You are asked to determine the thermometer correction for your assigned melting point apparatus. You obtain a pure sample of ben
zoic acid and determine its melting point range carefully. After several trials, you obtain a very sharp melting point of 115.1 degrees celsius. What is the thermometer correction at this temperature? For purposes of these questions, the melting point of very pure benzoic acid is 122.4 degrees Celsius. (The thermometer correction is the value that must be added to the observed thermometer reading. You have to type in your answer with a + or - sign. )In a recrystallization of benzoic acid, you begin with a sample of 4.00 grams. After several recrystallizations, a dry sample of 2.7 grams was obtained experimentally. What was your percent recovery? (The format of your answer is important, e.g. 33.2 percent would be entered as 33.2 without any percent symbol or the word percent.)
For different reasons a thermometer can not give the exact temperature that it is measuring, such as incorrect calibration. So the thermometer will have an error, and for this, we can have a thermometer correction, doing experiments with a substance that we know the temperature. In this question that substance was benzoic acid.
The thermometer correction (Tc) is the temperature that was measured less the real temperature, so:
Tc = 115.1 - 122.4 = -7.3ºC
It means that the temperature given by the thermometer is 7.3ºC less than the real.
Question 2:
Recrystallization is the process of transforming the liquid in its solid form (crystals). So, the sample of 4.00 grams of benzoic acid, there'll be water or other impurities. The total benzoic acid given was 2.70 grams, so its percentage will be:
We have to find the number of moles of N₂ that are present in a sample that has a volume of 40.0 L at STP.
STP means Standard Conditions of Temperature and Pressure. These conditions are 273.15 K and 1 atm. We know that 1 mol of N₂ will occupy 22.4 L. We can use that ratio to find the answer to our problem.
