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hardness of water
Durable in water

Hardness of water. Supply network water is described as soft or hard. Hard water does not foam easily with soap, but rather forms a buoyant, and requires more soap than soft water, which foams easily. Hard water has passed over and through rocks in which it has dissolved, such as limestone, chalk, and gypsum (CaSO4), and soft water has collected in areas with rocks that are insoluble in water, such as granite rocks.

The hardness of water results from calcium and magnesium salts dissolved in it. Mineral ions are practically responsible because they react chemically with soap, forming “floats.”

There are two types of hard water:
Temporary hardness The water contains hydrogen calcium carbonate as a result of somewhat acidic rain that dissolves chalk and limestone:

CaCO3 + H2O + CO2 = CalHCO3) 2
(Water) (Gas) (Liquid) (Solid)

Calcium hydrogen carbonate
Rain water
Calcium carbonate

This hardness is called temporary because it is easily removed by boiling, and the reaction reverses to form insoluble carbonates. Permanent hardness: Water contains sulphate, not calcium and magnesium sulphate, dissolved in it. It is not removed by boiling, and its removal is possible by adding sodium carbonate to precipitate insoluble carbonates. Soap forms buoyancy with hard water as a result of the formation of insoluble salts. This does not happen with detergents that do not contain soap. The use of hard water in boilers and immersion heaters makes it more difficult to use these devices over time because calcium carbonate accumulates on the heating rods and becomes ineffective. Materials such as Calgon and Permutit are used to make water softer through the use of ion exchange.

heat energy
energize calories

Thermal energy . All materials contain thermal energy. The higher the temperature of the substance, the greater its thermal energy. The source of this energy is the movement of atoms and molecules, i.e. kinetic energy. Thermal energy is taken up during endothermic reactions and released during exothermic reactions.


helium
helium m

Helium. An inert gas found in natural gas - natu ral gas. It is also found in a very small percentage in the atmosphere. It is a monatomic gas and is not reactive at all. It is used in balloons because it is eight times less dense than air and is not flammable. Helium is also used in deep-sea divers' breathing apparatus.


heterogeneous reaction
Reaction to heat


Heterogeneous reaction. When chemical reactions occur between substances with different physical states, i.e. gaseous, liquid and/or solid substances, the reactions are said to be heterogeneous.
See homogeneous reaction.

Examples:

Zn + 2HCI → ZnCl + H2
(Gas) (Aqueous) (Aqueous) (Solid)

2H2O + 2Na → 2NaOH + H₂
(gas) (water) (solid) (liquid)

2Na (solid) + CI2 (gas) → 2Na CI2 (solid)

CaCO3 (solid) → (solid) CuO CO2 + (gas)


Hofmann voltmeter
voltamètre m de Hoffmann

Hoffman volt-ampere meter. The ampere meter is filled by opening the two taps and pouring the electrolyte into the middle tube until the device is full. When the two taps are closed and the current is passed, any resulting gases collect in the two external tubes above the two paths.
The volume of gases can be measured, and gases can be collected and tested.


homogeneous reaction
Reaction to homogène

Homogeneous reaction. Reactions are homogeneous when...
All reactants and products are in the same physical state.

Examples:

(solid) Fes → (solid) S + (solid) Fe

N2 (gas) + 3H2 (gas) → 2NH3 (gas)


homologous series
Series f homologue

Identical series. A series of compounds that have the same general formula, such as:

Alkanes CnH2an + 2 alkane
CnH2n alkenes

The compound has the same functional groups and the same chemical properties. The physical properties of the identical chain change only gradually. Examples:

CnH2n+2: alkanes

CH4 Matan
n=1

CH6 etan
n=2

C3H8 propane
n=3