Alfred Ajibola
- Tue, 12th February, 2019 @ 11:12 AM
Topics in Chemistry
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 mixtures Physical properties of matter Chemical properties of matter explained with examples Differences between physical and chemical change in chemistry Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid state of matter: Characteristics of liquidsAcademic Questions in Chemistry
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
John Dalton's first atomic theory was modified based on a discovery made by _____.
A. Sir Isaac Newton
B. Albert Einstein
C. Avogadro
D. Rutherford
E. Boyle and Charles
F. Gay Lussac
Which of the following isn't an element of the periodic table.
A. J
B. Y
C. W
D. B
E. U
F. K
According to the periodic table, elements in the same group have got the same number of shells.
A. True
B. False
The periodic table of elements is also called the Mendeleev's table.
A. True
B. False
The simplest formula of a compound is termed _____.
A. Emperical formula
B. Molecular formula
C. Avogadro's number
D. Mass formula
E. Molar mass formula
F. Mole ratio
The amount or quantity of a compound (or molecule) in chemistry can be measured in a variety of ways. The measured quantities will include:
In this article, we will explore the concepts of molecular mass.
The term molecule refers to the composition and arrangement of atoms expressed in ratios. The atoms forming a molecule can be similar or different. For instance:
Recall that all elements have got their respective atomic masses. For instance, hydrogen (H) has an atomic mass of 1.00794 while that of carbon (C) is 12.011. The atomic mass of all 108 elements can be seen on the periodic table.
Please read on the periodic table here.
The molecular mass of a substance or molecule is usually defined in relation to 12C (Carbon-12). Based on this relationship with carbon-12, it’s preferably called the Relative Molecular Mass (RMM).
The relative molecular mass value is obtained from the sum of the atomic masses of the constituent atoms or elements that make up the molecule. Its unit is the Atomic Mass Unit (amu) or Dalton (Da).
Please read on elements and their characteristics here.
In order to calculate the relative molecular mass, we will have to take into consideration the atomic masses of each atom present in the molecule.
Calculate the relative molecular mass of methane (CH4). (Carbon=12.001 and H=1.00794).
Molecular Mass of Methane = 16.033 amu
You can Attempt Len Academy questions and answers on various subjects here.
Calculate the relative molecular mass of water (H2O). (Oxygen=15.9994 and Hydrogen=1.00794).
Molecular Mass of Water = 18.015 Da
Calculate the relative molecular mass of ethanol (C2H5OH). (Carbon=12.001, Oxygen = 15.9994 and Hydrogen = 1.00794).
Molecular Mass of Ethanol = 45.036 amu
Please read on Graham's law of diffusion with some worked examples here.
Note: We used 3 significant digits in all our answers. This is so because the relative molecular mass is always defined and expressed in terms of 12C (Carbon-12) whose atomic mass has 3 significant digits.
The atomic mass of 12C is 12.011
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.
Relative Molecular Mass prove to be useful only when we calculate substances with small and definite molecular sizes. This had been proven through the modifications of Dalton's atomic theory.
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
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:
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.
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.
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.
Calculate the Relative Molecular Mass of methane (CH4). (Carbon=12.001 and H=1.00794)
Molecular Mass = Atomic mass of carbon + Atomic mass of Hydrogen
Methane is composed of one atom of Carbon and 4 atoms of Hydrogen.
12.001 + (1.00794 x 4)
Molecular Mass of Methane = 16.033 amu
Calculate the Relative Molecular Mass of water (H2O). (Oxygen=15.9994 and Hydrogen=1.00794)
Molecular Mass = Atomic mass of Hydrogen + Atomic mass of Oxygen
Water contains 2 atoms of Hydrogen and 1 atom of oxygen.
(1.00794 x 2) + 15.9994
Molecular Mass of Water = 18.015 Da
Below are some facts about gold:
It is the only metal that has a gold (golden) color
Gold is present inside the earth crust in all the seven continents
Pure gold is soft and very stretchable (It can even be stretched into threads)
The Latin name of Gold is aurum which means 'shining dawn'. For this reason, its chemical symbol is 'Au'
Gold is a very good conductor of electricity. This is why it’s sometimes used in making USB and audio cables
Gold is non toxic and can be eaten with food. It is sometimes added to desserts in some expensive restaurants
The term Gold originated from an ancient English word 'geolu' which means yellow
24karat gold is the purest gold element
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