Mole Goncept QueStions

1. Calculate the mass of(a) 0.75 mol of NiClz.2HzO(b) 6.02x 103o bromine molecules

2. Calcuiate the number of moles of substance in each of the following:(a) 5.72g of sodium carbonate crystals, NazCO3 10H2O(b) ions in 4.A kg^of NazSO+(c) UF5 in 96 cm'of gaseous UFe at r.t.p.

112+sl[1 .60 x 10- g]

[0.02001t8/.ll

[4.00 x 10']

3. The booster rockets of the US space shuttle use a mixture of NH2ClOr and powdered aluminiumas fuel. A likely reaction in the booster rocket is as follows:

3 Al + 3 NHTGIO+---I Al2O3+ AlCl3+ 3 NO + 6 H2O700 tonnes of NHaClOareacts with aluminium. How much aluminium reacts? [161 tonnesJ

4. Propane, C3Hs is used as fuelwhen liquefied in containers under pressure. When the tap on thecontiainer is opened, the propane @mes out as a gas.(a) (i) Write an equation for the complete combustion of propane gas.

iiil Calculate the volume of oxygen and hence of air 'that

is required to bum _25 cm3 ofpropane gas at room temperiture and pressure [125 cm3; 626 cm3]

(b) Calculate the' ' (D number of moles of carbon dioxide in 75 cm3 of carbon dioxide at r.t.p.(ii) number of oxygen atomsin this amount of carbon dioxide.(iii) concentration in mol dm-, of dissolved carbon dioxide if this volume of gas dissolves in'

1.5dm3of solut ion. [3.13x103mol; 3.77x1021;z.odx 103moldm31

5. G6HrrOH----+ C6H16+ grgThe percentage yield is typically 80%. In order to obtain 12.5 g of C5H1s, what mass of CeHrrOHmust be used initialfy? 119.1 gl

6. Calculate the following:(a) The number of moles of KOH in 1.5 dm3 of 2.5 mol dm3 KOH.(b) The concentration of Fe2* in a solution containing 1.96 g of (NHr)zFe(SOn)z .6H2O dissolved in

0.1 dm"of solution.(c) The mass of Pb(NO3)2 needed to make 100 cm3 of solution containing 0.2 mol dfnt with

respect to nitrate ions. (3.75; O.O5O0 mol dm-3; 3.31 g)

7. A sample of 1.50 g of lead(ll) nitrate is mixed with 125 cm3 of 0.100 mol dm3sodium sulfate.(a) Write the chemical equation for the reaction that occurs.(b) Which is the limiting reactant? lPb(Nog)z](c) \rVhat are the concentrations of all ions that remain in solution after the reaction is complete?-

lo.20o moldm'3 Na*; 0.0725 moldm-3NOs; 0.0637 moldm-3Soq21

8. Calcium and hydrochloric acid react according to the equationGa (s) + 2 HGI (aq)+ CaCl2(aq) + Hz(g)

(a) 0.122 g of calcium metalwas added to 25.0 cm" of 1.23 mol dm" solution of hydrochloric acidand the hydrogen gas was collected at room temperature and pressure.(i) Calculate whether the calcium or the hydrochloric acid.was in excess' [HCl is in excesgl(ii) Hence calculate the volume of hydrogen gas produced. [73.0 cm']

(b) Calcium metal often contains an impurity of calcium oxide on its surface. This also reacts withhydrochloric acid, but does not produce a gas. ln the experiment in (a), it was found that only70.1 cm"of hydrogen was produced. Calculate the percentage purity of calcium. [96.0 %]

9. An antacid chewing gum was sent to the laboratory for testing and found to have 15.0 % by massof hydrotalcite, MgsA/2(OHheCOg4HzO. The active component is the carbonate anion. Each moleof solid hydrotalcite reacts with 2 moles of hydrochloric acid in the stomach to give carbondioxide, water and a soluble ionic salt.(a) Write a chemical equation for the reaction involving hydrotalcite and the hydrochloric acid.(b) Deduce the mass of chewing gum required to neutralize 1.50 g of hydrochloric acid. 182.7 gl

10. Indigestion remedies often contain a suspension of magnesium hydroxide. When a typical dose of10.0 cm" of sluspension was mixed with water and titrated against 0.200 mol dm-" hydrochloricacid, 35.0 cm" of acid was required. Find the mass of magnesium hydroxide in a dose. [0.204 g]

1 1 . 3.0 g of impure NazCOs 1 OH2O was dissolved to nlake 100 cm3 of solution. 1 0.0 cm3 was titratedagainst Hit of concentration a.Sg g dm-3. 16.4 cm3 of acid was needed for neutralization.(a) Calculate the number of moles of NazCOr used in the tibation?(b) What is the number of moles of NazCOg used in the titration?(ci Catculate the concentration of the sodium carbonate solution in mol.dm3.(Oi Wfrat is the percentage purig of the crystals? [1.97 x 103; 9.84 x 104; 0.09&4 moldm-3; 93.7Tol

12. PCl6(s) +4 HzO(l)----+ HrPOr(aq) + 5 HGI (iq)f 5.0; 103 mol of PCls is reacted with water and the solution madg up to 100 cm3, what volume of0.100 mol dm3 sodium hydroxide is required to react with 25.0 cm3 olthis solution? [100 cm3]

13. 1.55 g of an impure sample of ammonium chloride was warmed with 40.0 cm3 of 1 .00 mol dmi(excess) sodium hydroxide solution. When all the ammonia had been given off, the excesssodium hydroxide was titrated with hydrochloric acid of concentration 0.75 mol dm'3. lt was foundthat 26.7 cmo HCI was required for neutralization. Calculate the percentage of ammonium chloridepresent in the sample. [68.e %l

14. A solution of sodium lrydroxide containsl.S0 g of hydroxide ions per dm3. 2O.O cm3 of the solutionreacts with 25.00 cm" of 0.0400 mol dm-' phosphoric acid, HgPOr.(a) How many moles of sodium hydroxide react with 1 mole of phosphoric acid?(b) What will be the chemical equation for the reaction?

15. A 100 g sample of a mixture of sodium carbonate and sodium hydrogencarbonate was titratedwith O.2OO mol dm3 hydrochloric acid using phenolphthalein is indicator. lf 17.50 cm3 ofhydrochloric acid were required, what is the percentage by mass of sodium hydrogencarbonate inthe mixture? [62.90lo]

16. Willow bark can be used to relieve pain. The active chemical in willow bark was isolated in 1829and is called salicin, C13H16O7.(a) Calculate its percentage composition. \C,54.5o/o; H,6.29o/o; O,39.2o/ol(b) The pharmacologically active part of salicin is salicyclic acid. When his is analysed, it has the

foffowing percentage composition by mass: C, 60.86%; H, 4.35%; O, ?4.78o/o. Calculate itsempirical formula. lc7H6o3l

17. An organic acid has the given composition by mass: C, 4O.Oo/o; H,6.70/0 and O, 53.3%.(a) What is the empiricalformula? [CH2O]iOi O.gO g of the acid is neutralized by 10.00 cm3 of 1.0 mol dm€ sodium hydroxide. Catcuiate tne

relative molecular mass of the acid and hence deduce its molecular formula. [90.0, CaH6ql

18. Menthol, the substance we can smell in mentholated cough drops, is composed of C, H and O. A0.101 g sample of menthol is combusted, producing 0.285 g of CO2 and 0.116 g of H2O. What isthe empirical formula br menthol? lf its M, is 156, what is its molecular formula? lBoth CroHzoO]

19. 10 cm3 of a hydrocarbon mixed with 50 cm3 of orygen (excess) was completely combusted. Aftercombustion and cooling to room tempeqture and pressure a contraction of 20 cmt in volume wasobserved. A further contraction of 20 crn'occuned as the mixture was shaken with caustic potash(sodium hydroxide). What is the molecular formula of the hydrocarbon? [CzHj

20. The use of two different indicators makes the quantitative analysis of certain mixtures possible byusing an acid-base titration. The reaction between sodium hydroxide and hydrochloric acid occursin a single stage, whereas that between sodium carbonate and hydrochloric acid occurc in twostages, with the hydrogencarbonate ion as the intermediate product.

lonically: OH + H*+ HzO - (1)CO32' + H*+ HCO3 - e)HCO3+ H*--> H2O + CO2 - (3)

\Mth the phenolphthalein as indicator, the end-point is seen at the completion of reactions (1) and(2). With methyl orange as indicator, the end-point is seen at the completion of all three reactions.Mixture A contained solid sodium carbonate and sodium hydrogencarbonate, but mixture Bcontained sodium carbonate and sodium hydroxide.

One of these mixtures was dissolved in deionized water and the solution made up to 100.0 cm3.20.0 cm3 samples were lltrated using 0.200 mol dm3 hydrochloric acid. ln the presence ofphenolphthalein, 36.15 cm3 of acid was used, but a second 20.0 cm3 sample required 43.80 cm3of acid in the presence of methyl orange.

(a) \Mich mixture, A or B, was analysed?(b) Find the mass of both components in the original mixture. 11.14 g NaOH, 0.81 1 g NazCOgl

21. (a) Gallium exists as two isotopes, ttc" (65 %) and 71Ga (35 %).(i) Calculate the relative atomic mass of gallium. [6e.7](ii) Define the term relative atomic mass.

(b) Gallium nitride could revolutionize electric light bulb design as only a small filament is neededto give a bright light. Gallium reacts with nitrogen gas to form gallium nitride.(i) Write an equation for the formation of gallium nitride.(ii) Calculate the volume of nitrogen, at room temperafure and pressure, which will react with

10.0 kg of gallium. t1720 dm3l

22. By using the data in this question, estimate how much orygen a person requires on average in alift-time and how far a motor c€rr c€ln go using the same amount of oxygen. The typical daily foodrequirement of a person can be considered to be 1.2 kg of carbohydrate. The person obtainsenergy by the oxidation of the carbohydrate which can be represented by the formula (CH2O)".(a) (i) Construct an equation for the complete combustion of the carbohydrate (CH2O)n.

(ii) The empirical relative formula mass of the carbohydrate is 30. Use the equation above tocalculate the number of moles of oxygen required by the person each day. [40.Q mol]

(iii) How many mol of orygen will a person require in a life-time of 70 years? [1.02 x 10o mol](b) A typical motor car requires 6 dm" of octane, CsHra, to travel 100 km.

(i) Construct an equation for the comp^lete combustion of octiane.(ii) The densig of octane is 0.7 g cm-o. Calculate how many moles of octane are present in

the 6 dm" of octane.[M, of octiane is 1 14.] t36.8 moll(iii) Calculate how many mol of oxygen is required to bum the 6.0 dm3 of octane.

-[a61 mofi

(c) Calculate how many kilometers the car can travel using the same amount of oxygen a personuses in a life{ime (your answer to (a)(iii) 12.21 x 10' kml