FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 19 CHAPTER 3: THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION No. Term Definition 1 Relative atomic mass Average mass of one atom of the element when compared with of the mass of an atom of carbon-12. 2 Relative molecular mass Average mass of the molecule when compared with of the mass of one atom of carbon-12. 3 Mole The mole with symbol mol is a SI unit of amount of substance. One mole of substance contains 6.02214076 x 1023 elementary entities of the substance. This number is a fixed value known as the Avogadro constant, NA that is expressed in mol-1 . 4 Molar Mass Mass of one mole of any substance. 5 Molar volume of a gas Volume occupied by 1 mole of any gas which is 24 dm3 at room conditions or 22.4 dm3 at STP. 6 Chemical formula Representation of a chemical substance using alphabets to represent the symbol of atoms and subsript numbers to show the number of each type of atoms found in the elementary entities of the substance 7 Empirical formula The chemical formula that shows the simplest ratio of the number of atoms of each element in the compound. 8 Molecular formula The chemical formula that shows the actual number of atoms of each element that are present in a molecule of the compound. 1. The size of an atom is extremely small and it is difficult to determine their number and the mass of each atom. How do chemists overcome this problem? Chemists use the concept ‘relative atomic mass’ by comparing the mass of atom of an element to the mass of of atom of another element that is chosen as the standard. Therefore, we do not need to know the actual mass of an atom. 2. Chemists across the world agreed to use carbon-12 atom as the standard atom. State two reasons why carbon-12 is chosen as the standard atom. 1. …………………………………………………………………………………………………. 2. …………………………………………………………………………………………………. 3. Define relative atomic mass. ……………… mass of an ………… of the element compared to ………. of the mass of one ………………… atom RELATIVE ATOMIC MASS AND RELATIVE MOLECULAR MASS 3.1 Pupils are able to : 1. Conceptualise relative atomic mass and relative molecular mass based on carbon-12 scale 2. Calculate relative molecular mass and relative formula mass. Explain why there is a value of 1 12 in the definition of the relative atomic mass based on the carbon-12 scale. One atom of carbon-12 is given a definite mass of 12 units. So, 1 12 of the mass is the same as the mass of one hydrogen atom that is 1 unit.
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 20 4. Based on the diagram, the relative atomic mass of helium is _________. This means the average mass of one atom of helium is _______ times heavier than the mass of ______ of one carbon-12 atom. 5. Carry out this activity to have an idea on how this is being done. Teacher asks a group of 5 – 10 students of their respective weight and record the readings according to the ascending order. Table 1 Student’s name Mass (kg) A B C D E If the weight of each student is compared to the lightest student in the group, how does the order look like? Table 2 Student’s name Relative mass A 1 B C D E From table 2, we can say that: 1. Student B is ______ time heavier than student A. 2. Student C is ______ times heavier than student A. 3. Student D is ______ times heavier than student A. 4. Student E is ______ times heavier than student A. Exercise 3.1.1 No Questions Answers 1. How many times a cadmium atom is heavier than a lithium atom? (RAM : Li=7 ; Cd=112) 2. 4 atoms of element L have the same mass as a tellurium atom. Calculate the relative atomic mass of atom L. (RAM : Te=128) As 1 12 of one carbon12 atom One helium atoms 4 units Remember relative atomic mass does not have unit
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 21 3. How many atoms of helium are required to equalise the mass of one atom of krypton? (RAM : He= 4; Kr= 84) 4. How many atoms of neon are required to equalize the mass of two atoms of bromine? (RAM : Ne=20; Br= 80) 5. 10 atoms of element Y is 2 times heavier than 13 atoms of neon. Calculate the relative atomic mass of Y. (RAM : Ne=20) 6. Relative molecular mass ➢ Based on the diagram, methane molecule has relative molecular mass _________. The mass of one methane molecule is ______ times heavier than the mass of 1 12 of one carbon-12 atom. ➢ The relative molecular mass of a molecule can be calculated by summing up relative atomic masses of all the atoms that form the molecule. 7. Relative formula mass ➢ The concept of relative mass is also used for ionic substances. The relative mass of an ionic substance is called the relative formula mass, RFM. ➢ The relative formula mass is calculated by summing up relative atomic masses of all the atoms shown in the formula of the ionic substance. Exercise 3.1.2 Refer to the Data Table of Elements on page 276 in the textbook to obtain the relative atomic mass. 1. Calculate the relative molecular mass of the following elements: Elements Calculation i. Chlorine, Cl2 ii. Sulphur, S8 iii. Phosphorus, P4 2. Calculate the relative molecular mass of the following molecules: Molecules Calculation i. Benzene, C6H6 ii. Ethanoic acid, CH3COOH iii. Propanol, C3H7OH iv. Phosphoric acid, H3PO4 RAM C = 12 RAM H = 1 1 12 of the mass of one carbon-12 atom
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 22 3. Calculate the relative formular mass of the following ionic compounds: Ionic compounds Calculation i. Iron(III) hydroxide, Fe(OH)3 ii. Aluminium sulphate, Al2(SO4)3 iii. Ammonium phosphate, (NH4)3PO4 iv. Potassium dichromate, K2Cr2O7 v. Potassium thiocyanite, K2S2O3 vi. Hydrated copper(II) sulphate, CuSO4 .5H2O vii. Iron(II) sulphate heptahydrate, FeSO4.7H2O 4. The relative formula mass of M2CO3 is 138. What is relative atomic mass for element M? [RAM : C=12, O=16] 5. The element chlorine forms a compound with oxygen with the molecular formula Cl2Ox. The relative molecular mass of the compound is 183. Calculate the value of x. [RAM : Cl=35.5, O=16] 1. 2. In chemistry , we use the unit mole to measure the amount of substance. MOLE CONCEPT 3.2 Pupils are able to : 1. Define mole. 2. Interrelate the Avogadro constant,NA, the number of particles and the number of moles 3. State the meaning of molar mass. 4. Interrelate the molar mass, mass and the number of moles. 5. State the meaning of molar volume. 6. Interrelate the molar volume, volume of gas and the number of moles. 7. Solve numerical problems involving the number of particles, number of moles, mass of the substance and volume of gases. 1 dozen In our daily lives, we use the unit ‘dozen’ to represent 12 objects
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 23 3. Define mole. The mole with the symbol mol is _____________________________________________________ _______________________________________________________________________________ _______________________________________________________________________________ 4. Whether it’s an atomic substance, molecular substance or ionic substance, the number of particles in 1 mol of a substance is the same. 1 mole of copper contains ________________ copper atoms. 1 mole of water, H2O contains ________________ molecules. 1 mole of sodium chloride, NaCl contains _____________________ formula units. 5. Number of moles and Number of Particles We can convert the number of moles of any substance to the number of particles in it and vice versa by using the following relationship. Exercise 3.2.1 1. Calculate the number of atoms found in. (a) 0.25 mol of sodium, Na (b) 3.5 mol of neon gas, Ne 2. Calculate the number of molecules found in (a) 0.3 mol of water (b) 0.8 mol of ammonia gas, NH3 3. Calculate the number of hydrogen atoms in (a) 0.5 mol of hydrogen gas, H2 (b) 0.8 mol of water, H2O 4. Calculate the number of formula units found in (a) 3 mol of sodium chloride, NaCl (b) 0.25 mol of zinc chloride, ZnCl2 Atomic substance Mol Molecular substance Ionic substance ÷ ×
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 24 5. Calculate the total number of ions found in (a) 3 mol of sodium chloride, NaCl (b) 0.25 mol of zinc chloride, ZnCl2 6. Calculate the number of moles of each of the following substances: (a) 6.02 x 1024 lead atoms, Pb (c) 9.03 x 1022 bromine molecules, Br2 (b) 3.02 x 1024 magnesium oxide units, MgO (d) 3.612 x 1024 carbon dioxide molecules, CO2 7. A bottle contains 1.806 x 1025 units of copper(II) chloride, CuCl2. Calculate (a) How many moles of copper(II) chloride are found in the bottle? (b) Calculate the total number of ions found in the bottle. 8. A sample contains 0.2 mol of ethene gas, C2H4. (a) How many ethene molecules, C2H4 are found in the sample? (b) How many hydrogen atoms, H are found in the sample? (c) Calculate the total number of atoms found in the sample. 9. A container contains 1.806 × 1023 oxygen molecules, O2. A sample of 0.5 mol of oxygen gas, O2 is added to the container. How many molecules are there altogether in the container? 10. Differentiate (Number of molecule Vs Number of Atom) and (Number of formula units Vs Number of ions) (a) 1 mol ammonia gas, NH3 = ……………………………….. molecule = ……………………………….. atoms = ………………………………... nitrogen atom = ………………………………… hydrogen atom (b) 0.25 mol ammonia gas, NH3 = ……………………………….. molecule = ……………………………………………….. atoms = ………………………………........................ nitrogen atom = …………………………………………...…… hydrogen atom
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 25 (c) 2 mol of potassium oxide, K2O = ……………………………………………... formula units = ……………………………………………… ions = ………………………………..................... potassium ions = ……………………………………………… oxide ions (d) 0.2 mol of magnesium chloride, MgCl2 = …………………………………….. formula units = …………………………………….. ions = ……………………………………... magnesium ions = ……………………………………… chloride ions 1. State the meaning of molar mass. Molar mass is the mass of ………………. of substance. 2. Chemists found that the value of molar mass of a substance is the same as its relative mass. 3. The unit of molar mass is …………… . For example, relative atomic mass of carbon is 12. Thus, the molar mass of carbon is ……………… because 12 g of carbon, C contains 1 mol of carbon, C that is 6.02 x 1023 atoms of carbon, C. 4. Complete the table below. Substance Symbol RAM or RMM or RFM Mass of 1 mole Molar mass Carbon C 12 12g 12gmol-1 Aluminium Al Helium He Hydrogen H2 Carbon dioxide CO2 Ammonia NH3 Aluminium chloride AlCl3 5. We can convert the number of moles of any substance to the mass of a substance and vice versa by using the following relationship. NUMBER OF MOLE AND MASS OF SUBSTANCES
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 26 Exercise 3.2.2 [Refer to the Data Table of Elements on page 276 in the textbook to obtain the relative atomic mass] [Avogadro constant, NA : 6.02 x 1023 mol-1 ] 1. Calculate the mass of each of the following substances: (a) 0.5 mol of iron filings (c) 1.5 mol of carbon monoxide, CO (b) 2.3 mol of calcium nitrate, Ca(NO3)2 (d) 0.5 mol of sulphuric acid, H2SO4 2. Calculate the number of moles in each of the following substances: (a) 16 g of oxygen gas, O2 (c) 49 g of sulphuric acid, H2SO4 (b) 23.4 g of sodium chloride, NaCl (d) 8.88g of magnesium nitrate, Mg(NO3)2 3. An experiment requires 0.05 mol of ammonium sulphate crystals, (NH4)2SO4. What is the mass of ammonium sulphate, (NH4)2SO4 that should be used? 4. 0.2 mol of substance Y has the mass of 11 g. What is the molar mass of substance Y? 5. Calculate the mass of each of the following substances: (a) 3.01 X 1023 titanium atoms (b) 1.204 X 1023 argon atoms Molar mass Jisim molar mol × ÷
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 27 6. Geranial is a compound found in lemon grass (daun serai). Its molecular structure is shown below: (a) Determine the molar mass of geranial. (b) Calculate the mass of 0.02 mol of geranial. (c) Calculate the number of molecules present in 7.6 g of geranial. (d) Calculate the mass of 7.525 X 1022 geranial molecules. 7. Piperazine pill is used to kill intestinal worms. Its molecular formula is C4H6N2. A pill contains 0.005 mol of piperazine. What is the mass of the piperazine in the pill? 8. A student dissolves 1.11 g of calcium chloride, CaCl2 in a beaker of water. Calculate the total number of ions in the beaker? 1. State the meaning of molar volume? Molar volume is the volume occupied by ____________ of a gas. 2. The molar volume of any gas depends on the condition, that is _____________ at STP or ____________ at room conditions. 3. This means at STP, • 1 mol of neon gas, Ne occupies 22.4 dm3 • 1 mol of carbon dioxide gas, CO2 occupies 22.4 dm3 4. While at room conditions, • 1 mol of neon gas, Ne occupies 24 dm3 • 1 mol of carbon dioxide gas, CO2 occupies 24 dm3 NUMBER OF MOLE AND VOLUME OF GAS • The conditions 0oC and 1 atm are called the standard temperature and pressure(STP). • The temperature and pressure at room conditions are 25oC and 1 atm respectively. • Molar volume is used only for gases and not for solids and liquids. Chemistry Lens
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 28 5. The formula and relationship between number of moles and the volume of gas by using molar volume are as follow: Exercise 3.2.3 [Molar volume : 22.4 dm3 mol-1 at STP or 24 dm3 mol-1 at room conditions] 1. Calculate the volume of of the following gases : (a) 0.3 mol of oxygen gas, O2 at room conditions. (b) 4 mol of helium gas measured at STP. 2. Calculate the number of moles of the following gases: (a) 48 dm3 of chlorine gas, Cl2 at room conditions. (c) 560 cm3 of carbon dioxide, CO2 gas at STP. (b) 39.2 dm3 of carbon dioxide, CO2 gas at STP. (d) 960 cm3 of hydrogen chloride, HCl at room conditions. 3. A sample contains 0.2 mol of methane gas, CH4 and 0.3 mol of ethane gas, C2H6. What is the volume of the sample at room conditions? mol ÷ ×
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 29 Exercise 3.2.4 1. Complete the relationship between the number of particles, number of moles, mass of substances and volume of gases in the Diagram below. 2. Based on diagram below, explain the relationship between the volume, mass and the number of molecules of carbon dioxide, CO2 at room conditions. Carbon dioxide gas with a volume ________ has a mass of _________ and contains ____________________ molecule is _______ mol. 3. Calculate the number of molecules in the following gases. (a) 1.46 g of hydrogen chloride gas, HCl. (b) 16 g of oxygen gas, O2. 4. What is the mass of nitrogen that contains 6.02 × 1023 nitrogen molecules, N2? 24 dm3 44 g of carbon dioxide gas, CO2
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 30 5. How many molecules of carbon dioxide, CO2 are produced when 120 cm3 of the gas is released during a chemical reaction between an acid and a metal carbonate at room conditions? 6. Calculate the mass of magnesium which contains the same number of atom as in 32 g of copper. 7. Calculate the mass of water that contains the same number of molecules as in 22 g of carbon dioxide. 8. Calculate the mass of carbon monoxide that contains twice the number of molecules as in 48 dm3 of carbon dioxide at room conditions. 9. A container contains 2.2 g of carbon dioxide gas at room conditions. Calculate [RAM : C=12, O=16, Molar volume = 24 dm3 mol-1 , Avogadro constant = 6.02 × 1023 mol-1 ] (a) the volume of carbon dioxide gas in cm3 (b) the number of atoms of carbon dioxide 10. 4 g of hydrogen gas, H2 has greater number of molecules than 14 g of nitrogen gas, N2 Do you agree with the above statement? Give your reason.
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 31 1. State the meaning of chemical formula. Chemical formula is a representation of a chemical substance using alphabets to represent the ___________________ and ____________ numbers to show the ___________________________ found in the elementary entities of the substance. 2. The chemical formula of an element represents its atoms. Some elements, however, naturally exists as molecules. Therefore, their chemical formulae represent their molecules. 3. The chemical formula of a compound shows all the elements that are present in the compound and the number of atoms of each element. Empirical Formula and Molecular Formula 1. There are two types of chemical formulae, namely empirical formula and molecular formula. Empirical formula → Chemical formula that ..............................................…………………… of the …………….…....................... of each .……….............. in a compound. Molecular Formula → Chemical formula that .................................................…..………….. of each ………………….. found in a ................................. . CHEMICAL FORMULAE 3.3 Pupils are able to : 1. State the meaning of chemical formula, empirical formula and molecular formula 2. Determine the empirical formula of MgO through an activity 3. Determine the empirical formula of CuO through an activity. 4. Solve numerical problems involving empirical formula and molecular formula 5. Construct chemical formula of compounds H2 Subscript number shows hydrogen gas molecule consists of ……..... hydrogen atoms The letter H shows ………… …...................... ………………… H2O The letter H shows ……… …….................. ………………… and O shows ………………… ………………… The subscript number shows that ........... atoms of hydrogen combine with ........... atom of oksigen The formula shows one molecule of glucose consists of .…. carbon atom, ….. hydrogen atoms and ….. oxygen atoms The formula shows that the simplest ratio of the number carbon atoms to hydrogen atoms and oxygen atoms is …….… . Molecular formula of glucose: C6H12O6 Empirical formula of glucose: CH2O Ratio of number of atoms C atom : H atom : O atom = ….….. : ……….. : ………… = ……… : ……….. : …………
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 32 2. Write the empirical formula of the following substances. Substance Molecular fomula Empirical formula Water H2O Ammonia NH3 Hydrazine N2H4 Propene C3H6 Benzene C6H6 Exercise 3.7 Steps in determination of an empirical formula of a compound : 0.32 g metal X combines with 0.36 g of non-metal Y to form a compound. What is the empirical formula of this compound? [RAM: X=64, Y=35.5] Element X Y Mass (g) 0.32 0.36 Number of moles of atom 0.32 64 = 0.005 0.36 35.5 = 0.01 Simplest mole ratio of atom 0.005 0.005 = 1 0.01 0.005 = 2 Thus, empirical formula of this compound is XY2. 1. A sample of potassium bromide contains 6.24 g of potassium and 12.8 g of bromine. What is the empirical formula of potassium bromide? Element Mass (g) Number of moles of atoms Simplest mole ratio of atom The empirical formula is ____________ 2. 2.24 g of iron combines chemically with 0.96 g of oxygen to form an oxide. What is the empirical formula of the oxide ? Element Mass (g) Number of moles of atoms Mole ratio Simplest mole ratio of atom The empirical formula of the oxide is ____________ . Step 1 : Determine the mass of each element Step 2 :Divide each mass with its molar mass / RAM Step 3 : Divide each number with the smallest number, that is 0.005
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 33 3. A sample of oxide of metal V contains 56 g metal V and 24 g of oxygen. What is the empirical formula of the compound? Element V O The empirical formula of this compound is ____________ . 4. A potassium compound has a percentage composition as the following: K=26.57% ; Cr=35.36% ; O=38.07% What is the empirical formula of the potassium compound ? Element The empirical formula of this compound is ______________ . 5. A sample of 26.1 g of tin chloride contains 11.9 g of tin. What is the empirical formula of the tin chloride? Element The empirical formula of this compound is ____________ . 6. A chemist analysed the compound that gives smell to fully ripe bananas. He found that the compound contains 64.62% carbon, 10.77% hydrogen and 24.61% oxygen. What is the empirical formula of that compound? Element The empirical formula of this compound is ____________ .
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 34 Exercise 3.3.2 Determination of a Molecular Formula The molecular formula of a compound is its multiplied empirical formula. The value of n is a positive integer. Table below shows several examples. Substance Water Hydrazine Propene Benzene Empirical formula H2O NH2 CH2 CH Molecular formula (H2O)1 = H2O (NH2)2 = N2H2 (CH2)3 = C3H6 (CH)6 = C6H6 n 1 2 3 6 Therefore, to determine the molecular formula of a compound, we first need to know its empirical formula. [ Relative atomic mass : H= 1, C=12, Br=80, Zn=65, N=14, S=32, P=31, O=16] 1. The empirical formula of a compound is CH. Its relative molecular mass is 78. What is the molecular formula of the compound? 2. A carbon compound has an empirical formula of CH2 and a relative molecular mass of 70. What is the molecular formula of the compound? 3. Hydrocarbons consist of carbon and hydrogen. 5.7 g of hydrocarbon contains 4.8 g of carbon. If the relative molecular mass of the hydrocarbon is 114, determine its molecular formula. 4. : 2.07 g of element Z reacts with bromine to form 3.67g of a compound with an empirical formula of ZBr2. Calculate the relative atomic mass of element Z. Molecular formula = ( Empirical formula )n
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 35 5. Calculate the mass of zinc required to combine with 0.5 mol of chlorine to produce zinc chloride, ZnCl2? 6. Assume you are farmer. You want to choose a fertiliser with a high nitrogen content for your plants. Diagram below shows four types of fertilisers sold in shop. Which fertiliser would you choose? Give reason four your choice. Show the steps used in the calculation. Compare and contrast Empirical Formula and Molecular Formula Empirical formula Similarity Molecular formula Example : Glucose Empirical formula : CH2O • Both contains ................................................. ………………………………….. Contoh : Glukosa Formula molekul : C6H12O6 Differences Chemical formula that shows the simplest ratio of the number of atoms of each element in a compound. Example: This formula shows that simplest ratio of the number of carbon atoms to hydrogen atoms and oxygen atoms of one molecule of glucose is ........................ . Number of atoms in the formula Chemical formula that shows the actual number of atoms of each element in a compound. Sebagai contoh: This formula shows one molecule of glucose consist of ....... carbon ..........., ....... hydrogen ............ and ....... oxygen .......... .
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 36 Chemical formula of Ionic Compounds 1. Ionic compounds are made up of positively-charged ions, ____________ and negatively charged ions, _____________. In order to write the chemical formula of ionic compounds, your need to memorise the formula of cations and anions. 2. Charge of Cation Name of cation Formula +1 Hydrogen ion Lithium ion Sodium ion Potassium ion Silver ion Ammonium ion +2 Magnesium ion Calcium ion Barium ion Zinc ion Iron(II) ion Lead(II) ion Copper(II) ion Manganese(II) ion +3 Aluminium ion Iron(III) ion Charge of Anion Name of Anion Formula -1 Fluoride ion Chloride ion Bromide ion Iodide ion Hydroxide ion Nitrate ion Manganate(VII) ion -2 Oxide ion Sulphate ion Carbonate ion Thiosulphate io Dichromate(VI) ion -3 Phosphate ion
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 37 3. Construct a chemical formula for each of the following ionic compounds: (a) Magnesium chloride (b) Potassium carbonate (c) Calcium oxide (d) Copper(I) oxide (e) Silver sulphate (f) Zinc nitrate (g) Aluminium oxide (h) Iron(II) hydroxide (i) Lead(II) sulphate (j) Ammonium phosphate (k) Aluminium carbonate (l) Iron(III) nitrate 4. 5. Transition metals can form more than one ions, Roman numerals ( such as I, II, III ) are used to differentiate the ions. Fe2+ - iron (II) ion Fe3+ - iron (III) ion Greek prefixes like ‘mono’, ‘di’, and ‘tri’ are used to show the number of one, two and three respectively. Examples : CO – carbon monoxide CO2 – carbon dioxide CCl4 – carbon tetrachloride or tetrachloromethane SO3 – sulphur trioxide
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 38 Latihan 3.3.3 1. Name the molecular compounds with the following formula. Chemical formula Name of the molecular compound CO CO2 NO NO2 SO2 SO3 CCl4 PCl5 CS2 BF3 N2O3 2. A sample of 5.04g of oxide of phosphorus contains 2.48 g of phosphorus. [RAM : O=16, P=31] (a) If the relative molecular mass of the oxide is 126, determine its empirical formula and molecular formula (b) Name the oxide of the phosphorus ___________________________________________________________________________
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 39 3. Without referring the table of formula cation and anion, write the chemical formulae of the compound formed. Chloride ion Bromide ion Iodide ion Hydroxide ion Nitrate ion Oxide ion Carbonate ion Sulphate ion Potassium ion Sodium ion Silver ion Ammonium ion Magnesium ion Calcium ion Zinc ion Lead(II) ion Aluminium ion
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 40 1. Chemical equation shows a simple and accurate way to describe _________________________ . 2. Meaning : ➢ Reactants are written on the left hand side of the equation while products are written on the right hand side of the equation. ➢ The arrow ‘→’ means ‘produces’. ➢ The physical state of each substance : Symbol Physical states of substances s l g aq 3. Writing chemical equations. A chemical equation needs to be _________________ . Based on the law conversation of mass, matter can neither be created nor destroyed. Therefore, the number of atoms of each element on both sides of the equation must be the same. Example: Magnesium reacts with dilute hydrochloric acid, HCl to produce magnesium chloride, MgCl2 and hydrogen gas, H2. Write an equation to represent the reaction. Exercise 3.4.1 1. Write a balanced chemical equation for each of the following reactions: (a) Nitrogen gas reacts with hydrogen gas to form ammonia gas. (b) Iron reacts with sulphuric acid to form iron(II) sulphate and hydrogen gas. (c) Solid copper(II) carbonate decomposes into copper(II) oxide and carbon dioxide gas when heated. CHEMICAL EQUATION C (s) + O2 (g) CO2 (g) 3.4 Pupils are able to : 1.Write balanced chemical equations 2.Interpret chemical equations quantitatively and qualitatively 3.Solve stoichiometry numerical problems Mg + HCl MgCl2 + H2 Mg + 2HCl MgCl2 + H2 Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) 1. Write the correct chemical formula for each reactant and products. 2. Balance the equation. You need to adjust the coefficients in front of the chemical formulae. 3. Write the physical state of each reactant and product. This part is not mandatory in SPM.
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 41 (d) Heating of potassium nitrate strongly will decomposes to produce solid potassium nitrite (KNO2) and oxygen gas. (e) Burning aluminum powder in excess oxygen gas produces white aluminum oxide powder. (f) Copper(II) oxide reacts with aluminium to produce aluminium oxide and copper. a)(g) Ammonia gas reacts with oxygen gas to produce nitrogen monoxide gas and water. a) b)(h) Silver carbonate decomposes when heated to produce silver metal, carbon dioxide gas and oxygen gas. (i) Solid zinc nitrate decomposes into solid zinc oxide, nitrogen dioxide gas and oxygen gas when heated. (j) Burning of propane (C3H8) in excess oxygen gas produces carbon dioxide gas and water. (k) When lead(II) nitrate solution is added to sodium chloride solution, lead(II) chloride precipitate and sodium nitrate solution are produced. (l) When sodium hydrogen carbonate reacts with sulphuric acid, sodium sulphate solution, carbon dioxide gas and water are formed. (m) An aqueous solution of sodium thiosulphate, Na2S2O3 reacts with dilute hydrochloric acid to produce sodium chloride, sulphur dioxide, sulphur and water. (n) Iron(III) oxide is reduced by carbon monoxide gas to form iron metal and carbon dioxide gas. (o) Aluminium dissolves in hot hydrochloric acid producing aluminium chloride solution and hydrogen gas. (p) Reaction between carbon dioxide gas and lime water, Ca(OH)2 produces calcium carbonate precipitate and water.
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 42 Using Chemical Equations 1. Chemical equations can be interpreted qualitatively and quantitatively. From qualitative aspect, chemical equations enable us to identify the reactants and products as well as their physical states 2. From quantitative aspect, we can study the composition of substances involved in a chemical reaction. Coefficients in chemical equations show the ratio of substances involved, either as the ratio of elementary entities of substance or the mole ratio. For example : 3. The following equation shows the reaction of group 1 metal in water. State one qualitative information and one quantitative information can be obtained from chemical equation above. Qualitative information : ______________________________________________________________________________ Quantitative information : ________________________________________________________________________________ Exercise 3.4.2 Solving numerical stoichiometry problems Example Burning of aluminium in air is as follows: What is the mass of aluminium oxide produced if 5.4 g of aluminium is burnt completely in air? [RAM: O=16, Al=27] Remember Tips : MR.X M (Mol) 1. Number of moles of Al = 5.4 27 = 0.2 mol R (Ratio) 2. Mole ratio from chemical equation, Al : Al2O3 4 mol : 2 mol 0.2 mol : 0.1 mol X (Multiply) 3. Mass of aluminium oxide = 0.1 × [2(27) + 3(16)] = 10.2 g K(s) + H2O(l) KOH(aq) + H2(g) 4Al + 3O2 → 2Al2O3 Step 1 : Convert mass of Al → Number of moles of Al Step 2: Based on mole ratio, determine the number of moles of Al2O3 Step 3: Convert number of moles of Al2O3 → mass of Al2O3 Mole ratio: 2 mol of sodium react with 1 mol of chlorine gas to produce 2 mol of sodium chloride. Ratio of basic enitities (particles): Two sodium atoms react with one molecule of chlorine to produce two NaCl units.
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 43 1. Magnesium reacts with hydrochloric acid as follows: What is the volume of hydrogen gas produced at room conditions if 2.4 g magnesium reacts completely with hydrochloric acid. [RAM : Mg = 24, 1 mol of gas occupies 24 dm3 at room conditions] 2. Nitrogen and hydrogen gases react according to the following equation: How many molecules of ammonia, NH3 are produced if 6.72 dm3 of nitrogen gas at STP reacts completely with hydrogen gas? [RAM : N=14; H=1 , 1 mol of gas occupies 24 dm3 at room conditions] 3. A sample of iron(III) oxide is heated in a stream of excess hydrogen gas to produce 5.6 g of iron metal according to the following equation: Fe2O3 + 3H2 → 2Fe + 3H2O Calculate the mass of iron(III) oxide sample. [RAM : Fe=56, O=16] 4. 8.0 g of copper(II) oxide powder reacts completely in a flow of excess hydrogen gas to form copper and water. (a) Write the chemical equation for the reaction. (b) Calculate the mass of copper powder formed? [RAM Cu,64; O,16] Mg + 2HCl MgCl2 + H2 N2 + 3H2 2NH3
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 44 5. 0.46 g of sodium burns completely in chlorine gas at room conditions to produce sodium chloride. [RAM : Na=23 , 1 mol of gas occupies 24 dm3 at room conditions] (a) Write the chemical equation for the reaction. (b) Calculate the volume of chlorine gas that has reacted. 6. Decomposition of 16.55 g lead(II)nitrate by heating produces lead(II) oxide, nitrogen dioxide gas and oxygen gas. [RAM Pb=207; N=14; O=16; 1 mol of gas occupies 24 dm3 at room conditions] (a) Write the chemical equation for the reaction. (b) Calculate the volume of oxygen gas produced in the reaction. 7. Decomposition of hydrogen peroxide solution, H2O2 produces water and oxygen gas. [RAM H=1; O=16; 1 mol of gas occupies 22.4 dm3 at STP] (a) Write the chemical equation for the reaction. (b) Calculate the volume of oxygen gas produced at STP from the decomposition of 51.0 g of hydrogen peroxide. 8. Propane, C3H8 burns in excess oxygen gas to produce carbon dioxide and water. [RAM C=12; H=1, O=16] (a) Write the chemical equation for the reaction. (b) Calculate the mass of water are produced from the complete combustion of 3.0 g of propane.
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 45 9. Decomposition of potassium chlorate(V), KClO3 by heat produces potassium chloride and oxygen gas. [RAM K=39; Cl=35.5; O=16; 1 mol of gas occupies 24 dm3 at room conditions] (a) Write the chemical equation for the reaction. (b) Calculate the mass of potassium chlorate(V) needed to produce 1500 cm3 of oxygen gas. (c) Calculate the volume of oxygen gas produced if 2 kg of potassium chlorate(V) are used. 10. The diagram shows volcanic eruptions which releases gases as CO2, SO2, H2, steam (H2O), CO and HCl. To stimulate the eruption in the laboratory, a pupil added 12.6 g of ammonium dichromate(VI), (NH4)2Cr2O7 in a mortar and immediately ignited. The decomposition reaction of ammonium dichromate(VI) produces three substances, chromium(III) oxide, nitrogen gas and steam. [JAR: H=1, N=14, O=16, Cr=52, Molar volume of gas = 24 dm3 mol-1 ] (a) Write the chemical equation for the reaction. (b) Calculate the volume of steam produced at room conditions? CLONE SPM
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 46 1. The mass of two atoms of element Y is equal to that of three atoms of oxygen gas. What is the relative atomic mass of element Y. [RAM : O =16] A 14 C 32 B 24 D 36 2. The diagram shows two types of gases filled in two balloons. Which statement is correct about the number of particles in oxygen gas? [Relative atomic mass : H = 1, O = 16] A Same as in hydrogen gas B More than in hydrogen gas C Two times more than in hydrogen gas D 16 times more than in hydrogen gas 3. The formula of potassium hexacyanoferrate(II) is given as KyFe(CN)6. Its relative formula mass is 368. What is the value of y? [RAM : Fe=56, C=12, N=14, K=39] A 2 C 4 B 3 D 5 4. 0.58 g flavouring substance is used to improve the taste of a pineapple cake. What is the number of molecules of the flavouring substance? [Molar mass of flavouring substance=116 gmol-1 ] A 8.31 × 10-27 C 3.01 × 1021 B 3.32 × 10-22 D 1.20 × 102 5. Which of the following contains the same number of molecules as in 8.8 g carbon dioxide gas?. [Relative atomic mass : H = 1; C = 12; O = 16; S = 32; I = 127] A 3.6 g of water C 3.2 g of oxygen gas B 25.4 g of iodine D 9.6 g of sulphur dioxide gas 6. What is the number of nitrate ions, NO3 - in 2 mol of iron(III) nitrate? [Avogadro constant = 6.02 × 1023 mol-1 ] A 1.204 × 1024 C 3.010 × 1024 B 1.806 × 1024 D 3.612 × 1024 7. A compound of magnesium nitrite contains 72 % of magnesium and 28 % of nitrogen. What is the empirical formula of magnesium nitrite? [Relative atomic mass: N = 14; Mg = 24] A MgN2 C Mg2N3 B Mg2N D Mg3N2 8. The diagram shows the apparatus set-up to determine the empirical formula of magnesium oxide. Which step is correct to ensure the magnesium ribbon burnt completely? A Raise the crucible lid once in a while during heating B Heat the magnesium ribbon strongly in the crucible without its lid C Cover the crucible with its lid as soon as the magnesium ribbon starts burning D Repeat the process of heating, cooling and weighing until a constant mass is obtained Objective Questions 32 g oxygen gas 2 g hydrogen gas CLONE SPM CLONE SPM CLONE SPM CLONE SPM CLONE SPM CLONE SPM CLONE SPM
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 47 9. What is the percentage composition by mass of water in hydrated iron(Il) sulphate, FeSO4.7H2O? [Relative atomic mass: H = 1, 0 = 16, S = 32, Fe = 56] A 9.00 % B 14.12 % C 45.32 % D 71.20 % 10. The diagram shows a car fitted with air bags which will automatically inflated to protect passengers during accidents. The air bag contains solid sodium azide, NaN3 which will decomposed rapidly when heated to produce nitrogen gas that expand the air bag and also sodium metal. In an accident, an air bag expanded with 4.68 dm3 of nitrogen gas at room temperature and pressure. What is the mass of sodium azide needed to produce 4.68 dm3 of nitrogen gas? [RAM : N=14, Na=23, 1 mol of gas occupies 24 dm3 at room conditions] A 4.23 g B 8.45 g C 19.01 g D 25.35 g Paper 2 Section A 1. Table 1 shows the word equations for two experiments involving metal X and metal oxide Y. The empirical formula of X oxide and Y oxide are determined through Method I and Method II. Method Word equation I X + Oxygen → X oxide II Hydrogen + Y oxide → Y + Water Table 1 (a) What is meant by empirical formula? ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. [1 mark] (b) Suggest metal X and metal Y. Explain why you choose the metal. Metal X : …………………………………………………………………………………………………... Explanation : ……………………………………………………………………………………………… Metal Y : …………………………………………………………………………………………………... Explanation : ……………………………………………………………………………………………… [4 marks] CLONE SPM CLONE SPM
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 48 (c) (i) Draw the apparatus set-up to show how method I can be carried out in the laboratory. [2 marks] (ii) 1.08 g of X reacts with 0.96 g of oxygen. What is the empirical formula of X oxide? [RAM : X=27, O=16] [3 marks] (d) Which method is suitable to be used to determine the empirical formula for lead oxide? ………………………………………………………………………………………………………………. [1 mark] 2. Diagram 1 shows a bottle of vinegar which containing ethanoic acid. Diagram 1 (a) Write the molecular formula and empirical formula of ethanoic acid. Molecular formula : ………………………………………………………………………………………. Empirical formula : ………………………………………………………………………………………. [2 marks] (b) A sample of pure ethanoic acid weighs 120 g. [RAM : C=12, H=1, O=16, Avogadro constant = 6.02 × 1023 mol-1 ] (i) Calculate the number of ethanoic acid molecules in the sample. [2 marks] (ii) Calculate the number of carbon atoms in the sample. [1 mark] Ethanoic acid
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 49 (c) Lactic acid, which is produced in milk by bacteria, causes a sour taste in milk. It has a similar empirical formula with ethanoic acid. Given that three molecules of ethanoic acid have the same mass as two molecules of lactic acid. Find the molecular formula of lactic acid. [3 marks] 3. Diagram 2 shows green plant undergoes photosynthesis to produce compound X with the molecular formula of C6H12O6 and oxygen gas. Diagram 2 (a) What is the meaning of molecular formula? ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. [1 mark] (b) (i) Write chemical equation for the reaction occurs during photosynthesis process in Diagram 2. ………………………………………………………………………………………………………… [2 marks] (ii) Describe one qualitative information and one quantitative information that can be obtained from the chemical equation in (b) (i). …………………………………………………………………………………………………………. …………………………………………………………………………………………………………. …………………………………………………………………………………………………………. [2 marks] (iii) Calculate the volume of carbon dioxide gas required to produce 0.5 mol of compound X. [Molar volume: 24 dm3 mol- ] [2 marks CO2 O2 H2O
FUNDAMENTALS OF CHEMISTRY CHAPTER 3 : THE MOLE CONCEPT, CHEMICAL FORMULA AND EQUATION 50 Paper 2 Section B 4. (a) Diagram 3.1 and 3.2 show two methods used to determine the empirical formula for metal oxide X and metal oxide Y. Diagram 3.1 Diagram 3.2 (i) What is meant by empirical formula? [1 mark] (ii) Suggest metal X and metal Y. Explain why the metal was chosen. [4 marks] (iii) Based on Diagram 3.2, write the chemical equation for the reaction that occurs between hydrochloric acid and zinc. Calculate the mass zinc required in the reaction to produce 120 cm3 of gas to be used in the reaction. [RAM : Zn=65, Molar volume of gas = 24 dm3 mol-1 ] [5 marks] (b) The following is the information on the composition of a hydrocarbon P which can be used to determine the molecular formula. (i) Based on the information above, determine • Empirical formula of hydrocarbon P • Molecular formula of hydrocarbon P [RAM : H=1, C=12] [5 marks] (ii) Hydrocarbon P burn completely in air to produce carbon dioxide gas and water. Write the chemical equation for the complete combustion of hydrocarbon P. Calculate the volume of carbon dioxide gas released when 39.2 g of hydrocarbon P is burnt completely. [Molar volume of gas = 24 dm3 mol-1 at room conditions] [5 marks] • Carbon= 85.70% • Hydrogen= 14.30% • Relative molecular mass = 56