What do you see?
The invention of the Xray machine had radically improved medical diagnosis and treatment. For the first time, it was possible to see inside a person’s body to detect broken bones, tumors, obstructions, and other types of problems. Barium sulfate is often used to examine patients with problems of the esophagus, stomach, and intestines. This insoluble compound coats the inside of the tissues and absorbs Xrays, allowing a clear picture of the interior structure of these organs.
Predicting Precipitates
Knowledge of
Sample Problem: Predicting Precipitates
Will a precipitate of barium sulfate form when 10.0 mL of 0.0050 M BaCl _{ 2 } is mixed with 20.0 mL of 0.0020 M Na _{ 2 } SO _{ 4 } ?
Step 1: List the known quantities and plan the problem .
Known
 concentration of BaCl _{ 2 } = 0.0050 M
 volume of BaCl _{ 2 } = 10.0 mL
 concentration of Na _{ 2 } SO _{ 4 } = 0.0020 M
 volume of Na _{ 2 } SO _{ 4 } = 20.0 mL

Ksp of BaSO _{ 4 } = 1.1 × 10 ^{ 10 }
Unknown
 ion product [Ba ^{ 2+ } ][SO _{ 4 } ^{ 2 } ]
 if a precipitate forms
The concentration and volume of each solution that is mixed together must be used to calculate the [Ba
^{
2+
}
] and the [SO
_{
4
}
^{
2−
}
]. Each individual solution is diluted when they are mixed together. The ion product is calculated and compared to the
Step 2: Solve .
The moles of each ion from the original solutions are calculated by multiplying the molarity by the volume in liters.
\text{mol SO}_4^{2}&=0.0020 \ \text{M} \times 0.020 \ \text{L}=4.0 \times 10^{5} \ \text{mol SO}_4^{2}
The concentration of each ion after dilution is then calculated by dividing the moles by the final solution volume of 0.030 L.
\left [\text{SO}_4^{2}\right ] &=\frac{4.0 \times 10^{5} \ \text{mol}}{0.030 \ \text{L}}=1.3 \times 10^{3} \ \text{M}
Now the ion product is calculated.
Since the ion product is greater than the
Step 3: Think about your result .
Two significant figures are appropriate for the calculated value of the ion product.
Summary

Calculations are shown which allow the prediction of precipitate formation based on
Ksp .
Practice
Work the problems at the link below:
http://misterguch.brinkster.net/jan2002.pdf
A useful table for constants can be found here: http://users.stlcc.edu/gkrishnan/ksptable.html
Review
Questions
 What would be the equation for the ion product of BaCl _{ 2 } ?

What happens if the ion product is less than the
Ksp ?  Why did we not need to calculate an ion product for NaCl?