Topics in ChemistryLe 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 Mixtures: Characteristics of Mixtures Physical Properties of Matter explained with Examples Chemical Properties of Matter explained with Examples Differences between Physical and Chemical Change Ionic Theory and Electrolysis Physical and Chemical Properties of Acids States of Matter: Characteristics of Solids Liquid State of Matter: Characteristics of Liquids Gaseous State of Matter: Characteristics of Gases Molar Mass, Worked Examples and Differences with Molecular Mass Elements: Characteristics of Elements Salts and Types of Salt in Chemistry
Academic Questions in Chemistry
Which of the following isn't an element of the periodic table.
According to the periodic table, elements in the same group have got the same number of shells.
The periodic table of elements is also called the Mendeleev's table.
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
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)
Which of the following statement is false concerning hydrocarbons?
A. Hydrocarbons can be aromatic
B. Hydrocarbons are made up of carbon and hydrogen only
C. Alkynes are aliphatic hydrocarbons
D. Alkenes have a carbon-carbon double bond in their structure
E. Benzene ring has a carbon-carbon triple bond in its structure
F. Hydrocarbons are the main constituents of petroleum and natural gas
The ability of carbon to form long chain of itself is called _____.
A. Carbon chain reaction
E. Organic chemistry
F. Carbon moleculation
Calculate the relative molecular mass of methane. (Carbon = 12.001, H = 1.00794).
A. 13.00894 amu
B. 11.00206 amu
C. 12.00794 amu
D. 14.001 amu
E. 15.001 amu
F. 16.033 amu
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Acids have been defined in a variety of ways. All of these definitions are correct but some are more corect when compared to others.
Below are some of the definitions of an acid by various scientists:
An acid is a substance that produces hydrogen ions (H+) when dissolved in water (or when in the form of an aqueous solution).
Svante Arrhenius definition of Acid
According to Arrhenius, when hydrogen chloride gas is dissolved in water (to form aqueous HCl) , H+ will be produced.
Below is the equation:
An acid is a substance that donates a proton in a chemical reaction.
Brønsted Thomas Martin Lowry definition of Acid
Note: Recall that a proton has an atomic number of 1. Based on this fact, we can conclude that hydrogen ion (H+) is a proton (since it has an atomic number of 1).
Consider the equation below:
HCl(aq) + NaOH(aq) -> NaCl(s) + H2O(l)
Notice from the equation that the acid HCl (hydrogen chloride) donated it's proton (H+) to NaOH (sodium hydroxide), forming water (H2O) in the process. Simultaneously, NaOH (sodium hydroxide) donated it's Na+ to HCl to form the salt NaCl (sodium chloride).
An acid is a substance that accept an electron pair in a chemical reaction.
Gilbert Newton Lewis definition of Acid
Note: Recall that valence electron(s) are electrons present in the outermost shell of an atom.
Consider the equation below:
2NH4+(aq) + Ag+(aq) -> 2H4AgN
Notice that silver ion (Ag+) accepts a pair of electron (2 electrons or 2H+) from 2 moles ammonium molecule (2NH4+) to form ammonium silver (2H4AgN).
The fact that silver ion (Ag+) accepts a pair of electron from ammonium qualifies it as a Lewis acid. In short, any substance that accepts a pair of hydrogen ion (2H+) which is equivalent to 2 electrons is a Lewis acid.
Note: In any redox (oxidation and reduction) reaction, electron is always lost and gained.
Lewis' definition of acid is quite encompassing because it accommodates for both oxidation and reduction.
In regards to redox reactions, always remember the following points:
Finally, acids can also be defined as substances that gives out hydronium ion (H3O+) when dissolved in water.
The equation below explains the above definition of acid:
HCl(aq) + H2O(l) -> H3O+(aq) + Cl-(g)
From the above equation, dissolving the acid (HCl) in water yields hydronium ion or oxonium ion (H3O+) as it's only positive ion.
Understand that positively charged ions are called cations while negatively charged ions are referred to as anions.
In summary, all acids will always contain the positive H+ (cation) and an anionic group in their formula. For instance, the acid HCl (Hydrogen Chloride) contains H+ as cation and Cl- as its anion.
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Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.
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Amazing facts in Chemistry
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:
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.
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