Chemistry Scheme of Work, SS1, Second Term

With regards to redox reactions, which of the following statement is wrong?

• A. Redox reaction are examples of chemical change

• B. Reduction is the gain of electron

• C. Substances that donates election during chemical reaction are termed reductants

• D. Oxidizing agents are always reduced in chemical reactions

• E. Oxidation occurs at the cathode in electrolysis

• F. Hydrogen is a reducing agent

In chemistry, physical change is associated only with the rearrangement of molecules while the internal composition of the substance remains the same.

• A. True

• B. False

_____ electron(s) is a term that describes the number of electron(s) in the outermost shell of an atom.

• A. Outer

• B. Excess

• C. Valence

• D. Positive

• E. Negative

• F. Last

_____ is the negative electrode in electrolysis.

• A. Anode

• B. Anion

• C. Cathode

• D. Cation

• E. Ion

• F. Electrolyte

The above diagram shows the _____ type of bond.

• A. Covalent

• B. Polar covalent

• C. Coordinate covalent

• D. Metallic

• E. Van dear walls

• F. Ionic

 Metals are referred to as _____ in their impure state.

• A. Diluted

• B. Consecrated

• C. Coloured

• D. Ores

• E. Stained

• F. Strained

Metals generally have the quality to shine, glow, sparkle, glitter, reflect light and be polished. This characteristic of metals is termed _____.

• A. State

• B. Ductility

• C. Luster

• D. Malleability

• E. Hardness

• F. Inflorescence

The _____ spectrometry experiment conducted on isotopic elements gave a confirmation for the existence of isotopes.

• A. Mole

• B. Volume

• C. Weight

• D. Number of moles

• E. Mass

• F. Amount of substance

Plastic and Glass can decompose, but not in our lifetimes. It takes an average time of 450 years for plastics to decompose. As for the decomposition of glasses, it takes about 4,000 years

The only letters that failed to appear on the periodic table are letters:

J     &     Q

Gold and copper are the only two non-silvery colored metals.

Copper is the only metal that is naturally antibacterial. For this reason, some children utilize 'copper water bottles' in schools

Water freezes faster when it’s warm than when it’s cold

Most element in their pure state exists physically in different forms. For instance, pure carbon can exist as both diamond and graphite. This phenomenon is called allotropy

If you pour a handful of salt into a full glass of water, the water level will go down rather than overflowing the glass.

Similarly, if you mix half liter of water and half litre of alcohol, the total volume of the liquid will be les than one litre

The periodic table, also called periodic table of elements or Mendeleev's table, is a table that shows an organized arrangement of the 118 chemical elements according to their atomic number.

Out of the 118 elements; elements 1 - 94 are present in nature while elements 95 - 118 are synthesized artificially.

The manner at which elements are arranged on this table reveals some similarities in their electronic configurations and chemical properties.

Please read on the periodic table of elements here.

A compound composed of iron (Fe) and oxygen (O) was analyzed and found to contain 69.94% iron and 30.06% oxygen. Find the empirical formula of the compound. (Molar mass of Fe=55.85, O=16)

• Solution:

Step 1: Identify the given parameter from the question.

• Fe = 69.94%,   O = 30.06%.

• Empirical formula = Fe_?O_?

Step 2: Convert the percentages to gram. (just attribute grams to the %).

• 69.94% = 69.94g while 30.06% = 30.06g

Step 3: To get the mole ratio of each element, convert the gram to moles using the formula (mole = mass/molarmass). Please merorize this formula because we always work with moles in emperical formula.

• Mole of Fe: 69.94/55.85 = 1.252mol

• Mole of O: 30.06/16 = 1.879mol

Step 4: Divide both sides by the smallest mole ratio.

• Iron has the smallest mole ratio in our case, therefore: 1.252/1.252 = 1,    1.879/1.252 = 1.5

• We now have the formula = Fe₁O_1.5

Step 5: Multiply each of the moles by the smallest whole number that will convert each into a whole number. (In our case, the number '2' is the smallest whole number that will make '1.5' and '1' whole numbers when multiplied by it.

• For iron (Fe), we will have 1 x 2 = 2

• For oxygen (O), we will have 1.5 x 2 = 3

Step 6: Write the empirical formula.

• The empirical formula= Fe₂O₃

• Iron(III)tetraoxosulphate(VI)

In chemistry, hydrocarbons can be classified as either aliphatic or aromatic. Recently, both classifications of hydrocarbon were based on their structure rather than their origin.

Aliphatic hydrocarbons are put into three main groups according to the types of bonds they possess. These are:

1. Alkanes

2. Alkenes

3. Alkynes

They are shown in the image below:

It's important to note the followings:

• Alkanes have single bonds (only) in their structures.

• Alkenes always have a carbon-carbon double bond present in their structure.

• Alkynes always have a carbon-carbon triple bond present in their structure.

Aromatic hydrocarbons are classified into:

• Arenes: They contain benzene ring as a structural unit. Below is the structure of a benzene ring.

• Nonbenzenoid aromatic hydrocarbons: They possess special stability but lack a benzene ring as a structural unit.

Organic chemistry is the study of carbon and it's compounds.

Carbon is the focus of organic chemistry because it has a wide chemical diversity in the sense that it can combine with other carbon atoms to form a long chain of carbon molecule. This ability and process whereby carbon can form a long chain of itself is called catenation.

Please read the introduction to organic chemistry here

A major challenge encountered when calculating molecular mass is that it becomes difficult or impossible to calculate especially when the relative molecular mass of large molecules, polymers and macromolecules are involved.

Examples of large molecules (with indefinite molecular masses) include carbohydrates, cellulose and complex sugars.

The large molecules (above) have no specific chemical formula throughout their volume.

Please read more on carbohydrates and sugars here

Understand that Relative Molecular Mass prove to be useful only when we calculate substances with small and definite molecular sizes. This was proven through the modifications of Dalton's atomic theory.

Please read on Dalton's atomic theory and its modifications here.