Laboratory Questions
Circle the questions that have been assigned.
1. Part A.1. The collected water sample is not filtered. Will this oversight result in the TDS value being reported too high
or too low? Explain.
2. Part A.2. The evaporating dish was not properly cleaned of a volatile material before its mass was determined. When
the sample is heated to dryness the volatile material is removed. As a result of this technique error, will the reported
TDS be too high, too low, or unaffected? Explain.
3. Part A.2. Some spattering of the sample onto the watchglass does occur near dryness. In a hurry to complete the
analysis, the chemist chooses not to return the spattered solids to the original sample and skips the first part of Part A.3.
Will the reported TDS for the water sample be too high or too low? Explain.
4. Part A.3 and Part B.2. The sample in the evaporating dish is not heated to total dryness. How will this error in tech-
nique affect the reported value for TDS--too high, too low, or unaffected? Explain. TSS--too high, too low, or unaf-
fected? Explain.
5. Part A.3. As the sample cools, moisture from the atmosphere condenses on the outside of the evaporating dish (beaker)
before the mass is measured. Will the presence of the condensed moisture increase or decrease the reported TDS in the
water sample? Explain.
6. Parts B.1 and B.2. The sample in the evaporating dish (beaker) is not heated to total dryness. As a result of this tech-
nique error, will the reported value for total solids (TS) be too high, too low, or unaffected? Explain.
7. Parts A and B. Suppose the water sample has a relatively high percent of volatile solid material. How would this have
affected the reported mass of:
a. dissolved solids--too high, too low, or unaffected? Explain.
b. total solids--too high, too low, or unaffected? Explain.
c. suspended solids--too high, too low, or unaffected? Explain.
8. Part D.2. When several drops of 0.010 M $AgNO_3$ are added to a test sample, a white precipitate forms. What can you
conclude from this observation? Explain.
