Define "chemistry" .

Classify different types of matter as pure substances (elements or compounds) or mixtures (homogenous or heterogenous) Differentiate between physical and chemical properties of substances . Correctly use significant figures in addition, subtraction, multiplication, and division . Convert numbers to and from scientific notation

1. define "chemistry".

Chemistry is the science that studies matter, how it is composed, its properties, its composition and how its structures are transformed after undergoing various processes or reactions than its elements and atoms.

It is worth mentioning that matter is everything that surrounds us, made up of molecules and atoms that react to various chemical changes, and that can be related to the release of energy in some cases.

Chemistry studies are conducted in laboratories and use the scientific method. This has allowed the discovery of various subjects, their compositions, how they are related or transformed. Hence, elements that are basic in other scientific studies have been discovered. The relevance of studying this science, regains importance when we understand its real implication, therefore it is important to know the properties of matter and energy.

Chemistry is a science that encompasses a large number of study areas that have generated different branches or classifications of chemistry studies. Such as: organic chemistry, inorganic chemistry, biochemistry, analytical chemistry, physicochemistry, industry chemistry.

 

2. classify different types of matter as pure substances (elements or compounds) or mixtures (homogeneous or heterogeneous).

Matter is anything that has mass and occupies a place in space. Matter is made up of atoms and molecules. Everything around us and even ourselves are made of matter. The air, the earth, the water, the animals, the plants, the buildings, the vehicles; they are made up of miles of millions of atoms and molecules that are part of our daily life.

The classification of the subject is organized into two main categories with their respective subcategories.

to. Pure substances.

-Elements

-Composites

b.Mixes.

-Homogeneous mixtures (or solutions or solutions)

-Heterogeneous mixtures

 

to. Pure substances

Pure substances are made up of atoms or molecules all the same, have specific properties that characterize them and cannot be separated into other substances by physical procedures. Pure substances are classified into elements and compounds.

-Element

Elements can also be called simple pure substances and are made up of a single class of atoms, that is, atoms with the same number of protons in their nucleus and therefore with the same chemical properties. The elements cannot be decomposed into other simpler pure substances by any procedure. All the chemical elements of the periodic table are pure simple substances. Substances made up of molecules made up of the same atoms are also considered elements, for example gaseous oxygen, molecular oxygen or dioxygen.

-Compound

Compounds are substances formed by the union of two or more elements of the periodic table in fixed proportions.

A characteristic of compounds is that they have a chemical formula that describes the different elements that make up the compound and their quantity. Physicists cannot separate a compound, they can only be separated in simpler methods by chemical methods, that is, by reactions.

For example, water is a pure substance, but if we subject it to electrolysis we can separate it into the elements that make it up, oxygen and hydrogen.

 

b. Mixture

A mixture resulting from the combination of two or more substances where the basic identity of each one is not altered, that is, they do not lose their properties and characteristics due to the fact of mixing, because when doing so, no chemical reaction occurs.

For example, if iron filings are mixed with sulfur, each substance retains its properties. The composition of the mixtures is variable, the substances that make up a mixture can be present in greater or lesser amounts. Another characteristic of mixtures is that they can be separated by physical methods.

In the mixture of iron and sulfur you can use the property of magnetism that iron exhibits to be separated from sulfur.

- Homogeneous mixture

Homogeneous mixtures are also called solutions. They have a completely uniform appearance so that their components cannot be distinguished with the naked eye. This type of mixture is said to have only one phase. In chemistry a portion of matter with uniform composition and properties is called phase. For example, seawater is made up of water and many soluble salts, where only one phase is observed.

- Heterogeneous mixture

Heterogeneous mixtures have a non-uniform composition, their components can be distinguished with the naked eye, in other words, different substances are observed in the mixture. The components of this type of mixture exist as distinct regions called phases. A heterogeneous mixture is made up of two or more phases. If you look at the granite stone, you can see areas of different color that indicate that the rock is made up of crystals of different substances.

 

3. Differentiate between physical and chemical properties of substances.

The physical properties of matter are those characteristics that can be measured without altering the atomic structure, while the chemical properties of matter are those characteristics that result in a change in the atomic structure.

The characteristic physical properties of a substance are those that allow it to be identified without altering its composition, such as: color, odor, taste, density, melting point, boiling point, hardness, gloss, ductility, malleability, solubility and viscosity, among others. For example, if we boil water at sea level we know that it does so at 100 ° C (or 212 ° F) and no other substance under the same conditions boils or boils at that temperature.

Chemical properties are those that relate the compositional changes of one or more substances when they react with other substances. For example, the gas that we use in our homes, when in contact with oxygen and with a flame, burns turning into water vapor and carbon dioxide, that is, it has the property of igniting under these conditions.

The physical properties, the changes are reversible, bone that does not affect the nature of the matter, you can return it to its previous state, We can measure magnitudes and predict them, just as we can observe how in a chemical reaction the element does not change (How to mix water and salt, the salt dissolves, but the water and salt are still there in the same amounts).

Unlike chemical properties, they are those that are observed when matter experiences a change in its composition, these changes are generally irreversible. A bone property that does not affect the nature of matter, you can return it to its previous chemical state of a substance is its behavior during a chemical change.

Another difference is, the physical and chemical properties, the physical properties are those that we see with a simple view, such as color or physical state, the chemical ones that we cannot see, more than anything, are at the atomic level.

 

4. Correctly use significant figures in addition, subtraction, multiplication and division.

-Significant figures in sums and differences

    Rule 7. In an addition or a subtraction, the number of digits of the result is marked by the position of the least common digit of all the numbers that are added or subtracted.

    Therefore, in an addition or subtraction, the number of significant figures of the numbers that are added or subtracted is not the criterion for establishing the number of significant figures of the result.

 

    For example:

    (a) 4.3 + 0.030 + 7.31 = 11.64 ? 11.6

    (b) 34.6 + 17.8 + 15 = 67.4 ? 67

    (c) 34.6 + 17.8 + 15.7 ? 68.1

 

    In examples (a) and (c) the lowest digit common to the addends is the tenth (first decimal), therefore the result must be expressed up to said decimal. In example (b) the smallest digit common to the three addends is unity, therefore the result must be expressed up to unity.

   -Significant figures in products and quotients.

Rule 8. In a product or a division, the result must be rounded so that it contains the same number of significant digits as the source number that has the least number of significant digits.

 

    Therefore, unlike addition or subtraction, in multiplication or division, the number of significant digits of the quantities involved in the operation is the criterion when determining the number of significant digits of the result.

    For example:

(a) q = 24 X 4.52 / 100.0 = 1.0848 ?1.1

(b) q = 3.14159 X 0.252 X 2.352 = 0.4618141... ?0.46

 

    In the three examples presented, the smallest number of significant figures of the different factors involved in the operations is two: it is specifically the number 24 in examples (a) and (b) and the number 0.25 in the example (c ). Therefore, the results should be rounded to two significant figures.

5. Convert numbers from scientific notation.

 

Scientific notation of a number.

Scientific notation represents a number using powers of base ten. The number is written as a product

A X 10 ⁿ

Where A is a number greater than or equal to one and less than 10, and n is an integer. Scientific notation is used to easily express very large or very small numbers. It is also very useful for writing physical quantities since only significant digits are written in scientific notation.

A number in scientific notation is expressed so that it contains a digit (the most significant) in the ones place, all other digits will follow the decimal point multiplied by the respective exponent.

    Examples:

• Average Earth-Moon distance = 384,000,000 m

Average Earth-Moon distance = 3.84 X 10⁸ m (three significant figures).

 

• Radius of the hydrogen atom = 0.000000000053 m

Radius of the hydrogen atom = 5.3 X 10^-11 m (two significant figures).

 

• Speed ??of light in vacuum = 299X792,458 km / ^s.

Speed ??of light in vacuum = 2.99792458 X 10 ⁸ km / ^s (9 significant figures)