Tag: molecular formula and valency

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Multiple choice chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

A formula tells about :

  1. number of atoms present in one molecule

  2. gives mathematical formula

  3. an element

  4. the source of the compound
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A Correct answer
Explanation

Molecular formulas describe the exact number and type of atoms in a single molecule of a compound. The constituent elements are represented by their chemical symbols, and the number of atoms of each element present in each molecule is shown as a subscript following that element's symbol. The molecular formula expresses information about the proportions of atoms that constitute a particular chemical compound, using a single line of chemical element symbols and numbers. Sometimes it also includes other symbols, such as parentheses, dashes, brackets, and plus (+) and minus (–) signs.

Multiple choice chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

The molecular formula is a short form representation of

  1. A compound

  2. An element

  3. A mixture

  4. An alloy
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A Correct answer
Explanation

 A chemical formula that shows the total number and kinds of atoms in a molecule, but not their structural arrangement or the molecular formula is a short form representation of a compound.

Multiple choice chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

When naming a binary compound, what determines the prefix for an element in a compound?

  1. The number of atoms of that element in the compound

  2. The number of valence electrons in the element

  3. The total number of atoms in the compound

  4. The number of shared electrons in the compound

  5. The number of different elements in the compound
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A Correct answer
Explanation

When naming a binary compound, the number of atoms of that element in the compound determines the prefix for an element in a compound.
For example, while naming  $N _2O _3 $, the prefix di is used for $N$ which indicates $2 N$ atoms and the prefix tri is used for $O$ which indicates $3 O$ atoms. Hence, the name dintirogen trioxide.

Multiple choice chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

The salt of an oxyacid of a metal M contains one sulphur and four oxygen atoms

The oxyacid of the salt is

  1. $H _{2}SO _{4}$
  2. $H _{2}SO _{3}$
  3. $H _{2}S _{2}O _{7}$
  4. $H _{2}S$
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A Correct answer
Explanation

The salt of an oxyacid of a metal M contains one sulphur and four oxygen atoms. The oxyacid of the salt is $H _{2}SO _{4}$. One sulphur and four oxygen atoms indicate sulphate ion $(SO _4^{2-})$. Hence, the salt is metal sulphate and the oxyacid is sulphuric acid.

Multiple choice chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

The trivial name of $Na _{2}CO _{3}$ is:

  1. soda ash

  2. soda carb

  3. soda

  4. baking soda
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A Correct answer
Explanation

Trivial name of $Na _2CO _3\longrightarrow$ Soda Ash

Chemical name of $Na _2CO _3\longrightarrow$ Sodium Carbonate
A chemical formula is of great importance
$\longrightarrow$ Name of compounds are represented by the chemical formula.
Example: Sodium bicarbonate$\longrightarrow NaHCO _3$
Sulphuric acid $\longrightarrow H _2SO _4$
$\longrightarrow$ It is known by chemical formula how many atoms of a particular element are present in the compound.
Example: Phosphoric acid
$H _3PO _4$ shows that there are $3$ atoms of hydrogen, $1$ atom of Phosphorus and $4$ atoms of oxygen.
$\longrightarrow$ It represents what elements are present in the compound by its symbol.
Example:- $NaCl\longrightarrow$ Sodium chloride has sodium and chlorine in it.

Multiple choice chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

Predict the formulae of the binary compounds formed by combination of the following pairs of elements:
(i)    Magnesium and nitrogen
(ii)   Silicon and oxygen

  1. $MgN _{2}, SiO _{2}$
  2. $Mg _{3}N _{2}, SiO _{2}$
  3. $Mg _{2}N _{3}, Si _{2}O _{3}$
  4. $MgN, SiO _{2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Three Mg ( $+2$ oxidation state) combine with two N ($-3$ oxidation state) to form $Mg _3N _2$.

One Si ( $+4$ oxidation state) combine with two O ($-2$ oxidation state) to form $SiO _2$.

Note: In a neutral molecule, the total charge on cations is numerically equal to the total charge on anions.

Multiple choice chemistry atoms, molecules and radicals molecular formula and valency valency and chemical formulae combining capacity and chemical formulae

Predict the formula of stable compound formed by an element with atomic number 114 and fluorine.

  1. $AF _{3}$
  2. $AF _{2}$
  3. $AF$
  4. $AF _{4}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Element A with atomic number 114 will share four electrons to attain stable noble gas electronic configuration. It falls in the Carbon family.

Fluorine shares one electron to attain stable noble gas electronic configuration. One atom of A combines with four atoms of F to form $AF _4$.

Hence, the correct option is $\text{D}$