CHEM125C                                                                                                    Fall, 2003

Hourly Exam # 2                                                                                             Dunnivant

 

Name (PRINTED) ____________________________________

 

There are 95 points.  The exam will be graded on a percentage basis.

 

The honor statement must be signed in order for your exam to be graded.

Closed book, closed Internet, closed notes, closed neighbor!

I have neither given nor received aid on this exam.  

                                                            Signature ________________________

 

Attachments:  Table 4.5

                        Appendix C

Specific heat of water = 4.18 J/goK

 

This exam will be graded on a 100% basis.

 

NOTES:

Show all work for partial credit.   Significant figures and units will be graded throughout the exam.

 

 

  1. (5 pts) Give the chemical formula for each of the following

 

a strong electrolyte            _________________

 

a weak electrolyte              _________________

 

a strong acid                      _________________

 

a strong base                     _________________

 

a weak base                       _________________

 

 

  1. (5 pts) For the following compounds determine which will be soluble or insoluble.  Place an S by the soluble ones and an I by the insoluble ones.

 

Cd(NO3)2                          _______

 

CaCO3                                        _______

 

Cesium chloride                _______

 

CaS                                   _______

 

PbBr2                                _______

 

  1. (5 pts) List five of the seven strong acids.

 

4.     (15 pts, 3 points each) Complete and balance the following molecular equations, and then write the net ionic equation. Also identify each reaction as an acid-base, redox, or precipitation reaction. For some of these reactions you will find Table 4.5 helpful.

 

Pb(NO3)2  +   KOH     Pb(OH)2  +   KNO3    

 

Al(s)  +  NiCl2(aq)  

 

Na2S  +  CdCl2    CdS  +   NaCl

 

2 MnO4-(aq)  +  5 H2O(aq)  +  6 H+(aq)    2 Mn2+(aq)  +  5 O2(g)  +  8 H2O(aq)

 

 HNO3  +  Ca(OH)2    2H2O  +  Ca(NO3)2                 

 

 

  1. (10 pts) A 1.452 g sample of limestone rock is pulverized and then treated with 25.00 mL of 1.035 M HCl solution.  The excess acid then required 15.25 mL of 0.1010 M NaOH for neutralization.  Calculate the percent by mass of calcium carbonate in the rock, assuming that it is the only substance reacting with the HCl solution.  (hint: the reaction between HCl and calcium carbonate yields CaCl2 and H2CO3).

 

  1. (10 pts) You need to make 100.mL of a 0.982 M solution of Ca(NO3)2. Show how you make this solution very accurately with calculations and words.

 

  1. The table below shows the specific heat for three substances. 

 

Substance                          Specific Heat (J/g-oK)

Hg(l)                                 0.14

Al(s)                                  0.90

H2O(l)                               4.18

 

(3 pts) For each of these substances where is the heat stored in a 5.00 g sample?

 

(2pts) Which substance will be the easiest to heat from 25oC to 45oC?

 

(5 pts) Which substance will make the best insulator?

 

8.  (10 pts) The specific heat of water is 4.184 J/goC for temperatures from 0.00 to 100.00oC.  In order to convert liquid water to steam (or vapor) requires 2260 J/g of water.  Steam has a specific heat of 2.00 J/goC.  If you have 100.g of water at 25.00oC, how much energy must you put into the system to heat the water to 105.00oC?

 

9. Given the following reactions,

 

N2(g)  +  O2(g)    2NO(g)                                       DH = + 180.7kJ

2NO(g)  +  O2(g)    2NO2(g)                                  DH = -113.1 kJ

2N2O(g)    2N2(g)  +  O2(g)                                               DH = -163.2 kJ

 

Part 1 (10 pts)

use HessΥs law to calculate the DH for the overall reaction

 

N2O(g)  +  NO2(g)    3NO(g)                                 DH = ?

 

Part 2 (10 pts)

Use the data attached in appendix C to calculate the heat of the reaction using only the final equation,

N2O(g)  +  NO2(g)    3NO(g)                                 DH = ?

 

10. (10 pts) Explain the difference between heat and temperature.  How can the two be related?