Cliffs AP Chemistry, 3rd Edition

Analysis:

1. Given that 1.00 m of the pure Mg ribbon weighs 0.816 g, determine the mass of Mg used
   in the experiment.
   .
   .
   ..
   ..

cm Mg

cm Mg

mMg

mMg

gMg

gMg

100

100

0 816

1

460

## 100 =0 0375

2. Calculate the number of moles of Mg used in the experiment.
   .
   ..

mol Mg

1 mol Mg

0 0375

24 3

1

0 00154

gMg

# gMg=

3. Calculate the partial pressure of the hydrogen gas in the mixture. The vapor pressure of
   the water at 26.3 °C is 25.7 mm Hg.

PH 2 = Ptot−PH 20

= 743 mm Hg −26 mm Hg = 717 mm Hg

4. Calculate the volume of the hydrogen gas at STP, assuming that the gas temperature
   equals the temperature of the aqueous HCl.

VV.^3 #.

P

P

T

T cm

mm Hg

mm Hg

K

K

40 44 760 34 8cm

717

299

(^2733)
21 = 21 ## 12 ==

5. Write the balanced equation for the reaction.

Mg(s)+2H+(aq)→ H2(g)+ Mg2+(aq)

6. Determine the number of moles of H 2 (g) produced, based on the moles of Mg used.
   .
   .

mol Mg..

mol Mg

mol H mol H

1

0 00154

100

(^100) 0 00154
#^2 = 2 ()g

7. Calculate the molar volume of the H 2 (g) at STP.

.

..
V mol H.

cm H

cm

L L mol

0 00154

34 8

1000

1 000 22 6

STP 2

(^32)
3

• ==#:- 1

8. What was the percent error in this experiment?

% %%.%

.

..

exp

exp

error

obs

L mol

L mol L mol

100 100 0 9

22 4

22 6 22 4

1

11

##

:

::

== =

• 
  
  
  
  • 
    
    
    
    • 
      
    
    
    
    
  
  
  
  

--

9. Determine the number of moles of hydrogen gas by using the Ideal Gas Law.
   PV = nRT

.

/.

n RTPV L atm K.

atm L mol K

0 0821 299 mol H

717 760 0 04044

:: :: 155 10 (^32)
== =# -
Laboratory Experiments