Lab # : Elements, Compounds, and Mixtures

Transcription

1 Lab # : Elements, Compounds, and Mixtures Background: Matter is anything that has mass and takes up space. Most of the matter around us consists of mixtures of many substances. Mixtures can be classified as either homogeneous or heterogeneous. A heterogeneous mixture is one that is not uniform in composition. If one portion of the mixture were to be sampled, its composition would be different from the composition of another portion. Examples of heterogeneous mixtures are sand in water and oil and vinegar salad dressing. A homogeneous mixture (solution) is a mixture that has a uniform composition. The components of the mixture are evenly distributed throughout the sample. Air, salt water, and brass are examples of a homogeneous mixture. Mixtures can be separated into pure substances by physical methods. A pure substance is one with a uniform and definite composition. Pure substances can be divided into two groups- elements and compounds. Elements are the simplest forms of matter which cannot be decomposed into simpler substances by any chemical or physical means. Some examples of elements are hydrogen, oxygen and carbon. Compounds are substances composed of two or more elements chemically combined that can be separated into simpler substances only by chemical means. Water is an example of a compound. Problem: Materials:

2 Prelab: Locate each element name or symbol on the periodic table and complete the following table. The first one has been done for you. Remember that spelling of element names COUNTS! Symbol Element Name Symbol Element Name C Carbon Sulfur P Si Al Ca Nitrogen Uranium Zn I Iron Helium Cu Cobalt O Ag Hydrogen Be K Magnesium Sodium Mn Chlorine Platinum Ne W Mercury Ti Au Lead

3 Procedure: 1) Take a weighing dish and zero it out on the balance. Then get about 5 grams of iron filing, 5 grams of zinc, 5 grams of sand, and 5 grams of sodium chloride. Make sure you use a separate dish for each chemical. Record the exact mass of each material to the nearest tenth of a gram in Table 1. 2) Carefully observe each of the four pure substances. Record observations of physical properties in Table 2. BE VERY DESCRIPTIVE! 3) Test each substance with a magnet by running the magnet underneath the weighing dish. Record these observations (magnetic or not magnetic) in Table 2. 4) Pour all four of these chemicals into a 400ml beaker. Record your observation of the new mixture in Table 3. 5) Pour the prepared mixture onto a piece of white paper. Place the magnet into a Ziploc bag and use the magnet to separate whatever material is magnetic. Collect all that magnetic material into a weighing dish. Take an empty weighing dish and zero it out and then re-mass the magnetic material and record the mass into Table 1. Record all observations of this magnetic material into Table 3. 6) Pick out the large material and place that material into a weighing dish. Remass the material after zeroing out a weighing dish and record the mass into Table 1. Record the observations of this large material into Table 3. 7) Add 50ml of water to the beaker with the remaining mixture and swirl the beaker gently. Record the observation of what you see when the water is added into Table 3. 8) Weigh a piece of wet filter paper and record the mass of a clean piece of filter paper into Table 4. Then fold the filter paper as seen below and insert the filter paper into the funnel. (you may need to wet the filter paper a little to keep it in place) 9) Weigh an empty 250ml beaker and record the mass in Table 4. Place the empty beaker on the counter and lay the funnel into the beaker. Gently pour the liquid mixture into the funnel but make sure no material is poured over the edges of the filter paper. BE PATIENT!

4 10) Make sure all the solid is out of the beaker and into the funnel. If you can t scrape it out, pour a little water in and swirl the beaker again to get the solid out! 11) Remove the filter paper and lay the paper out flat. Record your observations of the filter paper into Table 3. Weigh the filter paper and record the mass into Table 4. 12) Observe the contents of the 250ml beaker and record your observations into Table 3. 13) Place the 250ml beaker onto a hot plate set at medium heat. Allow most of the liquid to evaporate. Turn the heat down if spattering occurs. Let the liquid evaporate and when just solid is left turn the heat off and mass the beaker. Record the mass of the beaker into Table 4. Table 1: Mass of Materials Substance Initial Mass Final Mass Difference in Mass (Final Initial) Iron Zinc Sand Sodium Chloride Table 2: Observation before Mixing Substance Observations of Physical Properties Iron Zinc Sand Sodium Chloride

5 Table 3: Observations after Mixing Object to Observe Observations Mixture (all four) Magnetic Material Large Material Mixture with Water Filtrate (mixture in beaker after filter) Filter Paper Table 4: Mass Material Mass in Grams Filter Paper Filter Paper plus Solid Solid (filter paper plus solid filter paper) Empty 250ml Beaker Beaker plus Evaporated Liquid Evaporated Liquid (beaker empty)

6 Questions and Calculations: 1) What errors may have occurred which would cause there to be a difference in mass? (Be specific) 2) How do you determine which of these four substances are elements and which are compounds? Identify which are elements and which are compounds! 3) After you mixed the four substances together, is it possible to recover the original materials. Why or why not? 4) What physical or chemical property of the four starting substances did you use to separate out each material? 5) Calculate the percent error for iron, zinc, sand, and sodium chloride. Show the work in the space provided. [(actual experimental) / actual * 100] Iron: Zinc: Sand: Sodium Chloride:

7 6) Label each of the following as either a compound, element, heterogeneous or homogeneous mixture.