Physical and Chemical Changes
Apparatus and Material: evaporating dish, Bunsen burner, wood splint, test tubes, micro spatula, dropper, mortar and pestle, test tube holder, safety goggles, lab apron. Piece of paper, NaCl (sodium chloride), water, 6 M HCL (hydrochloric acid), 0. 1 M AgNO3 (silver nitrate), Mg ribbon, 6 M HCL (hydrochloric acid), CuSO4 5 H2O, 0. 50g iron fillings, 0. 50g of powdered sulfur, magnet, copper sulfate solution, zinc metal Safety: When heating a substance in a test tube, be sure the open end of the test tube points away from yourself and others. Handle all acids with extra caution.
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Always wear safety goggles when handling acids.
Report all acid spills to your teacher, and flush with cold water and a dilute solution of sodium bicarbonate. Give heated glass ample time to cool before handling it. Glass retains heat. Wear your lab apron and safety goggles at all times during the lab. Procedure: 1. Tear a piece of paper (about 5cm x 10cm) into small pieces. Set an evaporating dish on an insulating square and place the pieces of paper on the glass. Ignite the paper with a mater and allow to burn. 2. Add a micro spatula scoop of NaCl (sodium chloride) to 5 mL of water in a test tube. Shake the contents of the tube.
Next, use a dropper to add 10 drops of 0. 1 M AgNO3 (silver nitrate) to the NaCl water. 3. Obtain a piece of magnesium ribbon about 5 cm long from your teacher. Place the ribbon into a test tube and add a few drops of 6 M HCL (hydrochloric acid). Touch the bottom of the test tube and record your observations. Invert another test tube above the mixture to collect any gas that may form. Using a lighted splint, test for the presence of hydrogen gas. Record your observations. 4. Use a mortar and pestle to grind several crystals of CuSO4 5 H2O into a uniform powder. Place one micro spatula of the powder into a test tube.
Heat gently over the burner flame until the color changes. Allow the sample to cool and then a few drops of water. Record your observations. 5. Using a lab balance, measure out the following samples: 0. 50g iron fillings and 0. 50g of powdered sulfur. Mix the two samples thoroughly in a test tube. Run a magnet along the outside of the test tube. Record your observations. 7. Add 5mL of copper sulfate solution to a test tube. Add a piece of zinc metal and watch for 5 minutes. Record your observations. Observations and data: 1. The paper appears white, odorless, thin, two-dimensional, and very smooth; length – 5. cmx10. 0cm. When lighted, the pieces of paper change from white to dark brown, then to black; the paper also shrinks as it shrivels up. An energy release (exothermic reaction) takes place as the burning material releases heat. After the paper turns black the fire goes off, leading to gas emission and a burning smell. The burned paper appears to be light-grey, cool and extremely soft at touch; in fact, it turns into ash immediately after contact. 2. Sodium chloride is a white crystallized solid, small and rough. Sodium chloride seemingly disappears when added to water, dissolving in it.
Addition of colorless AgNO3 to the NaCl water solution produces a white, milky precipitate that has higher viscosity than water. When exposed to sunlight, the solution separates into 2 parts with the silver precipitate on the bottom and a purple-grayish substance on top. The latter gradually changed from silver to purple, then to dark-grey with a purple tint. 3. Magnesium ribbon is a light-silver, small (length – 5cm) and shiny solid with a very light mass. Addition of hydrochloric acid to the magnesium ribbon resulted in an exothermic reaction – it rapidly released heat, making the tube extremely hot, and created white foam with fizzing.
The magnesium ribbon partially dissolved. The presence of hydrogen gas as the product of the reaction was confirmed when a lighted splint, when submerged into the gas, made a loud popping sound. 4. CuSO4 5H2O crystals are small turquoise solids; when grinded, it is a light-blue powder. Heated crystals change color from blue to white; water vapor forms on the walls of the test tube. Addition of water turns the heated crystals from white back to dark-blue, almost teal color. 5. Sulfur appears as yellow powder; iron is dark-brown powder; mixed together, they look like dirt.
Iron becomes attracted to the magnet, following it if it’s close enough; sulfur does not. Magnet can be used to separate the two mixtures. 6. On heating the iron-sulfur mixture, the sulfur melts and reacts with the iron exothermically to first evaporate into a yellow gas, then form a reddish-orange, solidified substance that “glows”. The substance releases an unpleasant odor of rotten eggs. The iron on the bottom turns black and does not react with a magnet. The glowing substance turns out to be a soft solid when probed. 7. Zinc is a silver solid with a light mass.
Addition of zinc metal to copper sulfate solution results in an exothermic reaction that produces a brown-reddish precipitate (copper). Zinc becomes coated with the copper precipitate, thus becoming dark. Conclusions and data: 1. a) tearing paper – physical change; retaining of properties, no new substances created b) burning paper – chemical change, gas and heat given off (evidence of chemical reaction) c) dissolving NaCl – physical change; solution formed, but individual properties retained; separation possible by distillation. ) mixing NaCl and AgNO3 – chemical change; white precipitate, or new substance, is formed
e) tearing Mg ribbon – physical change; retaining of properties, no new substances created f) adding HCL to Mg – chemical reaction; exothermic reaction by release of heat, which is evidence of a chemical reaction. g) grinding CuSO4 H2O – physical change; ground crystals retain their properties and molecular arrangement. h) heating CuSO4 H2O – physical change; evaporation of water is a change of state (phys. rop. ) i) mixing Fe and S – physical change; no new properties are formed. j) heating a mixture of Fe and S – chemical reaction; new substance is formed that has different properties from that of iron (no reaction to magnet). 2. Giving off of heat and formation of gases is an indicate that a chemical reaction occurred. Some examples are a reaction of Mg and hydrochloric acid (giving off heat and production of H2), and the burning of paper (production of CO2 gas and heat release).
3. New substances in the burning of paper are gases (CO2) and water (H2O). NaCl and AgNO3 produce a silver precipitate, or new substance (NaNO3 + AgCl). HCL and Magnesium produce MgCl and hydrogen gas. Iron-sulfur mixture produce an orange-red glowing substance and black iron sulfide on the bottom. Copper sulfate and zinc react to produce a dark-red copper precipitate. 4. a) Change of color resulted in heating of CuSO4 5H2O crystals, but it only resulted in evaporation of water and didn’t change the chemical composition of crystals. ) tearing of paper resulted in its mass loss, but it retained its original properties c. ) NaCl seemingly “disappeared” when mixed with water; the salt dissolved, but two compounds retained their chemical properties and could be separated by distillation. 5. Substances in a mixture can be separated by magnetic separation; substances in a compound can be separated by distillation. Magnetic separation separated the iron-sulfur mixture. Distillation of CuSO4 5H2O separated the compound by evaporating the water.