TOPIC 4: THE MOLE CONCEPTS INTRODUCTION The mass is gram (g) of 1 mole of substances is called its.. 1 mole of substances has.. particles of a substances The mass of 1 mole of substances is always equal to its relative molecular mass in gram 1. 1 mole of H atom weight 1g 2. 1 mole of... has mass of =..g CuSO 4 5H 2 O 3. 1 mole of.. has mass of. = g FYI To convert moles to mass, one may apply the formula 1. Mass of 2 moles of H atom = O 2 CuSO4 7H2 O 2. Mass of 4 moles of molecules = 3. Mass of 3.44 moles of = 1. One mole of substance is the relative mass or molecular mass of a substances in g 1 MOLE = Ar 1 MOLE = Mr 2. One mole of substance contain particle (atom, molecules or ions). This number is called Avogadro Constant 3. 4. The percentage (%) of an element in compound is Mass of ELEMENT in COMPOUND Mr of COMPOUND X 100% Page 1 of 12
a. What is the % by mass of Sulphur in Magnesium Sulphate? b. The percentage of element in compound can be used to find mass of element in a given mass of compound. For example, what is the mass of copper in 20 tonnes of copper (ll) sulphate? Page 2 of 12
MOLES Chemist measure number of particles in moles (symbol = mol ) Particles can be atoms, molecules or ions 1 mole = 6.23 x particles 10 24 H 2 O 1. How many moles of molecules are in 3 x of? 2. How many moles of atom is in 4 x 10 26 of Cl? 10 23 Al 3+ 3. How many moles of ions are in 6 x of? Page 3 of 12
DETERMINE THE EMPIRICAL AND MOLECULAR FORMULA OF COMPOUND Empirical formula only shows the simplest number of RATIO of different types of atom in compound example CO Molecular formula shows the real number of RATIO of different types of atam in compound example where Molecular is intregral multiple of empirical formula Molecular formula=n(empirical formula) where n is integers EXAMPLEs MOLECULAR FORMULA MOLECULAR FORMULA MOLECULAR FORMULA MOLECULAR FORMULA C 10 H 12 C 10 H 10 Cl 8 H 2 O 2 Ca 2 H 2 Cl 2 EMPIRICAL FORMULA EMPIRICAL FORMULA EMPIRICAL FORMULA EMPIRICAL FORMULA How to determine? Na y CO 3 1. Sodium Carbonate has the formula. The Mr of this compound is 106. What is the value of y and hence what is the formula of the compound? 2. A sample of iron sulphide contains 5.373g iron & 4.627g of Sulphur. What is the empirical formula of the compound? 3. A compound has the composition by mass: 29.4% Calcium, 23.5% Sulphur and 47.1% Oxygen. Find the empirical formula? Page 4 of 12
CH 2 O 4. A compound has empirical formula and relative molecular mass of 60g. what is the molecular formula of compound? 5. An anesthetic compound is found to contain element : C, H & Cl. The % by mass of this element are C=10.04%, H=0.84% and Cl=89.12%. 1 mole of the compound has a mass of 120g. calculate its molecular formula? FYI 1. Calculation should be rounded off according to number of significant figures given in the question. 2. Glucose has a formula. Molecular formula is. Empirical formula is 3. A compound of Ibuprofen has the following structural formula: Molecular formula is... Empirical formula is. Page 5 of 12
: MASS & MOLAR VOLUME OF GAS Mass of gases at room temperature and pressure (rtp) are calculated in same manner at liquid and solid The volume of 1 mole is called molar volume of the gas At rtp temperature is and pressure is and occupy volume of gas 24 or.. (so 1 ) At stp temperature is. And pressure is. And occupy volume of gas 22.4 =......... cm 3 or. By Avogadro s Law when we have equal volume of gases, at same temp and pressure it contains equal number of molecules. GAS FORMULA MR VOLUME AT rtp VOLUME AT stp Hydrogen gas Oxygen gas Hydrogen Atom methane Carbon Dioxide Finding mass or molar volume of a gas : cm 3 1. Calculate number of moles of Ammonia in 3600 at rtp? cm 3 2. Calculate number of moles of Ammonia in 3600 at stp? Page 6 of 12
3. Calculate the volume of 4g of methane, at rtp? FYI 1. The volume of Zinc Oxide formed will not be at 24 because it.. 2. Only the same number of moles of gases have same volume at rtp 3. CO + O 2 CO 2 20cm 3 of CO are react with 10cm 3 of O 2..... Page 7 of 12
CONCENTRATION OF SOLUTIONS The concentration of solution always indicates the amount of solute present in 1 of a solution Concentration of solution can be stated as. AND. EXAMPLE Unit of concentration of solution is.. Usually in chemistry, the concentration of a solution is expressed in MOLARITY (SYMBOL = M) where M is.. A molar solution is one that contains 1 mole of solute in 1 1. A solution contains 5.0g of HCl in 1. Calculate concentration in mol/? of solution 2. A solution contains 0.20 mol of KMnO 4 per 2. Calculate mass of the compound in 1? 3. Calculate the number of moles of FeSO 4 in 100 cm 3 of 0.10 mol/ solution? Page 8 of 12
cm 3 4. A 20 solution contains 5.0g of HCl. Calculate the molarity of HCl solution? 5. 60g of NaOH is dissolved ig 500 of solution. Calculate the concentration of the solution in a) g/ and b) mol/? cm 3 6. The concentration of a solution of NaOH is 0.5 mol/. How many moles of NaOH are contained in 4.0 of solution? FYI H 2 O H 2 O H 2 O 1. is liquid and not gas so, 24 of DOES NOT CONTAIN 1 MOLE OF Page 9 of 12
CALCULATION INVOLVING CHEMICAL EQUATIONS A chemical equation a way of showing the changes that take places in chemical equation. An equation always shows: The formulae of reactant and product The ratio of the moles of the substances involved. Calculation involved 5 mains steps, though not all step required in each calculation The steps as follow: Workout the number of moles as balancing equation Write down the balance chemical equation List down the ratio moles of substances to be found from question Calculate the number of moles of the substances to be found Workout the mass or molar volume or concentration to be found CO 2 1. Measure the volume of gas produces in rtp from the combustion of 2 moles of propane? 2. What is mass of Zinc Carbonate reacts with 36.5g HCl? 3. Limestone decomposes according to the equation. Calculate the mass of limestone required to produce 3 of carbon dioxide? Page 10 of 12
PERCENTAGE YIELD (ALWAYS ABOUT PRODUCT) The quantity of product formed when all the limiting reactant reacts is called the theoretical yield. This value must be calculated from equation The amount of product actually obtained through experiment is called the actual yield. THE FORMULA % YIELD = actual yield theoretical yield 100 1. 50.0 cm 3 of.105 mol / aqueous Calcium Chloride was treated with excess of Silver Nitrate. White Silver Chloride was formed and precipitate weighed after dryng. A mass of 1.45g was recorded. What is % yield? FYI 1. When you have gram or kilogram. Both ans will do. 2. ACTUAL YIELD always less than the value of theoretical yield. ACTUAL YIELD VALUE IS ALWAYS GIVEN! Page 11 of 12
PERCENTAGE PURITY (ALWAYS ABOUT REACTANT) It indicate the amount of pure substances present in a sample of chemical substance. Mass of Sample is ALWAYS GIVEN! THE FORMULA % PURITY = mass of pure substance in sample mass of sample 100 1. Manganese (IV) Oxide reacts with concentrated hydrochloric acid according to equation. A 4.35g mol / cm 3 sample of manganese (IV) Oxide was added to 1 hydrochloric acid. 48 of the acid was needed to react with manganese (IV) Oxide in the given sample. Calculate % purity of Manganese (IV) Oxide? 2. A 5g sample of copper powder was contaminated with copper (ll) Oxide. The copper (ll) Oxide in the sample was founded to react with 0.020 mole of hydrochloric acid. Write the equation for the reaction and calculate % of copper metal in the sample. (Ar : O = 16 ; Cu = 64) Page 12 of 12