Test yourself - At School

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In which language do deaf people think?

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Phrasal Verbs: Take

Everyday Chemistry - All about natural mosquito repellents

Wonder why mosquitoes always attack you and not your friend wearing fewer clothes? Mosquitoes have complex methods of detecting hosts. Different types of mosquitoes react to different stimuli and you can avoid being bitten by making sure that you are not attracting them. Here is all that you need to know about mosquitoes and how to avoid them next time!

1. Dark Clothing - Most mosquitoes use vision to locate their hosts from a distance. Dark clothes and foliage are initial attractants for the mosquitoes.
2. Carbon Dioxide - Mosquitoes generally get attracted to people who discharge more CO2. So if you have been exercising and perspiring a lot, watch out for them!
3. Lactic Acid - If you exercise, eat foods that are salty or high in potassium, you are more likely to attract mosquitoes.
4. Floral or Fruity Fragrances - Do you use perfumes, hair products or anything else that emits strong floral fragrance? Be careful! Mosquitoes get attracted to such fragrances.
5. Skin Temperature and Moisture - Mosquitoes are drawn to people with slightly cooler temperatures and also to perspiration. Even moist plants or mud puddles are enough to attract them.

Hate the pungent smell of mosquito repellents available in stores? Here are some easy suggestions to make your own natural mosquito repellent. But remember that you will be required to apply these natural repellents at least every two hours. Here are some of the oils that you can mix to prepare a natural mosquito repellent: Lemon Eucalyptus Oil, Cinnamon Oil, Castor Oil, Rosemary Oil, Lemongrass Oil, Peppermint Oil, Clove Oil.

However, you need to remember that 'natural' does not automatically imply 'safe'. Many people may be sensitive to plant oils so make sure you test on a small area of skin before you use them.

CAN you now answer the questions:

What makes you so attractive to mosquito?

Can you make your own natural repellent?

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Prasal Verbs: Make

Everyday Chemistry - Why does snow look white?

One of the reasons why we love snow is that it's clean, pure and white. Snow wouldn't be snow if it wasn't white. But if you think about it, it seems weird that snow is white at all, since it's just a bunch of transparent ice crystals stuck together. So where does it get its color?

To understand where the whiteness comes from, we need to back up and look at why different things have different colors in the first place. Objects have different colours because they absorb different frequencies of light than others. A couple of different things can happen to the light frequencies that are not absorbed. The color of an opaque object is simply the combination of the light energies that the object's particles did not absorb.

Now, snow is frozen water, and we all know that frozen water is clear, then why does snow have a distinctive color? To understand this, we need to back up and look at an individual piece of ice. Ice is not transparent; it's actually translucent. This means that the light doesn't pass right through the material in a direct path - the material's particles change the light's direction. This happens because light particles (called photons) interact with the molecules of ice. The result is that the light photon's path is altered and it exits the ice in a different direction than it entered the ice.

When a light photon enters a layer of snow, it goes through an ice crystal on the top, which changes its direction slightly and sends it on to a new ice crystal, which does the same thing. The "color" of all the frequencies in the visible spectrum combined in equal measure is white. So this is the color we see in snow. So even though individual ice crystals are clear, their combined form - which is snow - bounces off light frequency in such a way that the final result, as we see it is "white snow".

CAN you now answer the questions:

What causes snow colour?

Is ice transparent?

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Phrasal verbs: Get

Fruity Facts - About carboxylic acid

Do you remember the amazing refreshing feeling of a glass of lemonade on a hot summer's day? You may have noticed the sharp sour taste of the lemonade. This tartness is a result of carboxylic acids. This is an organic acid that is found in a variety of fruits including grapes, lemons and vinegar.

Carboxylic acid is a form of organic acid. You can identify these acids by their structure. They all contain one carbon atom, one oxygen atom and one hydroxyl group. The combination of one carbon, one oxygen and hydroxyl group (COOH )is called a carboxyl group. It is because of this that acids derived from them are called carboxylic acids.

The combination of one carbon, one oxygen and hydroxyl group (COOH )is called a carboxyl group. Carboxylic acids are widely found in nature. You can find them as free acids like citric acid, tannic acid and malic acid. Esters the products of acids and alcohols also contain carboxylic acids. These include fats and oils, flavours of fruits and odours of flowers. Some bacteria can also cause natural reactions in which these acids are formed. Some examples include acetic acid from wine or cider, lactic acid found in sour milk and the butyric acid in rancid butter.

CAN you now answer the questions:

What is a carboxylic acid?

Where do you find carboxylic acids?

Everyday Chemistry - Why do onions make us cry?

The mere thought of chopping onions can literally make you cry. But the moment your knife touches the onion, your eyes start burning and you have tears in your eyes. Here’s why it happens...

Onions contain amino acid sulfoxides that form sulfenic acids in the onion cells. Both the enzymes and the sulfenic acids are kept separately in the cells. When you cut the onion, the otherwise separate enzymes start mixing and produce propanethiol S-oxide, which is a volatile sulphur compound that starts wafting towards your eyes. The gas that is emitted reacts with the water of your eyes and forms sulphuric acid. The sulphuric acid thus produced causes burning sensation in your eyes and this in turn leads to the tear glands secreting tears. Thus you end up with watery eyes every time you cut onions at home.

It is the sulphur compound in the onions that also leave a typical odour of onions on your hands and utensils even after washing.

Tips to avoid the tears:

• Make sure that you keep your fans off while cutting onions. If it is running, the air is on constant circulation, which will lead to the spread of gas and increase the burning sensation in your eyes.
• Refrigerate the onion before cutting. By refrigerating, you freeze the enzymes from mixing with the sulfenic acids and the production of propanethiol S-oxide is stopped. As a result, sulphuric acid is not formed when you chop the onions.
• Cooking the onion inactivates the enzyme. So cook the onion after you de-skin and before letting the knife touch the onion. Soak onions in water before cutting. Water absorbs the gas.

CAN you now answer the questions:

What do onions contain?

How can you avoid the tears?

Why do onions make us cry?

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Phrasal verbs: Go

For the third-year students

Communicative cliche

Why is chocolate bad for animals?

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Everyday Chemistry - Why do we smell when we sweat?

Sweating can be quite annoying especially since it tends to leave a big wet patch either on your back or under your arms. It makes it especially worse when your sweat tends to smell really foul. Although the bad news is that there is no way to prevent it, the good news is that you can at least tackle it.

Sweating or perspiration is our body's natural way of cooling us down. We may feel the heat more when we sweat but the truth is that the body is cooling itself by releasing all the built in heat. Our body needs to maintain a normal temperature of 98.6 Fahrenheit failing which we are likely to suffer a heart stroke. Sweat is released through small holes known as pores in our skin. When sweat comes in contact with the atmosphere, it evaporates leaving a cool feeling behind. Sweat is almost made of water with small amounts of chemicals like ammonia, urea, sugar and body salts like sodium. Our body has approximately two million tiny sweat glands.

We have two types of sweat glands in our body; eccrine and aprocine glands. Eccrine glands are the common ones and are located in our palms, forehead and soles of our feet. Aprocine glands are found in our armpits and the end of our hair follicles. There is a difference in the type of sweat released by both these glands. Eccrine releases sweat that is more of water and thin in nature. Aprocine releases thicker sweat that has a yellow colour to it because of the presence of fatty acids and proteins.

You start stinking only when the bacteria that live on your skin start mixing with the sweat. Also, when you reach puberty, certain hormones in our body affect the sweat glands especially those in the armpits and lead to an odour. You can keep the stinky smell under control by regular washing of your body with a mild soap. Many people also believe that using deodorant helps.

CAN you now answer the questions:

Why do we sweat?

Why does it smell?

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Phrasal verbs: Come