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Lab 4: metathesis: to exchange or not

Objectives

  • To give practice writing equations for metathesis reactions, including net ionic equations
  • To illustrate the concept of solubility and the effect of temperature and crystallization

 Grading

You will be determined according to the following:

  • Pre-lab (10%)
    • Must attach graph
  • Lab Report Form (80%)
    • Must include detailed observations for each reaction
  • TA Evaluation of lab procedure (10%)

Before coming to lab…

  • Complete the pre-lab exercise, including the plot (due at the beginning of lab)
  • Read the instructions for the lab and refresh your memory on anything that isn’t clear by reading your textbook

Introduction

In molecular equations for many aqueous reactions, cations and anions appear to exchange partners. These reactions conform to the following general equation:

Equation 1: AX + BY AY + BX size 12{"AX"+"BY" rightarrow "AY"+"BX"} {}

These reactions are known as metathesis reactions. For a metathesis reaction to lead to a net change in solution, ions must be removed from the solution. In general, three chemical processes can lead to the removal of ions from solution, comcomitantly serving as a driving force for metathesis to occur:

1. The formation of a precipitate2. The formation of a weak electrolyte or nonelectrolyte3. The formation of a gas that escapes from solution

The reaction of barium chloride with silver nitrate is a typical example:

Equation 2: BaCl 2 ( aq ) + 2AgNO 3 ( aq ) Ba ( NO 3 ) 2 ( aq ) + 2AgCl ( s ) size 12{"BaCl" rSub { size 8{2} } \( "aq" \) +"2AgNO" rSub { size 8{3} } \( "aq" \) rightarrow "Ba" \( "NO" rSub { size 8{3} } \) rSub { size 8{2} } \( "aq" \) +"2AgCl" \( s \) } {}

This form of the equation for this reaction is referred to as the molecular equations. Since we know that the salts BaCl 2 size 12{"BaCl" rSub { size 8{2} } } {} , AgNO 3 size 12{"AgNO" rSub { size 8{3} } } {} , and Ba ( NO 3 ) 2 size 12{"Ba" \( "NO" rSub { size 8{3} } \) rSub { size 8{2} } } {} are strong electrolytes and are completely dissociated in solution, we can more realistically write the equation as follows:

Equation 3: Ba 2 + ( aq ) + 2Cl ( aq ) + 2Ag + ( aq ) + 2NO 3 ( aq ) Ba 2 + ( aq ) + 2NO 3 ( aq ) + 2AgCl ( s ) size 12{"Ba" rSup { size 8{2+{}} } \( "aq" \) +"2Cl" rSup { size 8{ - {}} } \( "aq" \) +"2Ag" rSup { size 8{+{}} } \( "aq" \) +"2NO" rSub { size 8{3} rSup { size 8{-{}} } } \( "aq" \) rightarrow "Ba" rSup { size 8{2+{}} } \( "aq" \) +"2NO" rSub { size 8{3} rSup { size 8{-{}} } } \( "aq" \) +"2AgCl" \( s \) } {}

This form, in which all ions are shown, is known as the complete ionic equation. Reaction occurs because the insoluble substance AgCl precipitates out of solution. The other product, barium nitrate, is soluble in water and remains in solution. We see that Ba 2 + size 12{"Ba" rSup { size 8{2+{}} } } {} and NO 3 size 12{"NO" rSub { size 8{3} rSup { size 8{ - {}} } } } {} ions appear on both sides of the equation and thus do not enter into the reaction. Such ions are called spectator ions. If we eliminate or omit them from both sides, we obtain the net ionic equation:

Equation 4: Ag + ( aq ) + Cl ( aq ) AgCl ( s ) size 12{"Ag" rSup { size 8{+{}} } \( "aq" \) +"Cl" rSup { size 8{ - {}} } \( "aq" \) rightarrow "AgCl" \( s \) } {}

This equation focuses our attention on the salient feature of the reaction: the formation of the precipitate AgCl. It tells us that solutions of any soluble Ag + salt size 12{"Ag" rSup { size 8{+{}} } "salt"} {} and any soluble Cl salt size 12{"Cl" rSup { size 8{ - {}} } "salt"} {} , when mixed, will form insoluble AgCl. When writing net ionic equations, remember that only strong electrolytes are written in the ionic form. Solids, gases, nonelectrolytes, and weak electrolytes are written in the molecular form. Frequently the symbol (aq) is omitted from ionic equations. The symbols (g) for gas and (s) for solid should not be omitted. Thus, Equation 4 can be written as

Equation 5: Ag + + Cl AgCl ( s ) size 12{"Ag" rSup { size 8{+{}} } +"Cl" rSup { size 8{ - {}} } rightarrow "AgCl" \( s \) } {}

Consider mixing solutions of KCl and NaNO 3 size 12{"NaNO" rSub { size 8{3} } } {} . The ionic equation for the reaction is

Equation 6: K + ( aq ) + Cl ( aq ) + Na + ( aq ) + NO 3 ( aq ) K + ( aq ) + NO 3 ( aq ) + Na + ( aq ) + Cl ( aq ) size 12{K rSup { size 8{+{}} } \( "aq" \) +"Cl" rSup { size 8{ - {}} } \( "aq" \) +"Na" rSup { size 8{+{}} } \( "aq" \) +"NO" rSub { size 8{3} rSup { size 8{-{}} } } \( "aq" \) rightarrow K rSup { size 8{+{}} } \( "aq" \) +"NO" rSub { size 8{3} rSup { size 8{-{}} } } \( "aq" \) +"Na" rSup { size 8{+{}} } \( "aq" \) +"Cl" rSup { size 8{ - {}} } \( "aq" \) } {}

Questions & Answers

how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Gen chem lab. OpenStax CNX. Oct 12, 2009 Download for free at http://cnx.org/content/col10452/1.51
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