Chemistry

Mole Concept and Stoichiometry

365 Questions

The mole concept is a core area of chemistry focusing on the quantitative relationships between reactants and products in chemical reactions. Questions cover molecular mass calculations, stoichiometric conversions, and determining the number of molecules. This topic is essential for most science entrance and competitive examinations.

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Mole Concept and Stoichiometry Questions

Multiple choice

Which of the following statements is false about a compound, which is combined in the fixed proportion?

  1. 4 grams of hydrogen combine with 32 grams of oxygen to give 36 grams of water.

  2. In the molecule of carbon dioxide, carbon and oxygen are present in fixed ratio of 3 : 8 by mass.

  3. In the molecule of water, hydrogen and oxygen are present in the ratio of 1 : 8.

  4. 12 grams of carbon combine with 32 grams of oxygen to give 40 grams of carbon dioxide.

  5. In the molecule of carbon monoxide (CO), the ratio of carbon and oxygen is 3 : 8.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

In the molecule of carbon monoxide (CO), the ratio of carbon and oxygen is 3 : 4, but not 3 : 8[CARBON : OXYGEN = 12 : 16 = 3 : 4]

Multiple choice

If M is molecular wt of the ion IO4-, what is the equivalent mass if it is converted into I2 in acidic medium?

  1. <span style="font-size:11.0pt;line-height:115%;font-family:"Calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;mso-bidi-theme-font:minor-latin;mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">M/6

  2. <span style="font-size:11.0pt;line-height:115%;font-family:"Calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;mso-bidi-theme-font:minor-latin;mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">M/7

  3. <span style="font-size:11.0pt;line-height:115%;font-family:"Calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;mso-bidi-theme-font:minor-latin;mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">M/5

  4. <span style="font-size:11.0pt;line-height:115%;font-family:"Calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;mso-bidi-theme-font:minor-latin;mso-ansi-language:EN-US;mso-fareast-language:EN-US;mso-bidi-language:AR-SA">M
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For conversion of IO4- to I2 in acidic medium the reaction is as under. IO4- + 7e- → I2……………… here oxidation state of I in IO4- is +7 and in I2 is 0, so gain in number of electrons is of +7. We know that equilibrium weight is given by eqilibrium weight = molecular mass/gain in number of electrons = M/7

Multiple choice

The molecular weight of a substance can be calculated by measuring

  1. density in liquid state

  2. freezing point

  3. vapour density

  4. vapour pressure
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Vapor density is the density of a vapor in relation to that of hydrogen. It may be defined as mass of a certain volume of a substance divided by mass of same volume of hydrogen. 

Multiple choice

A formula representing the simplest ratio of atoms in a molecule is

  1. chemical formula

  2. molecular formula

  3. empirical formula

  4. structural formula

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

An empirical formula represents the simplest whole number ratio of various atoms present in a compound. If the mass per cent of various elements present in a compound is known, it's empirical formula can be determined. Molecular formula can further be obtained if the molar mass is known.

Multiple choice

Given compound always contains exactly the same proportion of elements by weight. This is

  1. law of multiple proportions

  2. law of conservation of mass

  3. avogadro law

  4. law of definite proportions
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This law was given by, a French chemist, Joseph Proust. He stated that a given compound always contains exactly the same proportion of elements by weight. Proust worked with two samples of cupric carbonate — one of which was of natural origin and the other was synthetic one. He found that the composition of elements present in it was same for both the samples

Multiple choice

Formula of a compound is used to calculate

  1. molecular mass

  2. formula mass

  3. average atomic mass

  4. atomic mass
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Some substances such as sodium chloride do not contain discrete molecules as their constituent units. In such compounds, positive (sodium) and negative (chloride) entities are arranged in a three-dimensional structure. It may be noted that in sodium chloride, one Na+ is surrounded by six Cl-- and vice-versa. The formula such as NaCl is used to calculate the formula mass instead of molecular mass, as in the solid state sodium chloride does not exist as a single entity.

Multiple choice

Which of the following is not indicated by the formula 'CO2'?

  1. Molecular weight of carbon dioxide is 44.

  2. Carbon dioxide contains 32 parts by weight of carbon.

  3. Carbon atom is joined with the oxygen atoms by chemical bonds.

  4. There are three atoms in the molecule.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

It contains 12 parts by weight of carbon.