Industrial Standard Solutions and Titrations
Standard solutions are solutions containing a known concentration of a substance or element used to identify a substances concentration which os unknown. To prepare standard solutions in the college lab we need: a measuring balance, sodium hydroxide pellets, 250cm3 beaker, distilled water, funnel, pipette, 2 x 250cm3 volumetric flask, glass stirring rod and a 25cm3 bulb pipette and filler. First, we have to weigh out 1.00g of sodium hydroxide into the beaker and add 100cm3 of water, stirring using a glass rod. Using a funnel, the solution is then put into a volumetric flask and topped up with water.
Standard solutions can be prepared by dissolving primary standards in solvents. Primary standards are soluble solid compounds that are very pure and have high molar mass. They can be used in lots of different types of industry, for example Sodium carbonate (Na2CO3) is well known for its use as a water softener but it can also be used in the manufacturing of glass and is also used in swimming pools to raise the pH. The equipment needed in the procedure of preparing a standard solution of sodium carbonate include: a measuring balance, distilled water, volumetric flask, 1.300g of anhydrous sodium carbonate, small beaker, funnel, pasteur pipette and a stopper.
First of all, we have to make sure that the volumetric flask is clean swirling distilled water around the flask to rinse it then discarding it. If the flask is dirty, there will be water droplets inside the flask, this must be washed with detergent, rinsed and dried and then it is read to use. Next, we weigh out 1.300g of readily prepared anhydrous sodium carbonate onto a clean and dry small beaker, ensuring to work quickly to prevent the sodium carbonate absorbing moisture from the atmosphere. Then, a funnel is placed in the flask, making sure to leave a small air gap around the funnel (this will make sure that water will run through the funnel). We can now put some of the sodium carbonate into the funnel, washing it into the flask using a small amount of distilled water and repeat until all the sodium carbonate has been transferred. The beaker can then be positioned over the funnel, pouring a small amount of distilled water over it to transfer any microscopic amounts of sodium carbonate to the flask and repeat the process. To dissolve the sodium carbonate, swirl the flask gently. After this, slowly pour distilled water through the funnel into the flask until the bottom of the meniscus is about 1cm from the graduation mark on the neck of the flask. Remove the funnel and use the pipette to transfer distilled water to the flask until the bottom of the meniscus sits on the graduation mark on the neck of the flask, seen at eye level. Finally, put the stopper on the flask and invert it several times ensuring it is thoroughly mixed and then label the flask with the name of the reagent, the date it was prepared and its concentration.
Similarities and differences to standard solutions in prepared in industry and in the college lab:
• Most of the equipment used in this practical is the same but more advanced and upgraded which gives more accurate results.
• Generally, the practical is the same and has a similar method, but it is more precise. For example, the first step in the experiment was important because in industry there is little/no room for error as it is being sold to and used by the public, and if there was any kind of substance (especially a harmful substance) left in the flask, it could have bad consequences, e.g. it could cause irritation when used in water.
• The practical is a longer process than the one in the college lab, to make sure everything is done properly, but it is carried out by professionals who have done it many times before, so they will be able to do it at a quicker speed.
• The workers are highly trained and skilled whereas the practical in the lab is carried out by students. Therefore, in the college lab, mistakes are more likely to be made and there will be less accurate and reliable results.
• The scale of production in industry is much higher than the one in the college lab, this is because the standard solutions are used in real life rather than being discarded after they were made.
• In industry in general, different material is used which is more expensive but gives more accurate results.
• In industry, machines can read results which is a lot more accurate than in the college lab where we manually read results as there is more room for error.
Titrations are a method of quantitative chemical analysis used to find the concentration of known analytes. To carry out titrations in the college lab we need: a burette, burette stand, clamp, 100cm3 beaker, white tile, funnel, 0.10moldm-3 hydrochloric acid, 25cm3 bulb pipette and filler, sodium hydroxide solutions, 250cm3 conical flask, phenolphthalein indicator and distilled water. Using a funnel, we fill the clamped burette with hydrochloric acid until it is close to the zero point then open the tap to fill the jet. The conical flask is filled with 25.00cm3 sodium hydroxide solution A, indicator is added and stirred. The flask is put under the burette then the tap is opened, and hydrochloric acid is added and swirled until the its colour is pale pink, where it has reached its end point.
Titrations are used all over industry, for example in the analysis of precipitation, wastewater analysis, nutrition, wine and pharmacology etc. The equipment needed for typical titrations include: an Erlenmeyer flask, an analyte, indicator (like phenolphthalein), calibrated burette and a titrant. Other equipment needed depends on the type of titration done. Firstly, a specific volume of the analyte is put into the flask and a small amount of indicator is added. The flask is then placed underneath the calibrated burette which contains the titrant and is added until the indicator changes colour. When the endpoint is reached the used volume of the reactant is measured and used to calculate the concentration of the analyte.
Similarities and differences to carrying out titrations in industry and in the college lab:
• The equipment used in industry is more advanced than what’s used in the college lab, a lot of the equipment it automated which makes it much more accurate and reliable.
• The scale of production is much larger as the titrations are used in real life, e.g. to develop medications and to balance the acidity of wine etc.
• The workers are highly trained and skilled specifically for the job they do so their results will be more accurate and the pace they work will be quicker than in the college lab as they have more experience.
• It is extremely important that quality checks are made to ensure there are no mistakes, this is for the health and safety of the people involved with the titrations, including the people carrying them out and the public (e.g. wine consumers). It is less important for quality checks in the college lab because there will not be serious risks to the public if mistakes are made.
There are many different types of titrations, the most common types are acid-base titrations (which we carried out in the college lab), redox titrations and precipitation titrations.
Precipitation titrations are carried out to determine halides and they include the use of precipitation agents like silver nitrate. There are three methods in this type of titration: Mohr’s method, Volhard’s method and Fajan’s method. In Mohr’s method a chloride solution reacts with silver nitrate (a standard solution) forming silver chloride. The excess drop of the titrant causes a reaction between the silver and the indicator when the chloride is precipitated. When silver chromate forms the end point is reached (solution changes from yellow to a red precipitate).