Alfred Ajibola
- Thu, 20th June, 2019 @ 11:22 AM
Topics in Chemistry
Gas laws in chemistry Charles's law explained Calculation questions on Charles's law Examples of Charles's law in real life Boyle's law explained Calculation questions on Boyle's law Examples of Boyle's law in real life Summary on the kinetic molecular theory of gases Postulates of kinetic theory of gases Avogadro's number explained with worked examples Mole and Avogadro's Number explained Le Chatelier's Principle: Changes in concentration and pressure in dynamic equilibrium Chemical Equilibrium: Dynamic Equilibrium in Chemistry Static and Dynamic Equilibrium explained with their differences Chemistry Scheme of Work, SS1, First Term Chemistry Scheme of Work, SS1, Second Term Chemistry Scheme of Work, SS1, Third Term Compounds in Chemistry: Characteristics of Compounds Types of Mixture: Homogenous and Heterogeneous Mixtures What are mixtures? Characteristics of mixturesAcademic Questions in Chemistry
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
Having a solid understanding of physical and chemical change is one of the ideal knowledge a student who aspire to become excellent in chemistry should gain. Meanwhile, recall that chemistry is the study of matter and the changes they undergo.
Please read on the concept of matter here.
A physical change is a change that is easily reversible and no new substance is formed.
As an instance; when we add sodium chloride or common salt (NaCl) into water (H2O), a salt solution will be formed. This change that resulted from the mixture of salt and water is a physical change because we could easily separate the salt solution to get back its constituents: (that is, common salt and water).
You can read on elements, compounds and mixtures here.
Since no new substance is formed in the mixture of NaCl and H2O, the best name we could attribute to such mixture is a salt solution. However, understand that salt solution does not have any ideal chemical formula. In short, a mixture have no ideal chemical formula because it is associated with a physical change.
Please read on differences between physical change and chemical change here.
This salt solution in our instance above can be separated via a technique called evaporation.
A mixture of NaCl and H2O does not have a chemical name because a new substance is not formed.
Another example of a physical change is a mixture of red oil and water. There is no chemical name that can be attributed to this mixture since no new substance is formed.
Red oil and water are two immiscible liquids. As a result, their mixture can be separated via the separating funnel technique. Meanwhile, recall that water has a higher density than oil. For this reason, it remains at the bottom while the oil (with lower density) floats on it. During separation, the water is collected first, then the oil through the separating funnel.
Please read more on density and specific gravity here.
In separating a mixture of water and oil via the separating funnel technique, always remember that the denser liquid (water in this instance) remains at the bottom of the mixture, and is tapped first, leaving behind the oil (less lense liquid) which can be tapped later.
A third example of a physical change is the mixture of sand and water. Since no new substance is formed, no name can be ascribed to such mixture.
Decantation is the technique for separating water from sand; that is, an insoluble solid in a liquid. Sand is the insoluble solid in this instance.
The freezing of liquid water into ice is also a physical change since it can be easily reversible.
Moreover, the chemical formula of water and ice remains the same (H2O): thus, no new substance is formed.
Please read on the physical properties of matter here.
Having a good understand of physical change will give you a clue to what a chemical change entail.
A chemical change is a change that is not easily reversible and a new substance is always formed.
As an instance, if we exposed a piece of iron (Fe) to the atmosphere and rainfall (or water) for some period of time, we will observe that the iron gradually begins to rust until it finally erodes away. When this happens, we no longer have our iron (Fe) and unfortunately, there is no way we can recover it.
In the above instance, What we have now is referred to as rust and the process leading to the formation of rust is termed corrosion.
Please read on the chemical properties of matter here.
On the other hand, the rust formed from the exposed iron is an entirely new substance and it has a chemical name called iron (III) oxide, ferric oxide or hematite with a chemical formula Fe2O3.
We cannot reverse the formed rust (Fe2O3) into iron (Fe). This irreversibility of the new substance formed is the main idea behind a chemical change.
You can read on the physical properties of metals here.
Another example of a chemical change is the formation of water (H2O).
The constituent elements in the formation of H2O are hydrogen molecule (H2) and oxygen molecule (O2). The reaction is shown below:
2H2(g) + O2(g) -> 2H2O(l)
From the above equation, a new substance has been formed and that’s water (H2O).
Water is entirely different from hydrogen just as it is from oxygen. As a matter of fact, water cannot be reversed to its constituent elements which are hydrogen and oxygen respectively.
The new substance formed from the reaction between hydrogen and oxygen has a chemical name and that’s hydrogen oxide or water; with a chemical formula H2O.
Other examples of chemical changes seen around us include:
The burning of wood.
The rotting of leaves.
The decomposition of food.
The lightening of a match stick and so on.
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Amazing facts in Chemistry
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:
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
Notable points in Chemistry
Below are the physical properties of metals:
They exist in solid state.
The have high densities.
They are good conductors of heat and electricity.
The have the ability to be polished, to glow, sparkle and reflect light.
They can be bent, flattened and made into sheets called foils.
They can be drawn into wires.
Iron undergoes magnetism while most metals are poorly magnetized.
They typical have high melting point.
They generally have high boiling point.
With the exception of lithium, sodium and potassium, most metals are generally hard.
They have the ability to make sound when in contact with other objects or metals.
Please read details on the physical properties of metals here
John Dalton is an English chemist who brought clarity into the composition of matter and the basis for their chemical reactions.
Below are Dalton's Atomic Theory:
All matter consists of tiny indivisible particles called atoms.
Atoms of the same element are identical to each other in every aspect because they have the same shape and mass, while atoms of different elements are different in all respect.
Atoms are indestructible and can neither be created nor destroyed.
Atoms of different elements can combine with each other in simple whole number ratios to form compounds.
Atoms of the same element share similar physical and chemical properties. They can also combine in more than one ratio to form two or more compounds.
Meanwhile, understand that the above theories of John Dalton had been modified.
Please read on Dalton's atomic theory and its modifications here
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.
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)
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 %).
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 = Fe1O1.5
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:
Alkanes
Alkenes
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:
