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The percentage of calcium in limestone was obtained by weighing out a 1.7067 g sample of limestone dissolving it in acid neutralizing and precipitating the calcium as calcium oxalate. The calcium oxalate was then ignited to convert it to calcium carbonate. The residue after ignition weighed 0.7321 grams. What is the percentage of calcium in limestone?

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Beverley SmithLv2

13 Jan 2019

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4. The percentage of calcium in limestone wa s obtained byweighing out a 1.7067 g sample of limestone dissolving it in acidneutralizing and precipitating the calcium as calcium oxalate. Thecalcium oxalate was then ignited to conv ert it to calcium carbonate. The residue after ignition weighed 0.7321 grams. What is thepercentage of calcium in limestone.

5. A sample of a pure compound (CH 3 ) 4 NBrx weighing 0.0962 gwas di ssolved and treated with a reducing agent to ensure that allthe bromine was present as Br - . A precipitate of silver bromideweighing 0.1730 g was obtained. Calculat e the value of x in theformula of the compound.

6. Compounds of the elements yttrium (Y) and ytterbium (Yb) havevery similar chemical properties and are difficult to separate. A500 mg sample mixture containing only Y 2 O 3 and Yb 2 O 3 wasdissolved and the combined Y 3+ and Yb 3+ titrated with EDTA. Theresults of this titration showed that the sample contained a totalof 1.953 mmole of the two metal oxides. Calculate the pe rcentageof Y 2 O 3 and Yb 2 O 3 in the mixture.

7. The composition of an alloy containing only magnesium andaluminum was determined by dissolving a 0.3764 g sample in acid,precipitating Mg(OH) 2 and Al 2 O 3 â¢xH 2 O with base, and ignitingthe precipita te to MgO and Al 2 O 3 , respectively. Calculate th epercentage of Mg and Al in the sample if the ignited residueweighed 0.6850 g.

4.17.16%

5.x = 3

6.Y2O3= 72.4%

Yb2O3= 27.6%

7. Mg = 30.26%

Al = 69.74%

Prepare your solvent, which will be a 1.0 M Metal Free HCl solution. First, calculate the volume of the concentrated acid necessary to prepare 600.0 mL of 1.0 M HCL. (I believe we are give 3 M HCl to dilute here). Put about 300 mL of DIW in your 800 mL beaker, and then VERY carefully add the calculated volume of concentrated HCl to the water. YOU SHOULD ALWAYS ADD ACID TO WATER, NOT THE OTHER WAY AROUND. Do not pour the acid from the large bottle into your graduate cylinder; instead pour it first into a beaker then pour from the beaker into your graduated cylinder. After adding the acid, fill the beaker to ~600 mL and then transfer your solution into your 1.0 L stoppered bottle and label the bottle. You will use this solvent for the next two weeks.

Prepare a calcium standard solution by accurately weighing between 0.35 - 0.40 g (I'm using .38 specifically) of standard calcium carbonate and quantitatively transferring the solid to a 250 mL beaker. Slowly add dropwise 6 M HCl until the sample stops effervescing and completely dissolves. Make the volume up to about 50 mL with DIW. Quantitatively transfer the solution into a 250 mL volumetric and dilute to the mark. Mix the solution carefully. Calculate the concentration of the Ca²⁺ in ppm (or mg/L) using the correct number of significant figures assuming the 1.0 HCl has a density of 1.000 g/mL. Show these calculations clearly in your notebook and on your report form. Recall that calcium is only ~40% of the CaCO₃.

A solid laboratory sample contains two substances, lead(II) carbonate (PbCO₃) and barium carbonate (BaCO₃). A 5.000 g sample of this unknown was treated with aqueous nitric acid (HNO₃) to dissolve it, then, after further treatment to adjust the acidity, it was treated with an excess of potassium chromate solution (K₂CrO₄). The precipitate which formed, when dried carefully and weighed, has a mass of 6.276 grams. Calculate the percent, by weight, of lead(II) carbonate (PbCO₃) in this laboratory sample.