WHY IS GRIT SALT (SODIUM CHLORIDE AND SAND) OFTEN SPREAD ON ROADS IN WINTER?
The salt (sodium chloride) lowers the freezing point of water, preventing ice from forming.
SOME INDIGESTION TABLETS REACT WITH WATER TO MAKE BUBBLES OF GAS. WHY IS THIS FIZZING MORE VIGOROUS IF YOU CRUSH THE TABLET UP FIRST?
Bubbles form more quickly because the rate (speed) of reaction is increased. This is because reactions occur at the surface of solids, and by crushing the tablet you increase the surface area, allowing the reaction to take place more quickly.
WHEN AN APPLE IS CUT IN HALF AND LEFT EXPOSED TO THE AIR, IT WILL TURN BROWN. THIS IS DUE TO THE ACTION OF AN ENZYME IN THE APPLE. THE BROWNING CAN BE PREVENTED BY PLACING THE APPLE PIECES IN LEMON JUICE. EXPLAIN WHY.
Enzymes are sensitive to acidity. Lemon juice is acidic and prevents the enzyme from working. This causes the browning reaction to stop.
HAND-WARMERS ARE SACHETS CONTAINING CHEMICALS THAT CAN BE USED IN COLD WEATHER. HAND-WARMERS WORK BY AN EXOTHERMIC REACTION. WHAT IS MEANT BY AN EXOTHERMIC REACTION?
An exothermic reaction is a chemical reaction that produces heat.
AIRSHIPS WERE ONCE FILLED WITH HYDROGEN BUT NOW HELIUM IS USED INSTEAD. WHY IS THE NOBLE GAS HELIUM MORE SUITABLE THAN HYDROGEN?
Hydrogen reacts explosively with oxygen in the air, if a spark is provided. Helium, being a noble gas, is very unreactive and so it is much safer to use.
BEE STINGS ARE ACID. WHY IS IT POSSIBLE TO SOOTHE A BEE STING WITH BAKING SODA (SODIUM BICARBONATE)?
Sodium bicarbonate is a mild alkali. It reacts with the acid in the sting, neutralising it.
ACID RAIN CAUSES BUILDINGS MADE OF LIMESTONE TO WEAR AWAY. WHICH GASES ARE RESPONSIBLE FOR INCREASING THE ACIDITY OF RAINWATER?
Sulphur dioxide and nitrogen oxides.
PLASTIC WASTE IS NON-BIODEGRADABLE: IT IS BETTER TO RECYCLE PLASTIC WASTE THAN TO PLACE IT IN LANDFILL. WHAT IS MEANT BY NON-BIODEGRADABLE?
Non-biodegradable describes a material that will not be broken down easily by micro-organisms. This means that plastics placed in landfill will remain there for hundreds of years.
SOURCE: ROYAL SOCIETY OF CHEMISTRY
HOW DO HUMAN BODIES RESPOND TO CHANGES INSIDE THEM AND TO THEIR ENVIRONMENT?
The nervous system and hormones enable us to respond to external changes. They also help us to control conditions inside our bodies. The menstrual cycle is controlled by hormones.
WHICH HUMAN CHARACTERISTICS SHOW A SIMPLE PATTERN OF INHERITANCE?
What sex human beings are and whether or not they inherit certain diseases show a very simple pattern of inheritance. Some disorders are inherited - such as Huntington's disease, a disorder of the nervous system, and cystic fibrosis, a disorder of cell membranes which must be inherited from both parents.
HOW DOES EXERCISE AFFECT THE EXCHANGES TAKING PLACE WITHIN THE BODY?
During exercise, a number of changes take place. The heart rate increases, the rate and depth of breathing increases and the arteries supplying the muscles dilate. These changes increase the blood flow to the muscles and so increase the supply of sugar and oxygen and increase the rate of removal of carbon dioxide.
WHY ARE INDIVIDUALS OF THE SAME SPECIES DIFFERENT FROM EACH OTHER?
These differences are due partly to the information in the cells they have inherited from their parents and partly to the different environments in which the individuals live and grow. Animals may be adapted to cope with specific dangers in their environment, such as poisons and predators.
WHAT NEW METHODS DO WE HAVE FOR PRODUCING PLANTS AND ANIMALS WITH THE CHARACTERISTICS WE PREFER?
Non-sexual reproduction - cloning - can be used to produce individuals who are identical to their parents. Scientists can now add, remove or change genes to produce the result they want.
WHAT ARE SOME OF THE NEW CLONING TECHNIQUES NOW AVAILABLE?
Modern cloning techniques include - tissue culture (using small groups of cells from part of a plant) and embryo transplants (splitting apart cells from a developing animal embryo before they become specialised, then transplanting the identical embryos into host mothers.
WHY HAVE SOME SPECIES OF PLANTS AND ANIMALS DIED OUT? HOW DO NEW SPECIES AND PLANTS AND ANIMALS DEVELOP?
Changes in the environment of plants and animals may cause them to die out. Particular genes or accidental changes in the genes of plants or animals may give them characteristics which enable them to survive better.
WHAT HAPPENS TO THE WASTE MATERIAL PRODUCED BY PLANTS AND ANIMALS?
Many trees shed their leaves each year and most animals produce droppings at least once a day. All plants and animals also eventually die. Microbes play an important part in decomposing this material so that it can be used again by plants. The same material is recycled over and over.
SOURCE: ASSESSMENT AND QUALIFICATIONS ALLIANCE EXAM BOARD
HOW WAS THE UNIVERSE MADE?
Current evidence suggests that the universe is expanding, and that matter and space expanded violently and rapidly from a very small initial point, ie, The universe began with a big bang. The age of the universe has been estimated at 13.8 billion years.
HOW MANY PLANETS ARE THERE IN THE SOLAR SYSTEM?
Currently there are nine planets circling the Sun - but that could soon change to either eight or ten. Astronomers are meeting in Prague this week for a furious debate about what constitutes a "planet". The controversy was sparked after the discovery of an object bigger than the "ninth" planet, Pluto.
C P SNOW ONCE REMARKED THAT A PERSON WHO COULD NOT DESCRIBE THE SECOND LAW OF THERMODYNAMICS WAS AS CULTURALLY ILLITERATE AS ONE WHO HAD NEVER READ A WORK OF SHAKESPEARE. WHAT IS IT?
The second law of thermodynamics states that the entropy - or disorder - of a closed system always increases. It is one of the most important principles of physics.
WHAT IS NEWTON'S SECOND LAW OF MOTION, AND HOW CAN IT EXPLAIN WHY BULL BARS ON CARS CAN BE DANGEROUS?
The law states that the rate of change of the momentum of a body is directly proportional to the net force acting on it, and the direction of the change in momentum takes place in the direction of the net force. Bull bars on cars can be dangerous because they don't crumple on impact. The shorter the time of the impact, the bigger the force. In a collision even a small amount of give in a bumper will increase the time of the impact and reduce the force.
WHAT IS SOUND?
Sounds are mechanical vibrations that can be detected by the human ear. This means they are in the frequency range 20-20,000Hz.
WHY DO WE HAVE LEAP YEARS?
While we generally say a year has 365 days, it actually takes 365.2422 days for the Earth to orbit around the sun. Over time, that extra quarter day would add up, and every four years our calendar would fall behind one day. Thus, the "leap day" aims to get the calendar back on track. But there is still the matter of those .0078 days - accounted for by skipping the Leap Day every 100 years, on the "00" years.
WHY ARE PEOPLE WORRIED ABOUT MOBILE PHONES?
Mobile phones use microwaves . These waves do not cause cell damage through ionisation (like gamma rays, X-rays and ultra-violet radiation). However, they can warm things up. So putting a mobile right next to your head will heat up your brain by a small amount (up to about 0.1 degree C). Currently, this is thought to be safe (your body temperature fluctuates by more than this amount through exercise). But some people have expressed concern about prolonged use of mobile phones.
HOW DOES GRAVITY WORK?
Gravity is a force which acts on everything. Newton's law of universal gravitation says:
Each particle of matter attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
HOW ARE RAINBOWS MADE?
Sunlight contains all the colours of the rainbow. A rainbow is caused by sunlight bending when it enters and leaves raindrops. We call this bending "refraction". Light waves of different frequencies (colours) bend by different amounts. When refraction occurs, the light is split up into its constituent colours, so we see the colours of the rainbow.
IDENTIFY THE LIVE, NEUTRAL AND EARTH WIRES ON A CORRECTLY WIRED PLUG.
Live wire: brown
Neutral wire: blue
Earth: green and yellow stripesReuse content