make 500mL of 20% methanol (solvent A) per volume with ultra purified water this one is 100mL of methanol and 400mL of purified water

make 100mL 125mg/L caffeine in solvent A 125mg/L * 0.1L =12.5mg = 0.0125mg of caffeine needed

prepare dilution sof caffeine at 100,75,50,25mg/L in 25mL flask with solvent A

to dilute this use how much caffeine solution should I add in volumetric flask and am I right about the sample calculation

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Hubert KochLv2

13 Dec 2019

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Preparation of Required Solutions

(NOTE: the methanol is used in the NP solution simply to make the solvent conditions analogous to the NPA solution)

measure out 13.9 mg of NP (139.11 g/mol) - record the mass; place into a 100 ml volumetric flask

add 30.0 ml methanol; mix to dissolve

dilute to 100.0 ml total volume with deionized water; mix well

take 5.0 ml of this solution and place in separate container; add 45.0 ml deionized water; mix well

QUESTION: what is the [NP] in the NP stock solution?

Given the following data, calculate the percent by mass Fe²⁺ in the unknown sample. Assume the experimental data provided is obtained using the same procedure you will be using in the lab.

Unknown sample mass = 0.1700

Absorbance (average) of unknown sample = 0.343

Beerâs Law Data: Slope = 0.2143 L/mg Fe²⁺

y-intercept = -0.002

Additional Information (Lab procedure):

1. Obtain and clean three 100-ml volumetric flasks

2. Weigh 0.15-0.20g of the unknown accurately into a clean 100ml beaker

3. Add about 30ml distilled water and 1ml concentrated sufuric acid. Swirl to dissolve sample and quantatively transfer into a 100ml volumetric flask. Make up the flask to the mark with distilled water and mix thoroughly

4. Pipet 10.00ml of this solution into the second volumetric flask and make up to the mark

5. Pipet 10.00ml of this diluted solution ( from step 4) into the third volumetric flask. Add 10ml saturated sodium acetate and 10ml 10% hydroxylamine hydrochloride, and wait five minutes

6. Add 10ml 0.1% 1,10 phenanthroline to the flask. Wait 10 minutes, then make up the flask to the mark with distilled water