Basic Concepts of Chemistry
- The periodic table of the elements, is an ordered arrangement of the chemical elements into rows and columns.
- Periods:The horizontal rows are called periods.
- Groups:The vertical columns are called groups, and elements within the same group often share similar chemical properties.
- Chemical Symbol:A one or two-letter abbreviation for the element (e.g., H for Hydrogen, Fe for Iron).
- Atomic Number:The number of protons in the nucleus.
- Average Atomic Mass:The weighted average of the element’s isotopes.
- What is pH?
Ans: pH/pOH is the negative logarithm of Hydrogen ion/Hydroxyl ion concentration. Measurement of pH of any aqueous sample solution gives the degree of acidity or alkalinity of the solution. Mathematically it may be represented as follows;pH= – log [ H+ ].
pOH = – log [OH- ]. - Conductivity:
Conductivity is the measurement of materials ability to conduct electric current. Measurement of conductivity of sample solution gives the degree of electrical conductance in a defined volume of the solution.
- What is Molarity ?
- Definition: Number of Moles of substance dissolve in per liter of solution.
- Calculation:
Molarity= Number of Moles of substance________
Volume of solution in liter
- What is Normality ?
- Definition: Normality is the number of equivalents of a reactive species per liter of solution.
- Calculation:
Normality= Molarity x n
n=is the number of equivalents per mole.
- Reagent: Reagent is a substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs.
- Indicators: Indicators are reagents used to determine the specified endpoint in a chemical reaction which indicates the change in colour, to measure hydrogen-ion concentration (pH) or to indicate the desired change in pH has been effected.
- Buffer solutions: Buffer solutions are solutions that resist change in the activity of an ion on the addition of substances that are expected to change the activity of that ion.
- Molar solutions (M): Molar solutions are solutions that contain 1 gram molecule of the compound in 1 litre of solution.
- Normal solutions (N): Normal solutions are solutions that contain 1 gram equivalent weight of the compound in 1 litre of solution.
- Percentage weight in weight (%w/w): It expresses the number of grams of solute in 100 g of product.
- Percentage weight in volume (% w/v): It expresses the number of grams of solute in 100 ml of product.
- Percentage volume in volume (% v/v): It expresses the number of milliliters of solute in 100 ml of product.
- Percentage volume in weight (% v/w): It expresses the number of millilitres of solute in 100 g of product.
- Parts per million (ppm): “Parts per Million” is a way to quantify very low concentrations of substances. For example, 1 ppm is equivalent to 1 milligram of solute per litre of liquid (abbreviated as mg/L). 1 milligram of solute per millilitre of liquid (abbreviated as mg/ml).
1 mg/ml = 1000 ppm
- Flammable Chemicals: A flammable material can be a solid, liquid or gas. It is defined as any liquid having a flash point below 100o F (37.8oC). Example: Benzene, Methanol and Ethanol..
- Flash Point: It is defined as the lowest temperature at which a liquid can form an ignitable mixture in air near the surface of the liquid. The lower the flash point, the easier it is to ignite the material.
- What are the types of Volumetric Titration?
1. Acid-Base Titration:This involves the reaction between an acid and a base to form a salt and water. It is used to determine the unknown concentration of an acid or a base.
2. Redox Titration:
This type of titration is based on oxidation-reduction reactions where electrons are transferred between the titrant and the analyte.3. Precipitation Titration:
This method involves a reaction that forms an insoluble precipitate (a solid).4.Complexometric Titration:
This type of titration is used to determine the concentration of a metal ion by forming a stable coordination complex.24. What is Density?Density is the measure of mass per unit volume.
Density = Mass/ Volume
25. What is Specific Gravity/ Relative Density?
The ratio of a substance’s density to the density of a reference substance (Water).
26. What is Weight per milliliter (wt/ml)?
Weight per milliliter (wt/ml) is a measure of density with units like grams per milliliter (𝑔/𝑚𝑙). Wt/ml tells absolute weight of particular volume.
27. What is Oxidation?
The loss of electrons or addition of Oxygen in substance.
e.g. C + O2 → CO2 (oxidation of carbon)
28. What is Reduction?
The gain of electrons or addition of Hydrogen in substance.
e.g. N2 + 3 H2 → 2NH3 ( reduction of nitrogen).
29. What are mineral Acids?
Sulfuric acid (𝐻2𝑆𝑂4), Hydrochloric acid (𝐻𝐶𝑙), and Nitric acid (𝐻𝑁𝑂3).
30. What is difference Between Organic and Inorganic Compounds?
Organic compounds always have a carbon atom, while most of the Inorganic compounds do not contain a carbon atom in them. Almost all organic compounds contain carbon-hydrogen or a simple C-H bond in them.
31. What is difference between Molecular weight and Equivalent Weight?
Molecular weight is the mass of one mole of a substance, a fixed value for a given compound.
Equivalent weight, is a variable value that depends on the substance’s role in a specific chemical reaction, calculated by dividing the molecular weight by its “n-factor” or valence. The n-factor represents the number of reactive units, such as protons or electrons, that a molecule can donate or accept.
32. What is the principle of UV Spectroscopy?
The Beer-Lambert law is the principle behind UV-Vis spectroscopy, which explains that light absorbance is directly proportional to both concentration (𝑐) and path length (𝑙).
33. What UV & Visible Range?
Ultraviolet (UV) region from 190 to 400 nm and the visible light region from 400 to 800 nm.
34. What is Monochromatic light?
Light with a single wavelength or frequency.
35. What is TLC Plate?
It is combination of the plate’s stationary phase, support material, and any additional features like a fluorescent indicator. Common stationary phases include silica gel and alumina, while common support materials are glass, aluminum, or plastic.
36. What is Principle of IR?
The principle of Infrared (IR) spectroscopy is that molecules absorb infrared radiation at specific frequencies that match the vibrational frequencies of their chemical bonds, such as stretching or bending.
37. What is IR Range?
The full IR spectroscopy range is typically 12,800–10 cm⁻¹
Mid IR-4,000–400 cm⁻¹
38. What is the principle of Atomic absorption spectroscopy (AAS)?
The process involves atomizing the sample, exposing it to light of a specific wavelength from a hollow cathode lamp, and then measuring how much light is absorbed by the sample’s atoms as they make the transition from the ground state to an excited state.
39. What is the principle of Mass spectroscopy?
Mass spectrometry principle is to ionize a sample, separate the ions based on their mass-to-charge ratio (𝑚/𝑧), and then detect them to determine their relative abundance.
40. What is Gas chromatography (GC)?
Gas chromatography (GC) is a common analytical technique used to separate, identify, and quantify volatile compounds in a mixture. It works by passing a mobile gas phase through a stationary phase (a column), which separates compounds based on their boiling points, polarity, and adsorption properties.
41. What is the difference between Polar and Non-Polar Molecules?
Polar molecules have an unequal sharing of electrons, creating partial positive and negative ends, while nonpolar molecules have an equal sharing, resulting in no distinct poles.
42. What is Gravimetric analysis ?
Gravimetric analysis is a quantitative chemical technique that determines the amount of a substance by measuring its mass.
The four types of gravimetric analysis are precipitation, volatilization, electrogravimetry, and thermogravimetry.
44. What is the principle of colorimetry?
The absorbance of light by a colored solution is directly proportional to the concentration of the absorbing substance and the path length of the light through the solution.
45. What is Thermogravimetric analysis (TGA)?
Thermogravimetric analysis (TGA) is a technique that measures the weight change of a material as a function of temperature or time.
It is used to study a material’s properties, such as its thermal stability, composition, purity, decomposition reactions, and absorbed moisture content, by heating a sample in a controlled atmosphere.
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