a. In the laboratory, you have a 500 mL. stock solution that is 7.57x103 M in ca

Question

a. In the laboratory, you have a 500 mL. stock solution that is 7.57x103 M in caffeine. For an experiment to mimic the concentration of caffeine in coffee, you need to make a NEW 100. mL solution that has a caffeine concentration of 3.40x108 M Describe using WORDS and NUMBERS how to make this solution. Be Specific! OR b. Calcium oxide, can be produced by heating calcium hydroxide, Ca(OH)z via the following reaction: Ca(OH)2 CaO +H2O If 45.2 grams of calcium oxide are obtained from 1.00 mole of calcium hydroxide, what is the percent yield of the reaction?

Explanation / Answer

a. Preparation of solution

using,

V1 = C2.V2/C1

with,

C1 = 7.57 x 10^-3 M

C2 = 3.40 x 10^-8 M

V1 = ?

V2 = 100 ml

So,

the volume of stock needed to prepare solution (V1) = 3.40 x 10^-8 M x 100 ml/7.57 x 10^-3 M

                                                                                    = 0.00045 ml = 0.45 microliter

So we would taken 0.45 microliter of stock solution (7.57 x 10^-3 M) and dilute it with 99.99955 ml of water to get 100 ml of 3.40 x 10^-8 M solution.

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b. Ca(OH)2 --> CaO + H2O

1 mole of Ca(OH)2 would produce 1 mole of CaO

1 mole of Ca(OH)2 = 74.093 g

theoretical yield of CaO = 1 mol x 56.08 g/mol = 56.08 g

actual yield = 45.2 g

So,

percent yield = 45.2 g x 100/56.08 g = 80.60%

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