Alfred Ajibola
- 29th August, 2022 @ 11:00 PM
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
Avogadro's number refers to the number of particles or atoms or molecules present in one mole of a substance. This number is 6.02214076 × 1023. It is termed Avogadro's constant.
The calculations involving Avogadro's number may require us to find the number of particles, atoms or molecules. We should not be confused on these terms as they all point to the same thing. However, we may further be asked to find the moles, mass or molar mass of a substance in questions related to Avogadro's numbers.
Please read on molar mass here
Questions related to Avogadro's number, mole and molar mass will be solved in this article. Meanwhile, an understanding on the concept of mole and Avogadro's number is required.
Please read an introduction to mole and Avogadro's number here
2H2(g) + O2(g) -> 2H2O(l)
From the above equation, calculate the number of atoms present in the reactants. (Avogadro's number is 6.02 × 1023).
The reactants present in the reaction are two moles of hydrogen molecules and one mole of oxygen molecule.
Worthy of note is the number present in front of the molecules involved in the reaction. This number is the mole itself. Hydrogen has 2 in front (that is, 2 moles of hydrogen) while oxygen has nothing, and this signifies 1 mole of oxygen. Water is the product from the reaction. It has 2 anteriorly and can be appropriately referred to as 2 moles of water.
Recall that one mole of any substance = 6.02 × 1023. These substances can be an atom, a molecule or a compound.
From the question, two moles of hydrogen = 2 x 6.02 × 1023 = 12.04 × 1023
One mole of oxygen = 1 x 6.02 × 1023 = 6.02 × 1023
Therefore, the reactant 2H2(g) contains 12.04 × 1023 atoms while O2(g) contains 6.02 × 1023
You can read on molecular mass and its calculations here
How many moles are present in 120.4 × 1023 molecules. (Avogadro's number is 6.02 × 1023).
Recall that one mole of any substance will always contain 6.02 × 1023 atoms, particles or molecules. The question uses 'molecules' in this instance, but regardless, it is still the same as atoms or particles.
If 1 mole = 6.02 × 1023
Then Z moles = 120.4 × 1023
Cross multiply
Z x 6.02 × 1023 = 1 x 120.4 × 1023
Make Z the subject of the formula
Z = 120.4 × 1023 / 6.02 × 1023
Z = 20 moles
Therefore 20 moles of Z will contain 120.4 × 1023 molecules.
Please read on empirical formula here
3.01 × 1023 particles of sodium reacted with chlorine to produce sodium chloride. How many moles of sodium reacted and what is the molar mass of sodium according to the reaction. (Sodium = 23, Avogadro's number = 6.02 × 1023).
One mole of any substance contains = 6.02 × 1023.
If 1 mole of sodium = 6.02 × 1023
Then Y mole = 3.01 × 1023
Cross multiply
Y x 6.02 × 1023 = 1 x 3.01 × 1023
Make Y the subject of the formula
Y = 3.01 × 1023 / 6.02 × 1023
Y = 1/2 mol
Therefore, 1/2 mol of sodium is equivalent to 3.01 × 1023 particles of sodium.
Molar mass of sodium = 23g/mol
Since 1/2 mole reacted, the molar mass of sodium that reacted will be 1/2 x 23g/mol
11.5g/mol
You can read on Dalton's atomic theory and its modifications here
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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:
