water• Water is a colourless, odorless and tasteless liquid.• Water can exist in three state: - solid (ice) - liquid (water) - gas (steam)
The changes of water occur at specific temperature Point Explanation ExampleMelting The temperature which solid Meting point of ice point becomes liquid = O oCFreezing The temperature which liquid Freezing point of point becomes solid water = 0 oC Boiling The temperature which liquid Boiling point of point becomes gas water = 100 oC SOLID LIQUID GAS melting boiling freezing
Water test The presence of water can be determined by the tests shown below: Water test Observation/Result The freezing point The melting point of the water is 0 oC and and melting point the boiling point of the water is 100 oC (without any contamination) Anhydrous cobalt Changes from blue to pink chloride paperAnhydrous copper(II) Changes from white to blue sulphate
SOLUTIONS A solution is a mixture formed when one or more solutes dissolve in a solvent. Water(solvent) Sugar solution (solution) Sugar (solute)
Soluble and Insoluble SOLUBLE INSOLUBLE The substance will NOT The substance will dissolve in a liquid and dissolve in a liquid formed precipitate
When a solute dissolves in solvent, the solventbreaks down the solutes into smaller particles
Eventually, a homogeneous solution is formed.
HOMOGENEOUS SOLUTIONSUGAR WATER SOLUTION HETEROGENEOUS SOLUTIONCHALK WATER SUSPENSION
MASS OF A SOLUTIONMass of a solution = Mass of the solvent + Mass of soluteWhen a solute dissolves in a solvent, it didn’t disappear!! 5 grams 20 grams 25 grams SUGAR WATER SOLUTION
solventsWater is such a good solvent that it can dissolve almost every solutes and it’s known as universal solvent. A solution in which the water is the solvent is called aqueous solution. Example, salt solution (salt + water)
However, some substances do not dissolve in the water. Thus, organic solvents are used to dissolve it. Some of the examples are alcohol, kerosene, turpentine and acetone.
solutionsDiluted solution Concentrated Saturated solution solution Excess solute Has very little Has a lot of solute Has the maximum solute in it in it amount of solute in itCan dissolve a lot Can dissolve a Cannot dissolve any more solute little more solute more solute
Add more Add more copper suphate copper suphate Diluted copper Concented copper Saturated coppersulphate solution sulphate solution sulphate solution
CONCENTRATION OF A SOLUTION• A concentration of a solution = grams per dm3 (g/dm3) 1 dm3 = 1000 cm3Example 1,Solution A contains 10.0g of solute in 1000cm3 solvent.Concentration = mass of solutes (g) volume of solvent (dm3) = 10.0 g/1 dm3 = 10.0 g/dm3
Example 2,Solution B contains 5.0g of solute in 1000cm3 solvent.Concentration = mass of solutes (g) volume of solvent (dm3) = 5.0 g/1 dm3 = 5.0 g/dm3
Example 3,Solution C contains 1.0g of solute in 100cm3 solvent.Concentration = mass of solutes (g) volume of solvent (dm3) = 1.0 g/0.1 dm3 1000 cm3 = 1 dm3 = 10.0 g/dm3 100 cm3 = 0.1dm3
Example 4,Solution D contains 10.0g of solute in 10 000cm3 solvent.Concentration = mass of solutes (g) volume of solvent (dm3) = 10 g/10 dm3 1000 cm3 = 1 dm3 = 1.0 g/dm3 10 000 cm3 = 10dm3
Example 5,Solution D contains 5.0g of solute in 100 cm3 solvent.Concentration = mass of solutes (g) volume of solvent (dm3) = ?????
Example 6,Solution E contains 0.1g of solute in 10 cm3 solvent.Concentration = mass of solutes (g) volume of solvent (dm3) = ?????
Uses of solvents & solutions(A) HOME Water is used for cooking, drinking, & cleaning.
Water is used to dissolve detergents and many types of stains
Water is used to makedrinks and beverages.
Mineral salts and fertilizers are(B) AGRICULTURE dissolved in water so that plants can absorb them.
In hydroponics, the roots of plants are immersed in solutions containing dissolved mineral salts.
(C) MEDICINEMedicinal drugs are sometimes mixedwith sugar solutionsto make them taste better. Examples are coughmixtures and vitamin- C enriched drinks
(D) INDUSTRY Turpentine, alcohol and other types of solvents are used inthe manufacturing ofpaints, inks and dyes.
SOLUBILITY• A solvent can only dissolve a certain amount of solute.• Solubility is the maximum amount of solute in grams that will dissolve in 100g of solvent.• The solution produced is a saturated solution. Solubility = ______ g of solute /100g of solvent
THE FACTORS AFFECTING THE SOLUBILITY(1) The nature of the solvent(2) The nature of the solute(3) Temperature
(1) THE NATURE OF THE SOLVENT• The solubility of a solute is different in different solvents.• A polar (likes water) solute dissolved in polar solvent (water).• A non-polar (doesn’t like water) solute dissolved in non- polar solvent (ether or alcohol) Water Alcohol (Polar solvent) (Non-polar solvent) Salt (Polar MORE SOLUBLE LESS SOLUBLE solute)Iodine (Non- LESS SOLUBLE MORE SOLUBLEpolar solute)
Undissolved Dissolved iodineiodine in water in alcohol
(2) THE NATURE OF THE SOLUTE• Different solutes have different solubility in a given solvent. Solute Solubility at 20oC (g/100mL of water) Copper (II) sulphate 20 Potassium nitrate 30 Sodium chloride 38 ***Among the 3 solutes, sodium chloride is the most soluble in water.
(3) THE TEMPERATURE• Generally in many cases solubility increases with the rise in temperature• Decreases with the fall of temperature but it is not necessary in all cases.• Gases are more soluble in cold solvent than in hot solvent.
ACID AND BASE
acid• The word comes from Latin word ‘acidus’, which means sour.• Acid in food gives the food a sour and tangy taste.• Acids in the laboratory are harmful. Example: – Hydrochloric acid – Sulphuric acid – Nitric acid
Properties of acid (a) Acids taste sour
(b) Strong acids are corrosiveIf it comes into contact with the skin, it will burn.
(c) Acids turns the blue litmus paper into red.
(d) Dilute acids react with reactive metals to form hydrogen gas. Dilute + zinc hydrochloric Bubbles of acid hydrogen gas zinc + hydrogen chloride
To identify the gas produced: use a lighted splint. Hydrogen gas extinguished alighted splint with a “pop” sound.
(e) Dilute acids react with carbonates to produce carbon dioxide Dilute nitric + calcium acid carbonate calcium + water + carbon nitrate dioxide
Diluted acid + carbonate To identify the gas produced: pass it through some lime water (calcium hydroxide solution) A white precipitate is formed when carbon dioxide gas is bubbled into limewater.Limewater
alkali• Alkali is the chemical ‘opposite’ of acid• Alkali are often used in many household cleaners such as detergents, soap and etc• Alkalis that are commonly used in the laboratory are: – Ammonia solution – Sodium hydroxide – Potassium hydroxide
Properties of alkali (a) Alkalis have bitter taste and are soapy and slippery when touch
(b) Strong alkalis are corrosive.Strong alkali like sodium hydroxide are highly corrosive
(c) Alkalis turn the redlitmus paper into blue
indicatorsAn indicator is a dye or a mixture of dyes which changescolor according to the acidity or alkalinity of a substance.
Litmus paper The main use is to test whether the solution is acidic or alkaline. Test with acid Test with alkaliRed litmus paper No changes Red blueBlue litmus paper Blue red No changes
pH scale The pH scale is used to express acidity and alkalinity.Acidic Neutral Alkali
How to check the pH of the solution? Two ways Universal Universal indicator paper indicator solution
Results:Indicator paper Indicator solution
A pH meter is used tomeasure thepH values of substances quickly.
NEUTRALIZATION Acid + Alkali Salt + WaterAcidic Neutral Alkali
ALKALI To neutralize an acid, an alkali is used. The alkali is dripped into a conical flask containing acid and stop once the color changes from red (acidic pH) to green (neutral pH).ACID
ACID To neutralize an alkali, an acid is used. The acid is dripped into a conical flask containing alkali and stop once the color changes from dark blue (alkalic pH) to green (neutral pH).ALKALI
USAGE OF NEUTRALIZATIONAn alkali, magnesium hydroxide is used in the toothpaste to neutralize the acids produced by the bacteria in the mouth
Farmers add slaked lime (calcium hydroxide) to neutralize excess acid in the soil
A mild alkali such as sodium hydrogen carbonate is used to treat a bee sting which is acidic.