Aim: To show that air contains oxygen.
Procedure:
1. Stick a candle on the base of the basin using some plasticine.
2. Pour some water into the basin.
3. Light the candle and cover it with a glass jar.
Observation:
After some time, the flame goes out and the water rises to about a fifth of the jar.
Conclusion:
Air contains oxygen
Explanation:
Burning requires oxygen. When oxygen is used up in the glass jar, water rushes in to take the space left by the oxygen, which is about one fifth of the air. The water cannot fill the jar completely because the rest of the air contains mainly nitrogen which occupies the space in the jar.
Thursday, 23 September 2010
Independent Experiment 3
Aim: To show that when compounds combine together chemically, new compounds are formed.
Procedure:
1. Stick two candles on two separate plates using plasticine.
2. Add one teaspoon of baking soda to a glass of vinegar.
3. When bubbles form in the glass, hold a cardboard tube near the flame of one of the candles without touching it.
Observation:
The flame goes out when the cardboard tube is brought near the candle although the other candle continues to burn.
Conclusion:
A new compound, carbon dioxide, is formed.
Explanation:
The bubbles of gas produced are carbon dioxide. When this gas is directed towards the flame, oxygen is being 'pushed away' and it causes the flame to go out. The other candle serves as a control to show that it will continue to burn as it has an uninterrupted supply of oxygen. This is an example of how fire extinguishers work. In this reaction, when baking soda is added to vinegar they react to produce carbon dioxide.
Procedure:
1. Stick two candles on two separate plates using plasticine.
2. Add one teaspoon of baking soda to a glass of vinegar.
3. When bubbles form in the glass, hold a cardboard tube near the flame of one of the candles without touching it.
Observation:
The flame goes out when the cardboard tube is brought near the candle although the other candle continues to burn.
Conclusion:
A new compound, carbon dioxide, is formed.
Explanation:
The bubbles of gas produced are carbon dioxide. When this gas is directed towards the flame, oxygen is being 'pushed away' and it causes the flame to go out. The other candle serves as a control to show that it will continue to burn as it has an uninterrupted supply of oxygen. This is an example of how fire extinguishers work. In this reaction, when baking soda is added to vinegar they react to produce carbon dioxide.
Independent Experiment 2
Aim: To show that a compound can be formed by combining two elements chemically.
Procedure:
Take a strip of magnesium and heat it
Observation:
Magnesium burns brightly, and leaves a white ash as the end product.
Conclusion:
A compound is formed when things are burned
Explanation:
When magnesium burns in the air, it combines with oxygen to form a white ash called magnesium oxide. Magnesium oxide has properties that are different from magnesium and oxygen. Therefore, magnesium + oxygen --> magnesium oxide
Procedure:
Take a strip of magnesium and heat it
Observation:
Magnesium burns brightly, and leaves a white ash as the end product.
Conclusion:
A compound is formed when things are burned
Explanation:
When magnesium burns in the air, it combines with oxygen to form a white ash called magnesium oxide. Magnesium oxide has properties that are different from magnesium and oxygen. Therefore, magnesium + oxygen --> magnesium oxide
Independent Experiment 1
Aim: To show that a compound can be broken down into simpler substances by heating.
Procedure:
1. Put some mercury oxide in a boiling tube
2. Insert a stopper, attached with a glass tube, at the mouth of tube.
3. Fill a test-tube full of water and invert it in a trough of water.
4. Heat the mercury oxide in the boiling tube.
Observation:
1. Drops of silvery liquid form at the sides of the boiling tube.
2. Bubbles are observed to escape from the glass tube into the test tube in the trough
3. When the air in the test tube is tested with a glowing splint, the splint rekindles.
Conclusion:
A compound can be broken down into simpler substances when heated.
Explanation:
The silver liquid is mercury while the gas collected in the test tube is oxygen as it rekindles the glowing splint. Compound mercury oxide is broken down into mercury and oxygen when heated.
Procedure:
1. Put some mercury oxide in a boiling tube
2. Insert a stopper, attached with a glass tube, at the mouth of tube.
3. Fill a test-tube full of water and invert it in a trough of water.
4. Heat the mercury oxide in the boiling tube.
Observation:
1. Drops of silvery liquid form at the sides of the boiling tube.
2. Bubbles are observed to escape from the glass tube into the test tube in the trough
3. When the air in the test tube is tested with a glowing splint, the splint rekindles.
Conclusion:
A compound can be broken down into simpler substances when heated.
Explanation:
The silver liquid is mercury while the gas collected in the test tube is oxygen as it rekindles the glowing splint. Compound mercury oxide is broken down into mercury and oxygen when heated.
About Toothpaste
Toothpaste is a paste or gel used with a toothbrush as an accessory to clean and maintain the aesthethics and health of teeth. Toothpaste is used to promote oral hygiene: it acts as an abrasive that aids in removing dental plaque and food from the teeth, and delivers active ingredients such as fluoride to help prevent tooth and gum disease. It is important to note that most of the cleaning is done by the mechanical use of the toothbrush, and not by the toothpaste. Most toothpastes contains trace amounts of chemicals that may be toxic when ingested, therefore toothpaste is not intended to be swallowed!!!
Did You Know?
The reason why halogens have varying reactivity is because some of them are more willing to gain electrons. A halogen with low reactivity such as astatine is very unwilling to gain electrons. This means that it is less likely to react with other elements and hence has a low reactivity. Conversely, a halogen with high reactivity such as fluorine would gain electrons easily. Therefore it will readily react with other elements, and hence has a high reactivity
Did You Know?
Buffers are extensively used in biological experiments in the lab, especially those pertaining to proteins or DNA. This is because proteins and DNA are extremely sensitive to changes in pH. A decrease in 1 pH can greatly damage a protein. Hence, buffers are used to minimise the effect the products have on the pH of the solution.
Buffers prevent the solution from getting to high or low in pH levels. This means that it will try to keep the pH of itself as close to the original as possible. However it is possible to change its starting pH by adjusting the amounts of the aid and salt. So if we want to make an alkaline buffer, we add more sodium ethanoate solution.
We can calculate the pH of buffers. This is done by the Henderson-Hasselbach equation, which states that:
To make a buffer, we need to make it with a weak acid (such as vinegar) HB and a salt that ionises to give the ion B-. Therefore, the pH can be calculated as follows:
pH=-log(Ka)+log([B-]/[HB])
This equation can also be used when we want to change the pH of a system to favour certain ions over another. For example, in the swimming pool, we want to favour the molecule instead of the ion. Hence we make the ratio of ([B-]/[HB]) as little as possible.
Buffers prevent the solution from getting to high or low in pH levels. This means that it will try to keep the pH of itself as close to the original as possible. However it is possible to change its starting pH by adjusting the amounts of the aid and salt. So if we want to make an alkaline buffer, we add more sodium ethanoate solution.
We can calculate the pH of buffers. This is done by the Henderson-Hasselbach equation, which states that:
To make a buffer, we need to make it with a weak acid (such as vinegar) HB and a salt that ionises to give the ion B-. Therefore, the pH can be calculated as follows:
pH=-log(Ka)+log([B-]/[HB])
This equation can also be used when we want to change the pH of a system to favour certain ions over another. For example, in the swimming pool, we want to favour the molecule instead of the ion. Hence we make the ratio of ([B-]/[HB]) as little as possible.
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