Circle the questions that have been assigned. Part A.1. During the cooling of th
ID: 569427 • Letter: C
Question
Circle the questions that have been assigned. Part A.1. During the cooling of the fired crucible, water vapor condensed on the crucible wall before its mass measure- water in the hydrated salt be reported as being too high, too low, or unaffected? Explain. oil from the fingers is burned off. Will the percent water in the hydrated salt be reported as being too high, too low, or e condensation did not occur following thermal decomposition of the hydrated salt in Part B. Will the percent ible is handled with (oily) fingers before its mass measurement. Subsequently, in Part B.1, the 3.) Part A. 1. The crucible is handled with (oily) fingers after its mass measurement but before the -3 g sample of the 4. Part A.2. Suppose the original sample is unknowingly contaminated with a second anhydrous salt. Will the reported S. After heating in Part A.1, the crucible is set on the lab bench, where it is contaminated with the cleaning oil used to 2. Part A.1. The fired cruci unaffected? Explain. hydrated salt is measured (Part A.2). Subsequently, in Part B.1, the oil from the fingers is burned off. Will the percent water in the hydrated salt be reported as being too high, too low, or unaffected? Explain percent water in the hydrated salt be too high, too low, or unaffected by its presence? Explain. clean t anhydrous salt is determined. While heating, the cleaning oil is burned off the bottom of the crucible. Describe the error that has occurred; that is, is the mass of the anhydrous salt remaining in the crucible reported as being too high or too low? Explain. he lab bench, but before its mass is measured. The analysis continues through Part B.1, where the mass of the 6. Part B.1. The hydrated salt is overheated and the anhydrous salt thermally decomposes, one product being a gas. Will 7) Part B.1.Some of the hydrated salt spatters out of the crucible because of a too rapid heating process. Will the reported 8. Part B.2. Because of a lack of time, Bill decided to skip this step in the Experimental Procedure. Will his haste in 90 Percent Water in a Hydrated Salt the reported percent water in the hydrated salt be reported too high, too low, or be unaffected? Explain. percent water in the hydrated salt be reported too high, too low, or unaffected? Explain. reporting the "percent H,0 in the hydrated salt" likely be too high, too low, or unaffected? Explain.Explanation / Answer
1) A hot substance draws moisture from the atmosphere while it is cooling down to room temperature. The moisture condenses on the surface of the hot crucible. This moisture doesn’t result from heating of the hydrated sample; rather the source of this moisture is external. Consequently, the recorded weight of the crucible (after cooling) and the anhydrous salt will be higher than the actual value. The mass of water lost on heating is obtained as
mass of water lost = (mass of hydrated salt before heating) – (mass of anhydrous salt after heating)
Since the mass of water lost is recorded low, consequently, the calculated moles of water in the hydrated salt will be low and hence, the percent hydrate in the hydrated salt will be low.
2) The mass of the crucible before heating will be high due to the oil from the fingers; therefore the mass of the hydrated salt will be recorded higher. However, since the oil is burned off, the mass of the anhydrous salt after heating will be ok and the mass difference, i.e, the mass of water lost will be calculated high. Therefore, the percent water in the hydrated salt will be calculated high.
3) The mass of the hydrated salt is given as
mass of hydrated salt = (mass of crucible plus hydrated salt) – (mass of empty crucible)
Since the crucible was handled with oily fingers after measuring the mass of the empty crucible, but before adding the salt, hence, the mass of the empty crucible will be recorded ok. Since about 3.0 g salt was added, the mass of the hydrated salt can be calculated fairly accurately. The oil was burned off during heating and hence, the mass of the anhydrous salt was recorded ok. Since there was no change in mass before and after heating, hence, the calculated percent water in the hydrated salt will remain unaffected.
7) A portion of the hydrated salt spattered out of the crucible during heating. The mass of the salt was weighed accurately before heating. However, due to spattering, some salt was lost and was not converted into the anhydrous salt. Consequently, the recorded mass of the anhydrous salt will be low and thus the mass difference, i.e, the mass of water lost will be high. Therefore, the calculated percent water in the hydrated salt will be high.