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
Mixtures will always require a form of separation. The reason is because a mixture must contain more than one substance.
Take for instance, water (H2O) is a pure substance; but when we add common salt (NaCl) to it, the water no longer becomes pure (since it has been mixed with another substance).
Please read more on mixtures and their characteristics here.
Together, the water and salt are considered to be mixtures and thus may be separated in order to regain its constituents, that is, the salt and water respectively.
A mixture will always contain two or more substances in any proportion.
You can read more on elements and their characteristics here.
Based on the uniformity of the mixture, we could classify a mixture as either homogenous or heterogeneous.
The composition of substances in a homogenous mixture is uniform all through. For instance, the mixture of salt and water will be homogenous.
The liquid that dissolves the solid in a homogeneous mixture is known as the solvent. Water in the above instance is a solvent.
The solid that is dissolved by the solvent is known as the solute. Salt is the solute in the above instance.
An example of a heterogeneous mixture is sand and water.
Please read on physical and chemical changes in chemistry here.
In chemistry, students are expected to work with substances like salts, acid and bases.
Recall that substances may be classified in two ways. These are:
It is important to state that the technique for separating one mixture will vary from another. This is due to the different nature of components present in the mixture, together with their physical properties like boiling point, melting point and solubility.
Please read on the physical properties of metals here.
Below are types of separation techniques (for separating mixtures):
Filtration is used as a method to separate an insoluble solid from a liquid. Examples of mixtures separated through filtration include:
Below is an image showing the filtration process:
The material utilized in carrying out the process of filtration could be a filter paper, sieve with microscopic pores or even a cotton material.
The liquid that is collected into the filtration flask is known as the filtrate while the solid that remains on the filter paper is called the residue.
Filtration as a separation technique is a commonly used process in the purification of a town’s water supply. In this case, filter beds are utilized.
You can read on compounds in chemistry and their characteristics here.
Decantation is a process used for the separation of an insoluble solid from a liquid; and the insoluble solid must sediment: that is, settle at the bottom of the container, leaving a clear liquid above.
An instance where decantation can be used is in the separation of water and sand. Sand is insoluble in water and will sediment at the bottom, leaving a clear liquid above.
The term 'sedimentation' is used when an insoluble solid settle at the bottom of a container. The clear liquid above the sediment is referred to as the supernatant.
During the process of decantation, we need to carefully pour off or decant the top/upper clear liquid (called supernatant), leaving behind the insoluble solid (sediment) in the container.
Although decantation may be quite similar to filtration with regards to what is separated, the fact remains that decantation is less effective since it cannot ensure complete separation of the insoluble solid from the liquid.
A separating funnel is used to separate two immiscible liquid. Examples of immiscible liquids are water and oil, kerosene and water, etc.
The two immiscible liquids that are to be separated will usually have different densities or weights; and as a result, one will always rise above the other.
Please read more on density and specific gravity here.
With regards to water and oil, water has a higher density of 1.003g/m3, and will remain at the bottom (sinks). Consequently, the oil floats above it since it has a lesser density of 0.811g/m3.
Immiscible (or Non miscible) liquids do not dissolve in each other and they can be separated via the separating funnel.
A separating funnel is also called a separatory funnel.
Below is an image of a separating funnel:
When the mixture of the two immiscible liquid are put in the separating funnel, the tap/stopcock is opened and the liquid with the higher density is first collected (water in our case) followed by that with the lower density (oil).
Evaporation is used to separate the components of a soluble solid in a liquid and the solid must not be decomposed on heating.
A mixture of sodium chloride in water can be separated through evaporation. See the image below:
The basic apparatus required to carry out evaporation are:
After evaporation, the liquid will be lost to the atmosphere while the solid (salt in our instance) remains in the evaporating dish.
Please read on layers and composition of the atmosphere here.
Meanwhile, the solid that remains in the evaporating dish is termed as residue
Please read on the separation of mixtures - part 2 here
Please read on the separation of mixtures - part 3 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:
