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Lab: Gravimetric Analysis of a Metal Carbonate

Lab: Gravimetric Analysis of a Metal Carbonate. A Prelab Analysis. Water is Polar!!!.

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Lab: Gravimetric Analysis of a Metal Carbonate

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  1. Lab: Gravimetric Analysis of a Metal Carbonate A Prelab Analysis

  2. Water is Polar!!! • This is an important concept to get down as we move forward. Water is polar meaning that one side of water molecules is more negative than the other side of water molecules. The hydrogen side of water is more positive (has a partial positive charge) and the oxygen side of water is more negative (has a partial negative charge). This is because oxygen is more electronegative and pulls electrons in the covalent bond more to itself than hydrogen does. See below:

  3. Dissociation • When a soluble ionic compound is placed in water, the two ions of the compound are attracted to the opposite poles of water molecules and separate from one another. The solid ionic compound is now dissolved in the water…the ions have dissociated from one another and are hydrated.

  4. Gravimetric Analysis In gravimetric analysis, an ion of interest in solution is precipitated out (bonded onto an ion that creates an insoluble solid compound) completely with a known reagent. Then the mass of the precipitate can be determined. the mass of the ion of interest can then be determined. Example:

  5. Molar Mass • Remember, the molar mass of a substance is the mass in grams of 1 mole of the substance. • You can experimentally determine the molar mass of a substance by determining the mass of a sample of the substance by weighing and then determining the moles of the substance in the sample by gravimetric analysis. • Molar mass =

  6. Molar Ratios In this lab, the precipitation and chemical reactions necessary are as follows: M2CO3 (s) → 2 M+ (aq) + CO32- (aq) Equation 1 (This is the dissociation of the unknown metal carbonate…all ionic compounds with alkali metal ions are completely soluble) Ca2+ (aq) + CO32- (aq) → CaCO3 (s) Equation 2 (This is the reaction of the carbonate ion from the unknown carbonate to calcium ions that were introduced] Notice that one mole of the unknown carbonate reacts to form one mole of calcium carbonate. That means if you determine the moles of calcium carbonate produced, you know the moles of unknown carbonate you originally started with. Yay!

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