GENERAL CHEMISTRY_Q1_Mod7_Calculating Formula Mass, Empirical Formula and Molecular Formula.pdf

www.shsph.blogspot.com 11 General Chemistry 1 Quarter 1 - Module 7 Calculating Formula Mass, Empirical Formula and...

www.shsph.blogspot.com 11 General Chemistry 1 Quarter 1 - Module 7 Calculating Formula Mass, Empirical Formula and Molecular Formula 1 www.shsph.blogspot.com What I Need to Know? This module was prepared to guide you on how to write the formula mass, molecular mass and empirical formula of a given compound properly and correctly. Knowing the process of writing the said formulas of various compounds will help us to determine the actual mass and proportion of the elements that make up the compound. In addition, familiarization on the process on measuring the formula mass, molecular mass or empirical formula could help people who are involved in chemical-related industries to double check if the amount of the elements in a compound as indicated in their product labels are true and valid. The scope of this module covers many different learning situations where students could relate their personal experiences on different compounds. The language used recognizes the diverse vocabulary level of students. The lessons are arranged to follow the standard sequence of the course. But the order in which you read them can be changed to correspond with the textbook you are now using. After going through this module, you are expected to: 1. calculate molecular formula given the molar mass, (STEM_GC11PClf-33). 2. calculate the empirical formula from the percent composition of a compound, (STEM_GC11PCif-32). What I Know? (Critical Thinking) To check your prior knowledge about the topic, and to solicit the questions that you want to know about it, fill in the Know and Want to know components of the Know-Want to know- Learned (KWL) chart properly and correctly. For the Know component, you may write word/s or sentence. For the want to know component, state your responses in interrogative or question form. You may list as many responses as you want for each component. Write your responses on a separate sheet of paper. KWL Chart Topic Know Want to know Learned Formula Mass and Molecular Mass 2 www.shsph.blogspot.com Guide Questions 1. Based from what you have written on the Know component of the chart, what do you know about formula mass and molecular mass? 2. If you were to think of a question that you want to ask about formula mass and molecular mass, what question would that be? HOLD ON AMIGO!!! DIRECTION: After you have filled-in the K and W components of the chart and answered the guide questions, answer now the diagnostic assessment below within 10 minutes. PRE-TEST Sentence Completion. Complete each statement with a word/ concept in the blank of the item. 1. _____ refers to the total number of protons and neutrons in the nucleus of an atom. 2. How many carbon atoms in chemical formula CH 4 ? 3. ______ gives the lowest whole-number ratio of the elements in a compound. 4. Cl is the chemical symbol for ______ 5. Formula mass is used for compounds that are made up of ions and have primarily _____ bonding. HOLD ON AMIGO!!! DIRECTION: Rest for 1 minute then you may start reading the lesson 1 below about the chemical formula and chemical name of compounds. Lesson Formula Mass and Molecular Mass 1 Chemistry is a subject that involves a lot of concepts and formulas. Some concepts are confusing for some people because of their similarities in terms of the wordings. Three concepts which may confuse us are formula mass, molecular mass and molar mass. For a beginner student, these concepts are quite confusing to 3 www.shsph.blogspot.com them. But how is formula mass different from molecular mass and molar mass? Is there any difference among those concepts? This module will discuss the method of writing the formula mass or molecular of a given compound considering the type of chemical bond exist in the said compound properly and correctly. What’s In? LET US HAVE SOME FUN! Formula Analysis. Analyze the figures below then answer the corresponding guide questions. NaCl NO2 Figure A Figure B Guide Questions 1. Which figure show compound whose atoms are bonded by covalent bond? 2. What do we call to the formula represented by figures A and B? 3. What type of compound is in figure A? HOLD ON AMIGO!!! DIRECTION: After you analyze the given picture and answered the guide questions, let us proceed to what’s new. Read the direction carefully. 4 www.shsph.blogspot.com What’s New? (Communication) IMPORTANT VOCABULARY WORDS Read the description of important terms that you will encounter in this module. VOCABULARY WORD MEANING 1. Mas number It means characteristics, traits or qualities. 2. Molecular formula A formula that gives number of atoms of each element present in a molecule. HOLD ON AMIGO!!! DIRECTION: After finding out the meaning of important terms that you will encounter as you read the next part, make time to read the formula mass and molecular mass below thoroughly. What is Formula Mass and Molecular Mass? Formula Mass and Molecular Mass Formula mass is used for compounds that are made up of ions and have primarily ionic bonding. While Molecular mass or known as molar mass is used for compounds that are composed of molecules and have primarily covalent bonding. The term formula mass is suitable to use as it can be used for both ionic and covalent compounds. Molecular mass will only be used for covalent compounds. How to Write the Formula Mass of a Compound? Compound A substance which is made up of two or more atoms joined together by a chemical bond. Compounds may be classified into two based from the nature of the atoms that make up them, and the type of intramolecular bond that exist between atoms. The two classification of compounds are ionic compound and covalent compound. The ionic compound is formed between a metal atom and a nonmetal atom, and the type of intramolecular bond exist between atoms is ionic bond due to 5 www.shsph.blogspot.com the presence of ionic charges. Example of this is sodium chloride which is made up of metal sodium and nonmetal chlorine. Na+1 + Cl-1 Na 1 Cl 1 or NaCl Sodium Chlorine Sodium chloride The covalent compound is formed between two or more nonmetal atoms, and the type of intramolecular bond that exist between atoms is covalent bond. Example of this is Carbon tetrachloride. Cl C + Cl Cl C Cl Cl Carbon Chlorine Carbon tetrachloride So, in using the term formula mass or molecular mass, you must determine first the intramolecular bond that exists between atoms of compounds. How is Mass Number different from Formula Mass? If mass number is the total number of protons and neutrons in the nucleus of an atom, the formula mass is the sum of all mass numbers of the atoms that make up the compound. The mass number is very important in determining the formula mass of a certain compound. The mass number of each element can be seen in the periodic table. Below shows the mass number of element nitrogen in the periodic table which is 14.007 or 14.0 u. The mass number is always rounded off to the nearest tenths that is why the value of the mass number of nitrogen is 14.0 instead of 14.007. The symbol u means unified mass number unit or unified atomic mass unit that is used in all formula mass units. ATOMIC NUMBER MASS NUMBER 6 www.shsph.blogspot.com Can you determine the mass number of the following elements in the periodic table? 1. Ca - __________________________ 3. Cu - ___________________________ 2. Si - ___________________________ 4. P - ____________________________ If your answer to the mass number of Phosphorous is 31.0 u then you are correct. As seen in the periodic table, the mass number of phosphorous is 30.974 and has to be rounded off to 31.0 u. Important Steps in Solving the Formula Mass of a Compound In writing the formula mass of a compound, do the following steps below. We will use Al(OH) 3 as an example. Step 1. List down the atoms involved in the formula which are represented by chemical symbol. Write this in downward manner in the first column. Atom Al O H Step 2. Determine the number of atoms in the formula. Write this in the second column. Consider the subscript which is written outside the parenthesis. Atom Number of Atoms Al 1 O 3 H 3 Note that the number of oxygen atom and hydrogen atom have increased by 3 because of the subscript located outside the parenthesis. The subscript will only affect the atoms inside the parenthesis which can be seen in (OH) 3 of Al(OH) 3. Step 3. Write the mass number of each element in the third column. Atom Number of Atoms Mass number Al 1 27.0 u O 3 16.0 u H 3 1.0 u 7 www.shsph.blogspot.com Step 4. Multiply the number of each atom to its mass number to determine the total mass number of each atom. Write this in the fourth column. Atom Number of Atoms Mass number Total mass number of each atom Al 1 27.0 u 27.0 u O 3 16.0 u 48.0 u H 3 1.0 u 3.0 u Step 5. Get the sum of all total masses to determine the formula mass of Al(OH) 3. Atom Number of Atoms Mass number Total mass number of each atom Al 1 27.0 u 27.0 u O 3 16.0 u 48.0 u H 3 1.0 u 3.0 u___ 78.0 u Therefore, the formula mass of Al(OH) 3 is 78.0 u. PRACTICE EXERCISE : Problem Solving Calculate the formula mass of Copper sulfate, CuSO 4 Atom Number of Atoms Mass number Total mass number of each atom Cu 1 ___________ _______________ S 1 ___________ _______________ O 4 ____________ _______________ ______________ HOLD ON AMIGO!!! Did you understand what you have read about formula mass of a compound? If yes, let us proceed to the mini-performance task. You are about to perform the procedure as instructed in the Mini- performance task. Read and follow the procedure carefully. Good luck! 8 www.shsph.blogspot.com Mini-Performance Task (Collaboration) Activity 1 – FREEDOM WALL Procedure 1. Prepare manila paper, pentel pen, coloring materials and ruler 2. Given set of chemical formula, choose 1 that you want to present before your teacher. You need to follow the steps below to solve the problem. Write your complete answers in a manila paper. You may add design that you want or remark as your expression of your feelings or experiences towards the solving process. 3. Post your output on the wall and explain it before your classmates. Output Presentation FORMAT FOR FREEDOM WALL Atom Number of Atoms Mass number Total mass number of each atom SET OF CHEMICAL FORMULAS C6H12O6 (NH4)2SO4 C7H5NO3S QUESTIONS 1. What is the formula mass of your chosen chemical formula? 2. Are there atoms where mass numbers are identical? 9 www.shsph.blogspot.com What I Have Learned? (Critical Thinking) You have to fill in the L component of the KWL chart to generalize the things they have learned about the topic. KWL Chart Topic Know Want to know Learned Formula Mass and I have learned that Molecular Mass …. HOLD ON AMIGO!!! After you have filled-in the L component of the chart, proceed now to the what I can do. What I Can Do? (Character and Creativity) WORK IN PROGRESS Added task to you. Look for a product found at your home. Identify 1 chemical formula as written on its label then determine its formula mass as well as the uses. HOLD ON AMIGO!!! Congratulations Mi Amigo! You are almost done in this lesson. Let us do the last part which is the assessment. 10 www.shsph.blogspot.com Assessment (Critical Thinking) POST-TEST Problem Solving (10 pts.) Calculate the formula mass of Ca 3 (PO 4 ) 2 Atom Number of Atoms Mass number Total mass number of each atom Ca _________________ 40.0 u _____________ P _________________ 31.0 u _____________ O _________________ 16.0 u _____________ ______________ HOLD ON AMIGO!!! Congratulations Mi Amigo!!! We are done in this lesson. You may now proceed to the lesson 2 below. Calculating the Empirical Formula Lesson from Percent Composition, and 2 Molecular Formula from Molecular Mass Chemistry is a subject that involves a lot of calculations and formulas. Some formulas and calculations in Chemistry are quite difficult for some people because of their unfamiliarity of the said formulas and calculations. However, these calculations and formulas are very important in making accurate and precise measurements of chemical materials needed in the preparation or making of solutions of certain product. For a beginner student, studying these formulas and performing the correct procedure of calculations need a strict focus and patience. You make encounter confusion and mistake as you use the formula in actual calculation process but do not give up. It is ok to read again the concept and recalculate your actual computation to derive a correct answer to a given problem on empirical formula and molecular formula. 11 www.shsph.blogspot.com This module will discuss the process of calculating the empirical formula of a compound based from its percent composition as well as the molecular formula based from its molecular mass. What’s In? LET US HAVE SOME FUN! Problem Solving Analysis. Analyze the sample problem below then answer the corresponding guide questions. Determine the empirical formula of a compound whose percentage composition is 50.05% S and 49.95% O by mass. Guide Questions 1. What are the elements involved in the sample problem? 2. What will be solved in this problem? 3. What is empirical formula? HOLD ON AMIGO!!! DIRECTION: After you analyze the given problem and answered the guide questions, let us proceed to what’s new. Read the direction carefully. What’s New? (Communication) IMPORTANT VOCABULARY WORDS Read the description of important terms that you will encounter in this module. VOCABULARY WORD MEANING 1. Ratio It is the quantitative relation between two amounts showing the number of times one value contain or is contained with the other. 2. Atomic Mass The number of the protons and neutrons inside the nucleus of the atom. 12 www.shsph.blogspot.com HOLD ON AMIGO!!! DIRECTION: After finding out the meaning of important terms that you will encounter as you read the next part, make time to read the formula mass and molecular mass below thoroughly. What is Empirical Formula and Molecular Formula? Empirical Formula and Molecular Formula Empirical Formula is the lowest whole-numbered ratio of the elements in a compound. While Molecular Formula is the actual composition of a compound indicating the number of atoms per element; number of moles of each kind of atom per mole of compound. How to Calculate the Empirical Formula? In calculating the empirical formula of a compound, do the following steps below. We will refer to the sample problem below. SAMPLE PROBLEM: Determine the empirical formula of a compound whose percentage composition is 50.05% S and 49.95% O by mass. Step 1. Use 100 g of the compound as basis of calculation. Meaning there will be 50.05 g would be atoms of Sulfur and 49.95 g would be atoms of Oxygen. Step 2. Convert the given mass of each atom into their equivalent mole. To do this, convert the given mass of atom in the compound by using the mole of the atom as the conversion factor. Given Mass of Atom Mole of Atom Equivalent Mole of Atom 50.05 g S 1 mol of S atoms = 1.56 mol of S atoms 32.1 g S 49.95 g O 1 mol of O atoms = 3.12 mol of O atoms 16.0 g O Let us use Sulfur to determine the calculation process. First the given mass of sulfur is 50.05 g was multiply to 1 mol of S atoms. You may refer to the red straight arrow. The answer is 50.05 g S. mol of S atoms. Then the 50.05 g S. mol of S atoms was divided by 32.1 g S. You may refer to the red curved arrow. The answer is 1.56 mol of S atoms. The mole of atom is based on the mass number of the atom as indicated in the periodic table. The mass number of sulfur in the periodic table is 32.1 or 32. 13 www.shsph.blogspot.com Given Mass of Atom Mole of Atom Equivalent Mole of Atom 50.05 g S 1 mol of S atoms = 1.56 mol of S atoms 32.1 g S Step 3. The equivalent value of mole of each atom will be used as the subscript. Therefore, the formula maybe written as S 1.56 O 3.12 , but this formula does not have whole-number subscripts. One way to get a formula with whole-number subscript is to divide all the subscripts by the smallest subscript. S :1.56 = 1 and O : 3.12 = 2 1.56 1.56 Therefore, the empirical formula is S 1 O 2 or SO 2 because it has the lowest possible ratio of whole-numbered subscript. The chemical name of the compound is Sulfur dioxide. How to Calculate the Molecular Formula? In calculating the molecular formula of a compound, do the following steps below. We will refer to the sample problem below. SAMPLE PROBLEM: A sample is found to have 40.0% C, 6.6% H and 53.4% O by mass. The molecular mass of the compound is 180. What its empirical and molecular formulas? Step 1. Use 100 g of the compound as basis of calculation. Meaning there will be 40.0 g would be atoms of Carbon, 6.6 g would be atoms of Hydrogen and 53.4 g would be atoms of Oxygen. Step 2. Convert the given mass of each atom into their equivalent mole. To do this, convert the given mass of atom in the compound by using the mole of the atom as the conversion factor. Given Mass of Atom Mole of Atom Equivalent Mole of Atom 40.0 g C 1 mol of C atoms = 3.33 mol of C atoms 12.0 g C 6.6 g H 1 mol of H atoms = 6.6 mol of H atoms 1.0 g H 53.4 g O 1 mol of O atoms = 3.33 mol of O atoms 16.0 g O Step 3. The equivalent value of mole of each atom will be used as the subscript. Therefore, the formula maybe written as C 3.33 H 6.6 O 3.33. , but this formula does not 14 www.shsph.blogspot.com have whole-number subscripts. One way to get a formula with whole-number subscript is to divide all the subscripts by the smallest subscript. C :3.33 = 1 H : 6.6 = 2 O : 3.33 = 1 3.33 3.33 3.33 Therefore, the empirical formula is C 1 H 2 O 1 or CH 2 O because it has the lowest possible ratio of whole-numbered subscript. But what is the molecular formula? Step 4. Divide the molecular mass of the compound which is 180 by its molecular mass by empirical formula which is CH 2 O. The molecular mass of CH 2 O is 30 g/mol. Molecular Mass of compound divided by Molecular Mass of CH 2 O 80 / 30 =6 Step 5. Multiply the empirical formula (CH 2 O) by 6 would produce a molecular formula of C 6 H 12 O 6 HOLD ON AMIGO!!! Did you understand what you have read about empirical formula and molecular formula? If yes, let us proceed to the mini-performance task. You are about to perform the procedure as instructed in the Mini- performance task. Read and follow the procedure carefully. Good luck! Mini-Performance Task (Collaboration) Activity 2 – FREEDOM WALL Procedure 1. Prepare manila paper, pentel pen, coloring materials and ruler 2. Given a problem on molecular formula, solve the problem properly. You need to follow the steps below to solve the problem. Write your complete answers in a manila paper. You may add design that you want or remark as your expression of your feelings or experiences towards the solving process. 3. Post your output on the wall and explain it before your classmates. 15 www.shsph.blogspot.com Output Presentation FORMAT FOR FREEDOM WALL Step 1. Convert the given mass of each atom into their equivalent mole. Given Mass of Atom Mole of Atom Equivalent Mole of Atom Step 2. The equivalent value of mole of each atom will be used as the subscript. Step 3. Divide the molecular mass of the compound by its molecular mass by empirical formula. Step 4. Determine the molecular formula QUESTIONS PROBLEM A compound is found to contain 30.4% nitrogen and 69.6% oxygen. If it has a molecular mass of 92.0, what is its molecular formula? QUESTIONS 1. Is empirical formula related to molecular formula? 2. Did you find the problem difficult to solve? Why? What I Have Learned? (Critical Thinking) You have to fill in the L component of the KWL chart to generalize the things they have learned about the topic. KWL Chart Topic Know Want to know Learned Formula Mass and I have learned that Molecular Mass …. 16 www.shsph.blogspot.com HOLD ON AMIGO!!! Congratulations Mi Amigo! You are almost done in this lesson. Let us do the last part which is the assessment. Assessment (Critical Thinking) POST-TEST Problem Solving (10 pts.) Caffeine has 49.48 % C, 5.19% H, 16.48 % O and 28.85% N. Its molecular mass is 194.19. What is its molecular formula? HOLD ON AMIGO!!! Congratulations Mi Amigo!!! We are done in this module. You may now proceed to the next module. See you next time. 17 www.shsph.blogspot.com REFERENCES Mendoza E. and Religioso T. (2008). Chemistry Laboratory Manual. Phoenix Publication Mendoza E. (2003). Chemistry Textbook. Phoenix Publication Acknowledgements Writer: Gary R. Ramos, MAT-GS Editors: Ma. Teresa M. Chico- PSDS, Rosalina Aranzamendez- PSDS and Ma. Victoria Santos- PSDS Reviewers: Amalia C. Solis- EPS, Rebecca M. Roxas- EPS and Lucita A. Gener- EPS Management Team: Maria Magdelema M. Lim- Schools Division Superintendent- Manila, Aida H. Rondilla- Chief Education Supervisor, Lucky S. Carpio- EPS and Lady Hannah C. Gillo, Librarian II- LRMS 18 www.shsph.blogspot.com ANSWER SHEET Module 7 - Calculating Formula Mass, Empirical Formula and Molecular Formula Name: ______________________________ Grade/ Sec. ____________________ Score: ___ Teacher: ____________________________ School: _________________________ Date: ____ General Direction: Write your answers here from Pre-Test to Post-Test including the answers in the activities. Detach and submit this part to your teacher upon his/her direction which usually given after you have completed this module. KWL CHART Topic Know Want to know Learned Formula Mass and Molecular Mass PRE-TEST 1. 4. 2. 5. 3. POST-TEST- Lesson 1 Problem Solving (10 pts.) Calculate the formula mass of Ca 3 (PO 4 ) 2 Atom Number of Atoms Mass number Total mass number of each atom Ca _________________ 40.0 u _____________ P _________________ 31.0 u _____________ O _________________ 16.0 u _____________ ______________ 19 www.shsph.blogspot.com POST-TEST – Lesson 2 Problem Solving (10 pts.) Caffeine has 49.48 % C, 5.19% H, 16.48 % O and 28.85% N. Its molecular mass is 194.19. What is its molecular formula? PRACTICE EXERCISE : Problem Solving Calculate the formula mass of Copper sulfate, CuSO 4 Atom Number of Atoms Mass number Total mass number of each atom Cu 1 ___________ _______________ S 1 ___________ _______________ O 4 ____________ _______________ ______________ 20 www.shsph.blogspot.com Activity 1- FREEDOM WALL for Lesson 1 Output Presentation FORMAT FOR FREEDOM WALL Atom Number of Atoms Mass number Total mass number of each atom Answer to Questions 1.________________________________________________________________________________ __________________________________________________________________________________ 2.________________________________________________________________________________ __________________________________________________________________________________ Activity 2 Output Presentation – Lesson 2 FORMAT FOR FREEDOM WALL Step 1. Convert the given mass of each atom into their equivalent mole. Given Mass of Atom Mole of Atom Equivalent Mole of Atom Step 2. The equivalent value of mole of each atom will be used as the subscript. Step 3. Divide the molecular mass of the compound by its molecular mass by empirical formula. QUESTIONS Step 4. Determine the molecular formula 21