Conservation Of Mass D. Crowley, 2007

Conservation Of Mass  To be able to explain why mass is conserved when substances dissolve Saturday, September 05, 2015

Dissolving  See if you can identify as many facts about dissolving as you can…  What do you think will happen to the mass of water if salt is added to it?  Using these facts, write a small paragraph in your book why salt dissolves  See if you can identify as many facts about dissolving as you can…  What do you think will happen to the mass of water if salt is added to it?  Using these facts, write a small paragraph in your book why salt dissolves

Salt Dissolving  Some substances are soluble meaning they dissolve  They are able to mix completely with a liquid, forming a transparent mixture  Salt (the solute) dissolves in water (the solvent), and its particles become completely mixed in our newly formed solution.  But the mass stays the same - we do not loose any salt or water particles, they are just mixed up, which is why they become difficult to see  Some substances are soluble meaning they dissolve  They are able to mix completely with a liquid, forming a transparent mixture  Salt (the solute) dissolves in water (the solvent), and its particles become completely mixed in our newly formed solution.  But the mass stays the same - we do not loose any salt or water particles, they are just mixed up, which is why they become difficult to see SoluteSolventSolution

Particles Look at the particle model for the soluble sugar: - Sugar, added to the water Water

Particles Look at the particle model for the soluble sugar: - Water Sugar, added to the water Sugar and water solution

Particles

Demonstration  What will happen to the rice and peas when they are placed in water?  Can you identify what will happen in our particle model?  What can you say about the mass of the water and the peas?  What will happen to the rice and peas when they are placed in water?  Can you identify what will happen in our particle model?  What can you say about the mass of the water and the peas?

Mass  Remember - the mass always stays the same - even if the solute dissolves  Both substances are still there, however the solute may have mixed with the solvent forming a solution  Remember - the mass always stays the same - even if the solute dissolves  Both substances are still there, however the solute may have mixed with the solvent forming a solution

Getting Salt Back  Imagine you added some salt to water  The salt would dissolve in the water  How could you get your salt back?  Imagine you added some salt to water  The salt would dissolve in the water  How could you get your salt back?

Filtration  Filtration is great at seperating insoluble solids (like our pea) from the liquid  It does this by creating a barrier which the larger insoluble particles cannot pass  E.g. the large peas cannot pass through the filter (like using a sieve at home)  Why is this process no use in seperating salt from water (something which has dissolved)?  Filtration is great at seperating insoluble solids (like our pea) from the liquid  It does this by creating a barrier which the larger insoluble particles cannot pass  E.g. the large peas cannot pass through the filter (like using a sieve at home)  Why is this process no use in seperating salt from water (something which has dissolved)? Large peas do not dissolve (their particles remain together), so can be easily filtered using a sieve

Filtration  When something dissolves, the solute particles become spread throughout the solvent  Because the particles are so spread out, a barrier will not stop them (they pass straight through)  This is why filtration is no use  Instead we must use evaporation – boiling off the water and leaving the salt behind  You task it to dissolve 1 gram of salt in water and via evaporation get the salt back – most accurate wins!  When something dissolves, the solute particles become spread throughout the solvent  Because the particles are so spread out, a barrier will not stop them (they pass straight through)  This is why filtration is no use  Instead we must use evaporation – boiling off the water and leaving the salt behind  You task it to dissolve 1 gram of salt in water and via evaporation get the salt back – most accurate wins!

Dissolving  Remember, when something dissolves its particles spread throughout the solvent, forming a solution  This is a lot like diffusion, where the particles (net) went from an area of high to low concentration  How could you speed up dissolving?  Remember, when something dissolves its particles spread throughout the solvent, forming a solution  This is a lot like diffusion, where the particles (net) went from an area of high to low concentration  How could you speed up dissolving?

Heat!  The particles diffused quicker when they were heated - more heat gives them more energy, so they move quicker  This can be applied to diffusion - heat the particles and they will diffuse quicker  Try it yourself - get an equal quantity of water and sugar for two cups  With one cup, use tap water  With the other use boiling water  Add the sugar, and see which dissolves quicker! H/W - explain this to someone at home!  The particles diffused quicker when they were heated - more heat gives them more energy, so they move quicker  This can be applied to diffusion - heat the particles and they will diffuse quicker  Try it yourself - get an equal quantity of water and sugar for two cups  With one cup, use tap water  With the other use boiling water  Add the sugar, and see which dissolves quicker! H/W - explain this to someone at home!