A Guided Inquiry Lab 13B

Today's lab was a very fun exploration of what we had learned today involving solubility, solutions, solvents, and solutes. A solute is the lesser amount of a substance in a solution, while a solvent is the greater substance. Solubility is the measure of the amount of salute that will dissolve in a in amount of solvent - usually water. We were given an unknown ionic compound of salt that could either be NaCl, NaNO3, or KNO3. However, no laboratory procedure was given to us, so Ameera and I (aka probe buddies) had to figure out the unknown salt by ourselves using our own knowledge of all the 's' words and the solubility curve graph.

After some deliberation, Ameera and I came up with an action plan. We decided to heat up water in a beaker until the temperature reached exactly 44 degrees Celsius, and then we would pour approximately 6 grams of salt into the solvent and see what would happen. We chose these precise numbers because the combination of these two points on the graph is equidistant from NaCl, NaNO3, and KNO3, so if the salt dissolved or not we would have a clearer idea of which of the three substances it was.

To start, we measured the mass of our salt in the mini beaker on a balance, and then massed the mini beaker and used subtraction to found the mass of the salt to be 18.98 grams. Then we measured 10 mL of water into another mini beaker, because we had scaled down the graph by 10. Then we measured out 6 grams of our salt into a weigh-boat. We created a hot water bath using our small 10 mL beaker of water inside a larger beaker of water on the hot plate (below, left), so that the water would heat up in a more slow and controlled manner. Once the thermometer in the water bath read 44 degrees Celsius, we took out our small beaker of water, poured the salt in, and began stirring very aggressively with the stirring rod. Eventually, we realized that the salt was not going to dissolve, as shown in the photo on the right.

 

Since the point on the graph with our two values was below the NaNO3 and KNO3 curves but above the NaCl curve, it was apparent that our compound was in fact Sodium Chloride because the salt would have fully dissolved if it was NaNO3 or KNO3. However, we wanted to be extra sure that it was indeed NaCl, so we conducted another test. This time we heated the 10 mL of water to around 30 degrees Celsius and we measured out around 20 grams of salt and poured it in. If the we were correct that the compound was Sodium Chloride, then the salt would definitely dissolve as it was underneath the solubility curve of NaCl. Fortunately, it did dissolve! This left left us with no doubt that the our solute was NaCl. Sweet triumph :)

The dissolved NaCL :)

Proud Probe Buddies :)

Today we learned many things. We learned how to properly read a solubility curve graph, and that our first test resulted in a very saturated and incompletely dissolved NaCl solution, while our second test resulted in an unsaturated and fully dissolved solution. We learned that the solubility of a substance generally increases with the temperature (except in the case of NaCl); it is a direct relationship. It was a very fun lab. My favorite part was struggling along side my Probe Buddy, and creating memories as well as dissolved solutions. :)