In hotter water

Science questions and answers

Q How does the addition of salt affect the boiling point of water?

A Adding salt to water raises the temperature at which it boils, which is one reason why cooks put it in water - to boil things faster. Adding salt changes the chemical composition of the water (including things like the interactions between the molecules) and this alters the boiling point. The boiling point of any pure substance is always the same, but the slightest impurity can cause a change.

Q Why don't oil and water mix?

A The difference between oil and water is essentially one of charge and attraction. Water molecules are polar and attract things. This is not true for oil molecules, which are non-polar. Therefore, for energetic reasons, it's easier for oil and water to sit apart. A lot of energy is required to mix forcibly oil and water because of the repulsion of the molecules. This energy can be provided by shaking the oil and water.

Q Why do mints make your mouth feel cool?

A You might think the minty taste and cooling sensation many mints give are the effects of peppermint flavouring, but there's more to it than that. The taste of a mint is picked up by the four types of taste buds on the tongue (sweet, bitter, salty and sour) and by smell sensors in the nose. The peppermint flavouring is like a key that opens locks in the taste buds, which allow the message "Mmm, that's so minty" to be sent to the brain.

The cooling effect of a mint isn't anything to do with the peppermint flavouring or the senses of taste and smell. Cool sensations are sent to the brain along different nerves. A drop in temperature is the key that usually opens the locks in these nerves. Opening the locks allows the message "Mmm, that's so cool" to travel to the brain. But the chemical menthol in mints also opens this coolness lock, thus fooling the brain into thinking there has been a temperature drop.

Q What is the total global energy consumption per annum?

A According to the BP Statistical Review of Energy Consumption, the world used energy equivalent to 7.8 billion tonnes of oil in 1992. This figure is probably still fairly accurate as the amount of energy used per year has been fairly level for the past few years. This is because countries such as Russia have cut down on energy use.

n These questions and answers are provided by Science Line. You can use its Dial-A-Scientist service on 0345 600444.

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