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Calculations: 1. Combine equations (2), (3) and (4) to obtain equation (1). Reaction 2 1. Calculate the change in temperature for reaction (2). 2.
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Question

I need some help with my homework and my lab report that are due tomorrow.

So these are the questions I find tricky with my homework:

10.) What is the concentration of hydrogen ions in a solution obtained by dissolving 12 g of benzoic acid in 500 mL of water?


11.) The equilibrium constant for the following reaction is 7.2 x 10-10. What is the [H+] in a solution 1.0 M of this acid?

This is an image of a chemical equation. HCN + H2O, equilibrium reaction arrows, CN minus + H3O plus


And this is the lab report I am having difficulty with, because it involves Hess's Law:

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104419058_688491111719719_523358607897907530_n.png

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I would really appreciate the help! Thank you!

104384518_344473179849950_8532925334384497142_n.png
Calculations:
1. Combine equations (2), (3) and (4) to obtain equation (1).
Reaction 2
1. Calculate the change in temperature for reaction (2).
2. Calculate the energy released (AH) in (2) (in J), using Q=mcAT (recall AH = -Q). The
mass to be used is the mass of HCI. Assume the density of hydrochloric acid to be 1
g/mL.
3. Convert your answer into KJ
4. How many moles of Mgo were used?
5. Convert your answer into KJ/mol Mgo.
Reaction 3
1. Calculate the change in temperature for reaction (3).
2. Calculate the energy released (AH) in (3) (in J), using Q=mcAT. The mass to be used is the
mass of HCI.
3. Convert your answer into KJ.
4. How many moles of Mg were used?
5. Convert your answer into KJ/mol Mg.
6. Calculate the heat of reaction (1) in KJ/mol of Mgo by combining (2). (3) and (4) and their AH
values that you obtained, in order to get equation (1) and its AH for the combustion of Mg.
7. Determine the theoretical value for the combustion of magnesium, from the table of standard
enthalpies of formation
8. Calculate the percentage error.
Conclusion
Briefly state the results for the laboratory, in general. This should be no more than two sentences.
Please ensure that your lab report contains the following:
Title page
Purpose
Results
Calculations
Three sources of error
Conclusion
nless otherwise indicated, all images in this activity are from the public domain or are @ clipart. com or Microsoft clipart a
e used with permission.
104419058_688491111719719_523358607897907530_n.png
REACTION 2:
1. Pour 100 mL of 1.0 M hydrochloric acid into your polystyrene calorimeter.
2. Weigh out 1.00 g of magnesium oxide on a filter paper.
3. Place the thermometer in the hydrochloric acid to obtain the initial temperature, T1
(precise to 0.10C). It may take several seconds for the temperature to stabilize.
4. Add the magnesium oxide powder to the solution.
5. Use a glass stirring rod to stir the cup contents until a maximum temperature has been
reached and the temperature starts to drop
6. Record the maximum temperature, T2
REACTION 3:
1. Pour 100 mL of 1.0 M hydrochloric acid into your polystyrene calorimeter.
2. Weigh out 0.50 g of magnesium ribbon (this is about 46 cm). Roll it up loosely around a pencil
so that you end up with a coil. Make sure it is not too tightly coiled.
3. Place the thermometer in the hydrochloric acid to obtain the initial temperature, T, (precise to
0.10C). It may take several seconds for the temperature to stabilize.
4. Add the magnesium ribbon to the solution. n.
5. Use a glass stirring rod to stir the cup contents until a maximum temperature has been reached
and the temperature starts to drop.
6. Record the maximum temperature, T2.
Results
. Use the table of standard enthalpies of formation to calculate the theoretical value.
. Sample results are provided below.
. The specific heat capacity of hydrochloric acid is 4.184 Jig "C.
Table #1: Volume, Temperature and Mass Values for Reactions 2 and 3
Reaction 2
Reaction 3
(Mgo)
(Mg)
Volume of HCI
Final temperature (T2)
32.1'C
48.2'C
Initial temperature (T1)
24 C
24 C
Change in temperature (AT)
Mass of solid
0.96 g
0.55 g
104439130_625031608357801_1398457265285513481_n.png
Lab
Heat of Reaction for the Combustion of Magnesium
Although you will not be working with actual chemicals during this laboratory, since you will be doing
it virtually, the procedure is given in order for you to be aware of the process that would be followed
in a laboratory setting.
Introduction
In this experiment, you will use Hess's Law to determine the heat for a reaction that is difficult to
measure directly. Magnesium metal burns rapidly, releasing light and heat, as observed in photo
flashbulbs or by burning magnesium ribbon. The reaction is presented by the equation:
Mgo (s)
(1)
This equation can be obtained by combining equations (2), (3) and (4):
Mgo() + 2HClag) -> MgClarag) + Hog
(2)
Mgs) + 2HClag)
- MgCl2(aq) + Hara)
(3)
Hargi + 192(2)
(4)
By combining these three equations, you can obtain equation (1). The heats of reaction for
equations (2) and (3) can easily be determined by experiments. The heat of reaction for equation (4
can be obtained from a table of values for previously measured reactions.
Material
Chemicals
magnesium, magnesium oxide, hydrochloric acid
Apparatus:
Polystyrene calorimeter, graduated cylinder, electronic balance, filter paper, spatula, thermometer,
glass stirring rod, stop watch,
Safety
. Safety goggles and a lab apron should always be worn when working with chemicals.
. This lab will be performed using small quantities of chemicals (micro-scale chemistry).
Procedure
REACTION 2:
1. Pour 100 mL of 1.0 M hydrochloric acid into your polystyrene calorimeter.
2. Weigh out 1.00 g of magnesium oxide on a filter paper.
3. Place the thermometer in the hydrochloric acid to obtain the initial temperature, T1

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