Due on Saturday 26th Feb Study material is attached for Data & Results assignment. We can identify what something is through ob

Experiment 3 PROPERTIES AND CHANGES OF MATTER

Data Collection and Results Pages Name: __________________________ Date: ___________________

Observation

Type of Change (Physical or Chemical)

Reason(s) (for deciding the type of change)

I2 + heat

Mg + heat

Color, odor, and crystal structure of CaCl2

Color, odor, and crystal structure of CaCO3

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CaCl2 + H2O

CaCO3 + H2O

CaCl2 + 15% HCl

CaCO3 + 15% HCl

Mixture + H2O

Substance A (product after evaporation of water)

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(continued next page)

Residue + 15% HCl

Substance B (after evaporation of acid solution)

Substance A + 15% HCl

Substance B + 15% HCl

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Substance Identity (CaCl2 or CaCO3 ?)

Step 8 – Filtrate

Step 8 – Residue

Step 17 – Substance A

Step 17 – Substance B

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Purpose: To investigate physical and chemical properties and changes of various substances. Introduction Physical and Chemical Properties: A property is a characteristic of an object, living organism, or substance. Chemists often use the properties of an unknown substance to help determine its identity. And, when a new substance is discovered, its properties are carefully determined and reported to the scientific community. In chemistry, we are concerned with two types of properties—physical properties and chemical properties. Any characteristic of a substance that can be determined without changing the chemical composition of the substance is called a physical property. For instance, we can observe that the element mercury is a shiny silver liquid under normal room conditions without changing the mercury into some other substance. This means that shine (luster), color, and physical state (solid, liquid, or gas) must all be physical properties because we can observe them without changing the chemical composition of a substance. A chemical property, on the other hand, is a characteristic that can only be observed by allowing a substance to interact with something else. For instance, if a sample of mercury is heated in an oxygen atmosphere, it changes from a shiny silver liquid into a red solid. The fact that mercury reacts with oxygen is a chemical property of mercury. On the other hand, if there was no reaction with the oxygen, we would have been able to say that one of the chemical properties of mercury is that it is not combustible. Physical and Chemical Changes: A chemical substance can generally undergo two types of changes—one that does not alter its chemical composition and one that does. The change that does not alter the chemical composition is called a physical change while the change that results in a change in the chemical composition is called a chemical change (or chemical reaction). It is important to be able to distinguish between the two types of changes. A physical change, for example, could be any of the following:

• a change in size only (such as tearing a piece of paper in two or crushing a piece of chalk into powder),

• a change in concentration only (such as adding more water to a cup of black coffee), • a change in physical state only (such as melting a solid to a liquid which is known as

fusion; vaporizing a liquid to a gas which is known as vaporization; subliming a solid to a gas which is known as sublimation; depositing a gas to a solid which is known as deposition; or dissolving a sample in a solvent which is known as solubility). In terms of solubility, if a substance dissolves in another substance, the substance that is dissolved is said to be soluble and if the substance does not dissolve, it is said to be insoluble.

In contrast, a chemical change involves a change in the chemical composition of a substance. This may be accompanied by a change in physical state as well, and sometimes it is difficult to decide whether it is strictly a chemical or physical change. If the change does not fall in one of the three categories of physical change described above, it is likely to be a chemical change. The following are signs that indicate a chemical change has very likely taken place when a substance comes in contact with another substance:

• The color of the substance changes.

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• A substance is burning. • An evolution of a gas (effervescence) is observed even though no external heat has

been added. For example, compounds that contain the carbonate group (CO32-) such as CaCO3, give off carbon dioxide gas when they are mixed with acids. If evolution of a gas is observed only after a substance is heated, the substance may only be undergoing a physical change. (e.g. H2O(l) → H2O(g))

• A solid substance (called a precipitate) forms when two solutions are mixed. • Detection of a change in temperature of a substance may indicate a chemical reaction

has taken place but this is not definitive, as some physical changes could also be accompanied by a change in temperature. For example, dilution of a concentrated acid usually causes the temperature of the solution to increase. This is considered a physical rather than a chemical change.

It is important to keep in mind that mixing different substances together does not always lead to a chemical reaction. Also, it is possible for a chemical reaction to take place without any easily observable change being detected. In addition, the distinction between physical and chemical change is not always clear. Chemists often use the properties and changes/reactions of a substance to separate and identify the components of a mixture. Some mixtures can be separated by simple physical means such as decantation, filtration, distillation, and chromatography. Separation by physical means involves utilizing differences in physical properties, and the process does not involve a chemical change. The samples obtained after a physical means of separation have the same chemical formulas and properties as those of the components in the mixture before the separation. For example, NaCl dissolved in H2O

!"#$%$&"! !" !"#$"%%&$"'( NaCl(s) + H2O(l)

But the elements that make up a compound can be separated from each other only by chemical means. For example, separation of H2O into hydrogen and oxygen or the separation of NaCl into sodium and chlorine involves a chemical change. And, the products have different chemical formulas and properties from those of the individual compounds that separate. For example, 2NaCl(s)

!!!"#$%& !"#$% 2Na(s) + Cl2(g)

In this experiment, you will investigate various properties and changes of known substances and then you will use the knowledge gained to help you determine the identity of an unknown substance. Equipment/Materials Magnesium strip (~1 inch), lab burner, 400-mL beaker, iodine crystals (I2), evaporating dish, ice, hot plate, solid calcium chloride, solid calcium carbonate, a mixture of solid calcium chloride and solid calcium carbonate, 15% hydrochloric acid, 250-mL beaker, test tubes (~3-

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4 inch), 100-mL or 150-mL beaker, 50-mL beaker, 10-mL graduated cylinder, plastic disposable pipets, glass stirring rod, watch glass, ring stand, iron ring, filter funnel, filter paper, wire gauze, lab burner, wash-bottle with deionized water, magnifying glass, and scoopula. Procedure (Using a pen or pencil, record by hand all of your data and results on the Data Collection and Results Pages.)

I. Changes of Substances

1. Observe the changes taking place with the iodine in the set-up shown in Figure 3.1. The set-up consists of a large beaker containing some iodine crystals on a hot plate and covered with an evaporating dish containing a few ice cubes. The set-up will be located in the fume hood or in a corner in the lab. Locate the set-up and carefully observe and record the type of change, if any, taking place in the beaker. Figure 3.1

2. Next, set up a lab burner. This can be set up in the fume hood or in front of the fume hood (if your exhaust system is on the benches). If your lab is not equipped with fume hoods, set up the burner at your workstation.

3. Obtain about a 1 inch piece of magnesium metal. Warning: Magnesium burns with

a blinding white light. Shield your eyes. Do NOT look directly at the flame. Use a pair of crucible tongs to hold one end of the piece of magnesium metal and place the other end into the flame Remove the metal from the flame once it starts to burn. Carefully observe and record the type of change, if any, taking place with the metal.

II. Separation of a Mixture 1. Observe and record the color, texture, and odor of solid calcium chloride and solid

calcium carbonate.

ice chips evaporating dish

iodine crystals hotplate

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2. Take two clean test tubes and label one as calcium chloride and the other as calcium carbonate. Into the tube labeled calcium chloride, place a small spatula full of calcium chloride and into the other test tube, place the same amount of calcium carbonate. Then add 1-2 mL deionized water to each test tube. Swirl each tube and carefully observe and record what you see.

3. Take two clean test tubes and label them as in Step 2 above. Place a small spatula- full of calcium chloride into the tube marked calcium chloride and into the other test tube, place the same amount of calcium carbonate. Then add 1-2 mL of 15% HCl solution to each test tube. Swirl each tube and carefully observe and record what you see.

4. Obtain a vial containing a mixture of solid calcium chloride and calcium carbonate

from your instructor or weigh out about 2 grams of the mixture of calcium chloride and calcium carbonate provided. Transfer the entire mixture into a 50-mL beaker.

5. Measure out approximately 10 mL of deionized water with your 10-mL graduated cylinder and add it to the beaker. Stir the mixture thoroughly with a clean glass stirring rod and grind any lumps that you may find into fine grains. Do not use your metal scoopula as traces of the metal from it could affect the outcome of this experiment. Note what happens to the sample. Set the mixture aside.

6. Set up a gravity-filtration apparatus (as shown in Figure 3.2 below) in the fume hood

or directly in front of the fume hood if the exhaust system is on the benches. If your lab is not equipped with fume hoods, set up the filtration apparatus at your workstation. Place a clean 100- or 150-mL beaker under the funnel. As shown in the figure, also set up an iron ring, on top of which is placed a wire gauze. Place a lab burner under the iron ring, but do not light it (until you get to Step 10).

Figure 3.2

7. Place a piece of filter paper snugly in the long-stem funnel, and with a wash-bottle of deionized water, wet the sides of the filter paper to form a tight seal to the funnel.

iron ring

wire gauze

lab burner

100-mL or 150-mL beaker

long-stem funnel iron ring

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8. With your glass rod, stir the contents of the 50-mL beaker containing your mixture from Step 5, and before the solid settles to the bottom, pour the mixture onto the filter paper in the funnel. Make sure the mixture goes only into the center of the paper cone and the liquid level never overflows beyond the top of the filter paper. If it overflows you will end up with some of the solid seeping around the edges of the paper into the beaker below. You do not want that to happen! Use the glass stirring rod to help transfer as much of the solid as possible onto the filter paper but be careful not to poke a hole in the filter paper. The liquid coming through the filter paper is called the filtrate and the material left on the filter paper is called the residue. Write the letter “A” on the 100- or 150-mL beaker containing the filtrate.

9. After the filtration is complete, light the lab burner and adjust the air vents to get a

very hot flame. Place the burner under the wire gauze. The tip of the blue cone of the flame should be touching the bottom of the wire gauze. (Instructions for lighting the burner are given below. Your instructor might also demonstrate how it is done.)

10. Take the 100- or 150-mL beaker (labeled A) containing the filtrate and place it on

the wire gauze. Hold the base of the lighted burner and place it under the beaker sitting on the wire gauze. Place a clean 250-mL beaker under the funnel at the filtration setup and leave it there for later.

11. Allow the water to boil off the filtrate. Removal of the water will take about 10

minutes. Keep an eye on the progress. If you see a discoloration, you are overheating and you should lower the flame. When all the water has evaporated, turn off the gas (at the gas valve), carefully observe the contents of the beaker and record your observation. Then allow the beaker and its content to cool to room temperature and then set it aside. DO NOT WASH THIS OUT YET!

12. Clean your 50-mL beaker that was used earlier, wipe it dry and measure out 10 mL

of 15% HCl (from the large stock bottles, not the dropper bottles) and add it to the 50-mL beaker.

13. Check to see that the 250-mL beaker is in place under the funnel. With a plastic disposable pipet, add the HCl solution (from the 50-mL beaker) dropwise onto the solid residue on the filter paper and carefully observe and record what occurs. Continue to do this until you have used up all of the HCl solution. (Note: The residue that was left on the filter paper in Step 9 above should have reacted with the HCl that you added and the resulting solution dripped into the 250-mL beaker.)

14. After almost all of the HCl solution has drained through the filter paper (should not

CAUTION! HCl is corrosive to the eyes, skin, and mucous membranes. Avoid inhalation of the fumes and skin contact with the solution. Remember to keep your goggles on at all times. If you spill the acid on yourself, wash it off immediately. Then apply baking soda (NaHCO3) on the area where you contacted the HCl. Notify your instructor immediately.

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CAUTION! In this step, the heat will initially be boiling off the water, but near the end it is also going to boil off the HCl. Do not allow the vapors to come in contact with your eyes or skin. Do not breathe in the vapors.

be more than 10 minutes), remove the 250-mL beaker and place a watch glass under the funnel to catch any drops that may come through later. You do not want HCl dripping onto the iron stand as it will eat into the metal.

15. Place the 250-mL beaker with its contents on the wire gauze, light the burner as you did before and place it under the 250-mL beaker on the wire gauze. Evaporate off the water from this second filtrate as before. Keep an eye on the progress. If you see a discoloration, you are overheating.

16. Carefully observe the contents of the 250-mL beaker and record your observations. When the beaker has cooled down, label it as “B.” DO NOT WASH IT OUT YET.

17. Analysis of the two substances A and B: i) Take the beaker labeled A and the beaker labeled B, each with the solid left after

evaporation of the liquid in each. With a clean and dry scoopula or spatula obtain a small sample (size of a match head) of Substance A and transfer it to a small test tube labeled as “A”. Clean and dry your scoopula or spatula and place a small sample of Substance B in a test tube labeled as “B.”

ii) Add 10 drops of 15% HCl to each of the two test tubes and mix as before. Carefully observe and record what happens to each solid. (Note: A small amount of effervescence can be due to contamination and is not to be considered a positive result.)

18. Identify the filtrate A and the residue from Step 8 and Substances A and B from

Step 17.

Clean-up 1. Discard solid waste and excess HCl in the special waste containers. (Check with

your instructor to be sure.) All other chemicals may be discarded in the sink. 2. Remove all labels from your glassware. 3. Wash all non-disposable glassware with brushes provided at the sink under

running tap water and then rinse them with deionized water. Shake out excess water and wipe the outside dry with paper towels.

4. Wipe off your work area. 5. Wipe off and return the safety goggles to the cabinet (or place it in your drawer if

it belongs to you). Note that once you put away your safety goggles, you must leave the lab. Remember to wash your hands before leaving.

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