EXAMPLE EXPERIMENT UV-vis SPECTROPHOTOMETER

CONTENTS

CONTENTS	PAGE
Abstract	2
Introduction	3
Literature review	4
Objectives	6
Methodology	7
Results	8
Discussion	9
Conclusion and recommendation	11
Reference	12
Appendix	13

Abstract

This experiment wasabout concentration dependent absorbance values, determined using a UV-vis spectrometer which gives the value of absorbance of a solution based on the amount of light absorbed by the solution. The primary objective of this experiment is to determine the absorbance of copper sulphate solutions of different concentrations. Besides, the absorbance of a sodium chloride sample solution was also determined by using the same method.

In this experiment, copper sulphate solutions of concentrations 28g/L, 14g/L, 7g/L, 3.5g/L, and 1.75g/L were prepared in volumetric flasks from solid copper sulphate. The five solutions were labeled c₁ to c₅ following the sequence. A solution of NaCl was also prepared and labeled as X. These solutions, and distilled water were placed into the UV-vis spectrometer to determine their absorbance. Before the measurement was taken, the UV-vis spectrometer was adjusted so that the wave length of the emitted light was at a wavelength of 800nm. The absorbance value of distilled water was recorded as reference.

While measuring the absorbance of the solutions, the quartz cells containing the solutions must be clear from fingerprints because the fingerprints might affect the amount of UV light that reached the detector in UV-vis spectrometer. Therefore, tissue paper is used to wipe off the fingerprints before inserting the quartz cells into the UV-vis spectrometer.

The experiment basically showed that absorbance increases with the concentration of a solution, obeying Beer-Lambert’s Law.

Introduction

A UV-vis spectrophotometer is a research instrument used to gather information about a chemical sample by determining the absorbtion or transmission of UV-vis light by the sample. It can also be used to measure the concentration of the absorbing materials based on the calibration curves produced.

A UV-vis spectrophotometer exposes a chemical solution to the ultraviolet and visible region of the electromagnetic spectrum when the chemical solution is placed in the UV-vis beam. Depending on the type of chemical, a certain amount of light gets absorbed by the chemical which causes electrons to be promoted from one energy level to another. The amount of light which is not being absorbed will pass through the chemical to the detector. The amount of light that reaches the detector is then recorded as a spectrum. A spectrum is a graphical representation of the amount of light absorbed or transmitted by matter as a function of the wavelength. Since the samples are prepared in known concentrations, the graphed results make a calibration curve from which the unknown concentration can be determined by its absorbance. 

A UV-visible spectrophotometer measures absorbance or transmittance from the UV range from which the human eye is not sensitive to the visible wavelength range to which the human eye is sensitive to.

Literature review

When light passes through a substance, light of certain wavelength is being absorbed by the substance, while the rest of the light will pass through the substance, or being reflected by the substance. For example, when light passes through a solution of copper sulphate, the copper ions in the solution absorbed the visible lights from the red end of the spectrum. The blue light reflects into our eyes and this is why the copper sulphate solution appears to be blue to our eyes.

However, substances do not only absorb lights from the visible region of the wavelength. They also absorb invisible light, for example UV rays, dependent on the type of substance.

Since different substances absorb light of different wavelength, this can be used to determine the type of substance in a sample.

A UV-visible spectrometer can be used to measure the absorbance of solutions. light beams of wavelength in the visible region, and the UV region are passed through the solutions, where light of certain wavelengths are absorbed, and the rest will reach the detector. The detector converts the incoming light into a current. The higher the current, the greater the intensity of the light.

For each wavelength of light passing through the spectrometer, the intensity of the light passing through the reference cell is measured. This is usually referred to as I_o, where I is the intensity. The intensity of the light passing through the sample cell is also measured for that wavelength, given the symbol I.

The relationship between absorbance,A and the two intensities is given by:

From the equation, it is shown that A is a value without unit.

The derived equation, A=ebc

Where

A is absorbance
e is the molar absorbivity
b is the path length of the sample
c is the concentration of the compound in solution

shows that concentration of a solution is directly proportional to its absorbance value.

A UV-vis spectrometer is generallly used in analytical chemistry, especially in the quantitativeanalysis of transition metal ions, highly conjugated organic compounds, and biological macromolecules. Determination is usually carried out in solutions.

Objectives

1.      To determine absorbance of solutions at different concentrations.

The absorbance values of copper sulphate solutions of different concentrations is to be determined using a UV-vis spectrometer.

2.      To determine the concentration of given samples.

Methodology

Reagents and equipment

Solid CuSO_4, distilled water, solid NaCl, 5 100ml volumetric flasks, measuring cylinder, dropper, 200ml beaker, glass rod, 10-mm path length quartz cells, UV-vis spectrometer.

Method

1.      A CuSO₄  stock solution of 2.8g is prepared in 100ml distilled water.

2.      Four sample solutions is prepared in the 100ml volumetric flasks by diluting the stock solution, followed by each previously prepared solution, using sample concentrations of 14g/L, 7g/L, 3.5g/L and 1.75g/L.

3.      A small amount of NaCl (,0.1mg) is added in a 100 ml volumetric flask and the flask is filled with the stock solution. This sample is labeled as X.

4.      The absorbance of distilled water is measured and used as a reference.

5.      The absorbance values of the stock solution and of each of the other solutions are measured at 800nm.

EXAMPLE EXPERIMENT GAVIMETRIC ANALYSIS

CONTENTS

CONTENTS	PAGE
Abstract	2
Introduction	3
Literature review	5
Objectives	6
Methodology	7
Results	9
Discussion	10
Conclusion and recommendation	13
Reference	14
Appendix	15

Abstract

This experiment was about gravimetric determination of chloride. The experiment was carried out to understand the concept of gravimetric analysis from the determination of amount of analyte precipitate, silver chloride. The percentage of silver chloride was also predicted. 

In this experiment, silver chloride was precipitated from the reaction of silver nitrate and sodium chloride. The precipitate was then washed and filtered, followed by the drying and weighing processes to obtain the weight of the precipitate itself. With the known components of the silver chloride precipitate, the weight of chloride could be calculated, and thus the percentage of chloride in the sample of sodium chloride could be calculated. This prediction was based on the assumption that all chlorides in the sample had precipitated to form silver chloride which was then weighed accurately.

It was important to ensure that all the chlorides present had reacted in forming the precipitate. Thus, the settled precipitate was tested with more silver nitrate to ensure complete precipitation. Stirring helped to prevent bumping of the solution during heating and the danger of loss of precipitate. However, precipitate might not be completely dry because it was only heated in the oven for one hour. This caused the weight of silver chloride obtained to be higher than the predicted value because water was present in the precipitate.

Introduction

Gravimetric analysis, by definition, includes all methods of analysis in which the final stage of the analysis involves weighing. Often, its purpose is to determine the mass or quantity of an analyte in the original sample when the weight and quantity of the reacted sample is known.

Gravimetric analysis is one of the most accurate and precise methods of macro quantitative analysis. This is because it involves simple steps and usually simple equipment, therefore giving less room for instrumental errors. The calculation involved does not involve complicated calculation series which affects the accuracy of the result. This explains why gravimetric analysis is the method to obtain the atomic masses of many elements up to six figure accuracy.

Gravimetric analysis can be divided into two categories, namely precipitation and volatilization, both to produce a solid state of the analyte. In the process of gravimetric analysis by precipitation, the analyte is selectively converted to an insoluble form, with the reaction with suitable reagent. Filtration will then be carried out to separate the precipitate from the solution or mixture. The separated precipitate is dried or ignited, possibly to another form, and is accurately weighed. From the weight of the precipitate and knowledge of its chemical composition, the weight of anlyte can be calculated in the desired form.

While gravimetric analysis provides high accuracy and low probability of errors, it is often time consuming, requires considerable attention to details and is limited to single element or limited group of elements at a time.

EXAMPLE EXPERIMENT LIQUID EXTRACTION

CONTENTS

CONTENTS	PAGE
Abstract	2
Introduction	3
Literature review	5
Objectives	7
Methodology	8
Results	10
Discussion	11
Conclusion and recommendation	15
Reference	16
Appendix	17

Abstract

This is an experiment to study the effectiveness of two different types of liquid extraction, namely single extraction and multiple extractions. The solute, crystal violet was to be extracted from its aqueous solution.

Part A of the experiment involved simple extraction, which is single extraction using a fixed volume of organic solvent, 10ml dichloromethane. The extraction process was carried out using a seperatory funnel and the aqueous crystal violet left from the extraction was transferred into a test tube for later comparison with Part B of the experiment. In Part B of the experiment, similar procedure was carried out, but instead of using 10ml dichloromethane all in once, the extraction was done two times, with 5ml dichloromethane each. The aqueous crystal violet collected from this part of the experiment was compared with that in Part A of the experiment.

The colour intensity of the solutions gave an idea of how effective the extraction was. This is because the more crystal violet was present in the aqueous solution, the more purple the solution was. Higher amount of crystal violet in the aqueous solution indicated a less effective extraction, since less crystal violet was drawn into the organic solvent. Therefore, the aqueous solvent with a higher intensity of purple colour was obtained from a less effective extraction.

In this experiment, the organic solvent, dichloromethane must be handled with care and goggles must be worn, because excess exposure to the substance causes cancer. During the procedure of extraction, the seperatory funnel must be opened after shaking the contents in it because vigorous shaking of the contents produces vapour. The high pressure inside the funnel might explode the apparatus and cause injuries if it wasn’t released.

EXAMPLE EXPERIMENT CALORIMETRY

CONTENTS

CONTENTS	PAGE
Abstract	2
Introduction	3
Literature review	5
Objectives	7
Methodology	8
Results	10
Discussion	16
Conclusion and recommendation	19
Reference	20
Appendix	21

Abstract

This experiment is about calorimeter. This experiment was divided into two parts, Part A and Part B.  Part A was carried out to determine the specific heat of metal, where copper was used in this experiment.Part B was carried out to determine the quantity and direction of heat flow for the dissolution of a salt, which was natriumthiosulphate, Na₂S₃O₂.

For part A and B, polyform cups filled with water were used as the calorimeters. Thermometer was used to measure the change of temperature when the substances were added into each calorimeter. For Part A, copper was heated in a water bath, and then transferred into the calorimeter. The temperature of the water bath, the initial temperature and temperature change in calorimeter were measured with a thermometer. The weights of water and copper were also measured with an electronic balance. This information obtained from the experiment was used to calculate the specific heat of copper.

 For Part B, the salt Na₂S₂O₃is added into water where it dissoluted. Similar to Part A, the information and result were recorded to calculate for the quantity of heat transferred, and the direction of transfer.

During the experiment, several errors occurred. As too much time was taken to transfer the substances into the calorimeter, there was heat transfer between the surrounding and the substances. Na₂S₂O₃ salt did not dissolve completely after swirling, causing the reaction to be incomplete. Besides, the heat from the apparatus might be absorbed into the water and substances. Heat was also produced during the stirring process. There were some errors when the readings of the temperature and the weight of calorimeter, water, copper and Na₂S₂O₃were taken.

EXAMPLE EXPERIMENT BUFFER SOLUTION

CONTENTS

CONTENTS	PAGE
Abstract	2
Introduction	3
Literature review	5
Objectives	7
Methodology	8
Results	9
Discussion	10
Conclusion and recommendation	15
Reference	16
Appendix	17

ABSTRACT

This purpose of this experiment was to understand the nature of a buffer, to prepare a buffer from acetic acid and sodium acetate and also to test the ability of buffered and unbuffered solutions to resist pH changes when strong acids and bases are added. This experiment can be divided into three parts, where the first part was to prepare the buffer solutions needed, the second part tested the buffering action towards acid while the third part tested the buffering action towards base. In parts B and C, the acid and base were added 1ml once, drop by drop using a dropper so that they dissolved well in the solutions. The pH readings of the solution before and after adding each ml of the acid or base were measured by a pH meter which was calibrated to ensure accurate reading. During this experiment, several errors which can affect the results of the experiment had occurred. For example, the beakers used to contain the buffer solutions might be contaminated. This caused the pH reading taken to differ from the theoretical values. Besides, the calibration of the pH meter was not done well enough to acquire accurate readings for the measurements. This explained why the pH readings of the solutions measured are all lower than expected.

EXAMPLE EXPERIMENT LE CHATELIER'S PRINCIPLE

Contents

content	page
Abstract	2
Introduction	3
Literature review	5
Objectives	7
Methodology	8
Results	11
Discussion	14
Conclusion and recommendation	15
Reference	16
Appendix	17

Abstract

This is an experiment to study chemical equilibrium and Le Chatelier’s Principles. Chemical equilibrium is the stable state a chemical reaction reaches when there is no further undergoing reaction or change. Le Chatelier’s Principles state that when a chemical equilibrium is disturbed by certain changes, it will shift the position of equilibrium towards the side to minimize the effect of the changes applied.

In this experiment, six sets of chemical reaction were carried out to study the effect of adding particles or ions of reactants or products to the position of equilibrium.

(i)                  The saturated sodium chloride solution equilibrium

(ii)                The iron (III) thiocyanate ion equilibrium

(iii)               The acetic acid equilibrium

(iv)              The chromate-bichromate equilibrium

(v)                The bismuth chloride-water equilibrium

(vi)              The cobalt (II) chloride equilibrium

The shifting of equilibrium can be determined from the colour of the solution or mixture since the reactions chosen in this experiment have reactants of different colours from corresponding products, or undergo other distinct changes.For example, in the first part of the experiment, concentrated hydrochloric acid was added to a saturated solution of sodium chloride. The chloride ions yield by concentrated hydrochloric acid had increased the chloride ion concentration which is a product of hydration of sodium chloride. Hence, the changes were observed and shifting of this equilibrium position was deduced.

This experiment must be conducted very carefully and the substances must be measured and added very accurately because any slight error might influent the outcome of the experiment. Besides, the mixture of substances must be stirred well until the substances are will mixed and form a mixture of same physical state (homogeneous solution), in this experiment, liquid.

The experiment outcome supports Le Chatelier’s Principles in the aspect of concentration. When the concentration of a particle in an equilibrium is altered, the equilibrium position will shift to the direction to counteract the change. In this experiment, the concentrations of product or reactant particles were increased by adding like particles (the same substance or substance containing like ions). The equilibriums conducted shifted to the opposite direction of the increased concentration, and produced more particles of the substances it shifted to. 

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