Chem PD no. 2 (PAUL)

CAPE 2014 Lab
of 2
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  Paul Campbell 6B 1 Date: September, 2014 Practical No: Problem Statement: Two chemistry students were arguing about the caffeine content of two different types of coffee, that is instant coffee and grounded coffee. One of the student claimed that instant coffee contains more caffeine than grounded coffee and is more effective for studying while the other disagrees. Plan and Design an experiment to determine which of the student is correct. Hypothesis: Caffeine is a stimulant drug found in coffee. If liquid - liquid solvent extraction is done, it is likely that instant coffee while have more caffeine content that ground coffee.   Title: Aim: To determine if instant coffee has more caffeine than ground coffee or the former. Apparatus and Materials: starch, 0.05 moldm-3 standardised iodide solution, starch indicator, two  bottles of orange juice, burette, conical flask, clamp and stand, notebook , pencil  Method: 1.   Obtain two medium sized bottles of the same brand orange juice. Put both in a refrigerator for 1 week leaving 1 bottle open and the other closed. 2.   Label two conical flasks A and B noting which ones will contain the two different samples of orange juice. 3.   Pour the samples of orange juices respectively into labelled flasks. 4.   To each sample in the flasks labelled A and B add two drops of the provided starch indicator. 5.   Obtain a standardised solution of 0.05 modm-3 iodide solution. Fill the burette with this iodide solution. Record initial Volume. 6.   Begin the redox titration of iodide solution against orange juice containing ascorbic acid.  Note that the end point will be when a blue black colour is seen. 7.   Record data and tabulate results accordingly. 8.   Repeat steps 5 and 6 using the alternate sample of orange juice. 9.   Record data and tabulate results accordingly. Manipulated Variables ** the amount of time taken before the samples of orange juice were used (time in the refrigerator) Controlled Variables The volume of the starch solution added to the orange juice The brand of the orange juice used The concentration of the iodide solution Responding Variables The concentration of vitamin C found in the samples after titration. ** Colour change  Paul Campbell 6B 1 Data to be collected The concentration of the orange juice containing ascorbic acid Expected Results: Table Illustrating Results Expected from the Experiment SAMPLE A 1 2 3 Final Volume of I2/ cm3 Initial Volume of I2/ cm3 Volume Used /cm3 SAMPLE B 1 2 3 Final Volume of I2/ cm3 Initial Volume of I2/ cm3 Volume Used /cm3 Treatment of Results:     Determine the number of moles of iodine used to titrate completely the given sample of Orange juices (ascorbic acid)    Determine the number of moles of ascorbic acid using the balanced equation    Find the concentration of the samples of ascorbic acid.    Determine if the concentrations varied. Assumptions: 1.   There was no side reaction present involving added preservatives in the orange juice samples and the standardised iodide solution.  Limitations/Sources of Error: 1.   Human error in colour change. Colour is subjective and more iodine from the burette will be lost as colour varies amongst individuals
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