The water cycle
- Water in the rives, lakes and oceans on earth evapourates as the sum supplies it with energy
- The water vapour that it forms rises into the atmostphere where it cools and condenses (forms tiny water droplets rain)
- The clouds rise further and they cool more and rain dropplets get bigger
- Eventually the rain falls, replenishing hte water back into the lakes rivers and oceans.
- This is called the water cycle
What dissolves in water?
- To some extent gases are soluble in water
- Most ionic compounds
- IMPOSSIBLE to dissolve many covalent substances in water
We call he amount of solute which we can dissolve in a certain amount of solvent the solubility of that substence
- the solubility is measured in 100grams of the solvent at a particular temperature.
- The solubility of most solid solutes increases as the temperature increases
A saturated solution contains the maximum amount of solute that will dissolve at that temperature.
What are the Solubilty Curves Key Points?
- The solubility of most solid solutes increases as the temperature rises.
- The solubility of gases decreases as the temperature rises
- Solubility curves show how the solubility of a substence changes with temperature
What factors effect the solubility of a gas in wat
As the temperature increases, the amount of gas which will dissolve in a certain volume of water decreases when we keep the pressure constant.
If we keep the temperature constant, the solubility of a gas increases as we increase the pressure
Why must drinking water be checked for nitrate lev
- nitrate gets into our water from washing off crops into lakes ect,
- These must be checked at the nitrate ions in these can be very bad or babies and some adults.
- These therefore must be carefully monitored by companies who supply water to our homes.
Summary of Solubility Curves
The amount of a substance that will dissolve in water is shown by a solubility curve. The solubility of gases is affected by pressure and temperature. Gases are less soluble at high temperatures and more soluble a high pressures.
What ionic compounds dissolve in water?
- salts of SODIUM (Na), POTASSIUM (K), AMMONIUM (NH4)
- NITRATES (NO3)
- CHLORIDES (Cl) not silver or lead
- SULFATES (SO4) exept for barium ad lead.
How does water dissolve ionic compounds?
- water molecules start to surround the ions
- they disrupt the ionic bonding - so it gradually falls apart
What are water molecules?
Water molecules are polar.
They have a positive hydrogen side, and a negative oxygen side.
The slightly negative side attracts the positives ions and the slightly positive side attracts the negative ions.
- The solubility of a substance is given solvent is the number of grams the solute (usually a solid) that dissolve in 100g of solvent (the liquid) at a particular temperature
- The solubilty of (solid) solutes usually increase with temperature.
- A saturated solution is one that cannot hold anymore solid at that temperature and you have to be able to see solid on the bottom to be certain it was saturated.
How does a solubility curve show when a solution i
- A solubility curve plots the mass of solute dissolved in a saturated solution at various temperatures.
- The solubility of most solids increases as the temperature increases
- This means cooling a saturated solution will use cause some solid to crytalise
Example of a solubility curve question?
What mass of solid copper sulfate will crystallise when a saturated solution containing 100g of water is cooled from 100 c to 20 c?
100 c reads 75g on graph
20 c read 20g
therefore its 75g - 20g= 55g
''chlorine water'' is an example of a gas in water- used in pools to kill bacteria.
HIGHER PRESSURE MORE GAS DISSOLVES
LESS SOLUBLE AS TEMPERATURE INCREASES