I had to perform an experiment for the freezing point depression in which we had to determine the freezing points of water as a pure solvent, sodium chloride, sucrose, and ethylene glycol.
We had to work with a partner so I completed the experiment for water, NaCl, and the glycol and had to get the info for sucrose from my partner. The data that was collected was the freezing pint of DI water which was the corrected value for the thermometer that I used. We had to record the temp every 30 seconds until we saw ice crystals. We had to do the same thing for the NaCl, sucrose, and gycol. For the NaCl we started at 0.5 min in which the temp was 15.0 degrees celsius and crystals formed at 10.5 min at -2.0 degrees celsius.
We had to measure out 5.800g of NaCl and record the exact weight. First I weighed the measuring boat and then I poured in the NaCl so to get the exact weight I subtracted the mass of the measuring boat with NaCl from the mass of just the boat. Is this correct?
Also, I need to calculate the # of moles of solute for NaCl and sucrose. To do this for NaCl would I divide the mass of solute by the molecular weight of NaCl?
mass boat + NaCl - mass boat = mass NaCl
moles NaCl = grams/molar mass.
ok thank you!!!
Yes, your approach to measuring the exact weight of NaCl is correct. To get the accurate weight of NaCl, you need to subtract the mass of the measuring boat with NaCl from the mass of just the boat. This subtraction will give you the mass of NaCl alone.
To calculate the number of moles of NaCl, you need to divide the mass of NaCl by its molar mass. The molar mass of NaCl is the sum of the atomic masses of sodium (Na) and chlorine (Cl). The atomic mass of sodium is 22.99 g/mol, and the atomic mass of chlorine is 35.45 g/mol. Adding these two values gives a molar mass of NaCl as 58.44 g/mol.
So, to calculate the number of moles of NaCl, divide the mass of NaCl by the molar mass of NaCl:
Number of moles of NaCl = Mass of NaCl / Molar mass of NaCl
Similarly, to calculate the number of moles of sucrose, you would divide the mass of sucrose by its molar mass. The molecular formula of sucrose is C12H22O11, and its molar mass is calculated by summing the atomic masses of carbon (C), hydrogen (H), and oxygen (O) in the molecular formula. You can find the atomic masses of these elements from the periodic table.