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Dec 6, 2023

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Kelly Grogan Phoebe Bell-Lopez Zach CHE 111/029-044 09/20/2023 Experiment 4: The Chemical Structure of Limestone Introduction When find the Chemical structure of Limestone the amount of calcium carbonate was measured in a sample of limestone. To grasp a better understanding, we need to look at the geological background of limestone. Limestone encompasses about 10% of the sedimentary rocks on the earth’s surface. Limestone typically forms from the process of Lithification which is the compaction of sediment into rock. The loose sediment is often classified as different types of marine organisms, like coral or algae. Limestone may also be formed from the combination of carbon dioxide and rain because calcium carbonate is precipitation and usually comes from shallow, warm water. Limestone is typically classified as calcite or calcium carbonate. Limestone samples usually contain trace amounts of things like clay or silica or dolomite, and in order for a sample to be identified as limestone it must have a composition over 50% calcite and dolomite however, the percent may vary based on different types of various geological aspect in a specific area. (French et. Al 74) CaCO 3 ( s ) + 2 HCl ( aq ) →CaCl 2 ( aq ) + H 2 CO 3 ( aq ) H 2 CO 3 ( aq ) → H 2 O ( l ) + CO 2 ( g ) CaCO 3 ( s ) + 2 HCl ( aq ) →CaCl 2 ( aq ) + H 2 O ( l ) + CO 2 ( g )

The main goal of this lab is to find the amount of calcium carbonate that we can get from a sample of limestone. This can be solved by associating the solubility rules and using balanced chemical reactions in order to separate the calcium carbonate. Then we can use stoichiometry to then figure out the percent composition of calcium in limestone. The calcium that we find from the sample of limestone is reacted with HCl to produce a carbonic acid, which will decompose and form CO2. (French et. Al 75) Mass % of A = Mass of A Total Massof Substance ∗ 100 However, to ensure that there are no other substances aside from the calcium carbonate, we must use a filtration system to obtain the correct solids from the solution, and from the mass and known precipitate, we can find the original ion. Also, another way to get calcium carbonate is to determine how much calcium ion is in a sample of limestone. Methyl red can be used to indicate the PH of the previous mineral found. Then observe the color change due to the pH change between 4.4 and 6.4. At first, we can expect when the methyl read gets mixed in that we will find a beautiful, bright pink color, which indicates that the pH is closer to 4.4 in the current solution. As the PH rises, the solution will turn into a yellowish color. Procedures The procedure may be found in the General Chemistry Laboratory Manual, under “ Experiment 4 Quantifying the Composition of Limestone”. There were no changes that were made to the procedure. (French et. Al 78-80)

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