The pH scale and soil testing.

The pH scale.

The pH scale measures how acidic (or how alkaline) a substance is. Most of the substances which you handle in the lab have pH values between t and 14. A substance with pH 1 is very acidic. A substance with pH 14 is very alkaline. A substance with pH7 is neutral.

Soil testing.

When the smart family arrived at their new home, Fred looked at the garden, thought of his father, and shuddered. The garden was huge. His father was a gardening fanatic who did everything just as the book said. That meant lots of work for Fred!

Acids and alkalies.

There are very many different chemicals - so many that it’s impossible to study them all. To make things simpler, scientists Put chemicals which behave the same way into groups or sets. You Have already met the set of metals. Acids and alkalis are two More of these chemical sets.

You can find out if a substance is an acid, or an alkali, by dissolving it and adding universal indicator. The diagram shows you how to do this.

The indicator's colour changes if acid or alkali is added to it. And so, by matching the indicator colour to a colour chart. you can find out what kind of substance has been added.

Using un-reactive metals.

The two nails in the photograph look very different' The top one has been taken straight from the packet. It is still shiny. The bottom one has been in acid for a week. The acid has reacted with the iron in the nail and has started to eat it away. The nail has rusted or corroded.

A metal corrodes whenever a chemical attacks its surface. Water, air, and acid are three of the most common corroding chemicals.

How reactive are metals?

When you put a piece of magnesium into water, bubbles of hydrogen gas are produced. The bubbles appear very, very slowly. It could take about a week to collect enough hydrogen to 'pop'.

When you put a piece of magnesium into dilute hydroelectric acid, hydrogen gas bubbles off quickly.

The fuel of the future.

Hydrogen is the fuel of the future.

That's the claim made by a number of scientists. They think that hydrogen is such a good fuel that ii will one day replace all of the fuels used at present. Could the scientists be correct. Judge for yourself as you read on.

A good fuel should produce large amounts of heat when it burns. Heat energy is measured in kilo-joules’ (kJ). Burning 1g of hydrogen produces 143 k] of heat, enough to boil a large cupful of water. (Burning 1 g of petrol produces 48 kJ. Burning 1 g of natural gas produces 58 k).

A good fuel should be cheap and easy to produce. There is a very small amount of hydrogen gas in the atmosphere, but it

Cannot be easily separated from other gases.

A useful fuel.

Mixtures of hydrogen and air can explode when they are it. But if hydrogen is mixed with the correct amount of air, it burns with a hot, clean flame. a hot, Hydrogen is a very useful fuel.

Homes and factories can be heated with the help of hydrogen. For many years, British homes and factories were supplied with town gas,

containing ৫0% hydrogen. It was made at the local gas works, by heating coke (carbon) with steam.

This is hydrogen.

In this photograph, you can see a weather balloon. It's being filled with gas. Once it is filled, it will be released.

The balloon's job is to carry instruments high into the atmosphere. The instruments make measurements of the weather. Then they send the information back to Earth.

Hydrogen, metal,acids and alkali's.

Hydrogen gas, a metal and an acid all had a part to play in the successful flight of this pioneer balloon. The h

ydrogen was used to fill the balloon skin and so keep the balloon in the air. The metal and the acid were both used to make the hydrogen. It was made in A barrel by mixing iron with sulfuric acid and was fed from there along a pipe into the balloon.

The balloon was one of the earliest flying machines. It was designed and built by'a Frenchman. Jacques Charles. On 27th August, 1783. One took off from a park in the middle of Paris. Thousands of people watch the take off,

Making the most of a free gift.

In a time of energy shortage, you aren't likely to be impressed by a home which loses 99.9% of the heat supplied to it. And yet your home – the Earth-does just that. Every day, a huge quantity of heat energy, reaches the Earth from the sun. Much of this heat is absorbed, warming up the land and the sea, but then, at night, practically all of the absorbed heat is Lost again. It escapes into space as radiation while the Earth cools down.

Hot but no hotter.

It's very likely that the classroom where you are working just now is heated by part of a very large central heating system. Somewhere in the school, there wiII be a big boiler where water is heated by burners which use oil or gas. The hot water is piped to radiators in the classroom. There it gives out the heat to keep you warm.

Like every workplace, a school has to be run at a comfortable temperature. In fact, the law sets a minimum classroom temperature. Architects have to do some careful calculations when they are designing a school. They have to make sure that the boiler can supply Enough heat to keep aII the classrooms at the correct temperature even in the coldest weather. Heat energy is measured in kilojoules’:

Saving body heat.

The-most important heat to save is your body heat. If your body gets too cold' it won't work properly. Then you are said to be suffering from hypothermia.

You are unlikely to suffer from hypothermia - as long as you have shelter, enough clothes to wear (and, of course, "enough to eat). But some people like divers, mountaineers and astronauts, live and work in more extreme conditions. For them, hypothermia is a real problem. They have to wear special clothes to survive.

Two tone balloons.

How can the balloon be kept in the air? That's the problem facing every balloonist who wants to make a really long flight. Giving the balloon a two-tone, silver and black colour scheme doesn't solve the problem, but it certainly can help!

First across the Atlantic - Double Eagle II

The first balloon to cross the Atlantic (Double Eagle II) had a silver and black colour scherne. It was crewed by three Americans, Ben Abruzzo, Max Anderson, and Larry Newman. The crew, their equipment and bags of sand ballast were carried in the balloon's gondola, a small steel and fiber glass boat. The gondola and its contents were kept in the air by the balloon's envelope.

heat out,and in.

Giving heat out….

This is a heat picture called a thermogram. It was taken using a special camera which detects heat rays.

The thermogram shows someone drinking out of mug. (you can see a normal photograph of the person above) The colours on the thermogram show how much heat is being given out. Use the colour code, and the thermogram, to answer the questions.

1.   Which part of the person gives out: a) most heat.

b)least heat?

2.   Why do some parts of the person lose more heat than others?

3.   Which gives out more heat, the person’s head or arms?

4.   Is it a hot or cold drink?

Heat on the move:radiation.

When you toast bread under a grill, some heat travels downwards, from the grill to the toast.

This heat can't be carried by convection. Convection carries hot air upwards.

The heat can't have been conducted to the bread either. The air between the bread and the grill is a poor conductor.

The heat is travelling by-radiation.

Convection in nature.

The Monsoon

What can make a wind blow? Convection can. Whenever hot air rises from the Earth, cold air flows over the Earth's surface to take its place. This moving air is a wind.

The Monsoon is a wind which affects much of Asia. In summer, it is a warm, rain-carrying wind which blows from the sea to the land. In winter, it is a dry cool wind, blowing from land to sea.

Flying on hot air.

Have you ever wondered what keeps a glider in the air? Gliding does Seem to be a bit of a mystery. A glider has no engine to power it, yet it Can fly for long distances before landing. It can even climb through the Air.

The glider stays in the air, and climbs, because of air currents. At the Beginning of each flight, the glider has to be towed into the air. Once it Has been released, however, it can fly for as long as the pilot can find Rising air currents to keep it airborne.

Heat on the move: Convection.

Heat energy can travel through liquids. This must happen when you boil water in an electric kettle. The kettle's heating element only warms the water next to it, but the heat energy is carried all through the water until it boils.

Heat energy can travel through gases. This must happen when you heat a room sing an electric convector heater. The heater only warms the air inside it, but soon you can feel the warmth all through the room.

The right material for the job.

Aluminum is used for making saucepans, and it's not difficult to see Why. Aluminum:

• is a good conductor (and so let’s heat flow easily from the cooker to The food)
• has a high melting point (and so does not melt on the cooker)
• Is not much affected by chemicals or corrosion'

Aluminum is the’ right material for the job''

Trapped air.

It's hard to believe, but it's true. The man in the photograph is kept warm by the holes in his string vest! The air in the holes is what matters. When the man pulls on his shirt, it traps air in the holes in the vest. The air is an excellent insulator. It prevents his body heat from escaping and so keeps him warm.

A string vest may seem to be a rather strange piece of clothing, but, in fact, aII of your clothes keep you warm in the same way. Clothes have tiny pockets of air trapped between their fibers and so act as insulators.

Heat on the move conduction.

Conductors...

Heat can travel through solids, if you have ever tried to stir boiling soup using a metal spoon; you will know that, Heat energy quickly flows from the soup, through the spoon, to your hand.

Your fingers begin to get hot!

The movement of heat through the solid metal is called conduction.

The metal spoon conducts heat from the hot soup to your hand. The metal is called a good conductor because heat can flow easily through it.