Teachers Guide for Evaluating Percentages of Contents in a Mixture - Lab Report Example

Teacher’s Guide for Evaluating Percentages of contents in a Mixture Overview and Purpose In this experiment, separation of the components of mixture is done through a solubility-based experiment. The students will evaluate the mass of the components on order to calculate the percentage of compounds in the mixture. The lab will demonstrate: 1. Separation of contents of mixture based on physical properties 2. Calculation of masses of contents and percentages of contents by mass in mixture. 3. Designing a straight forward procedure including all the necessary details of the experiment. The experiment requires students to focus carefully. For this reason, the procedure of the experiment should be precise. The expedients will help the students to utilize similar principles in other experiments. The students may have question regarding the experiments and during the experiment, so be attentive to help the students. Procedures 1. In the experiment students will dissolve the given mixture in water. The designed procedure by students will demonstrate how to solve the mixture and how to filter the insoluble part of the mixture. The students will remain uncertain about the quantity of water that they should use to dissolve the mixture. It is necessary to inform them about the quantity of water and what will be the result of adding too much or too little water. 2. In order to fid the mass of the content in the mixture is to boil the mixture till all the water evaporates and then calculate the mass of soluble component. The mass of insoluble component can be attained by subtracting the mass of soluble component from the mass of mixture. However, students will apply the same method to evaluate the mass of sugar and caramelize the sugar in the end that would alter its mass. Advice the students to gently reduce the heat as the volume of solution reduce. 3. Other method that is used is to evaluate the mass of dry sand. This can be done by utilizing a rubber policeman to scarp the sand from the filter paper and transfer it to the evaporating dish. The dish is then heated to till it completely dries. 4. It should be advised to the students to pour the solution, which has dissolved the soluble component, into another beaker and give it some rinses to free it from the any remaining sand particles. The method is important incase of fine sand particles. In the similar manner, covering the evaporating dish and beaker while heating will not allow the mass due to splattering. 5. More precise way is to measure the masses of both the mixed components. However, it is not necessary; the mass of other component can be attained by difference. 6. Student should be advised to determine the solute in the solution. Salt can be identified with the help of light bulb assembly as salt solution conduct electricity. In the similar manner Silver nitrate precipitate with chloride and acid make bubbles with bicarbonate. 7. Discuss result after experiment and discuss the causes of errors. Questions & Prompts 1. Why the students having similar sample of mixtures have same results? 2. Define mixture? 3. Define percent composition? 4. Why the teams with different sample of mixtures have different percentage compositions? 5. List some important material required for the experiment. 6. Does the lab require physical or chemical changes to separate the components of the mixture? 7. Is the experiment utilized physical properties? Why or Why not? 8. Is the experiment utilized chemical properties? Why or Why not? 9. Is t important to separate the components of mixture in real world? 10. If the mass of both the soluble and insoluble components of the mixture are evaluated separately without difference, it the total percentage will be 100%? 11. What are the sources of error in experiment? 12. How errors can be reduced? Common Misconceptions & Errors 1. Calculating mass of water at any stage. 2. Trying to melt the soluble components. 3. Discourage over use of water, as it would increase the time duration of experiment. In the similar discourage too little quantities of water, as salt will not dissolve completely in too little water. 4. Some students do not rinse the beakers. 5. Encourage students o filter second time if water appears cloudy. 6. Splattering during evaporation. Use a watch glass as a cover. 7. Making pores in the filter paper 8. Uncovering the beakers during splattering. Apparatus for Evaluating Percentages of contents in a Mixture Apparatus from the shelves: 1. 6 Hot plates 2. 6 250 ml 3. 6 400 ml beakers 4. 12 Watch glasses to cover beakers 5. 6 Rubber policemen 6. 6 Stirring rods 7. Coarse filter paper 8. 6 Funnels 9. 6 Beaker tongs 10. 6 Evaporating dishes Each bench should have: One sample from the three given sample on each bench. The sample should have a mass of about 10-15 grams precisely. The percentage of components in each mixture should be known but not indicated on the samples. Sand should be thoroughly washed before making mixture. Following mixtures can be used in the experiment. 1. Sand and salt 2. Sand and sugar 3. Sand and sodium bicarbonate Instructor should have: 1. Vinegar 2. Solution of silver nitrate 3. A battery and light bulb assembly Handout for Evaluating Percentages of contents in a Mixture Scientists and forensic investigators work with mixtures with different compositions of contents. Forensic experts are often hired to separate the components of mixtures and analyze the percentage composition of contents in the mixture. Mr. Ramsay, a renowned owner of a hotel chain in London, hired you as the forensic expert to forensically investigate the salt bags that he received from a contractor overseas. He analyzed a little sand particle in a sample of salt. He wants you to analyze the percentage of sand in four salt bags. He will return the salt bags, if the sample has more than 1% of sand. Objective of Lab: What is the percentage of contents in the mixture given to you? Lab Assignment: Find the percentage of soluble and insoluble contents in the mixture given to you. The insoluble component in sample is sand and soluble component is unknown. Formulate procedure and calculation to find the percentage composition. References Adapted from V.L. Lechtanski, Inquiry-Based Experiments in Chemistry, Oxford University Press (2000) Read More