Creating Solutions of Standard Molarity
Madelene Andersson
Sarah Toadvine
CHEM 1251L-013
10/13/2014
Introduction: The purpose of this lab is to find the unknown concentration of Cu+2 by comparing the solution to a set of standard concentrations, different known concentrations, which are prepared by diluting approximately 2.5 grams of copper (II) sulfate pentahydrate. A concentration is the amount of solute relative to the volume of a solution, the more solute the more concentrated the solution will be. Concentrations are reported using molarity (M) which is the moles of the solute by the volume of solution in liters. A spectrophotometer called the Spec 20 and the Beer-Lambert law is used to determine the concentrations of solutions. The Spec 20 is used to measure the amount of light that passes through a solution. This is measured in terms of absorbance which is the amount of light a solution absorbs or transmittance which is the amount of light that passes through a solution. The relationship between absorbance and transmittance is A= -log T or A=2-log (%T).
The Beer-Lambert Law establishes the quantitative relationship between absorbance and a solution’s concentration.
The formula is A=ԑbc
A=absorbance
ԑ=molar absorptivity constant b=the path length (cm) through which light travels c=molar concentration of solution
The Beer-Lambert plot (absorbance vs. concentration) establishes a calibration curve that is used to determine the concentration of a solution of the same
This experiment is based on determining the chemical formula for a hydrated compound containing copper, chloride, and water molecules in the crystal structure of the solid compound, using law of definite proportion. The general formula of the compound is CuxCly•zH2O, and aim is to determine chemical formula of this compound.
With these absorbance numbers a concentration curve was constructed and the unknown solution was determined by finding the point of absorbance on the curve.
In this task the concentration of an unknown sample of copper sulphate using colorimetry was used to find the concentration. In this investigation copper sulphate was used which is CuSO4.5H20 as a formula. To make a standard solution which was 1M, the same clean equipment was used to make up the standard solution as used to make sodium carbonate. However there was one difference and that was that the hot distilled water was used to dissolve the copper sulphate crystals. There had to be enough hot water in order to dissolve the crystals into the beaker and then add cold distilled water to cool the solution.
10 microliters of the sample is then added and the assay absorption is measured at 340nm. If absorbance was above 1.5, samples were diluted.
The ending result of this experiment confirms that as five test tubes are lined up with the varying level of absorbance, different results in the level of absorbance will appear as well, this is visible in above table. Thus, this is due to the varying amount of water in the solution. The blank sample had a 0.30 in its level of absorbance.
The Beers Law calibration experiment used many concentrations of crystal violet solutions. Each of these solutions were test and analyzed in order to determine the absorbance of each concentration The results were than graphed and produced a slope of 1.00E05 with an intercept of -2.21E-02.
The Copper Cycle is a popular experiment used to determine if an element, in this instance, copper, reverts to its elemental form after a chain of reactions. This experiment is very dangerous because of the reactions between the strong acids and bases. In this experiment I performed a series of reactions starting with copper metal and nitric acid to form copper (II) nitrate. Then I reacted copper and several other solutions such as, sodium hydroxide, sulfuric acid, ammonium hydroxide, and hydrochloric acid to form precipitates. In conclusion my percent recovery
A spectrophotometer is an instrument which measures the amount of light of a specified wavelength which passes through a medium. This instrument is usually used for the measurement of reflectance of solutions. Light is separate into different wavelengths and is being passed through the sample solution. The sample solution will have its own wavelength and will absorb a certain amount of light. The higher the molecular concentration, the higher the absorbance value.
The absorbance is measured using a Plate reader and a Standard curve is generated. Also, the different types of pipetting techniques are assessed in this Assay.
The lab performed required the use of quantitative and analytical analysis along with limiting reagent analysis. The reaction of Copper (II) Sulfate, CuSO4, mass of 7.0015g with 2.0095g Fe or iron powder produced a solid precipitate of copper while the solution remained the blue color. Through this the appropriate reaction had to be determined out of the two possibilities. Through the use of a vacuum filtration system the mass of Cu was found to be 2.1726g which meant that through limiting reagent analysis Fe was determined to be the limiting reagent and the chemical reaction was determined to be as following:-
The absorbance obtained from the results of each test sample, then put into the equation of calibration curve in accordance with the respective raw substances, after which it would have obtained the value of molar absorptivitas. The molar absorptivitas results obtained are used in the determination of the percentage of the sample levels
Each tube was measured by a spectrometer to find absorbance. The Beer-Lambert Law was used to find the concentration (shown below in Table
When we add metal ion in the solution and dilute with HNO3, we tried to find out the concentration of metal ion. And HNO3 is solution and metal ion is solute. And through the data and graph, we know that absorbance and concentration are in direct proportion, so it means that when the solution has high concentration, and less light can pass through the solution, it means transmission is smaller. But absorbance is in contrast.
Understanding Beer’s Law, we know that A=ɛbc with A equaling the absorbency, ɛ is the molar absorptivity (M-1cm-1), b being the pathlength measured using cm, and c is the molar concentration of a solution. Beer’s law specifically explores the quantitative analysis of a concentration of the radiation absorbed vs. the concentration of the absorbing chemical. The light absorbency of the beam
The reaction characteristics of basic copper carbonate 〖mCuCO〗_3⋅n〖Cu(OH)〗_2 were observed by changing the reaction mole ratio. The reaction mole ratio of sodium carbonate to copper chloride (II) was controlled from 1.08 to 1.68. Fig. 1 shows the XRD patterns of copper carbonate powder. At a reaction ratio of 1.08, paratacamite (Cu_2 Cl(OH)_3 ), beside alkali copper carbonate, was formed because of incomplete reaction at a copper content of 53.9 wt%. Lack of sodium carbonate may cause incomplete reaction with copper chloride (II) because of low pH (6.0) of the solution [12]. The copper content according to the reaction mole ratio were 57.7, 50.5, 58.8, 59.3, and 59.8 wt% at the reaction mole ratios of 1.20, 1.32, 1.44, 1.56, and 1.68, respectively.