Name: Shashwath Murthy

Physical and chemical changes lab II

Background information: When a physical change occurs only the form of the substance changes, not its actual composition. For example, when water boils and becomes steam, it is still water-just in a different state. Chemical changes, however, result in the formation of new substances with different properties. Some general signs of a chemical change include a change of color or odor, the formation of a precipitate (solid), the formation of a gas, and a change in heat or light. In this lab you will perform different activities and based on your observations determine whether a chemical or physical change has taken place.

Purpose: To determine how physical changes differ from chemical changes.

Pre-lab questions:

1. Complete this table:

Definition Example

Physical PropertyA property that can be observed without a chemical reaction Hardness

Chemical Property A property that can only be observed with a chemical reaction  Oxidation

Physical Change  A change that creates no new substances  Evaporation

Chemical Change  A change that creates new substances  Sodium and Water

2. What are the signs of a chemical change that you might observe in this lab?

Heat, Light, and byproducts (solid, liquid and gas)

3. What are two safety precautions you should take in this lab?

Do not look directly at the flame, and wear gloves when handling the chemicals

Safety: Take care not to look directly at the burning magnesium. Do not inhale the fumes! The HCl is corrosive. Handle it with extreme care. Safety goggles must be worn for this lab.

Procedure:Perform each of the following activities and carefully observe what happens. After each activity, record your observations in your data table.

*The teacher will demonstrate the first three procedures.*

1. Magnesium + Water – Drop the 1-cm strip of magnesium into the a few milliliters of water in a test tube.

2. Magnesium + HCl – Put 10-12 drops of 6M hydrochloric acid (HCl) in a clean test tube. HCl is corrosive and can cause severe injury. Handle with care. Put the 1-cm piece of magnesium in the test tube with the acid.

3. Burning Magnesium – Light the Bunsen burner. Grasp one end of the 3-cm piece of magnesium with the crucible tongs. Hold the strip in the flame until the magnesium ignites, then pull it out of the flame. DO NOT LOOK DIRECTLY AT THE BURNING MAGNESIUM. ITS FLAME IS VERY BRIGHT AND CAN DAMAGE YOUR EYES. DO NOT INHALE THE FUMES THAT ARE GIVEN OFF.

4. Crushing chalk – Use a mortar and pestle to crush a piece of chalk.5. Mixing crushed chalk with vinegar – In a well in the well plate, mix a small amount of the crushed chalk from

Activity #2 with vinegar.

Name: Shashwath Murthy

6. Mixing crushed chalk with water – In a well in the well plate, mix a small amount of the crushed chalk from Activity #2 with water.

7. Mixing AgNO3 and NaOH solutions – In a well in the well plate, combine 10 drops each of the silver nitrate and sodium hydroxide solutions.

8. Mixing AgNO3 and NaI solutions – In a well in the well plate, combine 10 drops each of the silver nitrate and sodium iodide solutions.

9. Mixing PbNO3 and NaI solutions – In a well in the well plate, combine 10 drops each of the lead (II) nitrate and sodium iodide solutions.

10. Mixing NaOH and NaI solutions – In a well in the well plate, combine 10 drops each of the sodium hydroxide and sodium iodide solutions.

Wash and dry the equipment that you used. Wash your hands thoroughly.

Data table:Activity title Chemical or physical change Evidence/observationsMg+H2O Chemical Gases formedMg+ HCL Chemical Gases formedBurning Mg Chemical Gases forms, Heat and light generatedCrushing Chalk Physical No new substances formedChalk + Vinegar Chemical Gases formedChalk + H2O Physical No new substances formedAgNO3 + NaOH Chemical Chemical Change, New substance (brown and non-

transparent)AgNO3 + NaI Chemical Chemical Change, New substance (Yellow white

and thick)PbNO3 + NaI Chemical Change, in new substance (Mustard yellow,

opaque)NaOH + NaI Physical No new substances formed

Post-lab questions:1. State in your own words the Law of Conservation of Mass.

2. Although mass is always conserved in a chemical reaction, none of the chemical reactions in this experiment would have demonstrated this law because of the way in which they were done. Can you explain why?

Conclusion: On a separate piece of paper, write a concise conclusion as a group using the prompts below. Discuss the following in paragraph format. Write this in the third person- this means you should refrain from saying I or we. Instead refer to the data or what was observed.

Restate the purpose on this lab. Summarize the results of the activities. Which were chemical changes/Which were physical changes? How could

you tell the difference between each?