5. conservation of matter€¦ · web viewd. law of conservation of matter. key term challenge....

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5. Conservation of Matter

Driving QuestionsEarly chemists determined that matter is composed of fundamental particles (atoms) which could not be created or destroyed, only changed into different forms. After much experimentation, evidence eventually confirmed this law of conservation of matter. Some experimentation produced a change in mass. How can this change in mass be explained? Does the law of conservation of mass hold true for both physical and chemical changes?

BackgroundMatter can change its appearance. Sometimes this is the result of a physical change, such as when ice melts into liquid water or when liquid water becomes steam. During physical changes the molecules making up the substance may speed up, slow down, spread out, or be compressed together, but the molecules themselves remain unchanged. In the case of ice, liquid water, and steam, all of the molecules are H2O.

In a chemical change, the atoms making up the molecules rearrange to form new molecules of a different substance. Water (H2O) is formed when molecules of hydrogen (H2) and oxygen (O2), two completely different substances, react to produce a new substance, H2O.

The law of conservation of matter states that matter cannot be created out of nothing or be destroyed and disappear; matter can only change form. The number of atoms there are before a change must be the same as the number of atoms there are after the change.

In cases where reactants form a product that is a gas, the gas may escape from the reaction to the atmosphere. This happens if the system is “open.” If the system is "closed," gas is unable to escape because the reaction is sealed off from its surroundings.

Materials and Equipment

For each student or group:

Balance 0.1 M Sodium sulfate (Na2SO4), 5 mL

Test tube (2), 15-mm x 100-mm 0.1 M Strontium chloride (SrCl2), 5 mL

Beaker, 250-mL Sodium bicarbonate (NaHCO3), 8 g

Plastic soda bottle (with cap), 500-mL 5% Acetic acid (HC2H3O2), 30 mL

Sodium nitrate (NaNO3), 5 g Distilled (deionized) water, 10 mL

SafetyFollow all standard laboratory procedures.

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Conservation of Matter

Sequencing ChallengeThe steps below are part of the Procedure for this lab activity. They are not in the right order. Determine the proper order and write numbers in the circles that put the steps in the correct sequence.

ProcedureAfter you complete a step (or answer a question), place a check mark in the box () next to that step.

Collect Data

Part 1 – Sodium Sulfate Solution and Strontium Chloride Solution

1. Place 5.0 mL of sodium sulfate solution (Na2SO4) into a test tube, and place the test tube in a 250-mL beaker.

2. Place 5.0 mL of strontium chloride solution (SrCl2) into another test tube, and place it in the 250-mL beaker with the other test tube containing Na2SO4.

3. Determine the total mass of the solutions, test tubes, and beaker by placing them on a balance. Record this initial mass below.

Initial mass of Na2SO4, SrCl2, and glassware (g): ______________________________

4. Predict the amount of product that is produced from these reactants.

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5. Carefully pour the strontium chloride solution and the sodium sulfate solution into the beaker. Observe the chemical reaction and record your observations below.

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6. How do you know a chemical reaction took place?

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Determine the total mass of the starting substances and the glassware they are contained within.

Measure the starting substances and place in them into a 250-mL beaker.

Compare the mass and of the starting substances and the ending substances.

Mix the starting substances and record any observations.

Measure the mass all of the final substances and glassware.

Student Inquiry Worksheet___________________________________________________________________________________________

7. Place both test tubes back inside the beaker and measure the mass of the test tubes, beaker, and solution again. Record the final mass below.

Final mass of Na2SO4, SrCl2, and glassware (g):

______________________________

8. Why is it important to measure the mass of all the glassware together after the reaction occurs?

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9. Dispose of the solutions according to your teacher’s instructions and then clean your glassware so that it may be used in the next part of this investigation.

Part 2 – Dissolving of Sodium Nitrate

10. Place approximately 5 g of solid sodium nitrate (NaNO3) into a 250-mL beaker.

11. Place 10 mL of distilled water into a test tube, and place the test tube inside the 250-mL beaker containing the 5 g of NaNO3(s).

12. Determine the total mass of the water, test tube, NaNO3(s), and beaker by placing them on the balance. Record this initial mass below.

Initial mass of NaNO3, H2O, and glassware (g):

______________________________


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14. Pour the water into the beaker with the solid and swirl the mixture until all of the solid dissolves. Record your observations below.

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15. Does a chemical reaction take place? Explain your reasoning.

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16. Place the test tube back inside the beaker and measure the mass of the test tube, beaker, and solution again. Record the final mass below.

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Final mass of NaNO3, H2O, and glassware (g): ______________________________

17. Dispose of the solutions according to your teacher’s instructions and then clean your glassware so that it may be used in the next part of this investigation.

Part 3 – Sodium Bicarbonate and Acetic Acid (Open System)

18. Place approximately 5 g of solid sodium bicarbonate (NaHCO3) into a 250-mL beaker.

19. Pour 10 mL of 5% acetic acid (HC2H3O2) into one test tube and an additional 10 mL into a second test tube. Place both test tubes inside the 250-mL beaker containing the NaHCO3(s).

20. Determine the total mass of the HC2H3O2, test tubes, NaHCO3(s), and beaker by placing them on the balance. Record this initial mass below.

Initial mass of NaHCO3, HC2H3O2, and glassware (g):

______________________________


___________________________________________________________________________________________

___________________________________________________________________________________________

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22. Pour the acetic acid from one of the test tubes into the beaker with the solid and swirl the mixture until the reaction subsides.

23. Pour the acetic acid from the second test tube and swirl the mixture until the reaction stops. Record your observations below.

___________________________________________________________________________________________

24. Does a chemical reaction occur? Explain.

___________________________________________________________________________________________

25. Place the test tubes back inside the beaker and measure the mass of the test tubes, beaker, and solution again. Record the final mass below.

Final mass of NaHCO3, HC2H3O2, and glassware (g):

______________________________

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Student Inquiry Worksheet26. Dispose of the solutions according to your teacher’s instructions and then clean

your glassware so that it may be used in the final part of the experiment.

Part 4 – Sodium Bicarbonate and Acetic Acid (Closed System)

27. Place approximately 3 g of solid sodium bicarbonate (NaHCO3) in a clean 500-mL plastic soda bottle.

28. Pour 10 mL of 5% acetic acid (HC2H3O2) into a test tube.

29. Carefully slide the test tube inside the plastic bottle containing the NaHCO3(s), making sure not to spill any of the acetic acid.

30. Screw on the cap of the plastic bottle tightly.

31. While still being careful not to spill the acetic acid, place the bottle and its contents on a balance. Record this initial mass below.

Initial mass of the soda bottle and its contents (g):

______________________________

32. Why must you be careful not to spill the acetic acid at this point in the experiment?

___________________________________________________________________________________________

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33. Gently tip the bottle until the test tube inside spills the acetic acid into the sodium bicarbonate. Record your observations below.

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34. Once the reaction is complete, and without unscrewing the cap, measure the mass of the bottle and its contents. Record the mass below.

Final mass of the closed soda bottle and its contents (g):

____________________________

35. Remove the cap from the bottle and allow the gas to escape.

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Conservation of Matter36. Why did the pressure inside the bottle increase?

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37. Compared with the mass of the bottle and its contents before unscrewing the cap, do you expect the mass to be greater, less, or the same after the gas escapes?

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38. Screw on the cap and measure the mass of the bottle and its contents. Record the final mass below.

Final mass of the open soda bottle and its contents (g):

_____________________________

39. Dispose of the solutions and clean up according to your teacher’s instructions.

Data Analysis

1. Determine the change in mass for each process. Record the results in Table 1 below.

Table 1: Initial mass, final mass, and change in mass

ExperimentInitial Mass (g)

Final Mass (g)

Change in Mass (g)

Part 1: Na2SO4 + SrCl2

Part 2: Dissolving NaNO3

Part 3: NaHCO3 + HC2H3O2 (open system)

Part 4: NaHCO3 + HC2H3O2 (closed system before opening the bottle)

Part 4: NaHCO3 + HC2H3O2 (closed system after opening the bottle)

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Student Inquiry Worksheet2. How many grams of gas (CO2) were formed in part 3 and part 4 of this

investigation? How do you know?

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3. Calculate the percent change in mass for each part of the experiment and record them in Table 2.

Table 2: Percent change in mass

Experiment Show Your Work Here Percent Change in Mass

Part 1: Na2SO4 + SrCl2

Part 2: Dissolving NaNO3

Part 3: NaHCO3 + HC2H3O2 (open system)

Part 4: NaHCO3 + HC2H3O2 (closed system before opening the bottle)

Part 4: NaHCO3 + HC2H3O2 (closed system after opening the bottle)

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Analysis Questions

1. Why is the percent change in mass not always exactly 0%?

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2. What happens to the mass in part 3 and the second part of 4? Is this a case where the law of conservation of matter is untrue? Explain.

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3. Do your results confirm the law of conservation of matter? Why or why not?

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4. Does the law of conservation of matter apply to both physical and chemical changes?

___________________________________________________________________________________________

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Student Inquiry Worksheet

Synthesis QuestionsUse available resources to help you answer the following questions.

1. In the process of electrolysis, electricity is used to convert water into its gaseous elements, hydrogen (H2) and oxygen (O2): 2H2O(l) → 2H2(g) + O2(g). If electrolysis is performed using 30 grams of water, how many grams of gas are produced?

___________________________________________________________________________________________

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2. Pyrite is a shiny yellow mineral also known as “fool’s gold.” It is composed of iron and sulfur. If a 36.4 gram sample of pyrite is broken down into its elemental components and 17.3 grams of iron are produced, how many grams of sulfur are produced?

___________________________________________________________________________________________

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3. When a log burns, the resulting ash has less mass than the log. Why does this loss of mass not violate the law of conservation of matter?

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Multiple Choice QuestionsSelect the best answer or completion to each of the questions or incomplete statements below.

1. In a chemical reaction how does the mass of the products compare with the mass of the reactants?

A. Greater than B. Less than C. Equal toD. Depends on if the reaction is endothermic or exothermic

2. If 7 grams of sodium (Na) reacts with 12 g of chlorine (Cl2), how much table salt (sodium chloride, NaCl) is produced?

A. 5 gramsB. 13 gramsC. 19 gramsD. 26 grams

3. What is the mass of the resulting gas when 3 grams of dry ice (solid carbon dioxide, CO2) sublimes to gaseous CO2?

A. 0 gramsB. 2 gramsC. 3 gramsD. 5 grams

4. During a chemical reaction how does the total number of atoms of the reactants compare with the total number of atoms of the products?

A. Equal toB. Greater than C. Less thanD. Depends on the type of reaction

5. Which of the following states that matter cannot be created or destroyed?

A. Kinetic molecular theoryB. Collision theory C. Atomic theoryD. Law of conservation of matter

Key Term ChallengeFill in the blanks from the list of words in the Key Term Challenge Word Bank.

1. The ________________________ states that ____________ cannot be created or destroyed, only changed in form. This means that any atoms present at the beginning of a reaction must also be present at the end of the reaction. The ____________ of atoms can be

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Student Inquiry Worksheet

counted in the laboratory by using a ____________ and measuring the ____________ of the reactants and the products. The mass before a change and after a change is ____________.

2. During ____________ changes atoms do not rearrange to form new substances even though the ____________ of the substance changes. An example is ice melting into liquid water. During ____________ changes the atoms do rearrange to form new substances. If any of these new substances are gaseous, they may escape from a reaction. This occurs in ____________ systems. ____________ systems seal reactions from their surroundings so that gaseous products can be trapped and measured.

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Key Term Challenge Word BankParagraph 1 Paragraph 2atomic theory

Avagadro’s law

balance

chemical reaction

kinetic molecular theory

larger

law of conservation of matter

mass

matter

number

size

smaller

the same

thermometer

types

volume

appearance

atoms

chemical

closed

large

molecules

open

physical

small

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5. conservation of matter€¦ · web viewd. law of conservation of matter. key term challenge....

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