SLE 2 - Fluids and Solutions

2. Investigate and describe the composition of fluids, and interpret the behaviour of materials in solutiondistinguish among pure substances, mixtures and solutions, using common examplesinvestigate the solubility of different materials, and describe their concentration

•investigate and identify factors that affect solubility and the rate of dissolving a solute in a solventrelate the properties of mixtures and solutions to the particle model of matter

Properties arid the Particle ModelSolids - has a definite

______

Liquids - have no definitedefinite

___________

Gases - have no definite

and a definitebut they do have a

and no definite

QEO

\

The Particle Model of Matter

1. All substances are made of tiny particles.2. All particles in a pure substance are the same.bifferent pure substances are made of differentparticles.3. The particles have spaces between them.4. The particles are always in motion.5. The particles in a substance are attracted to oneanother. The strength of the attractive force depends onthe type of particle.

Particles in SolidsThe particles in solids are tightly packed together and cannotmove around freely but only vibrate. Solids can be pouredwhen ground into small pieces, e.g. sugar and will form piles(stop flowing). Solids are not true fluids.

Particles in LiquidsParticles in liquids have enough energy to pull away fromeach other. They can slide around each other while they arevibrating close together in small clusters. These particlescannot hold their shape. The particles in liquids are tightlypacked together and will flow to the lowest level, forming alevel surface.

Particles in GasesGas particles have a lot of empty space between neighbouringparticles. Gases appear to be invisible because there is so muchempty space. Gas particles can spread out so much that in abrief time they fill up the shape and space they are in. Mostgases do not flow to the lowest level possible. Gases fill up,down or sideways.

Flowing FluidsThe particles in substances which can flow are able to movearound one another. This can occur only in liquid and gasmolecules. Particles in solids do not move, they only vibrateagainst one another because they are tightly packed together.Only liquids and gases are considered true fluids because theirparticles have enough room between them to move around.

— Ex1earning• - -—- .— — —

Name: Date:

Student Exploration: Temperature and Particle Motion

Voàabjjijd: absolute zero, Kelvin scale, kinetic energy, Maxwell-Boltzmann distribution, molarmass, molecule, temperature, universal gas constant

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

1. Why is hot air hot?

2. Why is cold air cold?

____________________________________________________________

3. Air consists of tiny particles called rnolecj. How do you think the molecules move in hot

and in cold air?

Gizmo Warm-upThe Temperature and Particle Motion GizmoTM illustrateshow the molecules of gas move at different temperatures. Inthis Gizmo, temperature is measured on the Kelvin scald,which measures temperature from absolute zer, thecoldest possible temperature (-273.15 °C). Each unit on theKelvin scale is equivalent to I °C: 273.15 K = 0 °C, and373.15K= 100°C.

Check that the selected gas is Hydrogen and theTemperature is 300 K.

1. Describe the motion of the hydrogen molecules:

_______

‘4

c19

H

2. Are all of the molecules moving at the same speed?

I zmos

Activity A: Get the Gizmo ready:

. Check that the selected gas is Hydrogen and the —.Molecular motionsTemperature is set to 300 K -

Question: How is the temperature of a gas related to the motion of gas molecules?

1. Observe: Move the Temperature slider back and forth. Focus on the particle motion at left.

What do you notice?

____________________________________________________________

2 Analyze The ternperatuid of a substance is a measure of the average kinetic enerqj of itsparticles (kinetic energy is the energy of motion). The kinetic energy (KE) of a particle isequal to its mass times the square of its velocity, divided by two:

KE=mv2/2

A. Based on the formula for kinetic energy, how will the temperature change if you

increase the average velocity of the molecules in a gas?

________________________

B. How will the temperature change if you increase the mass of the gas molecules?

3. Predict: Oxygen molecules are sixteen times as massive as hydrogen molecules. At thesame temperature, which type of molecule would you expect to move faster? Explain.

4. Check: Test your prediction by choosing Oxygen from the Select a gas menu.

What do you see?

___________________________________________________________

5. Exrlain: Based on the definition of temperature given above, explain why oxygen molecules

move more slowly than hydrogen molecules at the same temperature.

__________________

,JIIflO%

Activity B: Get the Gizmo ready:

Average particle • Select Hydrogen gas. /velocity • Set the Temperature to 300 K.

Introduction: The graph on the right side of the Gizmo represents the MiUB1iandistnbutJój of particle velocities The curve represents the probability of a particle moving atthe velocity shown on the x-axis of the graph. The higher the curve, the greater the probability offinding a particle moving at that velocity will be.

Question: How are particle velocities distributed?

1. Observe: Move the Temperature slider back and forth. This time focus on the graph at right.

What do you notice about the shape of the graph?

2. Analyze: Look at the left side of the graph as you raise the temperature from 50 to 11000 K.

A. Even at the highest temperatures, are there still a few slow particles?

_____________

B. At what temperature do you see the widest variety of particle velocities?

___________

C. In general, is the Maxwell-Boltzmann curve a symmetrical or an asymmetrical curve?

3. Estimate: Because particles have a range of velocities at any given temperature, it is usefulto calculate the average velocity. Physicists express the average velocity in three ways:most probable velocity (va), mean velocity (v), and root mean square velocity (V,ms). -

Set the temperature to 200 K (the selected gas should still be Hydrogen).

A. Estimate the most probable velocity by looking at the peak of the curve. What is your

estimate?

_______________

B. Turn on Show most probable velocity. What is the actual value?

______________

C. Base on the shape of the curve, do you think most of the particles are moving faster

or slower than the most probable velocity?

_______________

(Activity B continued on next page)

.izmos

Activity B (continued from previous page)

4. Predict: The mean velocity is the average velocity of all of the particles. Based on the shapeof the curve and your answer to the previous question, do you expect the mean velocity tobe greater than or less than the most probable velocity? Explain your reasoning.

5. Check: Turn on Show mean velocity. What is the mean velocity?

_____________________

Was your prediction correct?

_____________________

6. Experiment: Try a variety of other gases and temperatures. Is the mean velocity always

greater than the most probable velocity?

___________________________________________

Explain why this is so:

___________________________________________________________

7. Calculate: Turn off Show most probable velocity and Show mean velocity. SelectHydrogen and set the Temperature to 100 K. You can calculate the most probable velocity(va), mean velocity (p), and root mean square velocity (V,ms) using the following formulas:

‘2RT - 8RT 3RTv ysvr=j2rM

In each formula, R stands for the universal gsconstan, or 8.3144 J / K mol, Tstands forKelvin temperature, and M stands for the molar rnas, in kg I mol. Hydrogen gas (H2) has amolar mass of 0.002016 kg I mol.

A. Calculate the most probable velocity (va):

_____________________

B. Check by turning on Show most probable velocity. Were you correct?

C. Calculate the mean velocity ():

_____________________

D. Check by turning on Show mean velocity. Were you correct?

E. Calculate the root mean squared velocity (v,):

_____________________

F. Check by turning on Show root mean square velocity. Were you correct?

_______

izmos

26 Solid,Iiquid,orgasOur world is made of matter. The earth’s crust is solid, the seais liquid, and the air is a mixture of gases. Some matter, suchas rocks and wood, are called solids. They don’t change theirshape. Lemonade and water are called liquids because theyflow easily. If you pour a liquid into a container, it flows to fillup the shape of the container. The surface of the liquid isalways level. Gases, like the air we breathe, spread to fillany space.

Substances remain as solids, liquids, or gases at certaintemperatures. If they are heated or cooled, they change.If you pour water into a container and leave it in the freezer ofa refrigerator, the liquid water changes into a solid, ice. If youheat water until it boils, the liquid water becomes a gas.

These Japanese macaque monkeyshave found a hot, steamypooltobathe in, even though there is snowon the ground. The waterbubbles to

Th the surface of the earth from deepinsidethe earth.

The molecules in ice do not move

around much. They cling together to

form a solid.

‘‘I

V. -

4I

I,

2

The molecules in liquid water move

around freely.

I

1(

,----

(.:-

When water becomes a gas, the

molecules move quickly and

spread out.“-

-7 Z) H

Changes of StateAll solids can become liquids through melting. Melting occurswhen the physical state of a substance is transformed intoanother state. Changes of state occur when the temperatureof the substance changes. The substances as they are heatedwill gain energy and the particles will speed up causing a changeof state.

6 changes of state

gas to liquid sublimation

liquid to gas condensation

liquid to solid sublimation

solid to liquid evaporation

gas to solid melting

solid to gas freezing

Name: Date:

Student Exploration: Phase Changes

VdcabuIai: altitude, boil, boiling point, freeze, freezing point, gas, liquid, melt, melting point,phase, solid

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

1. A family from Minnesota turns off the heat and flies to Florida for a winter holiday. Whenthey come home, all of their water pipes have burst. What do you think happened?

2. Spaghetti takes about 9 minutes to cook at sea level, but about 14 minutes in themountains. Why do you think this is so?

Gizmo Warm-upIn the Phase Changes GizmoTM, select the Micro view andset the Ice volume to 50 cc. Click Play () and observemolecules in the so!14 (ice), liquid (water), and ga (air)phased.

1. In which phase(s) are the molecules held rigidly together?

2. In which phase(s) do the molecules move freely?

3. In which phase(s) are the molecules held in a defined shape?

_______

4. In which phase(s) do the molecules take the shape of their container?

Activity A: Get the Gizmo ready:

Phase changes • Click Reset (ED) and select Macro view.• Set Ice volume to 0 cc.

Question: How is temperature related to phase changes?

1. Predict: Based on your prior knowledge, predict the following:

A. At what temperature will water change from a liquid to a solid (freei)?

________

B. At what temperature will water change from a solid to a liquid (mel])?

_______

C. At what temperature will water change from a liquid to a gas (b1)?

________

2. Investigate: Use the Gizmo to explore phase changes. Use the Water temperature andAddlremove heat energy sliders to control the water temperature. Record yourobservations in your notes, then answer the questions below:

A At what temperature does water freeze’?

_______

This is the freezlngpoinB. At what temperature does ice melt?

_______

This is the meIt1ngpoJj.

C. At what temperature does water boil?

________

This is the boillngpohi.

3. Observe: Set up the Gizmo to observe freezing. What do you notice about the temperature

while the water is in the process of freezing?

_________________________________________

4. Explore: Use the Gizmo to investigate melting and boiling. Does the temperature change as

either of these phase changes is occurring?

_________________________________________

5. Interpret: Select the GRAPH tab to see a graph of temperature vs. time. Click the “—“ buttonuntil the whole graph is visible. What does the graph look like during a phase change?

6. Extend your thinking: Why do you think the temperature does not change much during aphase change? If possible, discuss your answer with your classmates and teacher.

I irnos

Activity B: Get the Gizmo ready: I

Temperature and• Click Reset, and select the Micro view.

molecular motion • Set Ice volume to 0 cc.. Set Addlremove heat energy to 0 J15

Question: Why do phase changes occur?

1. Compare: Set the Water temperature to 0 °C and click Play. Observe the water molecules.Click Reset, set the Water temperature to 100 DC, and click Play again.

What do you notice?

2. Observe: Click Reset. The mean molecular speed of the water molecules is displayedbelow the container. Set the Water temperature to 0 °C and Addlremove heat energy to400 J/s. Click Play.

A. How does the average speed of the water molecules change as they are heated?

B. Does the mean molecular speed change as much as the temperature as thewater heats up? Explain.

3. Explain: How is temperature related to the motions of molecules?

______________________

4. Observe: Click Reset. Set the Water temperature to 20 °C and the Ice volume to 50 cc.Set Add/remove heat energy to 0 JIs. Click Play. How do the molecules in the liquidinteract with the molecules in the solid?

(Activity B continued on next page)

I !fllOS

Activity B (continued from previous page)

5. Observe: Click Reset. Set the Water temperature to 100 °C and the Ice volume to 50 cc.Click Play. How does this situation compare to the previous one?

6. ProDose a theory: Based on what you have observed, explain why you think phase changesoccur. If possible, discuss your theory with your classmates and teacher.

7. Extend your thinking: Click Reset. Set the Water temperature to 0 DC, the Ice volume to 0cc, and Add/remove heat energy to -400 JIs. Click Play and wait until all the water freezes.

A. What volume of ice is created from 200 cc of water?

__________________________

B. Why do water pipes sometimes burst in the winter?

____________________________

umos

Get the Gizmo ready:Extension:. Click Reset.Altitude and• Set Ice volume to 0 cc.phase changes• Set the Altitude to 5,000 meters (16,404 feet).

Question: The aItitiid of a location is its vertical distance above sea level. How doesaltitude affect phase changes?

1. Form a hypothesis: As altitude increases, the air pressure decreases. How do you think thelower pressure will affect the following? (Circle your answers.)

A. Freezing point: Increase Stay the same Decrease

B. Melting point: Increase Stay the same Decrease

C. Boiling point: Increase Stay the same Decrease

2. ExDeriment: Use the Gizmo to find the freezing, melting, and boiling points of water at 5,000meters (16,404 feet). Write these values below.

Freezing point:

________

Melting point:

________

Boiling point:

________

3. Analyze: How did altitude affect the freezing, melting, and boiling points of water?

4. Challenge: Try to explain these results based on the fact that air pressure decreases withaltitude, If possible, discuss your ideas with your classmates and teacher.

5. Apply: Why does pasta take longer to cook in the mountains?

__________________________

6. Apply: A pressure cooker allows food to be cooked under high pressure. Why is this useful?

0

Classification of Matter

-can exist in all 3 states of matter(solid, liquid, and gas)

-contain only one type of particle-contains two or more puresubstances

4-two or more parts canbee seen

- a substance whichcontains only one typeof atom

-a substance whichcontains more thanone type of atom

-appear to be onesubstance

DAFE: NAME:CLASS:

TOPIC I

I SKILL BUILDER i Classifying Pure Substancesand Mixtures

GLM 1-2

Goal • Practise classifying materials as pure substances and mixtures.

scrambled eggssugarrubbing alcoholsiliconbaking sodaaluminum

cooking oilfood colouringmouthwashquartzsulfurcementhelium

fresh-squeezed orange juiceginger aletoothpastesaltsulfuric acidsandblack coffee

ironraisin breadliquid oxgengoldcarbon dioxidecrude oilglucose

What to DoClassify each substance below as a pure substance or a mixture. Then beside each puresubstance identify it as an element or a compound. Beside each mixture identify it as amechanical mixture or a solution.

Element or Mixture orPure substances compound Mixtures Solution

0—-‘ -4

Copyright © 2001, McGraw-Hill Rycrson limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved.46 This page may be reproduced for classroom use by the purchaser of this book without the written permission of the publisher.

Part D: What is a substance?

Fluids usually fit into three categories, depending on what they are made

Pure SubstanceA pure substance is made up of one type of matter (material), behaves in aunique way (nothing else Is exactly the same) and can’t be separated intodifferent substances.

A solution Is made up of two or more different materials but the particlesare so small and they are mixed together so well that it is impossible to seethe different particles, but they could be separated through heatln9 orevaporation.

Use the information above to help you identify whether each of the followingexamples is pure, solution or mechanical mixture. Mark each example as A, B or C.

1.

_____

Orange juice made by mixing frozen coricentrate with water

2.

_____

Distilled water created by treating water to make sure there are noother substances in it

3.

_____

Iced tea made by mixing crystals of tea flavouring and sugar intowater

4. Mouthwash contains a mixture of alcohol and flavouring

5.

______

Olive oil is the natural “juice” of the fruit of an olive tree

6.

_____

Salad dressing made by mixing oil, vinegar and other substances hasto be shaken before it is used because it separates into layers whenleft to stand for a while

7.

_____

Ketchup is made with vinegar, tomato paste, salt, sugar and otheringredients. When you “pinch” ketchup you can feel the Hny lumpsand crystals in it.

of.

A

Solution

C Mechanical MixtureA mechanical mixture is made up of two or more different materials thatcan easily be separated. Depending on the size of the particles, you may ormay not be able to see the different particles In the mixture.

.Copyright Resource Development Serviret, Ia1nIt1r itt I1hlk Si I ink. .jIiI ,i t$ • \ iii.I I I. latter

Complete the following chart by listing examples ofpure substances; mixtures and solutions you can find in WARNING: This activityyour home or school. should be completed with

adult supervision. jHint: Try the following “tests” to help you putsubstances in the right category.

• Check the list of ingredients. Is there more than one?• Let a sample dry overnight. Do parts of the fluid stay and others disappear?• Hold it up to the light. Can you see different particles?• Let it stand overnight. Do the different ingredients separate?

Pure Substances Solution Mixture

Before you continue, read and learn the following definitions:

Solute SolventThe substance that is dissolved (mixed) The fluid that a solute is dissolvedinto a fluid to make a solution (mixed) into to make a solution

Copyright © Resource Development Services, Edmonton Public SchooI 2003. Grade 8 Mix and Flow of Matter

5

What makes Materials bissolve?

Forming a solution by mixing two or more materials together is calleddissolving.

bissolving occurs because of the attraction between particles (there may be astronger attraction to the particles of the same substances).

Solutes and Solvents

The solute is the substance thQt dissolves in a solvent.

The solvent is the substance that dissolves the solute to form asolution.

Solutes and solvents can be gases or liquids.

Examples

Solute Solvent

Water- The Universal Solvent

Water is called the ‘universal solvent because it can dissolveso many materials.

97% of water on Earth is Ocean Water (salt water)2% is frozen

about 0.5% is usable (and even this has materials already dissolved inthat can be harmful).

[solvent

Salty waterIf you stir a spoonfui of ordinary salt crystals into some water,the crystals seem slowly to disappear. The salt has dissolvedin the water. When something is dissolved in a liquid, theresult is called a solution.

The substance that dissolves is called the solute, and theliquid that does the dissolving is called the solvent. Liquidwater is a very good solvent. Try stirring half a teaspoonful ofdifferent solids into a glass of water. You will soon find outwhich substances are soluble, and will dissolve, and whichare insoluble, or cannot dissolve.

•

a.,

_IL__

Usolute

19

In a salt solution, the ions ofsodiumand chlorine are separated andsurrounded by molecules of water.

Why does salt dissolve?What happens to solids like salt crystals when they dissolve?The particles in a solid are fixed firmly together but theparticles in a liquid are free to move around. When salt mixeswith water, the ions of sodium and chloride attract the watermolecules. The molecules surround the ions and separatethem from each other. As more and more ions break free fromthe solid salt, it gradually seems to disappear.

If you put a lot of salt into a little water, there will not beenough water molecules to dissolve the salt ions. You needmore water to dissolve the salt completely. Some solidsubstances will not dissolve. The water molecules can’tseparate the solid’s atoms or ions from each other.

I I

I Isolution

• V V- • i .4 - -

• -1 •-— -. V ( 4

0 1What will dissolve?Consider: Will all white powders dissolve in water?

Hypothesis: (check the one you agree with)

D all white powders will dissolve in water

D only certain white powders will dissolve in water

Materials:

1/2 cup (each) of baking soda, flour, sugar, salt and talc (babypowder)

4 clear containers and spoons (or other utensils) and a supply of waterProcedure: (record information in the chart below)

1. Begin by predicting which powders you think will dissolve in water.2. Stir each powder (in turn) into a clean sample of water (at least icup).3. Stir until the powder dissolves (if it will) and then watch for 1 minute.

iPowder:________ Powder.________ Powder________ Powder- Powder________Prediction: Prediction: Prediction: Prediction: Prediction:

yes/no yes/no yes/no yes/no yes/no

2. Now, answer the original question using evidence from your investigation OR prove whyyour hypothesis was correct.

Copyright © Resource 1)eveloprnent Services, Edmonton Public Schools, 2003. Grade 8 • Mix and Flow of Matter

6

V I

Analysis/Conclusion:

1. What seemed to have an effect on whether or not the powder would dissolve? Explain.

The Rate of bissolvingThe speed at which the solute dissolves in a solvent is calledthe rate of dissolving and can be affected by:

• Agitation (stirring or shaking),• Temperature• pressure.

dissolving simulator

____

i

_______________

How fast will it dissolve?Consider: Does solvent temperature affect the rate (speed) of dissolving?Hypothesis: (check the one you agree with)

D increasing solvent temperature will increase the rate at which solute dissolves0 increasing solvent temperature will decrease the rate at which solute dissolves0 increasing solvent temperature will not affect the rate at which solute dissolves

Materials:

• clear container and spoon (or other utensil) and a supply of water• kettle• stopwatch (or clock with a seconds hand)

Procedure: (record information in the chart below)1. Stir 4 spoonfuls of salt into a clear sample of room temperature water (2 cups) whiletiming how long it takes for the crystals to dissolve (disappear).2. Stir 4 spoonfuls of salt into a clear sample of warm (halfway to boiling) water (2 cups)while timing how long it takes for the crystals to dissolve (disappear).3. Stir 4 spoonfuls of salt into a beaker of boiling water (2 cups) while timing how long ittakes for the crystals to dissolve (disappear)

Solvent temperature: Solvent temperature: Solvent temperature:j hot/warm/cold hot/warm/cold hot/warm/cold

._____________________

Analysis/Conclusion:

Answer the original question using evidence from your investigation OR prove why yourhypothesis was correct.

Challengel

Concentration is a word used to describe how much of asolute is in a solution. If you were to continue stirring saltinto each of your solutions, which ones do you think wouldbe able to get a higher concentration (more saltdissolved)? Make a prediction OR continue with your I predict/have proven that:experiment and find out for sure.

Copyright © Resource Development Services, Edmonton Public Schools, 2003. Grade 8 • Mix and [low of Matter7

How much can be dissolved?The limit to concentration is called solubility.

A

_____________

solution is one in which no more solutewill be dissolved in a specific amount of solvent at aspecific temperature.

An

______________

solution is one in which more solute can be dissolvedin a specific solution at the same specific temperature. (see solubilitychart p. 20).

Using the particle model of matter, the attractive forces between theparticles become balanced and no more particles can be attracted bythe particles of the solvent.

Beyond the Limit: Supersaturated solutionsit is possible to pass the saturation limit in somesolutions.

A solution that contains more solute than it normallywould at a certain temperature is a

______________________________

the solvent is key to make more

__________

dissolve in the solution.

If a substance is considered to be

__________,

it meansthat it will not dissolve with a particular solvent.

DATE: \AME:(ThiSS:

[ToPic 2

SKILL BIJILOER i Solubility and ConcentrationBLM 1-4

Goal • Practise your graphing skills, and demonstrate your understanding of solubility.

What to DoAnswer the following questions in the space provided.

1. Make a line graph using the data in the table below. Give your graph a title. Provide alegend to identify the three substances represented by the three lines.

0 20 40 60 80 100Temperature (°C)

Legend

LJ

0

.

Solubility (gIlOO g water) atSubstance0°C 20°C 40°C 60°C 80°C 100°C

copper sulfate 15 20 30 40 55 79lithium sulfate 35 35 33 31 30 29ammonium chloride 30 38 45 55 65 78

2. Answer the following questions using the data in the graph and the table.(a) Which substance has the greatest solubility at 0°C?

(b) Which substance has the greatest solubility at 100°C?

(c) Which substance decreases in solubility as its temperature increases?__________________(d) Which solutions are saturated at 60°C, with 40 g dissolved in 100 g of water?

D

d

100

a)

Ca 80

600)

4o

0Cl) 20

(e) ‘Which solution is the least saturated at 0°C, with only 2 g dissolved?

Copyright © 2001, McGraw-Hill Ryerson Limited, a Subsidiary of the McGraw-Hill Companies. All rights reserved.48 This page may be reproduced for classroom use by the purchaser of this hook without the written permission of the publisher.