CHEM TEST Notes - Certain HSC Chemistry dot points PDF

Preview

Summary

Certain HSC Chemistry dot points...

Description

CHEM TEST NOTES

Conduct a chemical analysis of a common household substance for its acidity or basicity: soft drink, wine, juice, medicine Substance Major acidic or basic species Soft drink Carbonic acid (dissolved CO2), phosphoric acid Wine Tartaric acid Orange juice Citric acid Aspirin Acetylsalicylic acid Hair dye Ammonia Vinegar Acetic acid Antacids Metal hydroxides and carbonates Chalk Calcium carbonate Quantities of the acids and bases in these substances can be determined by titration. The method of titration varies depending on the nature of the substance to be analysed, this is as: o o o

Indicators may not be suitable for intensely coloured substances (e.g. wine) Insoluble solids may need to be dissolved before titration (e.g. via a back titration) Many substances will require a dilution before titration.

Aspirin Aspirin or acetylsalicylic acid (C9H8O4) is an active ingredient in aspirin tablets. Aspirin is only found in individuals who have taken it, it is used as an analgesic (against minor pains and aches), antipyretic (against fever) and anti-inflammatory. Also has an anticoagulant effect and used in long-term lowdoses to prevent heart attacks and cancer. Acetylsalicylic acid is a weak, monoprotic acid with a pKa value of 3.5. It is not very soluble in water but can be dissolved in a solution of ethanol and water. It is then reacted with OH - ions in NaOH solution in a 1:1 ratio. In the analysis of aspirin, back titration is used, this is as: o

o

When doing direct titration, there is possible clumping of the powder, even when finely crushed which may cause the reaction to be incomplete, distorting results. A slow hydrolysis reaction may occur. Would involve a reaction between weak acetylsalicylic acid and strong NaOH which does not have a clear end point. In back titration, C9H8O4 reacts slowly with NaOH. When using excess NaOH, then titrating the excess NaOH with HCl, the true quantity of C9H8O4 can be determined. Also, a clear end point is obtained due to strong acid (HCl) and strong base (NaOH).

In both, the NaOH solution is standardised using the primary standard oxalic acid. Tablet also contains other ingredients such as starch but do not react with NaOH (only acetylsalicylic acid does). Back Titration Initially, a known number of moles of NaOH is added to the prepared aspirin sample. A neutralisation reaction occurs between them, then the product is further hydrolysed. The unreacted (excess) sodium hydroxide is then titrated against a standardised solution of HCl.

The difference between the number of moles NaOH originally added and the number of moles that remain (to be neutralised with HCl) is found. This is the number of moles used to react with C 9H8O4. Through this, the number of moles of C9H8O4 can be determined. Soft Drink Soft drinks contain dissolved carbon dioxide and a mixture of acids, primarily phosphoric acid. To determine the content of carbon dioxide and phosphoric acid separately, the soft drink can first be decarbonated to remove the carbon dioxide as a gas and determined gravimetrically.

Conduct a practical investigation to prepare a buffer and demonstrate its properties Describe the importance of buffers in natural system

TEST Q 1st booklet 1. Calculate the concentration of ethanol in wine 2. Describe how the burette and conical flask is prepared for titration The standard solution is placed in the burette which delivers accurately known volumes of solution to the conical flask. The volume of solution is controlled by the stopcock at the bottom of the burette. Generally a burette will be accurate to 0.1mL. It is rinsed with distilled water 3 times, then the solution it will be filled with 3 times. If washed with only water, titrant will be diluted and titration will take longer than it should. Conical flask usually contains the analyte of the volumetric analysis. The conical flask does not measure does not measure volume accurately and it is simply used as a vessel. The volume of the solution within the conical flask is accurately measured by the volumetric pipette. It is rinsed with distilled water 3 times only. If washed with an analyte solution, it would increase the concentration of the analyte and the titration will take longer than expected. 3. Table, find average volume, remove outlier before 4. Find the concentration of sulfur dioxide in wine 2nd booklet 1. Describe how you would do a private investigation on how to prepare a buffer and how to test for the properties in the buffer prepared The preparation of an acetate buffer. Add 100mL of 0.25M acetic acid solution to a clean dry 250mL beaker and add 2.05g (0.025mol) of sodium acetate and stir to dissolve. 2. Find the acid conjugate base in it 3. With reference to a specific example of a natural buffer, justify why it is needed in a natural system.

The pH of blood must be maintained between 7.35-7.45 for optimum function of the human body. Consequences can be fatal if pH drops below 6.8 or rises above 8.0, termed acidosis and alkalosis. The blood buffer is the carbonic acid/hydrogen carbonate system. Carbonic acid is produced from the cellular respiration process where CO2 dissolves in water in blood. CO2(g)+H2O(l)⇌H2CO3(aq)⇌H+(aq) +HCO3-(aq) H2CO3(aq) ⇌ HCO3-(aq)+H+(aq) 1 o o

When pH decreases due to increase in [H+], equilibrium shifts left to favour the reactants according to LCP, producing carbonic acid If pH increases, due to decrease in [H+], equilibrium shifts right to favour the products according to LCP

CO2(g)+H2O(l) ⇌H2CO3(aq) 2 CO2 is a product of cellular respiration and is removed by exhalation. Respiration is the process the body uses to obtain its energy. C6H12O6+6O2 ⇌ 6CO2+6H2O Increased oxygen intake during exercise, increases [CO2] and shifts right to increase [H2CO3] which shifts the other equilibrium to increase [H+] and [HCO3-], resulting in a decrease in pH. Hyperventilation: fast breathing, excessive removal of CO2 from the lungs. Equilibrium 2 shifts left to produce CO2, decreasing [H2CO3], causing equilibrium 1 to shift left, decreasing [H+] and [HCO3-], increasing pH. There are at least 3 buffer systems in keeping the blood pH between 7.35-7.45. If blood becomes too acidic or basic, enzymes required will not work and may be fatal. The carbonic acid buffer system is made up of carbonic acid and its conjugate base, hydrogen carbonate. H2CO3 + H2O HCO3- + H3O+ carbonic acid and its conjugate base hydrogen carbonate work effectively as buffers when at relatively equal concentrations. They act upon the shifts in equilibrium to maintain relative pH when the concentration of H+ ions in the blood increase or decrease. When [H+] ions are low, the equilibrium will shift to favour the forward reaction by producing more products and when [H+] is too high, the revers reaction will be favoured. A buffer is usually a mixture of a weak acid and its salt. Buffering resists changes in the pH of blood when acids or bases are added. It does this because added H+ ion reacts with the weak base and is removed and added OH- reacts with the weak acid and is removed. Therefore, the change in [H+] is minimised by the buffer and pH change is also minimised. Many process of natural systems will only take place within a narrow pH rang. If pH deviates too far from the optimum, the system will not work as well as it should 3rd booklet 1. The chemical name for the active ingredient in aspirin Acetylsalicylic acid 2. Draw the structural formula for it 3. Aspirin was made from boiling the bark of a white willow tree to produce salicylic acid. It is not an oral pharmaceutical. Find the problems and solutions to making this digestive pharmaceutical.

4. Draw the flow chart of the synthesis of aspirin from salicylic acid and acetic anhydride while showing reactions and more.

5. Assess the reliability, validity and accuracy of your sources Reliability: Before using information from sources, I cross-referenced specific information across multiple-sources and different platforms (websites, textbooks, videos). This ensures my information is consistent and reliable as a reference. Validity: Used sources that were relevant to the research topic by accounting for the source’s date of publication to account, only using sources published in the last 5 years. This ensures my information is specific to the research required, providing recent statistics and investigations. I chose sources accounting who wrote and published each source of information, ensuring sources are valid. Accuracy: I did not use Wikipedia when sourcing information due to the ability for anyone to edit information which may provide different information that is not true. Used scientifically journalised sources which ensures information is not based of a subjective perspective and unbiased. Environmental: water pollution, chemicals damage balance of pH in oceans and rivers. Aspirin and salicylic acid expected to biodegrade and/or hydrolyse rapidly. Salicylic acid is a naturally occurring substance (microorganisms, fruits, plants). Acetic acid can damage environment, carbon emission from high T flames. Social: pharmaceutical, analgesic (relieves mild pain), antipyretic (reduces fever) and an antiinflammatory (reduces swelling). Anticoagulant in blood, preventing strokes and heart attacks through preventing blood cells clotting and blocking blood vessels. Economic: production doesn’t require expensive processes, can be produced by small and large companies. High abundant resources makes it relatively cheap, more job opportunities. Allows it to be both cheaper and effective for pain relief for customers, saving potential $79.6 million for 1,000,000 patients over 10 years. Eco growth....