Topics in ChemistrySalts and Types of Salt in Chemistry Separation Techniques Separation Techniques part 2 Separation Techniques part 3 Physical Change, Chemical Change, Element, Compound and Mixture Electrolysis, Electrolyte, Electrode, Anode and Cathode Grahams law of diffusion Physical Properties of Metals Daltons Atomic Theory and its Modifications Periodic table and Classification of Elements
Academic Questions in Chemistry
The only metal that exist as liquid at room temperature is _____.
ANSWER is Mercury
Mercury is a liquid metal at room temperature. Its chemical symbol is Hg. The name mercury comes from its Greek name, hydrargyrum, which means "liquid silver" . Mercury has an atomic number of 80. Please read on the periodic table of elements here
The element mercury is also considered to be named after the fastest-moving planet in the solar system. You can read on solar system here.
Having a solid understanding of physical change, chemical change, elements, compounds and mixtures is one of the ideal knowledge a student who aspire to become excellent in chemistry should gain. In this article, we will break down each of these in simple terms.
A physical change is a change that is easily REVERSIBLE and NO NEW substance is formed.
For instance, when we add NaCl (sodium chloride or common salt) into H2O (hydrogen oxide or water), 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 it to get back the constituents materials that formed the mixture (that is, NaCl and H2O).
Note: 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; meanwhile salt solution does not have any ideal chemical formula. This salt solution can be separated by 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 liquid and as result, their mixture can be separated by using a separating funnel technique.
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. (The best we can name it is a mixture of sand and water)
Decantation is the technique used to separate water from sand, (that is, an insoluble solid in a liquid).
Note: 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.
Having a good understand of physical change will give you a clue on what a chemical change is.
A chemical change is a change that is NOT easily reversible and a NEW substance is formed.
Take for instance, when a piece of iron (Fe) is exposed to the atmosphere and rainfall (or water); after some period of time, the iron will gradually begin to rust until it finally erodes away. When this happens, we no longer have our iron (Fe) and unfortunately, there’s no way to recover it back. On the other hand, the rust that formed is an entirely new substance and it has a chemical name called iron oxide or ferric oxide or hematite. We cannot reverse the formed rust (Fe2O3) back to iron (Fe).
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:
From the above equation, a new substance has been formed and that’s water (H2O). Water is completely different from hydrogen and similarly, so is it completely different 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 (H2O).
Note: The burning of wood, rotting of leaves and decomposition of food are all chemical changes.
The table below shows the differences between a PHYSICAL CHANGE and a CHEMICAL CHANGE
It is easily reversible
It is not easily reversible
No new substance is formed
A new substance is formed
The change is not accompanied with a new chemical formula
This change is accompanied with a new chemical formula
The original matter can be recovered by using a separation technique
The original matter cannot be recovered
It results to a change in the physical properties of the substance, e,g color and shape
It results to a change in the chemical composition and properties of the new substance
This change only result in the rearrangement of molecules but the internal composition of the substance remains the same
This change results in the formation of new substance with an entirely different chemical composition
Everything in our world is composed elements and compounds. For instance:
In chemistry, an element is the simplest form of a substance that cannot be broken down by chemical means.
For instance, when one attempts to split a pure gold (element) in particles, all they see is the same thing (gold) on each particle, nothing else.
Elements are naturally occurring in the universe; in fact, life is present on earth because of the type of elements found in it. In other planets, the elements that are necessary for life are not present in sufficient quantities, for instance most will have little or no oxygen in their atmospheres.
Think of it, we can wear gold because there is an element called gold. We have water because of the elements hydrogen and oxygen. We have wires because of the elements copper, silver and aluminium.
A compound is formed from two or more elements chemically combined.
Compounds are not elements; rather, they are formed from elements.
H2O (water) is a compound formed from hydrogen and oxygen. It is neither hydrogen nor oxygen.
Once a compound is formed, it is very difficult to revert it to the constituents’ elements that formed it. As a result, the change that accompanies the formation of a compound is a chemical change.
Below are some reactions that show the formation of compounds:
A mixture is a combination of two or more elements physically combined. A mixture can be homogeneous or heterogeneous.
Homogeneous mixture is seen when it has a uniform composition all through. For instance, the mixture of salt and water is considered to be a homogeneous when properly mixed together. The solution of a homogeneous mixture appears to be pure.
Heterogeneous mixture is seen when different sections of the mixture have different composition of the substances that it’s made of. Examples are:
A mixture is always an attribute of a physical change.
When the term mixture is used on a substance, consider such substance to be easily reversible to it whatever formed it.
Amazing facts in Chemistry
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