Lab Investigation: Acid and Base Analysis What are the identities of the unknown chemical solutions?

Transcription

1 Lab Investigation: Acid and Base Analysis What are the identities of the unknown chemical solutions? Introduction. Acids have a ph below 7 and have a higher concentration of hydronium ions than hydroxide ions in solution. Bases have a ph above 7 and have a higher hydroxide ion concentration than hydronium ion. When acids and bases react they neutralize one another to form water and a salt. When equal moles of a strong acid and a strong base react they completely use each other up and form a neutral solution, which has a ph of 7. Indicators can used to determine the approximate ph of a solution. One indicator is phenolphthalein, which in an acidic solution is colorless or milky, but in a basic solution is magenta or dark pink. The Task. Your goal is to identify the unknown chemical solutions by systematically reacting them together in the same test tube. The four unknowns are water, 0.1 M HCl (aq), 0.1 M NaOH (aq), and phenolphthalein. You need to decide which unknown solution has which chemical identity. The guiding question of this investigation is: What are the identities of the unknown chemical solutions? Materials. You may use any of the following materials during your investigation: Equipment Consumables Test tube Unknown A Stirring rod Unknown B Unknown C Unknown D Safety Precautions. Students need to wear goggles, long pants, closed toe shoes, and a shirt with sleeves. All waste should be disposed of in the inorganic/ionic waste container. Getting Started. Before you can design and carry out your investigation, you must determine what type of data you will need to collect, how you will collect it, and how will you analyze it. You need to fill out the investigation proposal before starting. To determine what type of data you need to collect think about the following questions: What type of observations will allow you to distinguish between the unknown chemicals? What does it mean if the solution is pink? If it is clear? To determine how you will collect your data, think about the following question: How can you systematically react the unknown chemicals in order to find distinguishing observations? In order to determine how you will analyze your data think about the following questions: What evidence will you be looking for in order to identify your unknowns? What relevant chemical equations do you need to consider? Scientific Argument. Once your group has finished collecting and analyzing your data, you will need to develop an initial argument. Your argument must include a claim. The claim is your answer to the guiding question. Your argument must also include evidence in support of your claim. The evidence is your analysis of the data and your interpretation of what the analysis means. Finally, you must include a justification of the evidence in your argument. The justification needs to use a scientific concept or principle to explain why the evidence that you decided to use is relevant and important. Report. Once you have completed your research, you will need to prepare an investigation report that consists of three sections. Each section should provide an answer for the following questions: 1. What question were you trying to answer and why? 2. What did you do during your investigation and why did you conduct your investigation in this way? 3. What is your argument? Your report should answer these questions in 2 pages or less. Be sure to write in a persuasive style; you are trying to convince others that your claim is acceptable or valid!

2 Laboratory Investigation Proposal The Guiding Question What data will you collect? How will you collect your data? Your Procedure How will you analyze your data? Your actual data

3 The Guiding Question: My Claim: My Evidence: My Justification of the Evidence:

4 STUDENT WORK PRODUCT EMBEDDED IN INSTRUCTIONS Lab Investigation: Acid an y 'l1 ~hat are the identities of the unknown chemical solutions? Introduction. Acids have a ph below 7 and have a higher concentration of hydronium ions than hydroxide ions in solution. Bases have a ph above 7 and have a higher hydroxide ion concentration than hydronium ion. When acids and bases react they neutralize one another to form water and a salt. When equal moles of a strong acid and a strong base react they completely use each other up and form a neutral solution, which has a ph of 7. Indicators can used to determine the approximate ph of a solution. One indicator is phenolphthalein, which in an acidic solution is colorless or milky, but in a basic solution is magenta or dark pink. The Task. Your goal is to identify the unknown chemical solutions by systematically reacting them together in the same test tube. The four unknowns are water, 0.1 M HCI (aq), 0.1 M NaOH (aq), and phenolphthalein. You need to decide which unknown solution has which chemical identity. The guiding question of this investigation is: What are the identities of the unknown chemical solutions? Materials. You may use any of the following materials during your investigation: Equipment Consumables Test tube Unknown A Stirring rod Unknown B Unknown C Unknown D ~~ ~\ "-,;\ t"\ N(') 0 \'\ ~ ~0 r...,t\ -P hase. a Vreno\:v'~ \~'"' (Cio< \f5~ ~ Safety Precautions. Students need to wear goggles, long pants, closed toe shoes, and a shirt with sleeves. All waste shou ld be disposed of in the inorganic/ionic waste container. Getting Started. Before you can design and carry out your investigation, you must determine what type of data you will need to collect, how you will collect it, and how will you analyze it. You need to fill out the investigation proposal before starting. To determine what type of data you need to collect think about the following questions: What type of observations will allow you to distinguish between the unknown chemicals? What does it mean if the solution is pink? If it is clear? To determine how you will collect your data, think about the following question: How can you systematically react the unknown chemicals in order to find distinguishing observations? In order to determine how you will analyze your data think about the following questions: What evidence will you be looking for in order to identify your unknowns? What relevant chemical equations do you need to consider? Scientific Argument. Once your group has finished collecting and analyzing your data, you will need to develop an initial argument. Your argument must include a claim. The claim is your answer to the guiding question. Your argument must also include evidence in support of your claim. The evidence is your analysis of the data and your interpretation of wmat the analysis means. Finally, you must include a justification of the evidence in your argument. The justification needs to use a scientifi c concept or principle to explain why the evidence that you decided to use is relevant and important. Report. Once you have completed your research, you will need to prepare an investigation report that consists of three sections. Each section should provide an answer for t~e following questions: 1. What question were you trying to answer and why?-'f -\\\6 a.\~ C\. WY\\{) \XV\ c\~rrons*ra hytq mta 'fl nowt-e~ 2. What did you do during your investigation and why did you conduct your investigation in this way? 1 o.. ~"(c). 'Oors-e What is your argument?. ~ Your report should answer these questions in 2 pages or less. Be sure to write in a persuasive style; you afe others that your claim is acceptable or valid! ~

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6 The Guiding Question: My Claim:

7 Lab Investigation: Acid and Base Analysis I am identifying the unknown chemical solution and their identities by conducting trials that allow me to identify the 4 unknowns which are water, 0.1 HCL(aq), 0.1 M NaOH (aq) and phenolphlphthalein. To identify the unknowns I will observe color that results from mixing the unknown solution together which are water and, strong acid, strong base and phenolphthalein. When the 4 combinations of the 2 unknowns only in 1 pair A&B resulted in a pink color which concluded it was a base. Any colorless caused a neutral or acidic relationship. The addition of C to A&B resulted in no change to the A&B combination therefore Cis water. The addition to D to the A&B plus C mixture produces a colorless solution therefore D is an acid/hcl. The addition of A+B+C+D mixture produces a pink solution which indicates A is NaOH/base. I have concluded that since the experiment was conducted in a controlled and systematical way that my findings are conclusive and that unknown A is a base, B is an indicator/ phenolphthalein, Cis water and D is the base. This is how I have demonstrated my knowledge of acid and base reactions and neutralizations.