Chemistry
The group of elements known as alkaline earth metals is Group 2 of the periodic table.
This group includes the following elements:
- Beryllium (Be)
- Magnesium (Mg)
- Calcium (Ca)
- Strontium (Sr)
- Barium (Ba)
- Radium (Ra)
They are called alkaline earth metals because their oxides form alkaline solutions when dissolved in water and are found in the earth.
Valency, in chemistry, refers to the measure of the capacity of an atom to combine with other atoms. It is determined by the number of chemical bonds an atom can form.
Here are a few key aspects of valency:
- Combining Capacity: It represents the number of hydrogen atoms or other univalent atoms (atoms that form only one bond) that an atom can combine with.
- Determined by Electrons: Valency is related to the number of electrons in the outermost shell (valence shell) of an atom. Atoms tend to gain, lose, or share electrons to achieve a stable electron configuration, typically with eight electrons in their valence shell (octet rule).
- Variable Valency: Some elements can exhibit variable valency, meaning they can form different numbers of bonds depending on the chemical environment. Transition metals are particularly known for this.
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Examples:
- Hydrogen (H) has a valency of 1.
- Oxygen (O) has a valency of 2.
- Nitrogen (N) often has a valency of 3.
- Carbon (C) typically has a valency of 4.
For more detailed information, you can refer to these resources:
To standardize potassium permanganate (KMnO₄) using oxalic acid, you will perform a redox titration. Here’s a step-by-step procedure:
1. Preparation of Solutions:
- Oxalic Acid Solution: Accurately weigh a known quantity of oxalic acid (H₂C₂O₄•2H₂O) and dissolve it in distilled water to create a solution of known concentration. For example, you might dissolve around 0.630 g of oxalic acid in 100 mL of distilled water to make a 0.05 M solution.
- KMnO₄ Solution: Prepare an approximate solution of KMnO₄. The concentration does not need to be exact at this stage, as it will be standardized. A typical solution is around 0.02 M to 0.05 M. Since KMnO₄ solutions are not stable over long periods, standardization is crucial.
2. Titration Procedure:
- Preparation:
- Pipette a known volume (e.g., 20 mL) of the oxalic acid solution into a conical flask.
- Add about 20 mL of dilute sulfuric acid (1 M H₂SO₄) to the flask. The sulfuric acid provides the acidic medium necessary for the reaction.
- Heat the solution to about 60-70°C. This helps in speeding up the reaction between KMnO₄ and oxalic acid.
- Titration:
- Fill a burette with the KMnO₄ solution.
- Slowly add the KMnO₄ solution from the burette into the conical flask containing the oxalic acid solution. Continuously stir the mixture.
- Initially, the purple color of KMnO₄ will disappear as it reacts with the oxalic acid. As you approach the endpoint, the purple color will disappear more slowly.
- Continue adding KMnO₄ dropwise until one drop of KMnO₄ solution imparts a faint, permanent pink color to the solution that persists for at least 30 seconds. This indicates that all the oxalic acid has reacted, and you have reached the endpoint.
3. Calculation:
- Reaction Stoichiometry: The balanced chemical equation for the reaction is:
5 H₂C₂O₄ + 2 KMnO₄ + 3 H₂SO₄ → K₂SO₄ + 2 MnSO₄ + 10 CO₂ + 8 H₂O
From the equation, 2 moles of KMnO₄ react with 5 moles of oxalic acid. - Calculations:
- Calculate the number of moles of oxalic acid used:
- Use the stoichiometry of the reaction to find the number of moles of KMnO₄ that reacted:
- Calculate the molarity of the KMnO₄ solution:
Moles of H₂C₂O₄ = (Volume of H₂C₂O₄ solution in Liters) × (Molarity of H₂C₂O₄ solution)Moles of KMnO₄ = (Moles of H₂C₂O₄) × (2/5)Molarity of KMnO₄ = (Moles of KMnO₄) / (Volume of KMnO₄ solution used in Liters)
Example Calculation:
Suppose you prepared a 0.05 M oxalic acid solution, and you used 20 mL of it in the titration. The volume of KMnO₄ required to reach the endpoint was 20.0 mL.
- Moles of H₂C₂O₄ = (20/1000) L × 0.05 mol/L = 0.001 mol
- Moles of KMnO₄ = 0.001 mol × (2/5) = 0.0004 mol
- Molarity of KMnO₄ = 0.0004 mol / (20/1000) L = 0.02 M
4. Repeat Titrations:
Repeat the titration at least three times to ensure accuracy and precision. Average the molarity values obtained from multiple titrations to get a more reliable standardized concentration of the KMnO₄ solution.
Important Considerations:
- Ensure all glassware is clean.
- Use distilled water to prepare solutions.
- Heat the solution to 60-70°C to facilitate the reaction, but do not overheat, as oxalic acid can decompose.
- Stir the solution continuously during the titration.
- Observe the endpoint carefully to avoid overshooting.
The atomic number is the number of protons found in the nucleus of an atom. It is typically denoted by the symbol Z.
The atomic number uniquely identifies a chemical element. In other words, the number of protons determines what element an atom is. For example, all atoms with an atomic number of 1 are hydrogen atoms, and all atoms with an atomic number of 6 are carbon atoms.
Because an atom is electrically neutral, the number of protons is equal to the number of electrons. The number of neutrons, however, can vary, which creates different isotopes of the same element.
The atomic number is usually indicated along with the element symbol in the periodic table.
Combustion, also known as burning, is a chemical process involving rapid reaction between a substance with an oxidant, usually oxygen, to produce heat and light.
Here are key aspects of combustion:
- Exothermic Reaction: Combustion is an exothermic reaction, which means it releases energy in the form of heat and light.
- Fuel and Oxidant: Combustion requires a fuel (the substance being burned) and an oxidant (the substance that combines with the fuel). The most common oxidant is oxygen (O2) in the air.
- Ignition Temperature: Combustion typically requires an ignition temperature to initiate the reaction. This is the minimum temperature to which the fuel must be heated to start self-sustained burning.
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Products of Combustion: The products of combustion vary depending on the substances involved, but common products include:
- Carbon dioxide (CO2)
- Water (H2O)
- Heat
- Light (in the form of a flame)
More information about combustion can be found on the following resources: