Elementary Watson &Connections Revision

Mr. Isgro

Water as a solvent

Water as a solvent

Everyday life examples: • Drinking water rehydrates your body’s cells

that contain important chemicals that keep you alive

• Water can be used to clean/wash items that are dirty (water-soluble). Detergent can be added to water to clean substances that are insoluble in water alone.

Water as a solvent

Environmental examples: • The ocean and rivers contain

oxygen gas that enable organisms to breathe.

• Rain water can dissolve nutrients in the soil that are taken up by the roots of plants.

Water as a solvent

Industrial examples: Water is used in the manufacturing of many things such as: • paints (water-based);• food preparation;• drinks (coffee, soft drinks, etc…);• fertilizers;• liquid medicines / drips;• cleaning products (acids and bases); and so on…

Suspension

• A suspension is a heterogeneous mixture in which one substance does not dissolve in another (insoluble) and so gives an cloudy (opaque) appearance that settles over time.

Aqueous solution

An aqueous solution is a solution in which water is the solvent. • For example; salt water is an

aqueous solution because it contains a small amount of salt (solute) dissolved in a large amount of water (solvent).

A solute dissolves in a solvent to make a solution

Physical properties of matter

Solubility in different solvents:• Substances such as dried coffee, sugar and

copper sulfate are soluble in water (they are water soluble). Iodine is insoluble in water.

Physical properties of matter

Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a solution of the solute in the solvent.

EFFECT OF TEMPERATURE:

The rate at which a substance dissolves is influenced by temperature.

This can be demonstrated using a graph (solubility curves)

Physical properties of matter

Separation techniques depend on differences in the properties of substances.• Suspensions are different to solutions in that

they can be separated by filtration, sedimentation (and decanting) or centrifuge.

• Solutions can be separated by evaporation, crystallisation, distillation and chromatography.

Physical properties of matter

Particle size• Soluble substances will dissolve at a faster rate

if the particles are small. This is why coffee beans are ground up into a fine powder.

Physical properties of matter

Boiling point• Distillation depends on the boiling point of the

substances being separated. For example; ethanol (alcohol) has a boils at 80oC. This property makes it easy for ethanol vapors to be separated and collected.

Suspensions can be separated by sedimentation

Suspensions can be separated by decantation

• Decantation - a process for the separation of mixtures, by removing a layer of liquid, generally one from which a precipitate has settled. The purpose may be either to produce a clean decant, or to remove undesired liquid from the precipitate (or other layers).

Suspensions can be separated by filtration

• This is a more common method of separating an insoluble solid from a liquid. An example of such a mixture is sand and water.

• Filtration is used in water treatment plants, where water from rivers are filtered to remove solid particles.

Filtration: Drawing of Scientific Apparatus

Filtration: METHOD1. Set up the apparatus with the filter funnel

placed on the ring-clamp suspended over a beaker.

2. Filter paper is placed in a filter funnel. 3. The mixture of water and sand is poured into

the filter funnel. 4. The liquid part (filtrate) drains through the

filter paper into the beaker, leaving the solid sand particles (residue) trapped on the filter.

5. The residue can be left to dry before it is collected.

Evaporisation

• Evaporation is great for separating a mixture (solution) of a soluble solid and a solvent. The process involves heating the solution until the solvent evaporates (turns into gas) leaving behind the solid residue.

Evaporisation

Evaporisation

• To get the salt back from the salt water, the solution is heated to boiling point. As it boils, the water escapes as vapor (gas). After sometime, all the water evaporates, leaving a layer of salt at the bottom of the beaker.

Crystallisation

• Crystallisation is also a chemical solid–liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.

Distillation

• Distillation is the best method for separating a liquid from a solution. In a way, the concept is similar to evaporation, but in this case, the vapor is collected by condensation.

• For example, if you want to separate water from a salt solution, simple distillation would be great for this.

Distillation

Distillation

• A beaker of the salt solution is heated to the boiling point of the liquid. As it boils, the liquid turns into vapor (gas). The vapor is directed through tubes (condenser) connected to another beaker. As the vapor goes through the tube, it is cooled down by running cold water round the tubes. This forces the temperature of the vapor to fall, causing the gas to turn into liquidagain (condensation). The liquid is pure at this point, as it is free from salt. The process continues until all the liquid in the solution turns into vapor, leaving the saltresidue. The distilled liquid is called a ‘Distillate’

Chromatography

• This method is often used in the food industry. It is used to identify chemicals (coloring agents) in foods or inks. For example, if a scientist wants to know how many substances are in a particular blob of ink, paper chromatography can be used.

Chromatography

Chromatography

• Because different chemicals have different rates of attractions to the solvent, the chemicals will travel upwards in different amounts. Sometimes, a chemical may not react at all. If a different solvent is used, all the various chemicals may travel at a completely different rate.

Magnetism

Magnetism is ideal for separating mixtures of two solids with one part having magnetic properties. Some metals like iron, nickel and cobalt have magnetic properties whiles gold, silver and aluminum do not. Magnetic elements are attracted to a magnet.

Magnetism

Magnetism

• To separate this, spread out the mixture on a flat surface. Run a magnet bar over the surface.

• You will notice that the magnetic elements (iron filings) will be attracted to the magnet over it.

• After a number of runs, all the sand will be free from any iron filing.

CONNECTIONS

Classification

Why objects are classified into groups:• To make it easier to identify objects • To make it easier to communicate

Living or non-living?Mrs Gren - The 7 things all living animals do/have:

M – movement R – reproduction S – sensitivity

G – growthR – respirationE – excretionN – nutrition

Cells

• Living things are composed of basic units called cells.

Unicellular or Multicellular?• Organisms can be classified as either

unicellular (single cell) or multicellular (composed of many cells).

Unicellular (e.g. bacteria)

Multicellular (e.g. human)

Unicellular (single cell)BACTERIA

PROTISTS

Multicellular (many cells)

Animals

Plants

Fungi (excluding yeasts)

The 5 kingdoms

Living things are classified into 5 kingdoms• Animals• Plants• Fungi (fungus)• Monera (bacteria)• Protista (molds and sea weeds)

Levels of classification (taxon)

• A taxonomist is a scientist who classifies organisms. Organisms are grouped into different groups (called taxon) according to their features.

Taxon

More specific

Example of animals belonging to the same Order:

Mnemonic to help you memorise the order:

Species• All different types of living things are called

species.

Adaptations• An adaptation is a feature of an organism that

improves its chance of survival (e.g. beaks, long legs, webbed feet, digestive systems, thin leaves, thick bark, etc…).

Adaptations

Bilby (Macrotis lagotis)

• Powerful forelimbs and strong claws for digging.

• Their vision is poor, but their sense of smell and hearing are acute.

• They rarely need to drink.

http://www.alicespringsdesertpark.com.au/kids/plants/index.shtml

Spinifex (Triodia species)

• Spinifex thrives on the poorest, most arid soils • Spinifex roots go down a long way: 3 metres. • The spiky leaves contain a lot of silica which

makes them stiff and rigid.• Spinifex is tough and indigestible to most

animals except termites. These tiny grazers thrive on the Spinifex litter.

http://www.alicespringsdesertpark.com.au/kids/plants/index.shtml

ATTENTION!!!

• Please remember to practice past common tests and attempt the graphing section.