Ch#6 : Solutions Flashcards
Learn about solutions , the properties of solutions and gas laws
What are unsaturated , unsaturated and supersaturated solutions? How do we identify them?
Unsaturated solution : A solution which can dissolve more of the solute at a given temperature. Example : 5g of NaCl dissolved in 100g of water.
Saturated solution : A solution whicb cannot dissolve more of the solute given temperature is called a saturated solution. Example : 50g of NaCl in 100g of water at room temperature.
Supersaturated solution : If we heat a saturated solution and add more solute to it until it no longer dissolves and sinks down to the bottom , then it will be a supersaturated solution. A solution which contsins more of the solute than is contained in the saturated solution is called a supersaturated solution.
A supersaturated solution is unstable in the presence of crystals of solute.
Example : If we add a crystal of solute to a saturated solution , it simply falls to the bottom without dissolving.
If we add a crystal of solute to a supersaturated solution , crystallization will start. When the crystallization is finished , we will have a saturated solution in presence of crystals of solute.
Identification :
Saturated : When the solute dissolves when you add it.
Unsaturated : When the solute doesnt dissolve when you add it.
Supersaturated : When crystallization starts after adding a crystal of solute.
What is the difference between a dilute and concentrated solution? , What do we mean by the percentage of a solution? State the four ways to express percentage of a solution.
Dilute and concentrated : The quantity of solute in a given amoutn of solution is called its concentration.
A dilute solution is one whose concentration is relatively low and a concentrated solution is one whose concentration is relatively high.
Percentage : Commercially available H²SO⁴ is 98% and HCl is 37‰. This means that conc. H²SO⁴ contains 98g of H²SO⁴ in 100g of solution and conc. HCl contains 37g of HCl in 100g of solution.The quantity of solute and solvent can be expressed in g and cm³.
By the percentage of a solution we mean the mass or volume of solute dissolved in 100g or 100cm³ of solution.
Ways to express percentage : m/m , m/v , v/m and v/v.
Define molarity and state its formula.
Molarity : is defined as the number of moles of solute dissolved per dm³ of solution.
Molarity = no. of moles/volume in dm³ [1dm³ = 1000cm³].
Commercially available H²SO⁴ is 18M and HCL is 12.1M. This means that there are 18 moles of H²SO⁴ and 12.1 moles of HCl in dm³ of their solutions.
What is solubility? How do we find solubility? Also what is the solubility of NaCl and sodium thiosulphate at room temperature?
Solubility : The amount of solute dissolved in 100g of solvent at a particular temperature is called its solubility.
Solubility of NaCl at room temp is 35.7g per 100g of water and solubility of sodium thiosulphate is 50g per 100g of water.
Finding Solubility : Prepare a saturated solution of your solute in 100g of water. Put this solution in a pre-weighed china dish. Place the china dish on a burner and heat it slowly until the water evaporates completely. Calculate the mass of solute present in the china dish to find the solubility.
Explain the effect of temperature on solubility and draw the graph.
If we add 34.7g of KCl to 100g of water at 20°C , it will dissolve. But if we add more than that it will not dissolve. However if we increase rhe temperature it will readily dissolve. 56.7g of KCl dissolves in water at 100°C. When the temperature is decreased back to 20°C , 22g of KCl will crystalize out. This means temperature has a profound effect on solubility.
The solubility of ionic compounds generally increases with the increase in temperature. However the solubility of some solids decreases with temperature. For instance , the solubility of Na²SO⁴ decreases with the increase in temperature.
(Air example of decreasing solubility) : Heat water , you will see small bubbles form at the side of the container before water boils. These bubbles are composed of air. Since air is less soluble in hot water than in cold water , air comes out of water in the form of bubbles. This means that the solubility of air decreases with the increases with the increase in temperature. Fish in aquariums show signs of stress on a hot day because less oxygen dissolves in hot water.
Graph : First value is at 0°C and the other is at 80°C KNO³ : 17g ---> 140g NH⁴Cl : 30g --> 75g NaCl : 35g ---> 35g Na²SO⁴ : 60g ---> 40g KBr : 60g ---> 100g NaNO³ : 75g ---> 140g
Compare solutions , suspensions and colliods.
Solutions : Colloids : Suspensions
1. Homogeneous : Heterogeneous : Heterogeneous
- Particle Size : 0.1-1nm : 1-10³nm: Particle size > 10³nm
- The particles are invisble to the naked eye , ordinary microscope and electron microscope. : The particles are invisble to the naked eye and ordinary microscope but visible under a electron microscope : Visble to the naked eye.
- Particles can pass through ordinary and ultra filter paper : Particles can pass through ordinary filter paper but not ultra filter paper. : Particles cant pass through both ordinary and ultra filter paper.
- Cant scatter light : Scatters Light : Scatters Light.p
