Answer:
2. Hydrochloric acid (HCL) is an acid, while sodium hydroxide (NaOH) is a base.
Explanation:
so the two labels are missing, one method to differentiate them is by mixing each reagent with a base. Let's say we mix sodium carbonate(Na2C03) which is a base with each of the reagent, the sodium carbonate will likely react with Hydrochloric acid which is an acid to form NaCl and H2O, but it will not react with sodium hydroxide which is a base.
That why, by mixing the each reagent with a base, we could help place the correct label.
Another way to place the labels correctly is, the bottle containing hydrochloric acid will be sticky while the sodium hydroxide will be slippery. It is a known fact that acids are generally sticky while bases are slippery when touched.
3. Natural Acidity of Rainwater
Explanation:
Pure water has a pH of 7.0 (neutral); however, natural, unpolluted rainwater actually has a pH of about 5.6 (acidic).[Recall from Experiment 1 that pH is a measure of the hydrogen ion (H+) concentration.] The acidity of rainwater comes from the natural presence of three substances (CO2, NO, and SO2) found in the troposphere (the lowest layer of the atmosphere). As is seen in Table I, carbon dioxide (CO2) is present in the greatest concentration and therefore contributes the most to the natural acidity of rainwater.
Gas
Natural Sources
Concentration
Carbon dioxide
CO2 Decomposition 355 ppm
Nitric oxide
NO Electric discharge 0.01 ppm
Sulfur dioxide
SO2 Volcanic gases 0-0.01 ppm
Carbon dioxide, produced in the decomposition of organic material, is the primary source of acidity in unpolluted rainwater.
NOTE TO REMEMBER: Parts per million (ppm) is a common concentration measure used in environmental chemistry. The formula for ppm is given by:
Carbon dioxide reacts with water to form carbonic acid (Equation 1). Carbonic acid then dissociates to give the hydrogen ion (H+) and the hydrogen carbonate ion (HCO3-) (Equation 2). The ability of H2CO3 to deliver H+ is what classifies this molecule as an acid, thus lowering the pH of a solution.
Nitric oxide (NO), which also contributes to the natural acidity of rainwater, is formed during lightning storms by the reaction of nitrogen and oxygen, two common atmospheric gases (Equation 3). In air, NO is oxidized to nitrogen dioxide (NO2) (Equation 4), which in turn reacts with water to give nitric acid (HNO3) (Equation 5). This acid dissociates in water to yield hydrogen ions and nitrate ions (NO3-) in a reaction analagous to the dissociation of carbonic acid shown in Equation 2, again lowering the pH of the solution.
Acidity of Polluted Rainwater
But, human industrial activity produces additional acid-forming compounds in far greater quantities than the natural sources of acidity described above. In some areas of the United States, the pH of rainwater can be 3.0 or lower, approximately 1000 times more acidic than normal rainwater. In 1982, the pH of a fog on the West Coast of the United States was measured at 1.8! When rainwater is too acidic, it can cause problems ranging from killing freshwater fish and damaging crops, to eroding buildings and monuments.
