Improving Lab Practices: Chemical Safety and Quantitative Analysis Techniques

Categories: Chemistry

Analysis, Pages 8 (1778 words)

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Abstract

The laboratory setting demands rigorous standards for safety and accuracy, particularly when handling chemicals. This essay delves into the crucial aspects of risk assessment and quantitative analysis techniques in a laboratory experiment focusing on handling chemicals like Sodium Carbonate and Hydrochloric Acid. By systematically evaluating hazards and employing precise measurement and analysis methods, we can significantly mitigate risks and enhance the reliability of experimental outcomes.

Introduction

Risk assessment forms the cornerstone of laboratory safety, enabling the identification and mitigation of potential hazards associated with chemical handling.

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This essay outlines the steps taken to assess risks and implement safety measures during a laboratory experiment. It further explores quantitative analysis through titration and colorimetry, underscoring the importance of precise measurements in determining chemical concentrations.

Quantitative Analysis Techniques

The laboratory experiment involved quantitative analysis through titration and colorimetry to determine the concentration of Hydrochloric Acid (HCl) and Sodium Hydroxide (NaOH), respectively.

Acid ( NaCl + Co2 + H20

The balanced equation for this reaction is:

Na2CO3 + 2HCL > 2NaCl + CO2 + H20

Amount in moles = concentration ( in mol dm-3) x volume (in dm3)

25cm3 / 1000 = 0.

025vol

0.025 x 0.037784 = 9.446 x 10- 4 mol

Amount in moles of Hydrochloric Acid required to neutralise 25cm3 of Na2CO3.

(9.446 x 10 -4 ) x 2 = 1.8892 x 10-3 mol

Calculation of unknown concentration of hydrochloric acid using the mean titre concentration (in mol dm-3) = amount (in moles) / volume (in dm3)

Titration of Dilute Hydrochloric Acid Against Sodium Hydroxide

I also repeated the titration method, this time I titrated hydrochloric acid into the sodium hydroxide, using phenolphthalein. The solution needed to go from a pink colour to a colourless solution, or in other words from an alkali to an acid.

The first step I took, was to rinse my equipment. I had to rinse my conical flask using distilled water to make sure that there are no leftover atoms within the conical flasks, that may have affected the colour and results of the titre. I also rinsed my burette using dilute hydrochloric acid to make sure that only hy- drochloric acid is going into the titre. I used pipette number nine and also rinsed this with the sodium hy- droxide which is what the unknown concentration is also going to be.

After rinsing the burette with hydrochloric acid, I made sure that the tap was closed so that I could also add more hydrochloric acid for my titration. I then added up to 0 cm3 of the hydrochloric acid into the burette using the funnel and also while making sure I was holding the burette to have more control over the transfer of the hydrochloric acid.

I did this to makes sure that my face and arms were safe from being splashed with the hydrochloric acid, this may have happened if I was transferring the acid while it was clamped on the clamp stand using the funnel. So instead I was prepared wearing goggles and a buttoned up lab coat to protect my eyes and clothing from being splashed by the hydrochloric acid. After transferring the hydrochloric acid into the barrette, I then clamped the burette onto the clamp stand making sure that it was secure and that the funnel had been removed from the top. I also made sure that the burette was clamped high enough to allow the conical flask to sit underneath the burette. I also fitted the clamp with a white tile at the base of the clamp so that I could easily identify the change in colour of the solution.

The second step in this procedure was to take 25cm3 of sodium hydroxide using the pipette. I used the pipette and extracted 25cm3 of the solution until it reached the point of the graduation line and the menis- cus sat just above the graduation line. I then emptied this into the conical flask and then added two to three drops of the phenolphthalein to the conical flask, making it an alkali solution.

Learning Aim A – Keeping Up The Standards

I then placed the conical flask underneath the burette and slowly released some of the hydrochloric solution into the conical flask while stirring then stopping to see how much the hydrochloric acid has changed the solution. I did this until the solution became colourless and then repeated this again then measured the results until I got concordant results. In my case I only needed to repeat the procedure twice as I had gotten concordant results after my trial run and actual first run. The concordant results are below;

Determining the Concentration of the Sodium Hydroxide Solution

The equation for this reaction is:

NaOH + HCL > NaCl + H2O

This equation is already balanced as there are equal amounts of the chemicals on each side of the equation.

Calculation of the amount of hydrochloric acid in moles, used in the titration using the mean titre.

amount (in moles) = concentration (in mol dm-3) x volume (in dm3)

The concentration is the same as the concentration from step seven so 0.10394479 mol dm-3 and the volume is the mean titre/1000

So 0.10394479 x 0.021 = 2.182844559 x 10-3 mol

Calculation of the amount in moles, of Sodium Hydroxide in the 25cm3 used in the titration.

The relationship of the NaOH solution is a 1:1 relationship so the answer is the answer is the same as above: 2.182844559 x 10-3 mol

Calculation of the unknown concentration of the NaOH

Concentration (in mol dm-3) = amount (in moles) / volume (in dm3)

2.182844559 x 10-3 / 0.025 = 0.087313782 mol dm-3

Colorimetry

What is colorimetry? Colorimetry is the process that is used to determine the concentration of coloured compounds in a solution. This is done by calculating the concentration of a specific sample from the intensity of light before and after it passes through a sample using the Beer-Lambert law. In this practical I had to prepare a standard solution of CuSO4.5H2O or Cupric or Copper Sulphate Pen- tahydrate, and also produce a calibration graph. The calibration graph will also be used to help identify the unknown concentration of two solutions of CuSO4.5H2O or Cupric Sulphate Pentahydrate.

Step 1: Safety

In this step of the practical I had to make sure that the lab and the area around me was safe to work in. II did this by making sure that the area was clear and that chairs and bags were tucked in underneath the table to prevent any trip ups. I also wore a lab coat and had it buttoned to prevent the Cupric Sulphate Pentahydrate from falling onto my clothes. This is because the Cupric Sulphate Pentahydrate is a corro- sive and also harmful. I also wore goggles to prevent any of the Cupric Sulphate Pentahydrate from entering my eyes. I also made sure to wash my hands, if the chemical touched my skin to prevent any redness, irritation or burns that may have occurred, if I did not wash it off of my skin.

I also made sure to handle all of the equipment with care, this is because the equipment including the beaker, stirrer and volumetric flask were all fragile and care had to be taken as to make sure that no molecules were lost if the stirring rod was sat down, and also to make sure that the stirring rod did not shatter, if it had rolled around on the table.

Step 2: Preparation of Cupric Sulphate Pentahydrate Solution

To prepare the Cupric Sulphate Pentahydrate, I had to make sure that the units were accurate for the calculations. So to prepare 100cm3 of 0.25dm-3 solution of the Cupric Sulphate Pentahydrate, I had to divide the 100cm3 by 1000 to get 0.1dm-3 as a measure for the volume.

Calculation for amount in moles of the 0.25m of Cupric Sulphate Pentahydrate.

Amount in moles = concentration (in mol dm-3) x volume (in dm3)

0.25mol dm-3 x 0.1dm3 = 0.025 mol

Calculation for mass in g of Cupric Sulphate Pentahydrate required.

Mass (in grams) = amount (in moles) x molar mass (in g mol-1)

Molar mass of : CuSO4.5H2O = 249.6

0.025 x 249.6g mol-1 = 6.24g

For the next step in the preparation of CuSO4.5H2O or Cupric Sulphate Pentahydrate, I then weighed out the mass required on the scales using a weighing boat, after I had calibrated the bal- ances again.

I weighed the mass of the weighing boat and made a note of the mass. After this I then added the 6.24g of Cupric Sulphate Pentahydrate to the weighing boat and took the present mass of the weighing boat into account, so after I had finished adding the Cupric Sulphate Pentahydrate to the weighing boat, the total amount was 7.41g. The results for this are below.

After weighing out the CuSO4.5H2O, I then rinsed out a 100cm/ml beaker with distilled water to make sure that there were no existing chemicals inside the beaker already. I then transferred the Cupric Sulphate Pentahydrate to a regular 100cm/ml beaker and added ups to no more than 50cm/ml of distilled water, to prevent any spillages and a loss of molecules. I then stirred the solution with a glass stirring rod until the Cupric Sulphate Pentahydrate had been nearly almost dissolved with the distilled water.

Mass in g (grams)

Mass of weighing boat +

CuSO4.5H2O

Mass of empty weighing boat 1.17

Mass of CuSO4.5H2O used 6.24

After this step, I then transferred my solution into a volumetric flask that I had already rinsed be- fore hand using distilled water. I transferred the Cupric Sulphate Pentahydrate solution from the beaker to the volumetric flask using a funnel. After this I also rinsed the stirring rod and beaker at least twice before also transferring it to the volumetric flask , to ensure that all of the mo- lecules were collected.

I then added more distilled water to the volumetric flask, until the volume had increased and then also precisely added distilled water a few drops at a time until the meniscus had sat just above the graduation line. This is also known as the point of accuracy. I also incorporated the volume with the lid on until it had combined well.

Safety Precautions and Equipment Handling

Ensuring a safe laboratory environment necessitated meticulous preparation and handling of chemicals and equipment. Measures included wearing appropriate personal protective equipment, careful measurement and transfer of substances, and thorough rinsing of apparatus with distilled water to prevent contamination and ensure accuracy.

Conclusion

Risk assessment and quantitative analysis are integral to conducting safe and precise laboratory experiments. Through careful evaluation of potential hazards and the application of titration and colorimetry, the experiment demonstrated the effectiveness of these methodologies in determining chemical concentrations accurately while upholding safety standards. This approach not only safeguards the well-being of individuals conducting the experiment but also ensures the reliability of the data obtained.