Equilibrium: Solubilities of Salts and Gases Flashcards
How do salts (ionic compounds) interact?
Dissociate to give + and – ions
Why is water bad and good for dissolving substances?
- Good for dissolving ionic substances
- Bad for non-charged organic molecules
What does ppm stand for?
Parts per million
What does solubility stand for?
A measure of how much solute can be dissolved in a solvent - affected by temp and pressure
What does unsaturated mean?
Solution can still dissolve more
What does saturated mean?
Solution that contains the maximum of dissolved solute
What does supersaturated mean?
Unstable solution, contains > solute
solubility
What does precipitate mean?
Excess solute that comes out of solution
How does solubility of gases change with increasing temp?
Decreases
How does solubility of most solids change with increasing temp?
Increases
What is concentration?
Amount of solute in a solution
What is molarity?
Moles of solute/ Litres of solution
What is normality?
Normality (N) = equivalent of solute/1 litre of solution
What does equivalent mean in normality?
Where equivalent = equivalent weight = molecular weight/ion charge
What is the equivalent weight of calcium 2+?
= molecular weight/Z = 40/2
= 20 g per equivalent
What must all aqueous solutions maintain?
All aqueous solutions must maintain charge neutrality. The sum of the cations must equal the sum of all the anions
What is the equilibrium constant?
The ratio between the amount of reactant and the amount of product which is used to determine chemical behaviour
How do you find the equilibrium constant?
Always put products over reactants and raise each to the power of their stoichiometric coefficients
What can the Keq constant predict?
Equilibrium constant predicts the predominant direction of the reaction
What is the solubility product constant?
The equilibrium constant for a solid substance dissolving in an aqueous solution
What does Henry’s Law determine?
Amount of a gas in a liquid
What is solubility of a gas in a liquid proportional to?
The partial pressure of that gas in contact with the liquid
What is Henry’s law constant for oxygen?
1.28 x 10^-3
What does solubility in water depend on?
- Water temperature
- Partial pressure
- Salt content
Why is oxygen content in water very important?
Determines if there are aerobic conditions or anaerobic conditions
What are the dissolved oxygen requirements of different types of fish?
- Trout 4-5 mg/L
- Bass 3-4 mg/L
- Carp 2-3 mg/L
What is BOD?
Is a measure of water pollution
What does BOD measure?
It measures how much dissolved oxygen is consumed as microbes/bacteria break down organic matter
What does high BOD indicate?
High BOD indicates that levels of dissolved oxygen will fall, with potentially dangerous implications for biodiversity
What can high BOD be caused by?
- High BOD can be caused by high levels of organic pollution
- Microbiological activity uses up O2
What is BOD_5?
The amount of dissolved oxygen used in a water sample by micro-organisms in a closed system as they break down organic material at 20ºC over a 5 day period.
What is BOD_5 of clean water?
< 1 mg/L
What is BOD_5 of polluted water?
> 5 mg/L
Wha are the test conditions for BOD test?
- Test is run for 5 days
- Temperature is kept at 20ºC
- Bottles are kept in the dark
- Analysed by measuring the DO at the beginning and end of a time period
What does it mean if waste is really strong?
If waste is very strong, it is diluted with a known amount of water
