Ph Flashcards
What differentiates an acid and a base
An acid is any compound or ion that can give up an electron (H+)
A base is any compound or ion that can accept a electron (OH-)
What things can Ph effect?
- availability of nutrients
- toxicity of certain elements
- functioning of soil organisms
What is neutralization?
When acids and bases react to form water and a salt
Why is pure water neutral
because pure water contains equal concentrations of H+ and OH-
By how much does each value on the Ph scale increase with each whole number
For each whole number above 7 the alkalinity will be 10 times more
For each whole number below 7 the acidity will be 10 times more
What is the optimum soil Ph range for most plants
Ph 6.0 - 7.0
List some origins of acidity
- Release of hydrogen atoms under natural chemical processes
- Atmospheric CO2 reacts with water to form carbonic acid
- Organic molecules react with water and cause acid dissociation
- Oxidation of the ammonium form of nitrogen
- Fulvic and fumic acid products of organic decomposition
- Hydrolysis
- Nitric acid from lighning deposits
- Volcanic activity deposits sulphuric acid
- oxidation of ammonium based fertilizers
- Deposition of acid rain resulting from industrial pollution
What are the 3 sources (pools) of acidity in soil?
Active
-Quantity of H+ present in soil water solution. The active pool of H+ is in equilibrium with the exchangeable hydrogen ions that are held on the soils cation exchange complex. Most readily effects plant growth and can be measured using a Ph meter
Exchangeable
-Refers to the amount of acid cations (Al+ and H+) occupied on the cation exchange complex. When the CEC is high but has a low base saturation, it becomes more resistant to Ph changes
Residual
-Comprises of all bound aluminum and hydrogen in soil minerals. Least available of all pools.
What is the buffering capacity?
A.k.a. reserve acidity. Buffering capacity is a soils propensity to resist changes in Ph.
Why is an understanding of pH important in soil science?
Soil micro-organisms are sensitive to pH and nutrient availability and uptake by plants varies with pH.
What pH range do most soil organisms prefer?
5-8
Which nutrients tend to be leached at low pH?
Ca2+, Mg2+, K+, Na+
What happens when a soil drains and dries?
Ph returns to a more normal level as H+ and OH- are reabsorbed onto cation exchange sites
