3: The Ocean Flashcards
What is the relationship between solutes, solvents, and solutions?
solute + solvent = solution
What does it mean if a substance is soluble in a solvent and vice versa?
If a substance can dissolve in a given solvent, it is soluble in that solvent. If it cannot dissolve, it is insoluble in that solvent.
What is the difference between a dilute solution, a concentrated solution, and a saturated solution?
A dilute solution contains a small amount of a solute in a given volume of solution. It is not saturated.
A concentrated solution contains a large amount of solute in a given volume of the solution.
If in a concentrated solution no more solute dissolved in the solution at that temperature, it is a saturated solution.
saturated solution = solution with maximum possible concentration at that temperature.
How is concentration calculated?
It is the amount of solute dissolved in a stated volume of the solution. It can be obtained by dividing the mass or amount of the solute by the volume of the solution. Its unit is g dm-3 or mol dm-3.
What is decantation?
Decantation is a quick method for separating a much denser, insoluble solid from a liquid. In decantation, pour out the liquid and use a glass rod to guide the liquid flow until the container has no liquid left.
What is filtration and its working principle?
Filtration is a technique to remove suspended, insoluble solids from a liquid. A filter paper has tiny, microscopic holes. When you filter a mixture of a liquid and an insoluble suspended solid, particles of the liquid (and other particles that dissolve into the liquid) are small enough to pass through the filter paper, but the larger particles of insoluble suspended solids cannot. The solid stays behind on the filter paper as the residue while the liquid passes through as the filtrate.
Give two items that utilise the principle of filtration.
- face masks: they separate dust fom air
- vacuum cleaners
What is evaporation?
Evaporation is the conversion of a liquid to vapour at any temperature below the boiling point of the liquid.
It can be done gently in the lab by heating the liquid on a boiling water bath.
Give one scenario that utilises the principle of evaporation.
In hot countries, sea water is led into shallow ponds. The water evaporates in the sun and leaves the common salt behind.
What are two methods of crystallisation?
- by cooling a hot saturated solution: since the solubility of most solids decreases as temperature decreases, when the temperature drops, the solution can hold less solute and some solute crystallises out.
steps:
a. heat the solution until it becomes saturated.
b. leave the saturated solution to cool and wait for crystals to form.
c. filter the crystals. - by slow evaporation of a solution at room temperature: as the solvent evaporates, the remaining solution becomes more concentrated and gradually crystals start forming.
steps:
a. put a piece of filter paper with holes onto a beaker of the solution.
b. wait for the solution to evaporate and from crystals.
What is the disadvantage of evaporation and crystallisation?
The solvent is lost during the process.
What are the requirements and advantages of distillation?
Distillation is a method to retain both the solute and the solvent of a solution. It relies on the solvent having a much lower boiling point than that of solute so that when the solution is heated, the solvent boils but the solute does not.
Why should we add anti-bumping granules to a distillation set-up?
Sometimes, violent boiling may throw the liquid out of the container while it is being heated. This is called bumping. Adding anti-bumping granules ensure smooth boiling and cuts the risk of bumping.
What is the definition of miscible liquids?
Miscible liquids mix together completely, forming only one liquid layer when mixed. An example of a pair of miscible liquids are ethanol and water.
What is the procedure of flame test?
- Clean a nichrome wire by dipping it into concentrated hydrochloric acid and holding it in a non-luminous flame.
- Moisten the clean wire by dopping it into the acid again. Then dip it into the solid sample and let some solids stick to it.
- Hold the wire in the hottest part of a non-luminous flame and observe the colour of the flame.
What is the flame colour of a potassium compound?
Lilac
What is the flame colour of a sodium compound?
Golden yellow
What is the flame colour of a calcium compound?
Brick-red
What is the flame colour of a copper compound?
Bluish green
List two tests for the presence of water.
- Water turns cobalt(II) chloride paper from blue to pink.
- Water turns anhydrous copper(II) sulphate from white to blue.
What is the word equation for the electrolysis of sea water?
sea water direct current -> chlorine gas + hydrogen gas + sodium hydroxide solution
Where can the products after sea water is electrolysed be found?
Chlorine gas is formed at the electrode connected to the positive terminal of the d.c. power supply while hydrogen gas is formed at the other electrode. Eventually, the solution in the set-up becomes sodium hydroxide solution.
List 3 usages of hydrogen.
- As a rocket fuel
- For making ammonia
- For making hydrochloric acid
List 5 usages of chlorine.
- Making PVC (a plastic)
- Sterilising swimming pool water
- Sterilising drinking water
- Making hydrochloric acid
- Making bleach
List 3 usages of sodium hydroxide solution.
- Making soaps and detergents
- Making paper
- Making bleach
What is the definition of a physical change?
A physical change is a change in which no new substance is formed.
What is the definition of a chemical change?
A chemical change is a change in which at least one new substance is formed.
What is the definition of physical property?
Physical properties of a substance are properties that can be observed without changing the chemical composition of the substance.
What is the definition of chemical property?
Chemical properties of a sibstance are properties that can be observed or measured only when the substance undergoes a chemical change to form new substance(s).
