Notes

The unknown Group 1 metal carbonate was a solid that had a white color. The unknown had a powder-like consistency. When the unknown carbonate was heated in the crucible it became molten and glowed a bright orange, The unknown carbonate crystallized and became extremely hard as it was cooled. When the unknown carbonate was mixed with distilled water, it slightly dissolved and the water turned to a pinkish tint; however, much of the unknown carbonate remain undissolved. When the calcium chloride was added, at first the water was extremely cloudy and opaque but as time went on a precipitate formed and settled to the bottom. When mixed with calcium chloride and distilled water, the precipitate created a cloudy white appearance. The filtered liquid had a clear appearance while the precipitate in the filter had a white powdery appearance.

Analysis- The identity of the metal carbonate is Li2CO3. This was found because the mass of the metal carbonate was calculated to be 76.51 and was closest to Lithium carbonate. The percent error was 1.17%. One source of error could’ve been the thin layer of precipitate that formed at the top of the solution after settling which caused loss of metal carbonate during decanting and thus slightly skewed results. Another source of error could’ve been the absorption of water because of the property of Lithium Carbonate which makes it hygroscopic and thus prone to bonding to gaseous water which results in slightly higher results. Similarly, when drying not all of the liquid may be removed resulting in higher results than what would be expected. At first, when the Calcium Chloride solution was added to the water and metal carbonate the solution was extremely cloudly but over time the precipitate settled to the bottom and the solution became clear. Similarly, the dust from the air could’ve increased the mass of the metal carbonate and the mass of the calcium carbonate which could’ve increased the calculated molar mass and decreased it respectively. Another source of error could’ve been not heating the calcium carbonate for long enough resulting in a lot of the water staying in the calcium carbonate and making the calculated molar mass lower. Some improvements to the lab could have been heating up the calcium carbonate for longer periods of time in order to make sure all the water was gone and taking more accurate measurements.

When the unknown carbonate was put into the distilled water it dissolves because the strength of the ionic bonds between the alkali metals and the carbonates were weaker than the attractions of these ions to the dipoles of water, The alkali metal would be attracted to the partially negative dipole on oxygen because it pulls the electrons closer to its nucleus, while the carbonate would be attracted to the partially positive dipole on hydrogen allowing for the individual ions to be cleaved apart and for a hydration shell to form. Similarly, when the Calcium chloride solution is added to the water it dissociates because the individual ions of the compound are more attracted to the water around than to the other atom in the ionic compound which results in the ions being cleaved apart. However, when calcium and carbonate ions bond, the intermolecular forces between them are greater than the attraction to the water molecules resulting in them being insoluble and in a precipitate being formed. Furthermore, these bonds are stronger because of columbs law which says that an increase in the charges of two respective atoms will result in an increase in an attractive force between them. In this case, the attractive force between the two molecules of unknown carbonate with 1+ charges and the 2+ of the carbonate is not enough to overcome the attractive force of water; however, Calcium ions which have a 2+ charge, and carbonate ions which has a 2- charge form much stronger bonds because of the greater difference in their charges and these bonds are strong enough to prevent the compound from being cleaved apart by water. This precipitate can then be used to find the mass of unknown carbonate because the unknown carbonate has a 1 to 1-mole ratio with the calcium carbonate that is formed as a precipitate. Therefore, by isolating the calcium carbonate and finding the mass it is possible to deduce the molar mass of the unknown carbonate taking the grams of calcium carbonate over the number of moles because the molar mass of a substance is just the mass per mole of a substance. The other ions in the solution such as the unknown alkali metal ions and the chloride ions can be ignored since they are spectator ions that do not change throughout the course of the experiment and remain aqueous.