Primary and Secondary standard solutions PDF

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NAME: SANNAH HANIF

UNIT 19

M1 – WRITE A REPORT ABOUT THE IMPORTANCE OF PRIMARY AND SECONDARY STANDARD SOLUTIONS AND THEIR USES IN THE INDUSTRY? A primary standard solution is the reagent – a chemical that can be used in carrying out chemical tests, the reagent must be pure and stable. The primary standard solution is what is used to make the standard solution which is a solution that has an accurate measure of concentration. For example, the high purity of the primary solution can be dissolved in a solvent to make the primary standard solution. It should be anhydrous which means that it does not contain any water molecule in its molecular structure. A primary solution is very accurate because it is not calibrated with different or other solutions. A very good example of a primary standard solution is the solution that has low reactivity, high weight so that there is a less risk of errors in mass measurement, non-toxic and readily available at a good price. A secondary standard solution is when stoichiometry is done, this solution is does not have an accurate measure of concentration. Therefore, to work out the concentration, the titration using a primary standard solution is carried out. This is usually because the secondary solutions are not stable and they don’t absorb water or carbon dioxide from the air thus, their concentration changes constantly. The secondary standard is a chemical that has been standardized with a primary standard for use in specific analysis. Secondary standards are mostly used to calibrate analytical methods. An example would be NaOH, and once its concentration has been validated through the use of a primary standard, is can then be used as a secondary standard. An example of primary standard solution would be sodium hydroxide (NaOH) which tends to absorb moisture and carbon dioxide from the atmosphere, thus changing its concentration. To check the concentration of NaOH, a chemist must titrate a primary standard (for example a solution of potassium hydrogen phthalate (KHP). KHP does not absorb water or carbon dioxide. And an example of secondary standard solution would be a HCl solution is used as it can be prepared accurately and is quite stable. Because of this stability it is called a secondary standard. The importance of these standard solutions is that they can help to determine the concentration of an unknown substance. For the standardization to be very accurate, a titration can be carried out, a primary standard solution can also be used when calibrating a standard solution. Standard solutions are important in working out the unknown concentrations of experimental solutions. There are two forms - primary standards and secondary standards. The difference between primary and secondary standard solutions is that primary standard solutions have a high purity and less reactivity whereas secondary solutions have a less purity and high reactivity. The primary standard solution is used in the industry because it can standardize secondary standard solutions and other reagents. The use of secondary standard solutions in the industry is to carry out the important specific analytical experiments. A primary standard solution can be used for caffeine which can be used to determine the known mass of the caffeine in a known amount of water or perhaps milk as well and this is then compared to another sample of caffeine that has an unknown amount. Secondary standard solutions are mostly used to carry out titrations and helps to work out the unknown concentrations. An example of this is therefore in the food industry, where the secondary standard solutions are used to find out the amount of a reactant – to find the amount of sugar for example in a product or perhaps working out the concentration levels of vitamins such as vitamin C and E. A final example would be in the pharmaceutical industry where medicine is created. An example for this is the salicylic acid which can be used to determine how much of this contains aspirin.

NAME: SANNAH HANIF

UNIT 19

D1 – EXAMINE AND EVALUATE VOLUMETRIC TECHNIQUES USED TO MAKE ACCURATE STANDARD SOLUTIONS FOR TITRATIONS? The advantage of the spatula is that it can hold substances, the shape of the spatula is also effective and prevents substances from dropping. The size of the spatula is good because a student can hold the spatula from one end that is far away from the tip of the spatula and it is quite narrow which makes it easier to hold. The fact that the spatula is metal means that the substance won't stain the spatula. A top pan balance has only a 2dp maximum error which is 0.005 so the percentage error is 0.5%. The top pan balance has a big surface area and is easy to use because there are only a few buttons to use. However, a disadvantage to using a top pan balance is that when leaning on the surface it can affect the result of the mass of a substance. So therefore, any local movement carried out can give an incorrect mass. An improvement to using a top pan balance is to have a weighing room to prevent any movement. Top pan balance: this percentage is a very low percentage and therefore is considered minor as the practical can still be carried out.

Analytical balance has a 4dp maximum error which is 0.00005 so the percentage error is 0.005%. The analytical balance has a box around it to prevent other substances from getting in. The advantage of using an analytical balance is that it is it measures small amounts and therefore students wouldn’t need to use the top pan balance. However, the disadvantage of using an analytical balance is that it is really sensitive and therefore it can distinguish the mass of any substance. An improvement for an analytical balance would be to have a clear room without anything surrounding the balance. Analytical balance: this percentage is even lower and is more precise and therefore again isn’t a major problem as the practical can still be done.

NAME: SANNAH HANIF

UNIT 19

A method of weighing allowed the student to clearly understand how much solid substance there was and what the substance was. The advantage of a stirring rod is that it is used to help the dissolving of a solid. The flat end of the stirring rod allows students to crush the lumpy bits. The stirring rod has a grip that allows the student to hold the stirring rod easily. However, a triangular point for the stirring rod would be better as it would make the crushing of the lumpy bits easier and would require less effort and therefore less noise. However, a concave shape that is magnetic is also effective as a stirring rod and though it is still breakable, a magnetic stirrer is easier to stir. The funnel that is part of the equipment needed in this experiment is to stop the spillages of liquids, only a bit of liquid at once. Some drops of liquid can get stuck in the funnel. The funnel is plastic and has a good shape however because it drops some liquid, it comes to question if a funnel should be used at all during the experiment. I think that funnel is needed for the experiment despite the little drops of liquid. The use of a volumetric flask is good because it holds exactly 250ml and had a line to show where the liquid had to stop. The flask had a round heavy bottom that had less chance of falling over, the narrow neck kept the substance inside and was safe to hold. The maximum error was 0.15 so the percentage error is 15%. The disadvantage of using a volumetric flask is that it is glass and the glass could smash and there was difficulty with getting the substance to where the line was because it had to be exactly on the line also due to the fact that this type of equipment has never been used before so it took a while to understand. An improvement would be to keep using the volumetric flask to get more comfortable with it so it doesn’t waste time and so it can be used correctly. Beakers are used because in this experiment students have to put the chemicals inside it and students have to use these 100cm3 beakers because the beaker is effective and is needed to carry out this experiment. An improvement for this would be to clean the beakers and make sure there are no excess solids left inside the beaker. However the good thing about the beakers used is that it allows us to carefully transfer solids from one beaker to another which helps a lot during this experiment. Conical flasks have the advantage of being unlikely to fall and trip over and the slim neck of the flask which decreases the evaporate loss that can come out of the flask. The conical flask allows the mixture or solution to be swirled carefully without any spillages. The disadvantage of using the conical flask is that students might swirl the conical flask solution near to their eye which could cause accidents. An improvement for this would be to use a different apparatus such as volumetric flask or a beaker. Throughout this experiment, a pipette has the advantage of accuracy over the flexibility. Because If you want to make a standard solution then you need to be very precise. The disadvantage of using a pipette is that perhaps a volumetric pipette would be better to use as its cheaper. An improvement would also be to use a different pipette such as the volumetric. Using deionised water has an advantage which is that it removes water impurities particularly ions however the disadvantage is that the water is considered to be corrosive to certain metals. An improvement could be to use tap water which is easier to use. A white tile is very strong and helps when needing to see the instant colour change whilst carrying out the titration, however the disadvantage of this is that it can break and sometimes the white tile is

NAME: SANNAH HANIF

UNIT 19

actually a ceramic tile that isn’t pure white. The improvement here would be to use a piece of white paper or perhaps make sure that the tile is pure white and will allow you to get the result you need. The advantage of using a measuring cylinder is that it has values on it and can therefore be very precise and accurate when measuring out solutions. The disadvantage is that measuring cylinders are really difficult to pour solutions into and can cause spillages for example. A test tube rack with test tubes is important as the test tubes are glass and could break easily if dropped and therefore the use of a test tube rack ensures that the test tubes are in their own space and prevents the risk of breaking, the disadvantage is that using test tubes in the racks makes it difficult to see the contents in the test tube, the improvement would therefore be to put the solutions in the test tubes first before putting the test tubes in the racks as then it is easier to see the test tubes. With a spectrophotometer, the advantages are that it is easy to use as well as that it can quickly do analysis, the disadvantage would be that if anything is contaminated with it then that can destroy the proteins in the sample. The improvement would be to perhaps use a more effective piece of equipment such as a colorimeter. Using a burette is also very important in titrations because it allows the control of the amount of titrant that is being delivered from the large volumes to tiny drops, the disadvantage of this is that to read the burette properly you have to ensure that the bottom of the meniscus and see whether the value is between 0.1. The improvement for using a burette would be to ask two people to check the result at the meniscus. A filter funnel is also important for a titration because it allows the students to carefully pour the solutions down and to ensure that there aren’t any spillages. The disadvantage is that if you pour the water down too fast, it takes time for the funnel to let the solution go down and therefore requires being moved around until the solutions go down. The improvement would be to go slowly and carefully when pouring the solutions down. A 25cm3 bulb pipette is used in the titration process because it has the advantage of measuring the solution accurately, the disadvantage is that it’s really hard to squeeze. The improvement is that instead of using a bulb pipette a volumetric. A burette rack and burettes have the same advantage and disadvantage of the test tube and test tube racks because there are lots of safety issues if the glassware was dropped and broke. The improvement would be to ensure that students aren’t walking around with test tubes and the solutions inside as this could also be a potential risk of getting injured. Another good thing about the equipment was the method of mixing inverting flask. An improvement would be to use a weighing room....