Learning objective: To calculate expected and percentage yield 09/06/2016 On whiteboards…

A compound contains 59.4% carbon, 10.9% hydrogen, 13.9% nitrogen and 15.8% oxygen, by mass. Find the empirical formula of the compound. Find amount (moles) of each element – assume % = mass C = 59.4/12 = 4.95 H = 10.9/1 = 10.9 N = 13.9/14 = O = 15.8/16 = (Keep extra s.f. in calculator – but write down 3 s.f.) Find ratio: C = 4.95/ = 5.0; H = 10.9/ = 11.0; N = 0.992/ = 1.0; O = 1 Empirical formula = C 5 H 11 NO

Yield Percentage yield = 100 x actual yield/theoretical yield A limekiln produces 500 kg lime per tonne of limestone. Calculate the percentage yield. –Equation for the reaction CaCO 3 (s)  CaO (s) + CO 2 (g) –Calculate amount limestone in 1 tonne: = /( x 16.0) = moles –Calculate the amount of lime = amount limestone –Mass lime = x ( ) = kg –% Yield = 500x100/560.4 = 89.2%

Preparation of a soluble salt from an insoluble base Reaction Purification

Atom economy Raw material are valuable Unused material (i) costs money (ii) requires disposal (iii) can be dangerous (iv) wastes resources Atom economy = 100 x mass atoms in desired product/mass of atoms in reactants 2 Al 2 O 3  4 Al + 3 O 2 –Mass desired product = 4 x 27.0 = –Mass reactants = 2 x (27.0 x x 3) = –Atom economy = 100x108.0/204.0 = 52.9%

Atom economy Chlorine is manufactured by the electrolysis of saturated brine: 2 NaCl (aq) + 2 H 2 O (l)  2 NaOH (aq) + Cl 2 (g) + H 2 (g) Calculate the atom economy for this process –Mass desired product = 2 x 35.5 = 71.0 –Mass reactants = 2 x ( ) + 2 x (2 x ) = –Atom economy = 100 X 71.0/153.0 = 46.4 Actually the atom economy is 100%...how can this be?

Atom economy Calculate the atom economy for ammonia N 2 (g) + 3 H 2 (g) ⇋ 2 NH 3 (g) The yield, however, is only about 17%

What volume of mol dm -3 hydrochloric acid would react with 25.0 g of calcium carbonate? CaCO HCl  CaCl 2 + CO 2 + H 2 O Find amount (moles) of known amount = mass/molar mass = 25/( x 16) = moles Find ratio from equation: 2 HCl needed for each CaCO 3 Find amount of unknown amount HCl = 2 x = moles Find volume of unknown solution volume = amount/concentration = 0.500/0.100 = 5.00 dm 3

25.0 cm 3 of mol dm -3 sodium hydroxide solution reacted with cm 3 of sulphuric acid in a titration. Find the concentration of the sulphuric acid. Write equation H 2 SO NaOH  Na 2 SO H 2 O Find amount (moles) of known amount = concentration (moldm -3 ) x volume (dm 3 ) = 25.0 x x = moles Find ratio from equation: 2 NaOH needed for each H 2 SO 4 Find amount of unknown amount H 2 SO 4 = ½ x = moles Find concentration of unknown concentration = amount/volume = /(20.75 x ) = moldm -3

13.8 g of a solid monoprotic acid was dissolved in water and made up to 250 cm cm 3 portions of this were titrated against mol dm -3 sodium hydroxide, requiring 23.5 cm 3. Calculate the Mr of the acid. Write equation HA + NaOH  NaA + H 2 O Find amount (moles) of known amount = concentration (moldm -3 ) x volume (dm 3 ) = 23.5 x x 0.25 = moles Find ratio from equation: 1NaOH needed for each HA Find amount of unknown in 25.0 cm 3 amount HA = moles Find amount of unknown in 250 cm x 10 = moles molar mass = mass/amount = 13.8/ = 235 gmol -1

The solid booster rockets of the space shuttle are fuelled by a mixture of aluminium and ammonium chlorate (V) (NH 4 ClO 3 ). a)If no other reagents are involved, and the products are nitrogen, water, hydrogen chloride and aluminium oxide, devise an equation for this reaction. b)Each launch consumes about 160 tonnes of aluminium. What mass and volume of hydrogen chloride gas is produced in the atmosphere above the Cape Canaveral launch pad? Write equation Al + NH 4 ClO 3  N 2 + H 2 O + HCl + Al 2 O 3 Balance the equation 2 Al + NH 4 ClO 3  N 2 + H 2 O + HCl + Al 2 O 3 2 Al + 2 NH 4 ClO 3  N 2 + H 2 O + HCl + Al 2 O 3 2 Al + 2 NH 4 ClO 3  N 2 + H 2 O + 2 HCl + Al 2 O 3 2 Al + 2 NH 4 ClO 3  N H 2 O + 2 HCl + 2 Al 2 O 3

The solid booster rockets of the space shuttle are fuelled by a mixture of aluminium and ammonium chlorate (V) (NH 4 ClO 3 ). b)Each launch consumes about 160 tonnes of aluminium. What mass and volume of hydrogen chloride gas is produced in the atmosphere above the Cape Canaveral launch pad? (1 mole of gas occupies 24 dm 3 ) 2 Al + 2 NH 4 ClO 3  N H 2 O + 2 HCl + 2 Al 2 O 3 Calculate amount of known amount = mass/molar mass = 160 x 10 6 /27 = 5,925,926 mol Used balanced equation to find the ratio 2 mol Al give 2 mol HCl Find amount of unknown 5,925,926 moles HCl are made Find mass HCl mass = amount x molar mass = 5,925,926 x ( ) = 210 x 10 6 g = 210 tonnes Find volume HCl gas volume = amount x gas molar volume = 5,925,926 x 24 = 142 million dm 3