Datasets:
JK-TK
/
form

Dataset card Data Studio Files
xet
Community
text
stringlengths
1
1.32M
Stir carefully with the thermometer and record the highest temperature change to the nearest 05oC
Repeat the procedure above with other portions of the base to complete table 1 below
Table 1Sample results
aComplete the table to determine the change in temperature
bPlot a graph of volume of sodium hydroxide against temperature change
67T2
T oC
From the graph show and determine
ithe highest temperature change T
T T2T1 highest temperatureT2 from extrapolating a correctly plotted graph less lowest temperature at volume of base0 T1
T 67 00 670C
iithe volume of sodium hydroxide used for complete neutralization
From a correctly plotted graph 1675cm3
cCalculate the number of moles of the alkali used
Moles NaOH molarity x volume 2M x 1675cm3 00335 moles
1000 1000
dCalculate H for the reaction
H mass of solutionacidbase x c x T
250 1675 x 42 x 67 1174845 J 1174845kJ
1000
eCalculate the molar enthalpy of neutralization of the alkali
Hn Hn 1174845kJ 350701kJ
Number of moles 00335
dStandard enthalpyheat of solution Hs
The standard enthalpy of solution Hsis defined as the energy change when one mole of a substance is dissolve in excess distilled water to form an infinite dilute solution An infinite dilute solution is one which is too dilute to be diluted further
Dissolving a solid involves two processes
i breaking the crystal of the solid into free ionscations and anionThis process is the opposite of the formation of the crystal itself The energy required to form one mole of a crystal structure from its gaseous ions is called Lattice energyheatenthalpy of lattice Hl Lattice energy heatenthalpy of lattice Hl is an endothermic process Hl
The table below shows some Hl in kJ for the process MXs M g X g
iisurrounding the free ions by polar water molecules This process is called hydration The energy produced when one mole of ions are completely hydrated is called hydration energy heatenthalpy of hydrationHhHydration energy enthalpy of hydrationHh is an exothermic processHh
The table below shows some Hh in kJ for some ions
The sum of the lattice energy Hl endothermic and hydration energy Hh exothermic gives the heat of solutionHs
Hs Hl Hh
Note
Since Hl is an endothermic process and Hh is an exothermic process then Hs is
iexothermic if Hl is less than Hh and hence a solid dissolve easily in water
iiendothermic if Hl is more than Hh and hence a solid does not dissolve easily in water
aDissolving sodium chloride crystals
i NaCl breaking the crystal into free ions Na g Clg Hl 771 kJ
ii Hydrating the ions
Na g aq Naaq Hh 406 kJ
Clg aq Claq Hh 364 kJ
Hs Hh Hs 406 kJ 364 kJ 771 kJ 10 kJmole1
NaCl does not dissolve easily in water because overall Hs is endothermic
Solubility of NaCl therefore increases with increase in temperature
Increase in temperature increases the energy to break the crystal lattice of NaCl to free Na g Clg
bDissolving magnesium chloride crystals MgCl2 s MgCl2 aq
i MgCl2 breaking the crystal into free ionsMg 2g 2Clg Hl 2493 kJ
ii Hydrating the ions
Mg 2g aq Mg 2g aq Hh 1920 kJ
2Clg aq 2Claq Hh 364 x 2 kJ
Hs Hh Hs 1920 kJ 364 x 2 kJ 2493 kJ 1550 kJmole1
MgCl2 s dissolve easily in water because overall Hs is exothermic
Solubility of MgCl2 s therefore decreases with increase in temperature
cDissolving Calcium floride crystals CaF2 s CaF2 aq
i CaF2 Ca 2g 2Fg Hl 760 kJ
ii Hydrating the ions
Ca 2g aq Ca 2g aq Hh 1650 kJ
2Fg aq 2Faq Hh 506 x 2 kJ
Hs Hh Hs 1650 kJ 506 x 2 kJ 760 kJ 19020 kJmole1
CaF2 s dissolve easily in water because overall Hs is exothermic
Solubility of CaF2 s therefore decreases with increase in temperature
dDissolving magnesium bromide crystals MgBr2 s MgBr2 aq
i MgCl2 breaking the crystal into free ionsMg 2g 2Brg Hl 2226 kJ
ii Hydrating the ions
Mg 2g aq Mg 2g aq Hh 1920 kJ
2Brg aq 2Braq Hh 335x 2 kJ
Hs Hh Hs 1920 kJ 335 x 2 kJ 2226 kJ 3640 kJmole1
MgBr2 s dissolve easily in water because overall Hs is exothermic
Solubility of MgBr2s therefore decreases with increase in temperature
Practically the heat of solution can be determined from dissolving known amount massvolume of solute in known mass volume of watersolvent
From the temperature of solvent before and after dissolving the change in temperatureT during dissolution is determined
To determine the Hs ammonium nitrate
Place 100cm3 of distilled water into a plastic beakercalorimeter Determine its temperature and record it at time 0 in table I below
Put all the 50g of ammonium nitrate potassium nitrateammonium chloride can also be usedprovided into the plastic beakercalorimeter stir using a thermometer and record the highest temperature change to the nearest 05oCafter every minute to complete table I
Continue stirring the mixture throughout the experiment
Sample results Table I
aPlot a graph of temperature against timexaxis
220T1
temperatureoC T
bFrom the graph show and determine the highest temperature change T
T T2T1 lowest temperatureT2 from extrapolating a correctly plotted graph less highest temperature at volume of base0 T1
T 187 220 330C
cCalculate the number of moles of ammonium nitrateV used
Moles NH4NO3 mass used 50 00625 moles
Molar mass 80
dCalculate H for the reaction
H mass of water x c x T
100 x 42 x 33 1386 J 1386kJ
1000
eCalculate the molar enthalpy of dissolution of ammonium nitrateV
Hs H 1386kJ 22176kJ mole1
Number of moles 00625 moles
fWhat would happen if the distilled water was heated before the experiment was performed
The ammonium nitrateVwould take less time to dissolves Increase in temperature reduces lattice energy causing endothermic dissolution to be faster
gIllustrate the process above in an energy level diagram
NH4 g NO3g
H NH4 aqNO3aq EnergykJ H H 22176kJ NH4NO3s Reaction path progresscoordinate
h 100cm3 of distilled water at 25oC was added carefully 3cm3 concentrated sulphuricVIacid of density 184gcm3The temperature of the mixture rose from 250C to 38oCCalculate the molar heat of solution of sulphuricVIacid S320H100160
Working
Molar mass of H2SO4 98g