## Flame tests to identify some metal cations and metals.

Flame tests are a simple and effective way to identify the presence of certain metal cations in a sample. The principle behind flame tests is that when a metal cation is heated in a flame, it will emit light of a specific color that can be used to identify the metal cation.

Experimental Method:

1. Obtain a Bunsen burner and a clean wire loop.
2. Prepare a solution of the metal cations to be tested.
3. Dip the wire loop into the solution and hold it in the flame.
4. Observe the color of the flame and compare it to a known color chart or reference.
5. Repeat the test for different metal cations to identify them.

Data Analysis:

The color of the flame can be used to identify the metal cation present in the sample. Different metal cations will emit different colored flames. For example, sodium ions produce a yellow flame, copper ions produce a blue-green flame, and lithium ions produce a red flame.

Conclusion:

Flame tests are a simple and effective way to identify the presence of certain metal cations in a sample. By observing the color of the flame, it is possible to identify the metal cation present in the sample. It’s important to note that flame tests can give false positives, so chemical tests like spectroscopy should be used to confirm the results.

## Momentum

Momentum is a measure of an object’s inertia or its resistance to changes in its motion. It is calculated as the product of an object’s mass (m) and its velocity (v). So, the formula for momentum (p) is:

p = m x v

Where: p = momentum m = mass of the object (in kg) v = velocity of the object (in m/s)

Example: If an object has a mass of 5 kg and is moving at a velocity of 10 m/s, then its momentum would be: p = 5 kg x 10 m/s = 50 kg m/s

Momentum is a vector quantity, which means it has both magnitude and direction. The magnitude of momentum is simply the product of an object’s mass and velocity, as described by the formula p = mv. The direction of momentum is the same as the direction of an object’s velocity.

For example, consider a car moving east with a mass of 1000 kg and a velocity of 20 m/s. The magnitude of its momentum would be: p = mv = 1000 kg x 20 m/s = 20,000 kg m/s

The direction of the momentum would be in the east, the same as the direction of the car’s velocity.

Another example is a ball thrown upwards with a mass of 0.2 kg and a velocity of 10 m/s upward. The magnitude of its momentum would be: p = mv = 0.2 kg x 10 m/s = 2 kg m/s

The direction of the momentum would be upward, the same as the direction of the ball’s velocity.

It’s important to note that in collisions and other interactions between objects, the total momentum of a closed system (systems with no external forces) is conserved, which means that the momentum of all objects before and after the collision will be equal. This is the principle of conservation of momentum.

## PHYSICAL SCIENCES GRADE 11 CONTROLLED TEST TERM 4 2021

Paper shared with the help KC Kakinda

## Resultant of perpendicular vectors

The resultant of two or more perpendicular vectors is the vector sum of those vectors. The magnitude of the resultant vector is equal to the square root of the sum of the squares of the magnitudes of the individual vectors.

Mathematically, if vectors A and B are perpendicular to each other and have magnitudes A and B, respectively, the magnitude of their resultant vector R is given by:

R = √(A^2 + B^2)

The direction of the resultant vector is given by the angle that it makes with the positive direction of one of the axes.

In two dimensions, the direction of the resultant vector can be found using the Pythagorean theorem and trigonometry. In three dimensions, the direction of the resultant vector can be found using the scalar and vector products of vectors.

The concept of the resultant of perpendicular vectors is important in various fields, including mechanics, engineering, and physics, where it is used to analyze the relationships between forces and their effects on objects.

## Formal experiment 1: Heating and cooling curve of water

Aim

To investigate the heating and cooling curve of water.

Apparatus

beakers

ice

Bunsen burner

thermometer

water

Chipa Thomas Maimela‘s insight:

Method

Place some ice in a beaker.

Measure the temperature of the ice and record it.

After 1 minute measure the temperature again and record it. Repeat every minute, until at least 3 minutes after the ice has melted.

Plot a graph of time versus temperature for the heating of ice.

Heat some water in a beaker until it boils. Measure and record the temperature of the water.

Remove the water from the heat and measure the temperature every 1 minute, until the beaker is cool to touch.

Warning:

Be careful when handling the beaker of hot water. Do not touch the beaker with your hands, you will burn yourself.

See on everythingscience.co.za

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## The mole concept and Avogadro’s number explained

A mole is a unit of measurement used in chemistry to express amounts of a chemical substance. One mole of a substance is defined as the amount of substance that contains Avogadro’s number of entities. Avogadro’s number is defined as the number of entities (atoms, molecules, ions, etc.) in one mole of a substance and has a value of 6.022 x 10^23 entities/mole. This allows chemists to calculate the number of entities in a sample of a substance by using the relationship between the mass of the substance and Avogadro’s number. See the detailed explanation by Science is Lit in the video.

## The formation of the dative covalent (or coordinate covalent) bond

The formation of a dative covalent bond, also known as a coordinate covalent bond, occurs when one atom donates both of its electrons to another atom to form a covalent bond. This type of bond is also known as a “dative” bond because the electrons are donated by one atom to another, rather than being shared equally.

For example, in the case of H3O+ (hydronium ion) and NH4+ (ammonium ion), the dative covalent bond forms between the oxygen atom in H3O+ and the nitrogen atom in NH4+. The electron diagram for this formation is as follows:

H3O+:

```` `
``` O
/ \
H   H
``````

NH4+:

````  `  ```N
/ \
H   H
|   |
H   H
``````

The oxygen atom in H3O+ has a lone pair of electrons, while the nitrogen atom in NH4+ has a partially filled outer shell. When these two atoms come into close proximity, the oxygen atom donates one of its lone pair of electrons to the nitrogen atom, forming a covalent bond. This results in the formation of H3O+ NH4+ molecule.

The electron diagram for this molecule is:

H3O+ NH4+ :

````     `
```O
/ \
H   H
|
N
/ \
H   H
|   |
H   H
``````

In this case, the oxygen atom donates one of its electrons to the nitrogen atom, forming a dative covalent bond. As a result, the nitrogen atom now has a full outer shell of electrons, and the oxygen atom has a single lone pair of electrons.

It’s important to note that this type of bond formation can occur between other types of atoms and molecules as well, not just H3O+ and NH4+. Dative covalent bond formation can be observed in many chemical reactions and is an important concept in understanding the behavior of molecules and their interactions with other molecules.

## A chemical bond

A chemical bond is a force that holds atoms together in a molecule. It is formed by the attraction between the positively charged nuclei of atoms and the negatively charged electrons surrounding them. The strength of this attraction is determined by the distance between the atoms and the number of electrons involved in the bond.

There are several types of chemical bonds, each with its own characteristics and properties. The most common types of chemical bonds are covalent, ionic, and metallic bonds.

Covalent bond: It is formed when two atoms share electrons. The shared electrons occupy a region of space called a molecular orbital, which is located between the nuclei of the two atoms. The strength of a covalent bond is determined by the number of electrons shared and the distance between the atoms. Covalent bonds are typically found in molecules made up of non-metal elements.

Ionic bond: It is formed when one atom donates an electron to another atom. The atom that loses an electron becomes positively charged and is called a cation, while the atom that gains an electron becomes negatively charged and is called an anion. The strength of an ionic bond is determined by the attraction between the positively and negatively charged ions. Ionic bonds are typically found in compounds made up of metal and non-metal elements.

Metallic bond: It is formed by the attraction between positively charged metal ions and a sea of delocalized electrons. The strength of a metallic bond is determined by the number of delocalized electrons and the distance between the metal ions. Metallic bonds are typically found in compounds made up of metal elements.

The net electrostatic force two atoms sharing electrons exert on each other is the chemical bond that holds atoms together in a molecule. Understanding the properties of chemical bonds is essential for understanding the behavior of molecules and their interactions with other molecules.

## Names and formulae of substances.

• Water: H2O
• Carbon dioxide: CO2
• Nitrogen gas: N2
• Oxygen gas: O2
• Glucose: C6H12O6
• Methane: CH4
• Ethanol: C2H5OH
• Sodium chloride: NaCl
• Calcium oxide: CaO
• Sulfuric acid: H2SO4
• Ammonium hydroxide: NH4OH
• Hydrochloric acid: HCl
• Nitric acid: HNO3
• Acetic acid: CH3COOH
• Potassium hydroxide: KOH
• Magnesium oxide: MgO
• Iron(II) sulfate: FeSO4
• Copper(II) chloride: CuCl2
• Silver nitrate: AgNO3
• Gold chloride: AuCl3
• Sodium bicarbonate: NaHCO3
• Potassium permanganate: KMnO4
• Calcium carbonate: CaCO3
• Ferrous sulfate: FeSO4
• Copper sulfate: CuSO4
• Ammonium carbonate: NH4HCO3
• Aluminium hydroxide: Al(OH)3
• Iron(III) chloride: FeCl3
• Zinc chloride: ZnCl2
• Barium chloride: BaCl2
• Nickel(II) sulfate: NiSO4
• Magnesium nitrate: Mg(NO3)2
• Silver chloride: AgCl
• Platinum(IV) chloride: PtCl4
• Tin(II) chloride: SnCl2
• Titanium(IV) oxide: TiO2
• Chromium(III) chloride: CrCl3