Making Solutions of Differing % Mass/Volume Concentrations

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Making Solutions of Differing % Mass/Volume Concentrations
Lab Manual 3F

timeline Monday—Lecture Tuesday—Perform Lab Part I, II, III
Thursday—Perform Lab Part IV

Write-up Procedures (all will do the additional concentrations)—part IV #4 Data (include additional concentrations) (include additional concentrations) .3125% and % Data Analysis/Conclusion (answer all questions in from the text) Thinking Like a Biotechnician--#1,2,4 (Skip 3)—do 4 on notebook paper

Prep. for 3f Check for sodium hydroxide pellets, cupric sulfate 5 hydrate, gelatin, glass tubes Set-up spectrophotometer

Background Application Example
Fertilizer—”12-5-7” 12% nirogen, 5% phosporus 7% potassium in the 5 lb bag .12 x 5lb=.6lb nitrogen .05 x 5lb=.25lb phosphorus .07 x 5lb-.35lb potassium

Background Biuret reagent
Copper sulfate and sodium hydroxide make up a protein indicator called Biuret reagent 2 to 1 ratio of 10% sodium hydroxide and 5% copper sulfate When the copper reacts with certain amino acids in proteins, the solution goes from blue green or violet. The darker violet the solution, the more protein is present Copper also used as an indicator in Bradford reagent & BCA reagent as a protein indicator & in Benedict’s solution for glucose

Background Copper sulfate is only good for about 1 week before precipitating out Gelatin is made from fairly large protein molecules that do not easily go into solution, this is why gelatin must be heated to go into solution. The protein testing should be conducted at room temperature, so you need to plan ahead Gelatin solutions are fairly concentrated, to get obvious color difference

Formulas Volume desired (ml) x concentration desired (% g/ml converted to decimal value of g/ml)= ____g of solute

Safety Precautions Sodium hydroxide is dangerous (wear gloves and googles)—strong base Use hot plates not a flame

Lab 3F tips Do calculations in advance—show how units cancel
When making a solution, the solute is measured out first, and the solvent is mixed into the solute The mass takes up space, solutions are always prepared by raising the solvent to the final volume