1. The concentration of a 2M sulfuric acid could also be correctly expressed as:
a 1.96 g/100mL
b 1960 ppm
c 19.6 % w/v
d 19.6 g/L
i picked c, is that right?
2. In an attempt to find the concentration of ethanoic ( acetic ) acid in vinegar, a student titrated a 20.00mL sample of a standard sodium hydroxide solution with a diluted vinegar solution from a burette. The student obtained the following titration results: 18.65 mL, 19.15 mL, 19.20 mL and 19.10 mL.
The discrepancy in the first titration could be due to the student washing the:
a) conical flask with the sodium hydroxide solution only.
b) pipette with water only
c) burette with water only
d) pipette with sodium hydroxide solution only
e) burette with diluted vingar solution only
umm.. for this question is the diluted vinegar solution in a conical flask or in the burette? I thought normally the unknown concentration sample would be in the conical and the standard solution would be in the burette, but the question says "...diluted vinegar solution from a burette", and what would the answer be?
3. A manufacturer claims that a sample of lead nitrate, _2)
is 95.7% pure. A student wishes to check the validity of this claim by carrying out a gravimetric analysis. He aims to precipitate the lead ions as lead iodide (
has a solubility of 0.76 
).
The student carefully and accurately weights 15.07 g of the sample and dissolves it in water in a clean volumetric flask. He makes the volume up to 250.0 mL exactly. Using a clean, dry pipette he measures 20.00mL samples of this solution into three clean flasks. To each flask he adds an excess of sodium iodide solution. Lead iodide precipitates.
For each experiment he collects all of the solid and washes it carefully and thoroughly with water. Each sample is then dried for 1 hr at 90 deg C. Lead iodide does not decompose at this temperature.
a) The student obtained the following results:
mass of PbI_2 collected: 1.524g, 1.743g, 1.458g.
Suggest two reasons to explain the variation in his results.
Home
Help
Search
Login
