Quantitative Chemistry Overview IB Chemistry

Quantitative Chemistry Overview—IB Chemistry Moles Introduction Laboratory—IB Chemistry Assessment: CE and MS Objective: To measure the mass of a si...
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Quantitative Chemistry Overview—IB Chemistry

Moles Introduction Laboratory—IB Chemistry Assessment: CE and MS Objective: To measure the mass of a single particle of different substances. Instructions: Measure the mass of single particles of the following substances to the least uncertainty possible. Record all of your data properly. Extension: Time permitting, devise a system that measures all of the particles in terms of the smallest particle. Particle Types: 1. Rice 2. Pasta 3. Almond 4. Sugar 5. Bead 6. Corn 7. Lentil 8. Mustard seed 9. Semolina Product: You will turn in properly formatted data and a conclusion and evaluation that meets the IB requirements, as stated in the laboratory assessment sheet. • Conclusion: If your hypothesis was that you could, in fact, accurately and precisely measure the mass of individual particles of all of the substances, is that true? Base your conclusion on the DATA that you gathered and be sure to refer to your uncertainties and whether you encountered any random and/or systematic errors and why you think so. • Evaluation: A good evaluation comments on a) the processes involved in the lab, b) the equipment and c) management of time. It then goes on to identify weaknesses BASED ON THE DATA, comment on how signficant those weaknesses are and then give a realistic improvement for EACH of the weaknesses discussed. A good rule of thumb is to try and describe three significant weaknesses.

Empirical Formula of Magnesium Oxide—IB Chemistry Assessment: DCP and CE Introduction: This laboratory will be carried out as per the instructions on page 11 of your Chemistry Course Companion text book. We will then analyze the data, conclude and evaluate as an example of the IB standard for DCP and CE. Please pay special attention as this is the one time that we go through all of these things together.

A Traditional Acid-Alkali Titration—IB Chemistry Assessment: DCP, CE and MS Introduction: Neutralisation occurs between hydrogen ions and hydroxide ions in aqueous solution: H3O+(aq) + OH-(aq) _ 2H2O(l) ( or H+(aq) + OH-(aq) _ H2O(l) ) A suitable indicator is used which changes colour at the 'end point' of the reaction when the pH of the solution corresponds to the presence of the appropriate salt and water only. In this experiment you will use the traditional method of titration to determine the number of moles of water of crystallisation in solid crystals of ethane 1,2-dioic acid (oxalic acid) which has the formula (COOH)2.xH2O. This traditional method makes use of volumetric flasks, pipettes and burettes and relies heavily on accurate readings of relatively large volumes. Environmental Care: Although oxalic acid is quite poisonous it is a natural product (it occurs in the leaves of rhubarb) so dilute solutions of it should not affect the environment unduly and can be disposed of down the sink. Safety: You must use a pipette filler and not your mouth whenever you use a pipette. Remember oxalic acid is poisonous. Procedure: Weigh out accurately about 1.5g of crystals of oxalic acid. Dissolve it in distilled water and make up the total volume to 250 cm3 in a volumetric flask. Pipette 25.0 cm3 of 0.100 mol dm-3 sodium hydroxide solution into a conical flask, add two drops of phenolphthalein and run oxalic acid solution from a burette into the flask, swirling continuously, until the indicator just loses its colour. Repeat the procedure to get two accurate results (within 0.10 cm3 ). Calculations: 1. Write an equation for the reaction. (Remember oxalic acid is a dibasic acid, i.e. one mole of acid reacts with two moles of sodium hydroxide) 2. What amount (in moles) of NaOH is present in 25.0 cm3 of 0.100 mol dm-3 sodium hydroxide solution? 3. What amount of oxalic acid was present in the average volume required to react exactly with the sodium hydroxide solution? 4. What amount of oxalic acid was present in your 250 cm3 volumetric flask? 5. What is the mass of one mole of oxalic acid? 6. How many molecules of water of crystallisation are present in one mole? Discussion: 1. Estimate the degree of uncertainty in your readings using the balance, the volumetric flask, the pipette and the burette. How accurately can you quote your answer? 2. Compare your answer with the correct answer and work out the percentage error. 3. Suggest any other reasons for possible error. (Atlantic College Chemistry Department - Practical Programme )

Analysis of Aspirin Tablets—IB Chemistry Assessment: DCP and CE Introduction: For a long time the bark of the willow tree (salix alba) was used as a traditional medicine to relieve the fever symptoms of malaria. In the 1860's chemists showed that the active ingredient in willow bark is salicylic acid (2-hydroxybenzoic acid) and by 1870 salicylic acid was in wide use as a pain killer (analgesic) and fever depressant (antipyretic). However, because it is a relatively strong acid, salicylic acid has the undesirable side effect of irritating and damaging the mouth, esophagus and stomach membranes. In 1899 the Bayer Company of Germany introduced the ethanoate ester of salicylic acid, naming it 'Aspirin'. Since that time mild analgesics containing aspirin have appeared under many different brand names. The aim of this experiment is to determine the percentage of aspirin present in different commercial preparations and to find which is the best value for money. The analysis makes use of the fact that aspirin is a monoprotic (monobasic) acid and therefore reacts with sodium hydroxide according to the equation: C6H5(OCOCH3)COOH + NaOH

C6H5(OCOCH3)COO-Na+ + H2O

Environmental Care: None of the reactants or products are particularly harmful to the environment and the waste can be safely disposed of down the sink. Safety: No special precautions are necessary. You might like to consider why many doctors now recommend that you take paracetamol rather than aspirin for a headache even though aspirin is an effective mild analgesic. Procedure: Note the brand name and the price of the aspirin tablets you are using. Weigh out accurately one tablet (about 0.4 - 0.5g) into a 50 cm3 conical flask and dissolve it in 10.0 cm3 of 95% alcohol. Titrate with 0.100 mol dm-3 sodium hydroxide solution using two drops of phenolphthalein solution as an indicator. Calculations: 1. What amount of sodium hydroxide was required to react exactly with the aspirin? 2. What amount of aspirin was present in your weighed out tablet? 3. What is the mass of one mole of aspirin? 4. What is the percentage of aspirin in your sample? 5. Compare the mass of aspirin in the tablet that you have obtained with the value claimed by the manufacturer on the side of the box. What assumptions have you made that might not be true? 6. Pool your results with others and draw out a table for the different sources of aspirin showing their percentage purity and the cost per gram of pure aspirin. Which is the best buy? (Atlantic College Chemistry Department - Practical Programme )

Macroscopic Properties of Gases Design Lab—IB Chemistry Assessment: D, DCP, CE Introduction: You have been studying Quantitative Chemistry for some time now and have been introduced to the concept of gas properties and the equations that govern gas behaviour. Your task is to design and carry out an experiment on the macroscopic properties of gases. As you first effort at a design lab, I will be supporting you throughout this effort so that you can learn to design, carry out, analyze and evaluate a laboratory experiment to IB standards.

Molar Mass of an Unknown Gas—IB Chemistry Assessment: DCP, CE Introduction: You have been studying Quantitative Chemistry for some time now and have been introduced to the concept of gas properties and the equations that govern gas behaviour. Your task is to design and carry out an experiment to calculate the molar mass of the unknown gas in the lighter. Data Collection and Processing: Calculate the molar mass of the unknown gas. Be sure to note the literature value given in class and do percent error calculations. Conclusion and Evaluation: Draw your conclusion as to the molar mass of the unknown gas and use what you know about uncertainties and percent errors to evaluate the laboratory.

Determination of Concentration by Titration—IB Chemistry Assessment: DCP Introduction: If you know the concentration of one species in an aqueous reaction and have some way of determining the endpoint, it is possible to determine the concentration of the others species through titration, or reacting together known volumes of substances. Objective: To determine the concentration of an unknown solution of potassium permanganate using a known solution of iron(II) ions. The reaction under consideration is: -

MnO4 (aq) + 5 Fe

2+

(aq) --------> 5 Fe

Materials: burets ring stand buret clamp funnel 10 mL pipette pipette bulb potassium permangante solution--KMnO4

3+

(aq) + Mn

2+

3 beakers

(aq)

conical flask

ferroammonium sulphate solution--Fe(NH4)2(SO4)2 sulphuric acid--H2SO4 Procedure: 1. Prepare buret by cleaning, rinsing with distilled water. 2. Take a 40-50 mL sample of the 0.100 M Fe

2+

solution to your bench in a 100 mL beaker. 2+

3. Pipette a 10.00 mL aliquot of the standard Fe solution into the conical flask. Add 5 mL of dilute sulphuric acid to each sample with a graduated cylinder. 4. Take 50-60 mL sample of the stock permanganate solution to your bench. Rinse and fill a buret with this solution of unknown concentration. 2+

5. Titrate the Fe with the permanganate solution. Repeat twice more for a total of at least three titrations. Record all data. Exemplar Data Table: Your data table needs to have space for trials, etc. for the following pieces of information. Volume Fe2+ Concentration Fe2+ Initial volume KMnO4Final volume KMnO4Change volume KMnO4Data Analysis: Calculate and present concentration of permangate. Abide by the “Data Processing and Presentation” IB practical assessment rubric.