Name Date Class

Matter and Chemical Reactions

One of the most interesting characteristics of matter, and one that drives the study and exploration of chemistry, is the fact that matter changes. By examining a dramatic chemical reaction, such as the reaction of the element copper and the compound silver nitrate in a water solution, you can readily observe chemical change. Drawing on one of the fundamental laboratory techniques introduced in this chapter, you can separate the products. Then, you will use a flame test to confirm the identity of the products.

Problem

Is there evidence of a chemical reaction between copper and silver nitrate? If so, which elements reacted and what is the name of the compound they formed?

Objectives

  1. Observe the reactants as they change into product.
  2. Separate a mixture by filtration.
  3. Predict the names of the products.

Materials

copper wire

AgNO3solution

sandpaper

stirring rod

50-mL graduated cylinder

50-mL beaker

funnel

filter paper

250-mL Erlenmeyer flask

ring stand

small iron ring

plastic petri dish

paper clip

Bunsen burner

tongs

Safety Precautions

Inline Figure
  1. Always wear safety goggles, gloves, and a lab apron.
  2. Silver nitrate is toxic and will harm skin and clothing.
  3. Use caution around a flame.

Pre-Lab

  1. Read the entire CHEMLAB.

  2. Prepare all written materials that you will take into the laboratory. Be sure to include safety precautions and procedure notes. Use the data table on the next page.

  3. Define the terms physical property and chemical property. Give an example of each.

    A physical property is a characteristic that can be observed or measured without changing the substance's composition--for example, color, shape, or mass. A chemical property is the ability of a substance to combine with or change into one or more other substances--for example, reactivity with water.


  4. Form a hypothesis regarding what you might observe if

    1. a chemical change occurs.

      You might observe a change in color or odor, the evolution of heat or light, the absorption of energy, or the formation of a gas, liquid, or different solid. A different product will form.


    2. a physical change occurs.

      You might observe a change in shape or in physical state, such as boiling, condensing, freezing, melting, evaporating, dissolving, or crystallizing.


  5. Distinguish between a homogeneous mixture and a heterogeneous mixture.

    A homogeneous mixture is one in which one or more substances are evenly distributed throughout another substance. A heterogeneousmixture is one in which there is an observable separation of component substances.


Procedure

  1. Obtain 8 cm of copper wire. Rub the copper wire with the sandpaper until it is shiny.
  2. Measure approximately 25 mL AgNO3(silver nitrate) solution into a 50-mL beaker. CAUTION: Do not allow to contact skin or clothing.
  3. Make and record an observation of the physical properties of the copper wire and AgNO3 solution.
  4. Coil the piece of copper wire to a length that will fit into the beaker. Make a hook on the end of the coil to allow the coil to be suspended from the stirring rod.
  5. Hook the coil onto the middle of the stirring rod. Place the stirring rod across the top of the beaker immersing some of the coil in the AgNO3solution.
  6. Make and record observations of the wire and the solution every five minutes for 20 minutes.

    Inline Figure

  7. Use the ring stand, small iron ring, funnel, Erlenmeyer flask, and filter paper to set up a filtration apparatus. Attach the iron ring to the ring stand. Adjust the height of the ring so the end of the funnel is inside the neck of the Erlenmeyer flask.
  8. To fold the filter paper, examine the diagram above. Begin by folding the circle in half, then fold in half again. Tear off the lower right corner of the flap that is facing you. This will help the filter paper stick better to the funnel. Open the folded paper into a cone. Place the filter paper cone in the funnel.
  9. Remove the coil from the beaker and dispose of it as directed by your teacher. Some of the solid product may form a mixture with the liquid in the beaker. Decant the liquid by slowly pouring it down the stirring rod into the funnel. Solid product will be caught in the filter paper. Collect the filtrate–the liquid that runs through the filter paper–in the Erlenmeyer flask.
  10. Transfer the clear filtrate to a petri dish.
  11. Adjust a Bunsen burner flame until it is blue. Hold the paper clip with tongs in the flame until no additional color is observed.CAUTION: The paper clip will be very hot.
  12. Using tongs, dip the hot paper clip in the filtrate. Then, hold the paper clip in the flame. Record the color you observe.

Reaction Observations
Time (min) Observations
5  Students should observe gradual formation of gray solid on the copper wire. The solution will turn blue-green.
10  
15  
20  
   Flame test: blue-green color

Cleanup and Disposal

  1. Dispose of materials as directed by your teacher.
  2. Clean and return all lab equipment to its proper place.
  3. Wash hands thoroughly.

Analyze and Conclude

  1. Classifying Which type of mixture is silver nitrate in water? Which type of mixture is formed in step 6? Explain.

    homogeneous; heterogeneous and homogeneous

  2. Observing and Inferring Describe the changes you observed in step 6. Is there evidence a chemical change occurred? Why?

    A grayish solid formed on the wire. The solution turned blue-green. Yes, a solid formed and a color change occurred.


  3. Predicting Predict the products formed in step 6. You may not know the exact chemical name, but you should be able to make an intuitive prediction.

    silver and copper nitrate

  4. Using Resources Use resources such as theCRC Handbook of Chemistry and Physics, theMerck Index, or the Internet to determine the colors of silver metal and copper nitrate in water. Compare this information with your observations of the reactants and products in step 6.

    Silver metal is white to gray. Copper nitrate is blue-green.

  5. Identifying Metals emit characteristic colors in flame tests. Copper emits a blue-green light. Do your observations in step 12 confirm the presence of copper in the filtrate collected in step 9?

    Experimental results should agree with blue-green light.

  6. Communicating Express in words the chemical equation that represents the reaction that occurred in step 6.

    Copper and silver nitrate solution react to form silver and copper nitrate.

  7. Error Analysis Compare your recorded observations with those of several other lab teams. Explain any differences.

    Copper wire may not have been clean. The better observations will be more detailed.

Real-World Chemistry

  1. Analytical chemists determine the chemical composition of matter. Two major branches of analytical chemistry are qualitative analysis–determining what is in a substance–and quantitative analysis–measuring how much substance. Research and report on a career as an analytical chemist in the food industry.

    Answers will vary but may include analysis of vitamin content, flavors, preservatives, or calorie content.