AP Chemistry Day 12. Wednesday, September 27 th, 2017

Transcription

1 AP Chemistry Day 12 Wednesday, September 27 th, 2017

2 Do-Now: Take out your FRQ packet and turn to FRQ #4: 1. Use the answer key to review your response 2. Keep in mind: AP FRQ keys are guidelines telling graders what to look for. They are not giving you complete responses. 3. Give yourself an approximate score for each sechon, and give yourself a total out of 6 points

3 Do-Now: Now, we will complete an FRQ analysis. Use the key and your response to complete the worksheet. Discuss with your group if needed Even if you think you received full points, think about how you could rewrite your answer to express your ideas clearly, concisely, and in a logical flow.

4 Announcements Unit Test Bring calculators and reference sheets FRQ/Response seckon on Friday MC seckon on Tuesday Lab next week Trade in dojo points

5 CW/HW Assignments 15. FRQ Meta-Analysis 9/ Mass Spec Notes + Packet 9/27 PLANNER Study for test J J J Get all stamps Finish FRQ Meta-Analysis and Mass Spec. packet

6 I will be able to: FLT Use data from mass spectrometry to idenkfy the elements and the masses of individual atoms of a specific element JusKfy the seleckon of a parkcular type of spectroscopy to measure properkes associated with vibrakonal or electronic mokons of molecules By comple1ng Mass Spec Notes

7 Mass Spectrometry

8 Recall

9 Photoelectron Spectroscopy (PES) Using PES, we can idenkfy specific elements and also compare their ionizakon energies for specific electrons Idealized PES spectrum of phosphorus Idealized PES spectra of boron and fluorine

10 Photoelectron Spectroscopy (PES)

11 Isotopes

12 Isotopes Are all atoms of a given element idenkcal? While atoms are neutral and have equivalent numbers of protons and electrons... The number of neutrons may differ Because atoms may have varying numbers of neutrons, their mass may also differ

13 Isotopes Frederick Soddy ( ) proposed the idea of isotopes in 1912 Isotopes = atoms of the same element having different masses, due to varying numbers of neutrons. Soddy won the Nobel Prize in Chemistry in 1921 for his work with isotopes and radioackve materials.

14 Isotopes Elements occur in nature as mixtures of isotopes.

15 Average Atomic Mass

16 Atomic Mass What is the mass of an atom of oxygen? It depends, because there are different kinds of oxygen atoms. We are more concerned with the average atomic mass. Average atomic mass = weighted average of the isotopes of a given element based on the abundance (%) in nature

17 Atomic Mass Each isotope has its own atomic mass, thus we determine the average from percent abundance.

18 Calculating Atomic Mass MulKply the atomic mass of each isotope by its abundance (expressed as a decimal), then add the results.

19 Example Calculate the average atomic mass of oxygen

20 Try this one in your groups:

21 a): SoluKon Let x = abundance of Ne x (1-x) = x = % abundace Ne-20 = 90.5%, Ne-22 = 9.5%

22 Average Atomic mass But how do scienksts determine percent abundance and average atomic mass?

23 Mass Spectrometry

24 Mass Spectrometry Mass spectrometry provides mass to charge rako and provides us with informakon to determine the molecular mass of atoms/ molecules in a sample. High-energy electrons bombard the sample, causing it to ionize An electric field separates the ions based on their mass to charge rako à this data is compiled into a mass spectrum (it separates isotopes by mass)

25 Mass Spectrometry

26 Mass Spectrometry Like PES, the relakve size of the peaks indicates the relakve number of parkcles

27 Based on this spectrum, what is the most common isotope of zirconium in our sample? Zr-90 has the highest intensity (tallest peak), so it is the most common Mass Spectrometry

28 Given Zr-90 is amu, Zr-91 is amu, Zr-92 is amu, Zr-94 is amu, and Zr-96 is amu, calculate the average atomic mass of zirconium. See how close you get to Mass Spectrometry

29 Based on the mass spectrum of atom Y, which of the following statements is false? a. peak A and peak D come from atoms that have the same number of electrons b. there are seven isotopes of atom Y c. peak C comes from the most abundant isotope of atom Y d. peak D comes from an atom with 4 more protons than the atom that gave peak B

30 The iden1ty of compound Y is: a. Zirconium b. Molybdenum c. Americium d. Einsteinium

31 Which peak comes from an atom with the greatest number of neutrons? a. A b. C c. D d. All peaks have the same number of neutrons

32 Mass Spec packet CW This packet goes beyond the level of understanding required on the AP Focus on interprekng/explaining/calculakng more than understanding how it works Ajempt all queskons Study for quiz