F2C6 Air Pressure

Air Pressure
1) According to the kinetic theory of gases, gases are made up of tiny particles called particles, and they move about randomly at high speed.
2) In an enclosed container, the air particles will collide with one another and with the wall of the container. The force they exert on the wall is air pressure.
3) When air is compressed, the particles collide more frequently, so the air pressure also increases.
4) The atmosphere around us consists of air that exerts pressure on everything on Earth. This is known as atmospheric pressure.
5) Air pressure is lower at high altitudes because air is thinner.

Factors Affecting Air Pressure

1. Space of enclosed container:

When space of enclosed container increases, the air pressure will decrease. This is because there will be more space for the air particles to move around. So the air particles will collide less frequently with the walls of the container.
When space of enclosed container decreases, the air pressure will increase. This is because there will be less space for the air particles to move around. So the air particles will collide more frequently with the walls of the container.

     2.  Temperature of air in an enclosed container:

When the temperature increases, the air pressure will increase. This is because the air particles will move faster and collide more frequently with the walls of the container.
When the temperature decrease, the air pressure will decrease. This is because the air particles will move slower and collide less frequently with the walls of the container.


Always remember that air from a place with higher air pressure will always go to a place with lower air pressure.

There is not much in this chapter that I can explain, you just have to know the applications of air pressure. You should read your textbook to find out more.

F2C5 Part 2: Acid and Alkali and everything after that

Acids and Alkalis
Acids and alkalis are solutions, and both are corrosive and only show their properties when dissolved in water, or when they are moist/wet.

To test whether a substance is acidic or alkaline, litmus papers or universal indactors are used

Properties of acid

• Has a sour taste
• pH value LESS than 7
• Turn blue litmus paper into RED
• Acid reacts with reactive metals like magnesium to produce hydrogen
• Acid reacts with carbonates to produce salt, carbon dioxides, and water.

Properties of alkali

• Has a bitter taste and a soapy feel
• pH value MORE than 7
• Turn red litmus paper into BLUE
• Alkali reacts with ammonium salts to release ammonia gas when heated

When a universal indicator has not been tested with acidic/alkaline substance or if it is tested with a neutral substance it will be green. The chart below shows the colour of the universal indicator if tested.

Above chart is the pH chart, pH0-6 are acidic,pH7 is neutral and pH8-14 is alkaline

Neutralisation

Neutralisation is the process where an acid reacts with an alkali to form salt and water.

The salt solution produced is neutral and has a pH of 7

The GENERAL word equation for neutralisation reaction is:

Acid + Alkali -> Salt + Water

The name of the salt produced depends on the type of acid and alkali used, examples are

Sodium hydroxide(Alkali) + Hydrochloric acid(Acid)  -> Sodium chloride + Water

Potassium hydroxide + Sulphuric acid -> Potassium sulphate + Water

Calcium hydroxide + Nitric acid -> Calcium nitrate + Water

Titration is used to completely neutralise an acid and an alkali. 

In this method a correct volume of an acid will be added drip by drip to neutralise a volume of alkali by using a burette. The conical flask will then be shook to mix the acid and alkali evenly.

Applications of Neutralisation in Daily Life

• Vinegar(a weak acid) is used to neutralise alkaline wasp stings.
• Bicarbonate powder (a weak alkali) is used to neutralise acidic bee stings.
• Slaked lime is added to acidic soil to reduce the acidity.

Water Purification

Natural water contains impurities such as microorganisms, dissolved substances, suspended substances, decomposed substances, and silt. Water can be treated in the following ways so it can be safe to be used:

1. Boiling
2. Chlronation
3. Filtration
4. Distillation

BOILING

Boiling kills most of the microorganisms but does not remove suspended and dissolved particles and substances

CHLORINATION

Adding chlorine to water kills microorganisms but cannot remove dissolved substances. Too much chlorine in water is harmful to health too.

FILTRATION

This method removes suspended solid particles but does not remove miccroorganisms and dissolved substances.

DISTILLATION

Distilled water is pure water and is free from microorganisms, suspended particles and dissolved substances.

Water Supply System

1. River water is pumped into reservoirs, mud and other suspended substances sink to the bottom.
2. Water then moves through a metal screen that screens out large solid particles.
3. Water is then pumped into the areation system to dissolve oxygen in the water and remove unpleasant smell.
4. Water is then pumped into the coagulation tank. Alum is added to make fine solid particles stick together to form large lumps. Slaked lime is added to reduce acidity of water
5. The water then flows slowly into the sedimentation tank. The large lumps of solid particles sink to the bottom.
6. The water then flows into the filter tank where the remaining particles are filtered.
7. In the Chlorination and fluoridation tank(replace this with disinfection in the pic, sorry), chlorine is added to kill remaining bacteria. Fluoride salt is added to prevent tooth decay
8. Treated water is distributed to homes.

MUST REMEMBER THIS, MOST IMPORTANT:Coagulation-->Sedimentation-->Filtration-->Chlorination

If there are any question please leave a comment or say something at the shoutbox on the right side of this place. If you find any mistakes please do inform me because most of the information are made by my memory.

F2C5 Water and Solution (pt1)

Hello, this time I am just focusing on the main points so I can finish faster and you can learn only the important things.

PHYSICAL CHARACTERISTICS OF WATER:
Water exists in three forms:

SOLID as in ICE

LIQUID as in WATER

GAS as in STEAM/WATER VAPOUR

1. Freezing point of water is 0°C
2. Boiling point of water is 100°C
3. Ice is less dense than water, so it floats on water. 
4. Water is a poor heat and poor electrical conductor. 

Impurities of water

1. Salt water and sea water has a HIGHER BOILING point and a LOWER FREEZING point.
2. Impurities of water increase the density of water. For example, sea water contains salt so people can float easier in sea water compared to pure water.

Compostion of water

Water is a COMPOUND (made up of two HYDROGEN atoms at the CATHODE(-) and one OXYGEN atom at the ANODE(+) )

Evaporation of water

Water evaporates at any temperature below 100°C. Factors that affects the rate of evaporation:

Humidity of air-The higher the humidity(that is the amount of water vapour in the air), the lower the rate of evaporation

Temperature of surroundings-The higher the tempature, the higher the rate of evaporation.

Surface area of water-The larger the surface area, the higher the rate of evaporation.

Air movement-When there is moving air(i.e wind), the rate of evaporation will be higher.

Solution and Solubility


The SOLUTE is the substance you dissolve in the SOLVENT to get a SOLUTION.
Example:
Solute-         Salt                
                      +
Solvent-     Water
                      =
Solution-Salt solution


All solutions are homogeneous, that is the solution will appear uniform(same) in color.
Mixing sand into the water does not make a solution because the salt does not dissolve and you can still see the sand.


Dilute, Concentrated, and Saturated Solutions.
There are three types of solutions with differences,
Dilute solutions-contains a small amount of solute, thus can dissolve a lot more.
Concentrated solutions-contains more solute than dilute solutions, thus can still dissolve a little more.
Saturated solutions-contains the maximum amount of solute, thus cannot dissolve anymore.

Solutions and Suspensions
Ill use two examples to explain solutions and suspensions and will compare two of them to show the differences:
For solutions I will use salt solution and for suspensions I will use sand and water:

This is the salt solution                                                                                         This is your sand and water.


1. Solution is a mixture which the solute dissolves in the solvent whereas a suspension is a mixture in which particles are suspended in a liquid or gas. PROOF: The salt dissolved in the water so you can't see it, the sand is suspended in the water so it is not dissolved so you can see it.


2.A solution contains dissolved substances but a suspension contains insoluble(cannot dissolve) substances. PROOF: The salt has dissolved in the water but the sand have not and cannot dissolve in the water.


3. A solutiion is transparent and clear, allows light to pass through, a suspension is opaque and cloudy and does not allow much light to pass through, in the sand solution although its not cloudy, but the sand is opaque. PROOF: obviously you can see the differences in the pictures above.


4. A solution is homogeneous or uniform(meaning it appears in the same colour) and a suspension is non-homogeneous/heterogeneous(meaning you can see the difference of colour). PROOF: In the salt solution you can only see clear water whereas you can see sand and water clearly seperated.


5. The size of particles in a solution is small and well dispersed(scattered) meaning there is space between the particles and the particles in a suspension is large and not well dispersed, meaning there is few space between the particles and are arranged closely.


6. When left to stand, no sediment is seen in the solution, but solid particles(i.e sand in the example) will settle to the bottom or float at the surface in a suspension.


7. When a solution is filtered, no residue is left on the filter paper; when a suspension is filtered residue is left on the filter paper.


Rate of Dissolving
Factors that affect rate of dissolving:
-Size of the solute particles, the smaller the size of the solute particles, the faster the solute dissolves in the solvent(e.g fine sugar dissolves faster in water compared to sugar cubes)
-Rate of stirring the solvent-the faster the rate of stirring, the faster the solute dissolves in the solvent
-Temperature of the solvent-The higher the temperature of the solvent, the faster the solute dissolves in the solvent.


Last but not least in this part, WATER is the UNIVERSAL SOLVENT

F2C1 The World Through Our Senses (part 1)

Sensory organs -- detect stimuli
Stimuli -- changes in the environment that cause our body to react

We have five sensory organs
1. Skin responds to TOUCH
2. Nose responds to SMELL ( also helps in tasting)
3. Tongue responds to TASTE
4. Ears respond to SOUND
5. Eyes respond to LIGHT


The Pathway from detecting a stimulus to producing a response in human beings


STIMULUS--->RECEPTORS(located in sensory organs)--->nerve impulses--->NERVES--->nerve impulses--->BRAIN--->nerve impulses--->NERVES--->nerve impulses--->EFFECTORS(muscles and glands)--->RESPONSE


THE SENSE OF TOUCH
1 Skin detects touch
2 The receptors in the skin are pain receptors, touch receptors, heat receptors, cold receptors, and pressure receptors.

PAIN receptors located at the top to detect the slightest pain.(e.g somebody pinching your face)


TOUCH receptors detects light touches and identifies textures of an object. (e.g touching)

HEAT receptors detects increase in temperature(e.g touching hot stuff)

COLD receptors detects decrease in temperature(e.g touching ice)

PRESSURE receptors detects any forceful pressure against the skin(e.g carrying a heavy object)


Sensitivity of the Skin
1 The skin on different parts of the body has different degrees of sensitivity.
2 The higher the number of receptors, the higher the sensitivity.
3 The thicker the epidermis, the lower the sensitivity.
4 Lips, the neck, the fingertips has high sensitivity
5 Legs, the elbows, the soles of the feet, the back of the body has low sensitivity

THE SENSE OF SMELL
1 The nose detects smell.
2 The nostrils open into a hollow space( the nasal cavity)
3 The nasal cavity is lined with mucus, mucus warms and moistens the air before it enters the lungs.
4 Hairs in the nostrils filter out dust and dirt so that clean air enters the lungs.
5 The roof of the nasal cavity has sensory cells/smell receptors to detect smell.
6 When a person has a cold, he/she cannot detect smells well because too much mucus is being produced and the mucus prevents the chemicals from simulating the smell receptors.


Detection of Smells
1 Chemicals(e.g in food, flowers, poop) present in inhaled air
2 Chemical particles enter the nasal cavity
3 Chemicals dissolves in mucus lining
4 Smell receptors are simulated and send out nerve impulses to the brain.
5 Brain identifies the smell.


THE SENSE OF TASTE
1 The tongue detects taste.
2 The tongue is covered with taste buds and taste buds contains many taste receptors.
3 The chemicals(e.g in food) must dissolve in saliva before they can be stimulated by the taste receptors
4 Different receptors are located at different parts of the tongue.

Areas of the tongue that are sensitive to taste

Detection of Taste

1 When we chew food, chemicals in food dissolves in the saliva

2 Dissolved chemicals stimulate taste receptors to produce nerve impulses

3 Nerve impulses travels to the brain

4 Brain identifies the taste.

Sense of Taste and Smell

The nasal and mouth cavities are connected. Chemicals from the food stimulates the taste receptors and also the smell receptors. This means that taste and smell are detected at the same time so that we can identify the flavours of food. When we have cold, smell cannot be detected by the smell receptors so we cannot detect the flavour of the food so the food becomes tasteless.

THE SENSE OF HEARING

1 The ear detects sound.

Structure of the ear

1. The pinna collects and directs sound waves into the ear canal(a.k.a auditory canal)
2. Ear canal directs sound waves to the ear drum(a.k.a tympanic membrane)
3. Ear drum vibrates and transfer vibrations to the ossicles
4. Ossicles[made up of Malleus(Hammer), Incus(Anvil), Stapes(Stirrup)] amplify the vibraions and transfer them to the oval window(before the cochlea)
5. Oval window transfers the vibrations to the inner ear. Vibrations cause the fluid in the cochlea to vibrate.
6. Vibration of the fluid stimulates the receptors in the cochlea. Nerve impulses are generated
7. Auditory nerves sends the nerve impulses to the brain which then will interpret the impulses as sounds.

Semicircular canals and Eustachian tube are part of the ear but NOT part of the hearing mechanism

Semicircular canals help the body maintain its balance.

Eustachian tube helps balance the air pressure on both sides of the eardrum.

THE SENSE OF SIGHT

1 The eyes detect light to allow us to see

2 The wall of the eyeball is made up of three layers:

1. Sclera (outer layer, that is the white part you see in your eye)
2. Choroid (middle layer, your iris is part of your choroid)
3. Retina (inner layer, has many photoreceptors called cones and rods that are sensitive to light)

Structure of the eye

1. Conjuctiva is a thin and transparent membrane that protects the cornea
2. Ciliary body contracts and relaxes to change thickness of lens. This changes the focal length of lens
3. Cornea is a curved, transparent layer and is a continuation of the sclera
4. Iris controls the size of the pupil and the amount of light that enters the eye
5. Pupil allows light to pass into the eye
6. Lens bend and focuses light to form images on the retina. The thickness of lens can be change to focus near and distant objects. ( When focusing on a near object, lens thickens, when focusing on a distant object lens become thinner.)
7. Aqueous humour helps to refract light and maintain the shape of the eyeball
8. Vitreous humour helps to refract light and maintain the shape of the eyeball
9. Suspensory ligaments hold the lens in place and is connected with the ciliary body.
10. Retina detects light stimuli and sends nerve impulses to the brain
11. Choroid supply nutrients and oxygen to the eye, the choroid has black pigments that absorb light and prevent internal reflection of light.
12. Sclera protects and shapes the eye.
13. Yellow spot (fovea) is the part most sensitive to light
14. Optic nerve sends nerve impulses to the brain
15. Blind spot is the point where optic nerve leaves the eyeball, thus there is no receptor cells, hence, cannot detect light.

Detection of Light
1 Light rays travel from an object and enter the eye through the pupil
2 The light is refracted by the cornea, aqueous humour, eye lens, vitreous humour
3 An inverted smaller image of the real object is formed on the retina
4 The image stimulates the photoreceptors and nerve impulses are sent to the brain. The brain then interprets the inverted image and converts it to an upright image

If there are any questions, please leave a comment or say something at the shout box on the right side of this page.

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