1 INTRODUCTION W1 WORKSHOP ON STOICHIOMETRY These notes and exercises are designed to introduce you to the basic concepts required to understand a chemical formula or equation. Relative atomic masses of all the elements can be found in the Periodic Table on the back cover of this Laboratory Handbook. Atomic, molecular and formula weights The smallest bit of matter that can be weighed reliably contains an enormous number of atoms and hence a convenient unit for describing a large number of atoms is required. This unit is called the mole and is the amount of substance that contains as many elementary units as there are carbon atoms in exactly 12 g of carbon-12. This number, approximately is called the Avogadro constant and given the symbol N A (or less commonly, L). One mole (1 mol) of hydrogen atoms contains H atoms One mole (1 mol) of helium atoms contains He atoms One mole (1 mol) of water molecules contains H 2 O molecules One mole (1 mol) of sodium ions contains Na + ions One mole (1 mol) of $1 coins is worth $ The relative atomic mass of any element is the mass (in gram) that contains 1 mol of atoms of that element. The relative atomic mass is often called the atomic mass or atomic weight. eg 1. What mass of copper contains Cu atoms? The relative atomic mass of Cu = By definition, g of copper contains 1 mol of Cu atoms; or g of copper contains Cu atoms. eg 2. How many neon atoms are present in 10.1 g of neon? The relative atomic mass of Ne = Therefore 20.2 g of neon contains Ne atoms By proportion, 10.1 g of neon contains = Ne atoms eg 3. The mass of one atom of an element X is found to be g. What is the relative atomic mass of element X? 1 atom of X has mass g Therefore 1 mol of atoms of X has mass ( ) ( ) g = 12.0 g. Therefore the relative atomic mass of X = W1-1
2 W1-2 Most elements exist naturally as a mixture of isotopes. Each isotope has its own characteristic atomic weight that is close to, but not exactly equal to its mass number. For example, isotope % natural abundance atomic weight 12 C (standard by definition) 13 C N N Br Br The relative atomic mass of an element is a weighted average of the relative masses of all isotopes of that element. eg 4. Bromine contains 50.69% of the isotope 79 Br and 49.31% of the isotope 81 Br. What is the relative atomic mass of bromine? Relative atomic mass = = The relative molecular weight of a molecule is the sum of the atomic weights of the constituent atoms multiplied by the number of those atoms present. The relative molecular weight is often called the molecular weight. H 2 has a molecular mass = = O 2 has a molecular mass = = H 2 O has a molecular mass = ( ) = CO 2 has a molecular mass = ( ) = The formula weight of an ionic compound is the sum of the atomic masses of the constituent atoms multiplied by the number of those atoms present in the empirical formula. NaCl has a formula weight = = MgCl 2 has a formula weight = ( ) = The general expression relating the number of moles to mass is: Amount of substance (in mol) = mass of substance formula weight or n = M m eg 5. What is the mass of 1.50 mol of carbon dioxide? The molecular weight of CO 2 = ( ) = Therefore 1.00 mol of CO 2 has mass of g Therefore 1.50 mol of CO 2 has mass of = 66.0 g eg 6. What is the mass of mol of the salt lithium fluoride? Lithium fluoride has the formula LiF. Therefore 1.00 mole of LiF has mass ( ) g = g. Therefore mole of LiF has mass g = 7.00 g.
3 W1-3 eg 7. What amount of calcium bromide is present in 6.76 g of CaBr 2? The formula weight of CaBr 2 = ( ) = Therefore g of CaBr 2 = 1.00 mol 6.76 Therefore 6.76 g of CaBr 2 = 1.00 mol = mol eg 8. How many molecules of H 2 O are present in mol of water? 1 mol of water contains H 2 O molecules Therefore mol contains ( ) = H 2 O molecules. eg 9. How many molecules are present in 2.00 g of table sugar, C 12 H 22 O 11? The relative molecular mass of C 12 H 22 O 11 = ( ) + ( ) + ( ) = Therefore 2.00 g = mol Therefore 2.00 g contains molecules of C 12 H 22 O = molecules. Gases The gaseous elements hydrogen, nitrogen, oxygen, fluorine and chlorine occur as diatomic molecules. That is, they exist naturally as H 2, N 2, O 2, F 2 and Cl 2 rather than as the atomic species. (Bromine, Br 2, and iodine, I 2, though not gases are also diatomic elements.) In contrast, the noble gases helium, neon, argon, krypton, xenon and radon all exist as monatomic species. 1 mole of any gas occupies 22.4 L at standard temperature and pressure. Standard temperature and pressure (STP) is defined as 0 C and 1 atmosphere mol of hydrogen (H 2 molecules) occupies 22.4 L at STP mol of helium (He atoms) occupies 22.4 L at STP L of chlorine (Cl 2 molecules) contains 1.00 mol of Cl 2 molecules at STP L of fluorine (F 2 molecules) contains mol of F 2 molecules at STP L of neon contains atoms of Ne at STP. eg 10. What is the volume of 76.0 g of fluorine at STP? The molecular weight of F 2 = = Amount of F 2 = = 2.00 mol Therefore volume = 2.00 mol 22.4 L mol 1 = 44.8 L. eg 11. What is the mass of 105 L of oxygen at STP? The molecular weight of O 2 = = L of O 2 = mol of O2 = mol 32 g mol 1 = 150 g
4 W1-4 Q1. Calculate the mass of 2.0 mol of silicon. Q2. Calculate the mass of 0.37 mol of barium chloride. Q3. Calculate the amount of S atoms (in mol) present in 2.8 g sulfur. Q4. Calculate the amount of H 2 O molecules (in mol) present in 36.0 g of water. Q5. Calculate the mass of molecules of hydrogen.
5 W1-5 Q6. Calculate the amount of CO 2 molecules (in mol) present in molecules of carbon dioxide. Q7. Calculate the amount of Ar atoms (in mol) present in 5.6 L of argon at STP. Q8. Calculate the mass of 50.0 L of nitrogen gas at STP. Q9. Calculate the atomic weight and the molecular weight of a natural sample of chlorine, which contains the isotopes: 35 Cl (at. wt , 75.77%) and 37 Cl (at. wt , 24.23%). Demonstrator's Initials
6 W1-6 Structural, molecular and empirical formulas The structural formula indicates the arrangement of the atoms and the bonds within the molecule, eg H O O H for hydrogen peroxide. The molecular formula shows the actual number of atoms of each element in a molecule of the compound, eg H 2 O 2 for hydrogen peroxide. The empirical formula of a compound is the simplest integer ratio of the elements in that compound, eg HO for hydrogen peroxide. Metals, ionic compounds, some non-metallic elements and many inorganic compounds consist of infinite lattices of regularly repeating units. The term molecular weight has no meaning when applied to such compounds, there being no molecules. For these compounds, the term formula weight should be used, where the formula is the empirical formula. (See page W1-2.) Percent composition of a compound Each pure compound always has the same composition by weight, regardless of how it is produced. For example, glucose, C 6 H 12 O 6, always has 6 C atoms, 12 H atoms and 6 O atoms in every one of its molecules. Given the atomic weights of the component elements, the % by weight for each element in the compound can be calculated. eg 12. Calculate the % composition of glucose. The molar mass (gram molecular weight) of glucose, C 6 H 12 O 6, = ( ) = g mol 1 From the formula of glucose, 1 molecule of glucose contains 6 atoms of C. Hence 1 mol of glucose would contain 6 mol of C. As 1 mole of C weighs g, then the mass of C in 1 mol of glucose = g = g. % C in C 6 H 12 O 6 = % = 39.99% by mass Similarly, the percentage of H and O can be calculated as follows: Each mole of glucose contains 12 mol of H and 6 mol of O, respectively. % H = % O = % = 6.71% H % = 53.28% O [Note that the sum of the % of all the elements must add up to 100%.]
7 W1-7 Recall that the empirical formula of a compound is the simplest integer ratio of the elements in that compound. Given the % composition of a compound, its empirical formula can be calculated. The processes involved are simply the reverse of those just done above. eg 13. Determine the empirical formula of a compound that returns the following data for % by mass: iron (Fe): 63.5 %, sulfur (S): 36.5 % From the data, in 100 g of compound, there would be 63.5 g of Fe combined with 36.5 g of S. To obtain the empirical formula, we need to determine the relative amounts of Fe and S present. Because Fe and S have different atomic weights, to calculate the number of moles of Fe and of S atoms present in the compound, it is necessary to divide the mass of each by the atomic weight of the element. Amount of Fe 63.5 = = mol of Fe Amount of S 36.5 = = mol of S Thus the ratio of amount of Fe to amount of S in the compound is mol of Fe : mol of S This is also the ratio of the number of atoms of Fe to the number of atoms of S. However, the empirical formula must have integer quantities for all the numbers of atoms in it. In this example, it is obvious that, within the usual allowable experimental error in analytical data of 0.3 %, the ratio of atoms of Fe: atoms of S = 1.00 : Thus the empirical formula is FeS. eg 14. Determine the empirical formula of an unknown compound that has the following % composition by mass: nitrogen 26.2%, chlorine 66.4%, hydrogen 7.50% [Note that these percentages total to 100%, within the experimental error. If they do not total to 100%, the difference is attributed to oxygen, whose analysis is difficult.] N : Cl : H = % N atomic weight N : % Cl atomic weight Cl : % H atomic weight H = : : * = : : = 1.00 : 1.00 : : 1 : 4 Thus the empirical formula is NClH 4. In order to convert these numbers to integers they must be divided by the highest common factor. A good starting point is to divide each by the smallest number, in this case *Note that you must divide each mass by the atomic weight of the element. [A common error is to divide by the molecular weight for species that occurs in nature as diatomic molecules, eg for N 2, for Cl 2, for O 2 or for H 2.]
8 W1-8 Q10. Determine the percentage by weight of bromide ion in potassium bromide (KBr). Q11. An iron ore has the composition of 70.0% Fe and 30.0% O by mass. What is the empirical formula of the ore? Q12. An organic compound containing only carbon, hydrogen and oxygen returns the % mass analysis: C 64.9 %; H 13.5 %. What is its empirical formula? Demonstrator's Initials
9 W1-9 Chemical Equations A chemical equation describes the changes occurring in a reaction. For example, the reaction between hydrogen gas and oxygen gas produces water. In words, the reaction may be written as: hydrogen + oxygen water The standard symbols are used to represent the chemical species involved. As explained on page W1-3, hydrogen and oxygen are diatomic gases - they have the molecular formulas H 2 and O 2, respectively. Water is composed of two hydrogen atoms and one oxygen atom, i.e. it has the molecular formula H 2 O. The reaction may be represented as: O 2 + H 2 H 2 O But does 1 hydrogen molecule react with 1 oxygen molecule to produce 1 water molecule? A quick look at the following diagram shows that the answer is no - one oxygen atom has just disappeared. O H H + O O H H Atoms are neither created nor destroyed in chemical reactions (The Law of Conservation of Mass). Consequently there must be the same number of atoms of any particular type on both sides of the equation, irrespective of how they are arranged. This can be achieved in our current example if two molecules of hydrogen react with one molecule of oxygen to produce two molecules of water. O O + + H H H H H O H + H O H or in symbols O 2 + 2H 2 2H 2 O This process of ensuring that the same number of atoms of any particular type appear on both sides of the equation is called balancing the equation. A number used as a prefix indicates the ratio of reacting species in the equation. In this case two hydrogen molecules react with one oxygen molecule to form two water molecules. As the numerical prefixes represent ratios, it is just as valid (and much more usual) to say that two mole of hydrogen reacts with one mole of oxygen to form two mole of water. The physical state of the various species is indicated by (s) for a solid, (l) for a liquid, (g) for a gas or (aq) for an aquated species. In this example the water is generated as a gas and the final balanced equation is written: O 2 (g) + 2H 2 (g) 2H 2 O(g)
10 W1-10 eg 15. Hydrogen and chlorine react to form the compound hydrogen chloride, all species being gases. Write the balanced molecular equation. H 2 (g) + Cl 2 (g) 2HCl(g) eg 16. The carbohydrate, glucose, is oxidised to carbon dioxide and water in biological systems. Write the overall molecular reaction. C 6 H 12 O 6 (s) + 6O 2 (g) 6CO 2 (g) + 6H 2 O(l) eg 17. Solid sodium metal reacts with chlorine gas to form sodium chloride. Give the equation. 2Na(s) + Cl 2 (g) 2NaCl(s) In this example, note how the empirical formulas, Na for the metal sodium and NaCl for the ionic compound sodium chloride, are used. Reactions in solution When an ionic solid dissolves in water to form a solution, the charges on the ions are indicated. NaCl(s) Na + (aq) + Cl (aq) Again, the atoms must balance. Notice also that the electrical charges present on both sides of the equation must balance as well. In another example: BaCl 2 (s) Ba 2+ (aq) + 2Cl (aq) In words, this means that 1 mole of barium chloride dissolves in water to produce 1 mole of barium ions and 2 mole of chloride ions. Silver nitrate and sodium chloride are both soluble compounds, and in water solution release their component ions, shown in the following ionic equations. AgNO 3 (s) Ag + (aq) + NO 3 (aq) NaCl(s) Na + (aq) + Cl (aq) Silver chloride is insoluble in water. When a solution of silver nitrate is mixed with a solution of sodium chloride, the Ag + (aq) ions react with the Cl (aq) ions to precipitate AgCl as shown in the following ionic equation. Ag + (aq) + NO 3 (aq) + Na + (aq) + Cl (aq) AgCl(s) + NO 3 (aq) + Na + (aq) Note that only the Ag + and the Cl ions have reacted, leaving the Na + and NO 3 ions free in the solution. As these last two ions have not in fact entered into a reaction, they should be deleted from the equation in much the same way as common terms are cancelled from both sides of a mathematical equation. Such ions are called spectator ions. [Initially it may be helpful to write down all the ions that are being mixed together in order to establish whether any combination can form an insoluble salt, and then cancel out the spectator species.] The net ionic equation is thus: Ag + (aq) + Cl (aq) AgCl(s)
11 W1-11 Q13. Balance each of the following molecular equations: Carbon is burnt in a limited supply of oxygen to produce carbon monoxide. C(s) + O 2 (g) CO(g) Nitrogen and hydrogen react to produce ammonia. N 2 (g) + H 2 (g) NH 3 (g) Sodium metal reacts with bromine to form sodium bromide. Na(s) + Br 2 (l) NaBr(s) Iron reacts with oxygen to form iron(iii) oxide. Fe(s) + O 2 (g) Fe 2 O 3 (s) Q14. Complete the following table. (See page E2-2 if you need help.) Formula Name Formula Name OH acetate ion nitrite ion CN nitrate ion HS C 2 O 4 2 permanganate ion perchlorate ion carbonate ion hydrogencarbonate ion phosphate ion S 2 O 3 2 H 2 PO 4 sulfate ion ammonium ion sulfite ion Cr 2 O 7 2 Q15. Indicate the charges on the ions and balance the following ionic equations: Potassium iodide is dissolved in water. KI(s) K (aq) + I (aq) Sodium carbonate is dissolved in water. Na 2 CO 3 (s) Na (aq) + CO 3 (aq) Ammonium chloride is dissolved in water. NH 4 Cl(s) NH 4 (aq) + Cl (aq) Calcium hydroxide is dissolved in water. Ca(OH) 2 (s) Ca (aq) + OH (aq)
12 W1-12 Q16. Write the ionic equations for the reactions that occur when solid sodium carbonate and solid calcium chloride dissolve in water. Also write the ionic equation for the precipitation of calcium carbonate resulting from mixing the two solutions. Dissolution of sodium carbonate Dissolution of calcium chloride Mixing above solutions Demonstrator's Initials Limiting Reactant A balanced chemical equation indicates the relative amounts of the chemicals that take part in a reaction. It bears absolutely no relationship whatsoever to the amounts of chemicals that a chemist might decide to mix together in a vessel. For instance O 2 + 2H 2 2H 2 O Molar ratios: Mass ratios: 32 g 4 g 36 g If 32 g of O 2 is mixed with 4 g of H 2 and the mixture ignited, 36 g of H 2 O will form. But what is the result if 16 g of O 2 and 4 g of H 2 are added to the reaction vessel? The oxygen will react completely to give 18 g of water and there will still be 2 g of H 2 left. In this case, oxygen is said to be the limiting reactant and hydrogen is said to be in excess.
13 W1-13 eg 18 Ammonia is oxidised at high temperature in the first step of the Ostwald process to produce nitric acid. The products of the reaction are nitric oxide and water vapour. If a g sample of NH 3 is reacted with g of O 2, what mass of the various products and reactants are present after the reaction is completed? Balanced equation 5O 2 (g) + 4NH 3 (g) 4NO(g) + 6H 2 O(g) Molar ratios Initial amounts = 2.00 = (in mol) change* final amounts (in mol) final amounts (in g) = * Mole ratio of NH 3 : O 2 from equation = 4 : 5 = 0.8 Mole ratio of NH 3 : O 2 from above calculations 3 : 2 = 1.5 That is, excess NH 3 is present and thus O 2 is the limiting reagent. (If the NH 3 : O 2 ratio had been less than 0.8, O 2 would have been present in excess and NH 3 would have been the limiting reagent.) Having established that O 2 is the limiting reactant and will all be consumed, the change in reactants and products is calculated from the equation as follows: 5 mol of O 2 reacts with 4 mol of NH 3 to give 4 mol of NO and 6 mol of H 2 O mol of O 2 reacts with g of O 2 reacts with 5 mol of NH 3 to give g of NH 3 to give mol of NO and g of NO and mol of H 2 O g of H 2 O. i.e g of O 2 reacts with g of NH 3 to give g of NO and g of H 2 O. No O 2 is left over, but g of the NH 3 remains unreacted. Solutions The concentration of a solute in a solution may be expressed as a molarity. Concentration is indicated by square brackets around the species to which the concentration refers and has units of mol L 1 or M. Concentration (in mol L 1 ) = amount (in mol) volume (in L)
14 W1-14 eg 19. What is the concentration of one litre of glucose solution containing 2 moles of glucose? 2 mol [Glucose] = = 2 mol L 1 = 2 M 1 L eg 20. One mole of sodium hydroxide is dissolved in water and made up to 250 ml. What is the concentration of the solution? 250 ml = L = L 1 mol concentration of NaOH in 1 L = = 4 mol L 1 = 4 M L eg 21. A solution of calcium chloride has a concentration of 0.30 M. What is the concentration of the individual ions in the solution? CaCl 2 (s) Ca 2+ (aq) + 2Cl (aq) That is, 1 mol of CaCl 2 (s) produces 1 mol of Ca 2+ (aq) and 2 mol of Cl (aq) ions. Thus, if concentration of CaCl 2 = 0.30 M, from the equation it can be seen that [Ca 2+ ] = 0.30 M and [Cl ] = M = 0.60 M. eg 22. Chromium(III) fluoride (6.66 g) is dissolved in water and the volume made up to ml. What is the concentration of the ions in the solution. Relative formula weight of CrF 3 = ( ) = Amount of CrF 3 = mol = mol mol concentration of CrF 3 = = mol L 1 = M L CrF 3 (s) Cr 3+ (aq) + 3F (aq) Thus, if concentration of CrF 3 = M, from the equation it can be seen that [Cr 3+ ] = M and [F ] = M = M. eg 23. What volume of solution is required to form a M solution of sodium chloride from moles of the salt? Concentration (mol L 1 amount (in mol) ) = volume (in L) amount (in mol) Therefore volume (in L) = concentration (in M) mol Therefore volume (in L) = = L = 25 ml M eg 24. What amount of chloride ion is in 150 ml of a 0.50 M solution of magnesium chloride? MgCl 2 (s) Mg 2+ (aq) + 2Cl (aq) [Mg 2+ (aq)] = 0.50 M and [Cl (aq)] = M = 1.00 M Concentration ( in mol L 1 amount (in mol) ) = volume (in L) Therefore amount (in mol) = Concentration (in mol L 1 ) volume (in L) = 1.00 mol L L = mol
15 W1-15 eg 25. What volume of 0.11 M hydrochloric acid will react with 25 ml of M sodium hydroxide solution? NaOH Na + (aq) + OH (aq) and HCl H + (aq) + Cl (aq) also H + (aq) + OH (aq) H 2 O [OH ] = M and 25 ml = L moles of OH = moles of H + = mol L L = mol Volume of H mol needed = mol L = L = 20. ml Q17. Calculate the mass of sodium carbonate (Na 2 CO 3 10H 2 O) required to make 250. ml of a M solution. Q18. What mass of barium sulfate will be precipitated when 125 ml of a 0.20 M solution of barium chloride is mixed with 200. ml of a 0.17 M solution of sodium sulfate. (Hint: work out which reagent is limiting.)
16 W1-16 Q19. Pure formic acid (HCOOH), is a liquid monoprotic acid decomposed by heat to carbon dioxide and hydrogen, according to the following equation: HCOOH(l) H 2 (g) + CO 2 (g) (i) The density of formic acid is g ml 1. How many moles of HCOOH are in L of pure formic acid? (ii) What mass of pure formic acid should be diluted to 1.00 L to form a 2.00 M solution? (iii) What volume of M sodium hydroxide solution would react with 30.0 ml of this dilute solution of formic acid, according to the following equation? HCOOH(aq) + OH (aq) HCOO (aq) + H 2 O(l) (iv) What is the maximum volume of carbon dioxide at STP that could be obtained by heating 1.0 mol of formic acid? (v) How many molecules of carbon dioxide would it contain?
17 W1-17 Q20. Consider the reaction 4Al(s) + 3O 2 (g) 2Al 2 O 3 (s) Identify the limiting reagent in each of the following reaction mixtures. What mass of Al 2 O 3 (s) will be produced in each case? 1.0 mol Al and 1.0 mol O mol Al and 0.50 mol O g Al and g O g Al and g O 2 Demonstrator's Initials
18 W1-18 POST-WORK The following questions are further examples of the basic types of stoichiometric calculations. Proficiency in these types of calculations is essential for any serious student of Chemistry. If time permits they may be done in your laboratory session, otherwise they should be done before your next laboratory session. Worked answers to all these problems are available from WebCT. Q1. Write the equation that relates amount of a substance to mass. Q2. Calculate the mass of 1.87 mol of sulfur trioxide. Q3. Calculate the amount (in mol) present in g of silicon tetrachloride. Q4. Calculate the mass of molecules of water. Q5. Calculate the volume (in L) present in atoms of helium at STP.
19 W1-19 Q6. Calculate the relative atomic mass of a natural sample of zinc, which contains the isotopes with masses and abundances given: isotope atomic weight abundance isotope atomic weight abundance 64 Zn % 68 Zn % 66 Zn % 70 Zn % 67 Zn % Q7. An iron supplement is used to treat anaemia and 50 mg (i.e g) of Fe 2+ is required per tablet. If the iron compound used in the tablet is FeSO 4 7H 2 O, what mass of this compound would be required per tablet to provide the desired amount of Fe 2+? Q8. Write the equation that relates concentration of a solution to amount of solute and volume of solution. Q9. Write the net ionic equation for the reaction that occurs when a solution of barium nitrate is mixed with a solution of sodium sulfate. A white precipitate of barium sulfate forms.
20 W1-20 Q10. One of the components of petrol is octane, C 8 H 18. (i) Write the balanced equation for the complete combustion of octane to form carbon dioxide gas and liquid water. (ii) What amount (in mol) of carbon dioxide is formed when 5.5 mol (1 L) of octane is burnt? (iii) What volume of carbon dioxide would this represent at STP? Q11. Hydrogen iodide gas (5.0 L at STP) is dissolved in water and the volume made up to 1.0 L. What is the molarity of the solution? Q12. What volume of M hydrochloric acid would be needed to react completely with a mixture of g of sodium hydroxide and g of potassium hydroxide?
21 W1-21 Q13. A solution was prepared by dissolving nickel (II) nitrate-6-water, Ni(NO 3 ) 2 6H 2 O, (29.1 g) in some water and making the volume up to 1.00 L with water. Assuming complete dissociation of the solid into ions, calculate: (i) The amount (in mol) of nickel(ii) ions in 100. ml of this solution. (ii) The amount (in mol) of nitrate ions in 100. ml of this solution. (iii) The number of individual nickel(ii) ions in 100. ml of solution. Q14. What volume of M silver nitrate solution will exactly react with 20. ml of M sodium chloride solution?
Chapter 3 Mass Relationships in Chemical Reactions Student: 1. An atom of bromine has a mass about four times greater than that of an atom of neon. Which choice makes the correct comparison of the relative
The Mole Atomic mass units and atoms are not convenient units to work with. The concept of the mole was invented. This was the number of atoms of carbon-12 that were needed to make 12 g of carbon. 1 mole
DP Chemistry Review Topic 1: Quantitative chemistry 1.1 The mole concept and Avogadro s constant Assessment statement Apply the mole concept to substances. Determine the number of particles and the amount
Chapter 3 Insert picture from First page of chapter Stoichiometry: Ratios of Combination Copyright McGraw-Hill 2009 1 3.1 Molecular and Formula Masses Molecular mass - (molecular weight) The mass in amu
35 MOLES ND MOLE CLCULTIONS INTRODUCTION The purpose of this section is to present some methods for calculating both how much of each reactant is used in a chemical reaction, and how much of each product
Chapter 1 The Atomic Nature of Matter 6. Substances that cannot be decomposed into two or more simpler substances by chemical means are called a. pure substances. b. compounds. c. molecules. d. elements.
Moles Balanced chemical equations Molar ratios Mass Composition Empirical and Molecular Mass Predicting Quantities Equations Micro World atoms & molecules Macro World grams Atomic mass is the mass of an
Chapter 1: Moles and equations 1 Learning outcomes you should be able to: define and use the terms: relative atomic mass, isotopic mass and formula mass based on the 12 C scale perform calculations, including
Chapter 3 ATOMS AND MOLECULES Multiple Choice Questions 1. Which of the following correctly represents 360 g of water? (i) 2 moles of H 2 0 (ii) 20 moles of water (iii) 6.022 10 23 molecules of water (iv)
3 Formulae, stoichiometry and the mole concept Content 3.1 Symbols, Formulae and Chemical equations 3.2 Concept of Relative Mass 3.3 Mole Concept and Stoichiometry Learning Outcomes Candidates should be
Molecular Formula: Example A compound is found to contain 85.63% C and 14.37% H by mass. In another experiment its molar mass is found to be 56.1 g/mol. What is its molecular formula? 1 CHAPTER 3 Chemical
Chapter 3. Stoichiometry: Mole-Mass Relationships in Chemical Reactions Concept 1. The meaning and usefulness of the mole The mole (or mol) represents a certain number of objects. SI def.: the amount of
Name Writing and Balancing Chemical Equations Period When a substance undergoes a chemical reaction, chemical bonds are broken and new bonds are formed. This results in one or more new substances, often
Stoichiometry Review There are 20 problems in this review set. Answers, including problem set-up, can be found in the second half of this document. 1. N 2 (g) + 3H 2 (g) --------> 2NH 3 (g) a. nitrogen
SCH 4C1 Unit 2 Problem Set Questions taken from Frank Mustoe et all, "Chemistry 11", McGraw-Hill Ryerson, 2001 1. A small pin contains 0.0178 mol of iron. How many atoms of iron are in the pin? 2. A sample
Chapter 3: Stoichiometry Key Skills: Balance chemical equations Predict the products of simple combination, decomposition, and combustion reactions. Calculate formula weights Convert grams to moles and
APPENDIX A Molarity of Ions in Solution ften it is necessary to calculate not only the concentration (in molarity) of a compound in aqueous solution but also the concentration of each ion in aqueous solution.
Aqueous Solutions and Solution Stoichiometry Water is the dissolving medium, or solvent. Some Properties of Water Water is bent or V-shaped. The O-H bonds are covalent. Water is a polar molecule. Hydration
HOMEWORK 4A Oxidation-Reduction Reactions 1. Indicate whether a reaction will occur or not in each of following. Wtiring a balcnced equation is not necessary. (a) Magnesium metal is added to hydrochloric
Topic 4 National Chemistry Summary Notes Formulae, Equations, Balancing Equations and The Mole LI 1 The chemical formula of a covalent molecular compound tells us the number of atoms of each element present
Chem 1100 Chapter Three Study Guide Answers Outline I. Molar Mass and Moles A. Calculations of Molar Masses B. Calculations of moles C. Calculations of number of atoms from moles/molar masses 1. Avagadro
STOICHIOMETRY LEARNING OUTCOMES At the end of this unit students will be expected to: UNIT 1 THE MOLE AND MOLAR MASS define molar mass and perform mole-mass inter-conversions for pure substances explain
Balancing Chemical Equations Worksheet Student Instructions 1. Identify the reactants and products and write a word equation. 2. Write the correct chemical formula for each of the reactants and the products.
Chapter 3 Stoichiometry 3-1 Chapter 3 Stoichiometry In This Chapter As you have learned in previous chapters, much of chemistry involves using macroscopic measurements to deduce what happens between atoms
1. How many iron atoms are present in one mole of iron? Ans. 6.02 1023 atoms 2. How many grams of sulfur are found in 0.150 mol of sulfur? [Use atomic weight: S, 32.06 amu] Ans. 4.81 g 3. How many moles
Chemistry: Chemical Equations Write a balanced chemical equation for each word equation. Include the phase of each substance in the equation. Classify the reaction as synthesis, decomposition, single replacement,
Chemistry B11 Chapter 4 Chemical reactions Chemical reactions are classified into five groups: A + B AB Synthesis reactions (Combination) H + O H O AB A + B Decomposition reactions (Analysis) NaCl Na +Cl
Unit 9 Stoichiometry Notes (The Mole Continues) is a big word for a process that chemist s use to calculate amounts in reactions. It makes use of the coefficient ratio set up by balanced reaction equations
St Peter the Apostle High School Chemistry Department Formulae, Equations & Formula Mass N4 & N5 Homework Questions Answer questions as directed by your teacher. National 4 level questions are first followed
Chapter Three Calculations with Chemical Formulas and Equations Mass and Moles of a Substance Chemistry requires a method for determining the numbers of molecules in a given mass of a substance. This allows
CHEMISTRY 123-07 Midterm #1 Answer key October 14, 2010 Statistics: Average: 74 p (74%); Highest: 97 p (95%); Lowest: 33 p (33%) Number of students performing at or above average: 67 (57%) Number of students
WRITING CHEMICAL FORMULA For ionic compounds, the chemical formula must be worked out. You will no longer have the list of ions in the exam (like at GCSE). Instead you must learn some and work out others.
T-27 Tutorial 4 SOLUTION STOICHIOMETRY Solution stoichiometry calculations involve chemical reactions taking place in solution. Of the various methods of expressing solution concentration the most convenient
Chemical Calculations: Formula Masses, Moles, and Chemical Equations Atomic Mass & Formula Mass Recall from Chapter Three that the average mass of an atom of a given element can be found on the periodic
Sample Exercise 3.1 Interpreting and Balancing Chemical Equations The following diagram represents a chemical reaction in which the red spheres are oxygen atoms and the blue spheres are nitrogen atoms.
Molar Mass Molar mass = Mass in grams of one mole of any element, numerically equal to its atomic weight Molar mass of molecules can be determined from the chemical formula and molar masses of elements
6 Reactions in Aqueous Solutions Water is by far the most common medium in which chemical reactions occur naturally. It is not hard to see this: 70% of our body mass is water and about 70% of the surface
44 Section 43 Questions 1 Define Avogadro s constant, and explain its significance in quantitative analysis 2 Distinguish between the terms atomic mass and molar mass 3 Calculate the mass of a molecule
Example Exercise 9.1 Atomic Mass and Avogadro s Number Refer to the atomic masses in the periodic table inside the front cover of this textbook. State the mass of Avogadro s number of atoms for each of
AP Chem Summer Assignment Worksheet #1 Atomic Structure 1. a) For the ion 39 K +, state how many electrons, how many protons, and how many 19 neutrons are present? b) Which of these particles has the smallest
Skills Worksheet Problem Solving Stoichiometry of Gases Now that you have worked with relationships among moles, mass, and volumes of gases, you can easily put these to work in stoichiometry calculations.
Stoichiometry 1 The total number of moles represented by 20 grams of calcium carbonate is (1) 1; (2) 2; (3) 01; (4) 02 2 A 44 gram sample of a hydrate was heated until the water of hydration was driven
Moles, Molecules, and Grams Worksheet Answer Key 1) How many are there in 24 grams of FeF 3? 1.28 x 10 23 2) How many are there in 450 grams of Na 2 SO 4? 1.91 x 10 24 3) How many grams are there in 2.3
Chapter 3 Calculation with Chemical Formulas and Equations Practical Applications of Chemistry Determining chemical formula of a substance Predicting the amount of substances consumed during a reaction
Chapter 8: Chemical Equations and Reactions I. Describing Chemical Reactions A. A chemical reaction is the process by which one or more substances are changed into one or more different substances. A chemical
Atomic Structure called nucleons Name Mass Charge Location Protons 1 +1 Nucleus Neutrons 1 0 Nucleus Electrons 1/1837-1 Orbit nucleus in outer shells The number of protons equals the atomic number This
TEKS REVIEW 8B Calculating Atoms, Ions, or Molecules Using Moles TEKS 8B READINESS Use the mole concept to calculate the number of atoms, ions, or molecules in a sample TEKS_TXT of material. Vocabulary
Chapter 3 Formulas, Equations and Moles Interpreting Chemical Equations You can interpret a balanced chemical equation in many ways. On a microscopic level, two molecules of H 2 react with one molecule
2. ATOMIC, MOLECULAR AND EQUIVALENT MASSES INTRODUCTION: EQUIVALENT WEIGHT Since hydrogen is the lightest of all elements, it was chosen as a standard for determination of equivalent weights. On this basis,
The position of hydrogen in the reactivity series Hydrogen, although not a metal, is included in the reactivity series because it, like metals, can be displaced from aqueous solution, only this time the
1 REACTIONS AND YIELD ANSWERS stoichiometry = the numerical relationships between chemical amounts in a reaction. 2C 8 H 18 (l) + 25O 2 16CO 2 (g) + 18H 2 O(g) From the equation, 16 moles of CO 2 (a greenhouse
Honors Chemistry: Unit 6 Test Stoichiometry PRACTICE TEST ANSWER KEY Page 1 1. 2. 3. 4. 5. 6. Question What is a symbolic representation of a chemical reaction? What 3 things (values) is a mole of a chemical
Micro World atoms & molecules Laboratory scale measurements Atomic mass is the mass of an atom in atomic mass units (amu) By definition: 1 atom 12 C weighs 12 amu On this scale 1 H = 1.008 amu 16 O = 16.00
Experiment 9 - Double Displacement Reactions A double displacement reaction involves two ionic compounds that are dissolved in water. In a double displacement reaction, it appears as though the ions are
Introduction Chapter 5 Chemical Reactions and Equations Chemical reactions occur all around us. How do we make sense of these changes? What patterns can we find? 1 2 Copyright The McGraw-Hill Companies,
The Mole Chapter 10 1 Objectives Use the mole and molar mass to make conversions among moles, mass, and number of particles Determine the percent composition of the components of a compound Calculate empirical
Chemical Reactions Chemical Equations Chemical reactions describe processes involving chemical change The chemical change involves rearranging matter Converting one or more pure substances into new pure
Chapter 6 Oxidation-Reduction Reactions 1. Oxidation is defined as a. gain of a proton b. loss of a proton c. gain of an electron! d. loss of an electron e. capture of an electron by a neutron 2. Which
Problem Set #10 - Answers BIG IDEAS Fill in the blanks or circle the correct response in brackets. 1) When a reaction occurs, the stuff you start with is called the _reactants_ and the stuff you end up
1. The elements on the Periodic Table are arranged in order of increasing A) atomic mass B) atomic number C) molar mass D) oxidation number 2. Which list of elements consists of a metal, a metalloid, and
Name: Tuesday, May 20, 2008 1. What is the molecular formula of a compound with the empirical formula PO and a gram-molecular mass of 284 grams? 2 5 1. P2O 5 3. P10O4 2. P5O 2 4. P4O10 2. Which substance
Chapter 5 - Molecules and Compounds How do we represent molecules? In pictures In formula In name Ionic compounds Molecular compounds On the course website, you will find a list of ions that I would like
9.1 Naming Ions I. Monatomic Ions A. Monatomic ions 1. Ions formed from a single atom Unit 4 Conservation of Mass and Stoichiometry B. Naming Monatomic Ions 1. Monatomic cations are a. Identified by the
Description of the Mole Concept: Suppose you were sent into the store to buy 36 eggs. When you picked them up you would get 3 boxes, each containing 12 eggs. You just used a mathematical device, called
TYPES OF SOLUTIONS A solution is a homogeneous mixture of two substances: a solute and a solvent. Solute: substance being dissolved; present in lesser amount. Solvent: substance doing the dissolving; present
1 MOLECULAR MASS AND FORMULA MASS Molecular mass = sum of the atomic weights of all atoms in the molecule. Formula mass = sum of the atomic weights of all atoms in the formula unit. 2 MOLECULAR MASS AND
Chemical Equations and Chemical Reactions Chapter 8.1 Objectives List observations that suggest that a chemical reaction has taken place List the requirements for a correctly written chemical equation.
Mass, Moles, & Molar Mass Relative quantities of isotopes in a natural occurring element (%) E.g. Carbon has 2 isotopes C-12 and C-13. Of Carbon s two isotopes, there is 98.9% C-12 and 11.1% C-13. Find
CHEMICAL REACTIONS A chemical reaction is a rearrangement of atoms in which some of the original bonds are broken and new bonds are formed to give different chemical structures. In a chemical reaction,
Stoichiometry Atomic Mass (atomic weight) Atoms are so small, it is difficult to discuss how much they weigh in grams We use atomic mass units an atomic mass unit (AMU) is one twelfth the mass of the catbon-12
Chemical Equations & Stoichiometry Chapter Goals Balance equations for simple chemical reactions. Perform stoichiometry calculations using balanced chemical equations. Understand the meaning of the term
CHM-101-A Exam 2 Version 1 1. Which of the following statements is incorrect? A. SF 4 has ¼ as many sulfur atoms as fluorine atoms. B. Ca(NO 3 ) 2 has six times as many oxygen atoms as calcium ions. C.
Chem 115 POGIL Worksheet - Week 4 Moles & Stoichiometry Why? Chemists are concerned with mass relationships in chemical reactions, usually run on a macroscopic scale (grams, kilograms, etc.). To deal with
1. When the following equation is balanced, the coefficient of Al is. Al (s) + H 2 O (l)? Al(OH) (s) + H 2 (g) A) 1 B) 2 C) 4 D) 5 E) Al (s) + H 2 O (l)? Al(OH) (s) + H 2 (g) Al (s) + H 2 O (l)? Al(OH)
CHAPTER THREE: CALCULATIONS WITH CHEMICAL FORMULAS AND EQUATIONS Part One: Mass and Moles of Substance A. Molecular Mass and Formula Mass. (Section 3.1) 1. Just as we can talk about mass of one atom of
1 I am confident that I understand this and I can apply this to problems? I have some understanding but I need to revise this some more I don t know this or I need help because I don t understand it National
Sample Exercise 2.1 Illustrating the Size of an Atom The diameter of a US penny is 19 mm. The diameter of a silver atom, by comparison, is only 2.88 Å. How many silver atoms could be arranged side by side
96 Chapter 7: Calculations with Chemical Formulas and Chemical Reactions Chemical reactions are written showing a few individual atoms or molecules reacting to form a few atoms or molecules of products.
The Mole Concept Ron Robertson r2 c:\files\courses\1110-20\2010 final slides for web\mole concept.docx The Mole The mole is a unit of measurement equal to 6.022 x 10 23 things (to 4 sf) just like there
CHAPTER 3 Calculations with Chemical Formulas and Equations MOLECULAR WEIGHT (M. W.) Sum of the Atomic Weights of all atoms in a MOLECULE of a substance. FORMULA WEIGHT (F. W.) Sum of the atomic Weights
1 Introduction to Chemistry Atomic Weights (Definitions) Chemical Calculations: The Mole Concept and Chemical Formulas AW Atomic weight (mass of the atom of an element) was determined by relative weights.