I.6. Physical and chemical properties.
- I.6.1. Physical properties.
- I.6.2. Chemical properties.
- I.6.3. Observation of the physical and chemical properties of some substances.
- I.6.4. Apply what you learned in Physical and Chemical Properties.
The characteristic attributes with a help of which a substance is recognized are called properties.
Properties can be physical and chemical.
I.6.1. Physical properties.
Physical properties are those attributes that refer to appearance or transformations that do not change the composition of the substance.
Physical properties can be classified into:
1. Observable with the help of the sense organs:
- By sight: state of aggregation (solid, liquid, gas), color (colorless-without colour or colored), gloss (shine).
- By smell: odorless (has no smell), pleasant, irritating, specific smell (milk, chlorine, vinegar - we say they have a specific smell).
- By touch: plasticity, elasticity, soft (hardness), hard (hardness).
2. Measurable with the help of devices:
- Physical constants:
- Melting temperature (the temperature at which a solid substance begins to melt = Tt);
- Boiling temperature (the temperature at which a liquid begins to boil = Tv);
- Density
- Refractive index
- Solubility coefficient (shows how much substance dissolves in 100 g of water, at a certain temperature);
- Hardness (it is measured according to a scale of hardness from 1 to 10, called "Mohs Scale", where talc has 1 and diamond the highest hardness 10);
- Electrical and thermal conductivity (passage of electric current, respectively heat, without movement of substance).
I.6.2. Chemical properties.
Chemical properties are those properties that refer to transformations that change the composition of the substance.
Examples of chemical properties:
- The property of burning (after burning the paper, we no longer have paper, we have ashes);
- The property of fats to go rancid (the rancidity is a different substance than the non-rancid oil);
- The property of wine to turn into vinegar (vinegar is a different substance than wine);
- The property of milk to turn sour (sour milk has a different composition and other properties than sweet milk);
- The property of iron to rust (rust is a substance other than iron);
- Copper's property of coking (coking is a different substance from copper;
- The property of wood to rot (rot has a different composition than wood).
I.6.3. Observation of the physical and chemical properties of some substances.
π Experiment: The property of iron to rust
Required Materials: Test tube, iron filings, bowl of water.
Experiment description:
- Moisten a test tube and put iron filings on its bottom and turn it upside down in a bowl of water.
- Wait a day and see what happens.
Experiment conclusion: Iron has the property to rust - a chemical property, because iron changes its composition and turns into rust.
The property of some substances to burn
π Experiment: Burning Magnesium with a Blinding Flame π₯ Warning! This experiment is performed only in the presence of an adult! π₯ Warning! When working with fire sources make sure to keep your hair tight and don't wear clothes with wide sleeves! π₯ Warning! Do not look at the blinding flame from burning magnesium as it causes eye damage!
Required Materials:
Magnesium ribbon, spirit flask, metal pliers, match.
Experiment description:
- A ribbon of magnesium is held with tongs to the tip of the flame of a spirit flask and it is observed that after a while the magnesium ignites and burns with a blinding flame and turns into a white powder.
Experiment conclusion:
Some substances have the property of burning - chemical property, as the substance has changed its composition (magnesium has turned into magnesium oxide).
The property of some substances to burn
π Experiment: Burning copper
π₯ Warning! This experiment is performed only in the presence of an adult!
π₯ Warning! When working with fire sources make sure to keep your hair tight and don't wear clothes with wide sleeves!
Required Materials:
Copper wire, spirit flask, metal pliers, match.
Experiment description:
- A copper wire is held with tongs at the top of the flame of a spirit flask and it is observed that the copper wire burns with a greenish flame and turns black after burning (copper oxide is formed).
Experiment conclusion:
Some substances have the property to burn - chemical property, as the substance has changed its composition.
The property of some substances to burn
π Experiment: Burning iron
π₯ Warning! This experiment is performed only in the presence of an adult!
π₯ Warning! When working with fire sources make sure to keep your hair tight and don't wear clothes with wide sleeves!
π₯ Caution! Iron filings are flammable! Be careful not to burn yourself from the incandescent chips!
Required Materials:
Iron filings, spirit flask, metal pliers, match.
Experiment description:
- Sprinkle iron filings in the flame of a spirit flask. The iron filings burn with bright sparks and turn into a black powder (iron oxide).
Experiment conclusion:
Some substances have the property to burn - chemical property, as the substance has changed its composition.
Iron has the property of forming copper when placed in a solution of bruised stone (copper sulfate).
π Experiment: The reaction between iron and copper sulfate
π₯ Warning! This experiment is performed only in the presence of an adult!
π₯ Caution! Caution! Bruise stone (copper sulfate) is a toxic substance, do not touch or taste it!
Required Materials:
An iron nail, a Berzelius glass, bruised stone (copper sulfate) solution.
Experiment description:
- Insert the nail into the glass of bruised stone solution, so that part of it remains in the air. After a short time it is noticed that the part of the nail in the solution has been covered with a coppery substance.
Experiment conclusion:
Iron has the property of forming copper when placed in a solution of bruised stone - chemical property as the iron has changed its composition.
Electrical conductivity of some substances
π Experiment: Electrical conductors and insulators
Required Materials:
Circuit consisting of a battery, connecting wires, light bulb, metal wires, graphite lead, wood, glass, rubber gum.
Experiment description:
- Connect the bulb to the battery and at the ends of the two free ends of the circuit intercalate different substances (iron, copper, gold, silver, zinc, lead, aluminum, graphite, glass, wood, rubber) and observe on which substances the bulb lights up.
Experiment conclusion:
Some substances have the property of being electrical conductors, allowing electric current to pass through them (all metals, graphite). This property is called electrical conductivity β a physical property because it does not change the composition of the substance. Other substances are electrical insulators - that is, they do not allow current to pass through them (glass, wood, rubber, etc.).
Thermal conductivity of some metals
π Experiment: What is thermal conduction
π₯ Warning! This experiment is performed only in the presence of an adult!
π₯ Warning! When working with fire sources make sure to keep your hair tight and don't wear clothes with wide sleeves!
Required Materials:
Candle, spirit flask, metal tongs, test tube, water, copper wire, match.
Experiment description:
- Light a candle and drip the melted wax along the wire, let the wax beads harden.
- Hold the waxed wire with the tongs in the flame of the spirit flask and observe how the wax beads melt.
Experiment conclusion:
Metals have the property of conducting heat through them from the heated end to the unheated end, called thermal conductivity, that is, they are thermal conductors β physical property because they do not change the composition of the substance.
π Experiment: Water is a thermal insulator
π₯ Warning! This experiment is performed only in the presence of an adult!
π₯ Warning! When working with fire sources make sure to keep your hair tight and don't wear clothes with wide sleeves!
Required Materials:
Candle, spirit flask, metal tongs, test tube, water, match.
Experiment description:
- Put water in a test tube, up to the middle of the test tube;
- At the flame of a spirit flask, heat the water in the test tube at the top, holding the test tube with your hand at the bottom and pointing the mouth at the opposite side of you.
Experiment conclusion:
- After a while, the water on the surface begins to boil, while at the bottom you don't feel the heat at all.
- Water is a bad conductor of heat. All liquids (except mercury, which is a metal) are thermal insulators. The uniform heating of liquids and gases takes place by convection, with the help of currents (displacement of substance).
π Experiment: Air is a thermal insulator
π₯ Warning! This experiment is performed only in the presence of an adult!
π₯ Warning! When working with fire sources make sure to keep your hair tight and don't wear clothes with wide sleeves!
Required Materials:
Candle, spirit flask, metal tongs, test tube, match.
Experiment description:
- Take the empty test tube (ie with air) and insert a finger at the open end of the test tube;
- Heat the bottom of the test tube (the closed part) in the flame of the spirit flask, shaking it continuously so that it does not break.
Experiment conclusion:
- The finger in the test tube does not feel the heat at all.
- Air is a poor conductor of heat. In general, all gases are thermal insulators, but especially rarefied gases. The fibers of woolen clothes, animal fur, bird feathers, snow are thermal insulators, because they contain air.
π Experiment: Water has the property to boil at 100 Β°C
π₯ Warning! This experiment is performed only in the presence of an adult!
π₯ Warning! When working with fire sources make sure to keep your hair tight and don't wear clothes with wide sleeves!
Required Materials:
Erlenmeyer beaker with distilled water, rubber stopper fitted with thermometer, asbestos sieve, spirit flask, matches, clock or stopwatch.
Experiment description:
- Close the water in the glass with the stopper fitted with the thermometer so that the thermometer does not enter the water and heat the water through the strainer at the still flame.
- Measure the time since the start of the heating and complete the following table:
Experiment conclusion:
- Water has the property of boiling at 100 Β°C β physical property, because it does not change the composition of the substance (steam is still water, but in a gaseous state)
- Every liquid begins to boil at a certain temperature, called the boiling point, which is a constant of the material (see table of constants at the end of the manual). During boiling, the boiling temperature is constant.
I.6.4. Apply what you learned in Physical and Chemical Properties.
π Homework
1. Specify the type of property: physical or chemical.
A. Bruise stone (copper sulfate) is soluble in water.
B. Wood has the property of rotting.
C. The paper has the property of burning.
D. Iron has the property of being attracted to a magnet.
E. Carbon dioxide is a colorless gas.
F. Copper has the property of coking.
G. Sulfur is a thermal and electrical insulator.
H. Mercury is liquid.
I. Fog is formed by the condensation of water vapor in the air on the earth's surface.
J. The ice melts in the child's palms.