Topics in ChemistryElements, Compounds and Mixtures with their Characteristics Salts and Types of Salt in Chemistry Mixtures and Separation of Mixtures Mixtures and Separation of Mixtures - part 2 Mixtures and Separation of Mixtures - part 3 Physical and Chemical Change explained with their Differences Electrolysis, Electrolyte, Electrode, Anode, Cathode and Ionic Theory Diffusion - Grahams Law of diffusion and Importance of Graham's Law of Diffusion Metals - Physical Properties of Metals Daltons Atomic Theory and its Modifications Periodic table: Classification of Elements in the Periodic Table Emperical Formula - Explanation and Worked Examples of Emperical Formula Organic Chemistry - Hydrocarbon, Carbon and its Compounds Explanation, Worked Examples and Differences between Molecular Mass and Molar Mass Gold: Interesting Facts about Gold Matter, Mass, Weight and Characteristics of Solids, Liquids, Gases Acids - Definitions of Acids, Physical and Chemical properties of Acids
Academic Questions in Chemistry
The reaction involving an acid and a base is termed _____.
Which of the following is NOT a type of salt?
The only metal that exist as liquid at room temperature is _____.
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:
HCl(aq) -> H+ + Cl-
An acid is a substance that donates a proton in a chemical reaction.
Bronsted 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 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 donated it's proton (H+) to NaOH, forming water (H2O) in the process. Simultaneously (At the same time), NaOH donated it's Na+ to HCl to form the salt NaCl.
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
Image Credit: cnx
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 to being a Lewis acid. In short, an 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 gain.
Lewis definition of acid is quite encompassing because it accommodates for both oxidation and reduction.
Always remember that Oxidation is the loss of electron(s) during a reaction while Reduction is the gain of electrons(s).
Acids are also defined as substances that gives out hydronium ion (H3O+) when dissolved in water.
The equation below explains the definition
HCl(aq) + H2O(l) -> H3O+(aq) + Cl-(g)
From the above equation, dissolving the acid (HCl) in water yields hydronium ion (H3O+), sometimes called oxonium ion; as it's only positive ion.
Note: Cations are positively charged ions while Anions are negatively charged ions.
All acids usually 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 anion.
They have sour taste. (Acid in Latin means sour).
They will turn a blue litmus paper to red.
On a pH scale, they have a value less than 7 (<7). The pH scale is used to measure the degree of acidity or alkalinity substances. It's values ranges from 0-14.
They will change the color of methyl orange from orange/yellow to pink.
They will change color of phenolphthalein from pink to colourless.
They are corrosive. A corrosive substance can "rust metals" and "burn the human skin".
Aqueous form of acids can conduct electricity.
1. Neutralization reaction: This is a reaction in which an acid reacts with a base to form salt and water only.
HCl(aq) + NaOH(aq) -> NaCl(s) + H2O(l)
HNO3(aq) + NaOH(aq) -> NaNO3(s) + H2O(l)
Note: Normal salt is a type of salt formed from a Neutralization reaction.
NaCl and NaNO3 are Normal salts formed from the above reaction.
2. Reaction with Metals: When an acid reacts with metals higher than hydrogen in the activity or electrochemical series, hydrogen gas will be evolved or discharged.
Image Credit: Redefining Knowledge
Zn(s) + 2HCl(aq) -> ZnCl2(aq) + H2(g)
2Al(s) + 6HCl(aq) -> 2AlCl3(aq) + 3H2(g)
Notice that Zinc (Zn) and Aluminium (Al) are higher than hydrogen (H) in the electrochemical series, hence displacing it from the acid "HCl".
3. Reaction with carbonates: When an acids reacts with carbonates, salt and water is produced as carbon(IV)oxide (CO2) is given off.
Na2CO3(s) + H2SO4(aq) -> Na2SO4(s) + H2O(l) + CO2(g)
CaCO3(s) + H2SO4(aq) -> CaSO4(s) + H2O(l) + CO2(g)
4. Reaction with bicarbonates: It is similar to the reaction with carbonates in the sense that salt, water and carbon(IV)oxide is produced.
KHCO3(s) + HCl(aq) -> KCl(aq) + H2O(l) + CO2(g)
NaHCO3(s) + HCl(aq) -> NaCl(aq) + H2O(l) + CO2(g) + H2O(l)
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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. Please read some interesting facts about gold here
Copper is the only metal that is naturally antibacterial. This is why you would see some children carry copper water bottles to school
Water actually 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.
Please read on modification of Dalton's atomic theory here.
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