Digestion

Headline: Digestion.

In today's Science lesson, we went through the digestion worksheets which had to be completed during the March holiday. Digestion occurs in every human being. It is a process whereby large complex food molecules are broken down into smaller, simpler, soluble and diffusible molecules so that nutrients in the food can be absorbed by the body.

I learnt that there are two main processes in digestion, they are known as the physical and chemical digestion. When food is broken down into smaller pieces and its surface area increases, it is called a physical change. It is only known as a chemical digestion when large, complex food molecules are broken down into smaller, simpler, soluble and diffusible food molecules with the help of enzymes.

I learnt that special types of proteins, known as enzymes, are produced by our body so as to speed up specific chemical reactions. There are different types of enzymes called amylase (breaks down starch into maltose), maltase (breaks down maltose into glucose), protease (breaks down proteins into amino acids) and lipase (breaks down fats into fatty acids and glycerol).

Lastly, I also learnt that many athletes consume fruits such as bananas before a strenuous activity as they need energy and fruits, like bananas, are rich in sugar. The sugar can be easily digested and is able to provide instant energy for the athletes.

(Example of the human digestion system)

Sources: Google Images

Acids and Alkalis

Today, we were being taught on a new chapter, acids and alkalis. There are also many concepts and formulae that have to be learnt and memorised. Hence, we have to pay close attention to what Mdm Riza is teaching us as the concepts learnt may be tested in our examinations. We had also done quite a number of experiments in today's Science lesson.

I used to think that acids and alkalis are both the same. But now I think that they are DIFFERENT from one another in terms of their definitions and properties. An acid is a substance which is diluted in water to form solution and hydrogen ions are produced. The higher the amount of hydrogen ions, the stronger the acid is. The acid properties are present only when acids are dissolved in water. As for alkalis, they produce hydroxide ions when they are being dissolved in water. The stronger the alkalis, the higher the amount of hydroxide ions present. The three main differences between acids and alkalis are:

• Acids have a sour taste but alkalis have a bitter taste
• Acids turn moist blue litmus paper red, while alkalis turn moist red litmus paper blue
• Acids have a pH value lesser than 7. However, alkalis have a pH value more than 7

I used to think that acids and alkalis cannot be dissolved in water. But now I think that both of them are actually soluble in water. I also used to think that both acids and alkalis will react when being mixed with reactive metals and metal carbonates. But I was wrong. Now I think that only acids will then react with reactive metals (form salt and hydrogen gas) and metal carbonates (form salt, carbon dioxide gas and water).

I used to think that only litmus paper test that can help us differentiate between acids and alkalis. But now I think that there are also many other indicators that will tell us which are acids and which are alkalis. Other examples of indicators are:

• Universal indicator - turns into different colours, where each colour corresponds to a pH value, when it is added to different substances
• Phenolphthalein - use best on indicating alkalis as it changes to pink when alkalis are added to it. Stays colourless when being mixed with acidic/neutral substances
• Methyl orange - changes into yellow when being mixed with alkalis but turns red when acids are mixed into it
• Rose petals (made from plants)
• Red cabbage (made from plants) - blue (neutral), red (acidic), yellow (alkaline)

Lastly, I used to think that the hydrogen gas and carbon dioxide gas produced when acids react with reactive metals and metal carbonates respectively, are colourless and thus we cannot know if the substances reacting are acid or alkalis. But now I think that both gases can actually be tested. Hydrogen gas can be tested with a lighted splint as when they get in contact with one another, the splint will extinguish with a 'POP' sound. As for carbon dioxide gas, it can be tested by bubble the gas through limewater. When both the gas and limewater come in contact with one another, white precipitate will be observed in the limewater.

(Example of litmus paper test)

(Example of the pH scale)

Sources: Google Images

Chemical Change - Good or Bad?

Today's Science lesson, we discussed about the good and bad points of chemical changes and did some experiments on heating matters so as to see their reactions.

I used to think that when we heat sugar (white crystals), it would melt and would eventually turn into a colourless liquid and evaporate. Of course, I was wrong. But now I think that when we heat sugar (white crystals), it will melt and then turn into a black solid. In addition, a sweet smell will evolve.

I used to think that chemical changes usually have advantages and do not have any disadvantage on us or to the environment. But now I think that chemical changes have both advantages and disadvantages. Example of advantages in chemical changes is that they allow us to produce products, like medicines and petrol, which we can use in our daily lives. As for the example on disadvantages in chemical changes is that they may produce products, such as chemicals, that will cause pollutions and bring harm and damage to living and non-living things respectively.

(Sugar heated and turned into black solid)



Sources: Google Images

Science Common Test 1

Headline: Science Common Test 1.

Our common test paper was given back to us during today's Science lesson. Then, we went through the answers so as to correct our mistakes and also to check if our paper has been marked correctly.

After going through the paper, I learnt that:

• The smallest particle in an element is an atom while the smallest particle in a compound is a molecule. This is because element is a substance which cannot be broken down further by chemical methods and thus, its atoms stand on its own. As for compound, it is a substance which is made up of two or more different elements chemically combined together. Hence, its atoms are also combined together to form a molecule.
• The number of neutrons in the same type of atoms can differ from one another. For example, the number of neutrons in carbon (an element) can be 6 or 7.
• An atom is electrically neutral as the number of protons which have a positive charge of 1 is equal to the number of electrons which have a negative charge of 1.

(Atoms)

(Molecules)

Sources: Google Images

Chemical Changes

Well, we started off with a new topic, Chemical Changes, today. There are many concepts in this chapter that are very complicated. But after this lesson, I managed to get a better understanding on what the topic is all about and remember most of the concepts and ideas being taught to us.

3 Thoughts:
1) A chemical change is permanent where new substance is formed. The change is usually irreversible and a chemical reaction will always take place. A chemical reaction is a process whereby reactants (substances that are used for the reaction) are changed into new substances, also known as, products (substances formed). In addition, during a chemical reaction, no substances are destroyed or created. The atoms in them only re-arranged themselves so as to form new products.
2) A chemical reaction can be represented using equation. The equation can be written using words (word equation) or chemical formulae (chemical equation). Information on identity of reactants and the final products using chemical formulae and possible reaction conditions (e.g. temperature, physical state, etc.) are provided in a typical chemical equation. We can only say about the quantities involved in a chemical reaction when the equation is balanced. By balancing a chemical equation, we have to place numbers in front of the formulae of the substances in the equation.
3) There are four types of interactions which involve in chemical reaction. The four types are:

• Interaction between matter and heat (E.g. Combustion, Combination and Thermal Decomposition)
• Interaction between matter and light (E.g. Photosynthesis and Photography)
• Interaction between matter and electricity (E.g. Electrolysis)
• Interaction between matter and another matter (E.g. Digestion, Neutralization and Rusting)

2 Questions:
1) Why electrolysis can also be a physical change?
2) When there is a plus (+) sign at the left hand side of the chemical equation, then can it be eliminated from the right hand side? Or must the plus (+) sign still remains on the right side?

1 Useful application:
1) Chemical changes help us understand more about the things happening to us in our daily lives and we are also able to know what are the changes and interactions that are going on around us.

(Example of a chemical reaction where atoms re-arranged themselves)

(Example of a chemical equation)

(Example of a chemical reaction - Combustion)



Sources: Google Images

Preparation for Common Test

Headline: Preparation for Common Test.

Well, for today's lesson, we went through worksheets again so as to prepare us for the coming common test and correct the mistakes we had made.

I have learnt that the part of an atom which contains the protons and neutrons is called nucleon. The nucleon is positively charged and is densely concentrated in the centre of an atom.

I have also learnt that atoms usually gain or lose electrons but not the protons and neutrons as the protons and neutrons are found in the inner area of the atom. Thus, the electrons will be easier to be attracted by other atoms than the subatomic particles found in the inner area.

I learnt that the similarity between sulfur molecule and sulfur dioxide molecule is that both molecules are made up of more than one atom. As for their difference is that sulfur molecule contains one type of atoms but sulfur dioxide molecule has more than one type of atoms.

(Example of an atom. Inner part, nucleon - consists of protons and neutrons. Outer part - electrons orbiting in electron shells)



Sources: Google Images

Quiz

Headline: Quiz.

We did a quiz today so as to check on our understanding on the topic, Atoms & Molecules.

I have learnt that when a question asks us about the number of subatomic particles in an atom of XXX, we should list out the number of protons, electrons and neutrons but not the total number of subatomic particles in it. For example, if a question asks us about the number of subatomic particles in an atom of boron with a nucleon number of 10, we should not answer that the number of subatomic particles in an atom is 15. Instead, we should answer that there are 5 protons, 5 electrons and 5 neutrons.

I have also learnt that atoms form ions as atoms react when they are forming compounds. They tend to lose or gain electrons so as to get the electronic configuration of a noble gas.

(An example of a key in the periodic table)         



Sources: Google Images