Science 10
Brakke/Baier/Heathcote
ECA – Chemistry – Topic 01
Heat Change Associated with the dissolving of Ionic Compounds
Name ________________________________
Partner ________________________________
All chemical and physical changes are accompanied by a change or flow of energy. When heat is liberated, the reaction is said to be
exothermic. This energy is used to increase the temperature of the surroundings and attention must be paid to what the surroundings
are. Reactions that absorb heat are called endothermic and lower the surrounding temperature.
Because a calorimeter is a poor conductor of heat, it minimizes heat exchange with the environment. Since energy cannot be created
or destroyed, and when a reaction is completed in a calorimeter the overall energy is “trapped,” the heat change of the reaction must
be equal and opposite to that of the water. The equation is as follows:
energy lost = energy gained
q=-q
qwater = - qsubstance
(msΔT)w = - (msΔT)sub
In this activity, you will dissolve two different ionic solids in water and determine whether their reactions are endothermic or
exothermic.
The two chemicals you will use are both ionic compounds, when dissolved in water one will result in an endothermic reaction, the
other in an exothermic reaction. The equations are:
Na2S2O3•5H2O + H2O  Na+ + S2O32- + H2O
Na2S2O3(s)2 Na+(aq) + S2O32-(aq)
NaOH(s) + H2O(l) Na+(aq) + OH-(aq)+ H2O(l)
NaOH(s) Na+(aq) + OH-(aq)
ALL OF THE FOLLOWING MUST BE IN YOUR OWN WORDS.
Introduction:
 What an ionic compound is, and what it does when added to water.
 Literature values for the endo/exo – thermic properties of each compound.
 Describe a calorimeter and its purpose.
Variables:
 Independent
 Dependent
Materials: (also include an apparatus – drawing/picture of the lab set up)
 Sodium thiosulfate, 𝑁𝑎2 𝑆2 𝑂3 ∗ 5𝐻2 𝑂 (s)
 Sodium hydroxide, NaOH (s)
 2 Styrofoam Cups
 Thermometer
 Graduated Cylinder
 Balance/Scale
Procedures:
 Include a step by step procedure that includes:
o Compounds to be used (always with the amount and state (s, l g) in parenthesis).
o Danger precautions! If NaOH is touched or spilled, rinse with copious (lots of) amounts of water!!
o Explain how data should be recorded.
o The precision of the instrument (the smallest value of measurement divided by 2) .
 Example: if you measure with a ruler 5.45 cm, the last value 0.01/2 = 0.005 and your uncertainty is ±0.005
cm. Every measured value should have an uncertainty associated with it.
Data/Results:
 Produce your own data table using excel. This table should be labeled, well-organized and understandable.
 Produce a handwritten graph on graph paper of time vs. temperature for each of the reactions. These graphs should be neat,
accurate and contain a title and labeled axes.
 Draw a handwritten energy diagram for each reaction. These graphs should be neat, accurate and contain a title, labeled axes
labeled products and reactants and contain a sentence explaining if it is an exothermic or endothermic reaction.
 In a separate table, calculate the molar heats of solution for both ionic compounds (use information below). You must show
ALL your work.
Science 10
Brakke/Baier/Heathcote
ECA – Chemistry – Topic 01
Calculating the Molar Heat of Solution for each Ionic Compound.
Molar Mass of Na2S2O3•5H2O = 248.21 g/mol
Molar Mass of NaOH = 40.00 g/mol
qsub has the unit of Joules (J)
if x grams of substance (msub) are reacted then you must find how many moles of substance.
The molar mass has a unit of (g/mol), so if you know the number of grams and divide by this number
you will find the number of moles as follows in the example below:
100.0 g Na2S2O3•5H2O x
1 𝑚𝑜𝑙𝑁𝑎2 𝑆2 𝑂3 ∗5𝐻2 𝑂
248.21 𝑔𝑁𝑎2 𝑆2 𝑂3 ∗5𝐻2 𝑂
= 0.4163 mol Na2S2O3
If 15000.0 J were produced:
15000 𝐽
0.4163 𝑚𝑜𝑙𝑁𝑎2 𝑆2 𝑂3 ∗5𝐻2 𝑂
= 36032 J/mol = molar heat of solution