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Chemistry Labs
- The volume of the gas will be recorded for each of the pressures used. The data (values of pressure and volume) will be plotted on the graph in several ways in order to find a simple mathematical relationship between pressure and volume.
- A test tube containing a solid will be heated until the solid melts. The resulting liquid will then be allowed to cool, and the temperature of the substance will be recorded at regular time intervals until all of the liquid has re-solidified. The solid will then be reheated gradually, and temperature readings will be taken at regular time intervals during the heating process. Such time-temperature readings are valuable in determining the melting and freezing points of substances. The melting point and freezing point are the same temperature (and same phase change). The difference is just one of direction.
- In this experiment, you will use para-dichlorobenzene C6H4Cl2. The heat given off as the substance turns from a liquid to a solid will be used to change the temperature of a measured amount of water.
- You will learn the techniques of decanting, filtering, washing, and drying. Carry them out well, so you will be able to perform these laboratory procedures in future labs.
- An empirical formula gives the simplest whole number ratio of the different atoms in a compound. The empirical formula does not necessarily indicate the exact number of atoms in a single molecule. This information is given by the molecular formula. For certain compounds, the empirical formula and the molecular formula are the same; for other compounds the empirical and molecular formulas are different. In all cases, the molecular formula is a simple multiple of the empirical formula.
- In this experiment, you will determine the empirical formula of magnesium oxide, a compound that is formed when magnesium metal reacts with oxygen gas. In determining this empirical formula, you will make use of the law of conservation of mass.
QUANTITATIVE RELATIONSHIP BETWEEN GAS PRESSURE AND GAS VOLUME
- What is the relationship between the pressure applied to a gas and the volume it occupies? In this experiment, a given quantity of gas will be trapped in a syringe. The pressure on the gas will then be increased by weights (books) on top of the plunger of the syringe. The total pressure acting on the gas consists of the weight of the books plus the weight of the atmosphere.
TOTAL PRESSURE = PRESSURE DUE TO BOOKS + PRESSURE DUE TO ATMOSPHERE
- Mass is a measurement of the amount of matter in a sample, while volume is a measurement of the space occupied by a sample of matter. In this experiment, you will measure the mass and volume of metal samples. You will then use the data obtained, to determine whither there is any constant relationship between the mass and the volume of a given substance.
MELTING TEMPERATURE OF A SOLID
- Some substances melt more easily than others. Candle wax melts easily. Iron wire melts with great difficulty. How can we describe these qualitative observations in more detail? Numbers help. Let us be quantitative in our study of the melting os solids by measuring the melting temperature (or melting point) of a pure solid. Information about the melting point of a substance has many uses in chemistry.
- What energy changes occur when a liquid solidifies? When you studied phases of matter, you discovered two characteristic properties of substances: the temperature of melting is different for different pure substances, and the temperature of a melting solid or freezing liquid remains constant as long as both liquid and solid phases are present. The energy that was required to change a solid to a liquid is released when the substance changes from a liquid to a solid. Remember that the change that occurs when a solid melts or a liquid freezes is called a phase change.
- The amount of energy required to convert a solid to a liquid, at constant pressure and temperature, is called the heat of fusion of the substance. In this experiment, the heat of fusion of ice will be determined.
HEAT OF COMBUSTION FOR THREE ALCOHOL FUELS
- In this experiment you will determine the amount of energy (heat) involved in a chemical change. When alcohol burns it produces carbon dioxide and water as products. Energy is also released in the reaction. Let us determine the amount of heat (in calories) liberated when three alcohols burn, and compare their energy output (heat of combustion). We will be using methyl alcohol CH3OH , ethyl alcohol C2H5OH , and 2-propyl alcohol CH3CHOHCH3.
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The amount of heat energy that is required to raise the temperature of one gram of a substance by one degree Celsius is called the specific heat capacity, or simply the specific heat., of that substance. Water, for instance, has a specific heat of 1.0 calorie per gram degree Celsius [1.0 cal / (g x deg.C)].
The amount of heat energy involved in changing the temperature of a sample of a particular substance depends on three parameters -- the specific heat of the substance, the mass of the sample, and the magnitude of the temperature change.
In this experiment, you will determine the specific heat of a metal.
RELATIVE STRENGTH OF ACID SAMPLES
- In this experiment you will determine the relative strength of acid samples, by qualitative observation of the reaction.
PERCENTAGE OF ACETIC ACID IN VINEGAR
- By Titration
- The quality of acid in a sample of vinegar nay be found by titrating the sample against a standard basic solution. Most commercial vinegar is labeled as 5% acetic acid, but can have a mass percentage of between 4.0% and 5.5% acetic acid.
By determining the volume of sodium hydroxide solution of known molarity necessary to neutralize a measured quantity of vinegar, The molarity and mass percentage can be calculated. Industrial quality control chemists do this to maintain product quality.
QUANTITATIVE MEASUREMENT OF VITAMIN C IN FRUIT JUICE
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Vitamin C (ascorbic acid) is necessary to your body for proper teeth, bone, and red blood cell formation. It is also a part of enzyme systems that regulate chemical reactions in your cells.
In this lab, you will titrate a standard solution of vitamin C, and a sample solution of fruit juice. By comparing the two titrations, you will be able to calculate the amount of vitamin C in the fruit juice.
You will use an iodine solution as your titration solution, and starch as your end-point indicator. When ascorbic acid reacts with iodine, the ascorbic acid is oxidized (looses electrons) and the iodine is reduced (gains electrons). Reduced iodine cannot react with starch. When all the ascorbic acid has reacted, any added iodine will then be able to react with the starch. A purple color will form (and remain), giving you the end-point for the titration.
- In this experiment you will carry out a chemical reaction and determine the balanced chemical equation for the reaction.
STOICHIOMETRY OF A DOUBLE REPLACEMENT REACTION
- There are two types of chemical analysis; qualitative analysis which is the identification of a substance present in a material, and qualitative analysis which measures the amount of the substance. In this lab, you will perform a quantitative analysis of a two-step reaction. Copper(II) oxide will be synthesized from a known mass of copper(II) sulfate pentahydrate. Using the relationship of the balanced equation, and other stoichiometry relationships, you will calculate a theoretical yield of CuO, and your actual yield. You then will calculate a percent yield.
- In this experiment you will take a copper sample through a series of five reactions. The end product will be your original copper sample, making this a cycle of reactions. With careful attention to quantitative lab practices, you should be able to recover all the copper you started with.
FINDING MOLARITY BY QUANTITATIVE ANALYSIS OF A REACTION
- In this experiment, you will find the molarity of a nitric acid (HNO3) solution by quantitative analysis of its reaction with copper. Copper reacts with nitric acid to form three products.
FINDING MOLARITY OF AN HCl SOLUTION BY QUANTITATIVE ANALYSIS
- In this experiment, you will find the molarity of a hydrochloric acid (HCl) solution by quantitative analysis of its reaction with aluminum. Aluminum reacts with hydrochloric acid to form two products.
MASS RELATIONSHIPS ACCOMPANYING CHEMICAL CHANGES
- When a chemical reaction occurs, how do the masses of reactants and products compare? In this experiment, you will use the same number of moles of two reactants, lead nitrate, Pb(NO3)2 and potassium chromate, K2CrO4 , and allow them to react with each other. You will be making a comparison between the masses of reactants and products and the number of moles of reactants and products.
BEHAVIOR OF SOLID ZINC IN AN AQUEOUS SOLUTION OF LEAD ACETATE
- What mass and mole relationships are there in chemical reactions? In this experiment, you will find the mass of a sample of solid lead acetate and prepare a water solution of it. You will also find the mass of a zinc strip, place it in the solution, and observe its behavior. By finding the mass of the zinc strip at the close of the experiment, you will be able to investigate quantitatively any changes that occur.
DETERMINING THE PERCENT OF COPPER IN A POST 1982 PENNY
- Pennies produced before 1982 were made of pure copper. With the rise in the price of copper, the metal value of a penny was more than their face value as a coin. The US Mint began making pennies from a zinc wafer with a thin copper outer coating.
In this lab, you will determine the percent composition of copper in a penny minted after 1982. The penny will be cut in half and reacted with hydrochloric acid. The HCl will react with the zinc, but not the copper, leaving the copper behind after the reaction.
DETERMINATION OF AN EMPIRICAL FORMULA
- In this experiment, you will determine the empirical formula of a compound. In so doing you will gain a clear understanding of the difference between an empirical formula and a molecular formula.
PRODUCTION OF A PRECIPITATE FROM SOLUTIONS OF SODIUM IODIDE AND LEAD NITRATE
- How is the chemical formula for a substance determined? In this experiment you will react solutions of lead nitrate, Pb(NO3)2 , and sodium iodide, NaI , of known concentration, 0.500 M. You will observe the results when various volumes of these solutions are mixed. From the relative volumes of the solutions used and their molar concentration, and from the masses of the precipitate formed, it will be possible to determine the number of moles of the substances involved and the formula for the precipitate.
PRODUCTION OF A PRECIPITATE FROM SOLUTIONS OF SODIUM IODIDE AND SILVER NITRATE
- How is the chemical formula for a substance determined? In this experiment you will react solutions of silver nitrate, AgNO3 , and sodium iodide, NaI , of known concentration, 0.500 M. You will observe the results when various volumes of these solutions are mixed. From the relative volumes of the solutions used and their molar concentration, and from the masses of the precipitate formed, it will be possible to determine the number of moles of the substances involved and the formula for the precipitate.
ISOTOPE ABUNDANCE AND MOLAR MASS
- Most chemical elements consist of mixtures of isotopes. The molar mass values we use are derived by using the concept of weighted averages. In this experiment, you will simulate one way that scientists can determine the relative amounts of different isotopes present in a sample of an element.
- In this experiment you will find the mass of water driven off by heating and the amount of anhydrous salt that remains. with the formula of the anhydrous salt, you will be able to find the empirical formula of the hydrate.
- Preparation of soap
- In this experiment, we will make soap by the process of saponification. In the process of making soap, animal fat, which is a triglyceride, is hydrolyzed by the action of a strong base, such as sodium hydroxide, and heat. The resulting products are soap and glycerol.
- From Purple Cabbage
- The indicator that you will be making comes from purple cabbage. And is simply called cabbage extract indicator. You will then use your indicator to do some titrations.
MEASURING THE SIZE OF A MOLECULE
- Because atoms and molecules are so small, it is difficult to determine their sizes. Special instruments are normally needed for such measurements. Here, however, a simple experiment using water, soap, and chalk dust will be conducted to give an approximate measure of the size of a molecule.
COMPARING THE EFFECTIVENESS OF SEVERAL ANTACIDS
- In this investigation, you will mix an antacid tablet with water and a colored chemical called an indicator. The indicator changes color depending on whether an acid or a base is present. Then you will add acid to the solution to determine how much acid can be neutralized by the antacid tablet. You should test several different types of antacids to compare the effectiveness of various products.
- Sulfur is burned to produce sulfur dioxide, which is used to bleach and preserve foods, especially fruits. It prevents the growth of bacteria and mold. Apples, pears, apricots, peaches, and figs are dried and preserved with SO2. Although packagers try to remove as much of the sulfur compounds as possible, some usually remains. You may test for the presence of residual sulfur compounds by reacting fruit with barium chloride to form a new compound that is not soluble. A substance that is not soluble will form a cloudy precipitate. You will compare fruit preserved with sulfur and without sulfur. This is a two day lab.
- A polymer is a very large molecule that is like a chain of smaller (often identical), molecules linked together. In this experiment, you will mix two clear solutions in a paper cup. You will produce a fluid polymer. If green food coloring is added, the product will be like the commercial polymer, slime.
MAKING A SOLID POLYMER "SUPER BALL"
- Two common liquids are mixed, and the reaction makes a solid that has the properties of rubber. This solid is a polymer. In this lab, you will produce a solid, silicate based polymer.
- In this experiment, we will observe the plating of one metal with another by chemical means. We will plate zinc on the copper of a penny, which is just the opposite of what we normally would expect to happen.
We know from our study of ions that the Zn++ ion combines with two OH- ions to form zinc hydroxide Zn(OH)2. However, in the presence of sodium hydroxide NaOH, zinc will combine to form the complex ion known as a zincate ion.
| [Zn(OH)4] - - | or | [Zn(OH)3 * H2O] - |
IDENTIFYING UNKNOWN SOLIDS BY QUALITATIVE ANALYSIS
- Qualitative analysis is the process by which simple physical and chemical tests are used to identify an unknown. In this lab, you will use a series of tests (in a particular order) to identify 12 unknown chemicals. The procedure is set up similar to a dichotomous key used to identify organisms in biology. By performing the procedures for each test, and then going to the next test as directed, you will be able to identify all of the unknowns on the list.