not expect his Ernest Rutherford did not expect his light to go straight through the gold light to go straight through the gold foil, but it showed him that atoms foil, but it showed him that atoms were mostly empty space. A very were mostly empty space. A very important discovery.important discovery.

Many doctors Many doctors recommend 800 µg of recommend 800 µg of folate, 400 µg of vitamin folate, 400 µg of vitamin B12, and 50 mg of B12, and 50 mg of vitamin B6 per day to vitamin B6 per day to improve cardiovascular improve cardiovascular health. Based on this health. Based on this information and the information and the nutrition label, the nutrition label, the cardiovascular health cardiovascular health benefit of a 1-ounce benefit of a 1-ounce serving of this cereal is serving of this cereal is ——

AA doubtful because it doubtful because it provides insufficient provides insufficient folate and vitamin B6 folate and vitamin B6 and lacks vitamin B12and lacks vitamin B12

B B superb because it superb because it contains only 22 g of contains only 22 g of carbohydrates and 75 carbohydrates and 75 mg of sodiummg of sodium

C C excellent because it excellent because it provides all needed provides all needed vitamins and is low in fat vitamins and is low in fat and cholesteroland cholesterol

D D poor because it raises poor because it raises blood cholesterol levels blood cholesterol levels with its high fat and with its high fat and cholesterol contentcholesterol content

Since the question asks Since the question asks about the nutritional about the nutritional value based on Folate value based on Folate and the B vitamins, and the B vitamins, evaluate the answers evaluate the answers based on the same based on the same information. information.

B is not valid since no B is not valid since no information is given information is given as to what are good as to what are good levels. levels.

C is not valid as it does C is not valid as it does not provide all the not provide all the vitamins. vitamins.

D is not a valid answer D is not a valid answer since it is very low in since it is very low in fat. fat.

ANSWER: A ANSWER: A

Tools for Measurement Tools for Measurement

Clocks and stopwatches measure time.

A balance is used to measure mass.

A graduated cylinder, dropper, or

volumetric flask is used to measure liquid volume.

A metric ruler is used to find length, and therefore the volume of regular objects.

Measuring Units – System Measuring Units – System Internationale Internationale

Mass?Mass?

Volume? Volume?

Length? Length?

Grams Grams

LitersLiters MetersMeters

AccuracyAccuracy vs. vs. PrecisionPrecision

Which of the following will allow measurement of Which of the following will allow measurement of a liquid’s volume with the greatest precisiona liquid’s volume with the greatest precision??

A A 50 mL cylinder graduated in 1 mL increments50 mL cylinder graduated in 1 mL increments

B B 50 mL cylinder graduated in 0.5 mL increments50 mL cylinder graduated in 0.5 mL increments

C C 100 mL cylinder graduated in 1 mL increments100 mL cylinder graduated in 1 mL increments

D D 200 mL cylinder graduated in 5 mL increments200 mL cylinder graduated in 5 mL increments

Answer: B

Accuracy Accuracy

This is when a This is when a measurement is measurement is closest to its true closest to its true value (the bull’s value (the bull’s eye!).eye!).

PrecisionPrecision

This is the repeatability of a measurement. This is the repeatability of a measurement.

It It maymay or or may notmay not be accurate be accurate

It is possible to be accurate and precise!It is possible to be accurate and precise!

Is it accurate? Is it precise? Is it accurate? Is it precise?

AccuracyAccuracy depends depends on how close the on how close the measurement tool measurement tool is to the actual is to the actual measurement. measurement.

If the equipment If the equipment has been properly has been properly calibrated and calibrated and cared for it is cared for it is usually accurate.usually accurate.

PrecisionPrecision usually usually depends on the depends on the amount of amount of estimating that has estimating that has to be done. to be done.

The smaller the The smaller the measurement measurement markings on the markings on the tool, the more tool, the more precise it is. precise it is.

Four lab groups measured the volume of acid Four lab groups measured the volume of acid required to neutralize a standard solution of required to neutralize a standard solution of sodium hydroxide base. Which of the groups sodium hydroxide base. Which of the groups measured the volume with the highest measured the volume with the highest

precision?precision?

What equipment is used to What equipment is used to measure volume? measure volume?

In A, they are using two flasks. Not In A, they are using two flasks. Not very precise markings! very precise markings!

B is better, at least they are using a B is better, at least they are using a graduated cylinder. graduated cylinder.

C is a bad choice, since most test C is a bad choice, since most test tubes have no markings for volume. tubes have no markings for volume.

D is the best choice as the small D is the best choice as the small volume markings on the burette gives volume markings on the burette gives the most precise measurement. the most precise measurement.

Experimentation and Experimentation and SafetySafety

Use only labeled Use only labeled materials. materials.

Read labels twice to Read labels twice to make sure. make sure.

Know the procedure. Know the procedure. Ask about the MSDS Ask about the MSDS

((material safety data material safety data sheets) sheets) if you are not if you are not familiar with the familiar with the substance. substance.

Safety with Temperature Safety with Temperature ChangesChanges

Do not handle hot or Do not handle hot or cold containers. cold containers.

Use the proper Use the proper holder for the holder for the container. container.

When heating a When heating a substance, aim it substance, aim it away from everyone.away from everyone.

Safety with GasesSafety with Gases

Odors are tested by Odors are tested by wafting. wafting.

Reactions which Reactions which produce gases produce gases should be done in a should be done in a fume hood. fume hood.

Gases should be Gases should be trapped only in a trapped only in a large volume large volume container to provide container to provide for rapid expansion. for rapid expansion.

A science class is conducting an experiment A science class is conducting an experiment that produces noxious fumes. Because of that produces noxious fumes. Because of inadequate ventilation, some students inadequate ventilation, some students begin to feel nauseated and dizzy. The first begin to feel nauseated and dizzy. The first response should be to —response should be to —

A A neutralize the acid that is reacting to neutralize the acid that is reacting to produce the noxious fumesproduce the noxious fumes

B B carry the reactants outside, away from carry the reactants outside, away from other studentsother students

CC leave the room and go to an area with fresh leave the room and go to an area with fresh airair

D D spray the reaction with a fire extinguisherspray the reaction with a fire extinguisherNot D --Extinguishers should only be used on fires.

Don’t move it anywhere except under a fume hood, Too dangerous! Not B

Not A – Acids are not the only producers of fumes, and adding something else could make it worse!

Safety EquipmentSafety Equipment

Protective goggles are worn in lab at all times. Protective goggles are worn in lab at all times. Non-ventilated are worn if contact lenses are worn. Non-ventilated are worn if contact lenses are worn. Aprons should be worn when handling chemicals. Aprons should be worn when handling chemicals. Follow MSDS for safe handling of all chemicals. Follow MSDS for safe handling of all chemicals.

The safest way to dilute The safest way to dilute concentrated sulfuric acid is to concentrated sulfuric acid is to addadd — —A A a series of small a series of small

volumes of water to volumes of water to the acid while stirringthe acid while stirring

BB the acid to water the acid to water slowly while stirring slowly while stirring constantlyconstantly

C C the acid to a small the acid to a small volume of water and volume of water and then add more waterthen add more water

D D dilute sulfuric acid to a dilute sulfuric acid to a small volume of the small volume of the concentrated acid concentrated acid

The safety rule says The safety rule says always add acid to always add acid to water, so A & C are water, so A & C are out since they both out since they both add water to acid. add water to acid.

D doesn’t even make D doesn’t even make sense since you can’t sense since you can’t make concentrated make concentrated acid out of a dilute acid out of a dilute acid by adding to it. acid by adding to it.

So the answer is So the answer is

Which of these is the most appropriate unit of measure for reporting the density

of a solid?

A g/cm3

B g/cm C g/L2

D g/mm2

Density = Mass / Volume Density = Mass / Volume THIS IS FROM THE FORMULA PAGETHIS IS FROM THE FORMULA PAGE

A block of maple wood with a volume ofA block of maple wood with a volume of405 cubic centimeters and a density of405 cubic centimeters and a density of0.67 g/cm0.67 g/cm33 is sawed in half. The density is sawed in half. The densityof the two smaller blocks is now —of the two smaller blocks is now —

A A one-fourth the original densityone-fourth the original densityB B one-half the original densityone-half the original densityC C two times the original densitytwo times the original densityDD the same as the original density the same as the original density

If the block is cut in half, you cut the mass in half AND you cut the volume in half, so Mass/2 or Volume/2

Mass x 2 (which is really 1) so . . . .

Volume 2

A sample of an element has a volume of 78.0 mL and a density of 1.85 g/mL. What is the mass in grams of the sample? Record and bubble in your answer to the nearest tenth on the answer document.

Use the formula page, D = M/V

1.85 g/mL =

Multiply both sides by 78.0 mL and you get:

144 g Grid it in!

mL 78.0

x

How would you find the density How would you find the density of an irregularly shaped of an irregularly shaped

object?object?What equipment would you need?

What about phase changes?What about phase changes?

Solid, Liquid, Gas

How does density change???

Liquid DensityLiquid Density

If you pour together liquids that don’t If you pour together liquids that don’t mix and have different densities, mix and have different densities, they will form liquid layers.they will form liquid layers.

The liquid with the The liquid with the highest densityhighest density will be will be on the bottomon the bottom..

The liquid with the The liquid with the lowest densitylowest density will will be be on the topon the top..

Liquid Layers – Try on your Liquid Layers – Try on your own!own!

Imagine that the Imagine that the liquids on the right liquids on the right have the following have the following densities:densities:– 15g/cm15g/cm33 10g/cm 10g/cm33

– 3g/cm3g/cm33 9g/cm 9g/cm33

– 7g/cm7g/cm33 12g/cm12g/cm33

Match the colors to Match the colors to the correct the correct densities.densities.

3g/cm3

7g/cm3

9g/cm3

10g/cm3

12g/cm3

15g/cm3

EquipmentEquipment

Reading a Reading a graduated cylindergraduated cylinder

Reading a triple Reading a triple beam/electronic beam/electronic balancebalance

Parts of a Parts of a microscopemicroscope

OK, we are done!!!OK, we are done!!!