Physical and Chemical Changes



Physical and Chemical Changes Lab

Purpose

In this lab you will investigate the criteria used to distinguish between physical and chemical properties and changes in matter. Your eyes are powerful tools for studying chemistry. Many of the properties of matter and the changes it undergoes can be easily determined through careful observation. In this experiment, you will observe various materials and describe their physical properties. Some of the materials will undergo changes. Based upon your observations, you will determine whether the changes are physical or chemical.

Materials

safety goggles 2 magnesium ribbons (5-cm and 1 cm strip)

magnet 6M hydrochloric acid (HCl)

test tubes salt (NaCl)

water sand (SiO2)

Bunsen burner sodium bicarbonate (NaHCO3)

tongs 0.1M silver nitrate (AgNO3)

watch glass 0.1M sodium chloride (NaCl)

1 long piece of exposed film iron (Fe)

100-mL beaker sulfur (S)

funnel

ring stand

ring clamp

filter paper

evaporating dish

hot plate

test tube holder

Safety

1. Wear safety goggles at all times.

2. Do not look directly at the burning magnesium. View the reaction through exposed pieces of film. Do not inhale the smoke produced when the magnesium burns.

3. Hydrochloric acid (HCl) is very corrosive and can cause burns.

Procedure

Before you begin any individual part of the experiment you should make observations as to the physical properties of your starting materials and record your observations in the table provided. Matter has both physical and chemical properties. A physical property is a quality or condition of a substance that can be observed or measured without changing the composition of the substance. Physical properties include: color, odor, density, solubility, texture, shape, size, volume, mass, weight, and the state of matter.

Part A – Magnesium (Mg)

1. Position a watch glass near the gas burner. Using tongs, grasp one end of a 5-cm strip of Mg ribbon and hold it in the burner flame until the Mg ignites. Quickly position the burning Mg so that the combustion products fall on a watch glass.

2. Compare the appearance of this product with that of the original Mg ribbon.

3. Place an unburned 1-cm strip of Mg and the burned combustion product (ash) into two separate test tubes. Add 5 drops of 6M HCl (hydrochloric acid) to each tube.

4. Carefully feel the bottom of each test tube. Record your observations.

Part B – Salt and Sand (done as a class together)

1. Mix a spatula full of sodium chloride and sand on a clean paper towel.

2. Transfer the mixture to a clean 100-mL beaker. Add about 30 mL of tap water and stir. Record your observations.

3. Put a new filter into the filtration apparatus and filter the mixture. Record your observations.

4. Pour about 10 mL of the filtrate (what passed through the filter) into an evaporating dish. Gently heat the dish on a hot plate until the filtrate has completely evaporated.

5. Examine both the dry residue in the evaporating dish and the wet residue left on the filter paper and record your observations.

Part C – Sodium Bicarbonate

1. Transfer a small spatula full of the sodium bicarbonate (NaHCO3 aka baking soda) sample to a test tube. Carefully add 5 drops of 6M HCl.

2. Touch the bottom of the test tube with your hand and record your observations.

Part D – Silver Nitrate

1. Add 3-4 drops of 0.1M AgNO3 (silver nitrate solution) into a microwell.

2. Add a few drops of 0.2M NaCl (sodium chloride solution) and record observations.

Part E - Iron and Sulfur

1. On a sheet of white paper, add a small spatula full of sulfur (S) and a small spatula full of iron (Fe). Mix the two together with the tip of a spatula.

2. Run a magnet UNDERNEATH the sheet of paper and record you observations.

Observations

Data Table 1. Physical Properties of Starting Materials

|Substance |Solid, liquid, or |Color |Other Observations |

| |gas? | | |

| |(Physical State) | | |

| | | | |

|Magnesium | | | |

|(Mg) | | | |

| | | | |

|Hydrochloric Acid (HCl) | | | |

| | | | |

|Sand | | | |

|(SiO2) | | | |

| | | | |

|Salt | | | |

|(NaCl) | | | |

| | | | |

|Sodium Bicarbonate (NaHCO3) | | | |

| | | | |

|Silver nitrate solution (AgNO3) | | | |

| | | | |

|Sodium chloride solution | | | |

|(NaCl) | | | |

| | | | |

|Iron | | | |

|(Fe) | | | |

| | | | |

|Sulfur | | | |

|(S) | | | |

Data Table 2. Observations of Physical and Chemical Changes

|System |Observations |

|Part A - Magnesium | |

| | |

|burned in air | |

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|reacted with hydrochloric acid | |

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|ash reacted with hydrochloric acid | |

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|Part B - Salt and Sand | |

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|mixed with water | |

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|filtered | |

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|evaporated | |

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|Part C - Sodium Bicarbonate | |

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|- reaction with hydrochloric acid | |

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|Part D - Silver Nitrate | |

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|reaction with sodium chloride | |

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|Part E - Iron and Sulfur | |

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|magnet run underneath | |

| | |

Analyses and Conclusions

Please type your responses in paragraph form and turn in on due date listed on syllabus.

1. How do you decide whether an observed property (not change) of matter is a physical or chemical property?

2. Indicate whether each change was a physical change or a chemical change and give reasons for your answer.

Part A - Burning magnesium

- Mixing unburned magnesium with hydrochloric acid

- Mixing the ash of burned magnesium with hydrochloric acid

Part B - Mixing, salt, sand, and water

Part C - Mixing sodium bicarbonate and hydrochloric acid

Part D - Mixing silver nitrate with sodium chloride

Part E - Mixing iron and sulfur.

3. List five examples each of physical and chemical changes that you encounter in your everyday life.

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