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.

molecular mass calculationsstoichiometric conversionsmole fraction problemsheavy water reactionsoxidation calculations

Mole Concept and Stoichiometry Questions

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

Plaster of Paris has the formula:

  1. $CaSO _4.(1/2)H _2O$
  2. $CaSO _4.H _2O$
  3. $CaSO _4.2H _2O$

  4. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The composition of plaster of paris is $CaSO _4.(1/2)H _2O$ and the composition of gypsum is $CaSO _4.2H _2O$.

Hence the correct answer is option (A).

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

The average composition of Portland cement is:

  1. $CaO : 40 - 50\%$, $SiO _2 : 30 - 40\%$, $Al _2O _3$ and $Fe _2O _3 : 10 - 20\%$
  2. $CaO : 50 - 60\%$, $SiO _2 : 20 - 25\%$, $Al _2O _3 : 5 - 10\%$, $MgO : 2 - 3\%, Fe _2O _3 : 1 - 2\%$ and $SO _3 : 1 - 2\%$
  3. $SiO _2 : 40 - 50\%$, $CaO : 30 - 40\%$, $Al _2O _3 : 10 - 20\%$
  4. $CaO : 50\%$, $SiO _2 : 50\%$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Port land cement consists of raw materials mainly compounds of lime mixed with silica and alumina.

$ CaO \rightarrow 50-60$%
$ SiO _2 \rightarrow 20-25$%
$ Al _2O _3 \rightarrow 5-10$%
$ Fe _2O _3 \rightarrow 1-2$%
$ MgO \rightarrow 2-3$%
$ SO _3 \rightarrow 1-2$%
and few amount of oxides of iron, magnesium and sulphur.

Multiple choice chemistry the s-block elements (alkali and alkaline earth metals) some important compounds of calcium some important compounds of magnesium and calcium compounds of s block elements

The molecular formula of gypsum is :

  1. $CaSO _{4}.H _{2}O$
  2. $CaSO _{4}.2H _{2}O$
  3. $2CaSO _{4}.H _{2}O$
  4. $CaSO _{4}.3H _{2}O$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Gypsum is calcium sulphate dihydrate. Its molecular formula is $ CaSO _{4} \cdot2H _{2}O $. It is an ore of calcium.

Multiple choice commercial applications management of natural resources unequal distribution of resources protecting our environment rules are for everyone

What is the ratio of CH$ _4$ in a biogas?

  1. 1:2

  2. 1:3

  3. 2:1

  4. 3:1
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

CH$ _4$ is methane, which is the major component of biogas. Ratio is 3:1. 

75% of biogas is methane which is an inflammable fuel. Biogas is characterized based on its chemical composition and the physical characteristics which result from it. It is primarily a mixture of methane (CH$ _4$) and inert carbonic gas (CO$ _2$). However the name “biogas” gathers a large variety of gases resulting from specific treatment processes, starting from various organic waste - industries, animal or domestic origin waste, etc 
Thus, the correct answer is option D.

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

The mass of carbon anode consumed (giving only carbondioxide) in the production of 270 kg of Aluminium metal from bauxite by the Hall process is :

  1. 270 kg

  2. 540 kg

  3. 90 kg

  4. 180 kg
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In the Hall-Heroult process, aluminum is produced along with the consumption of carbon anodes which react with oxygen to form carbon dioxide according to the reaction 2Al2O3 + 3C -> 4Al + 3CO2. Stoichiometric calculations for 270 kg of Al give 90 kg of carbon consumed.

Multiple choice chemistry chemical changes applications of electrolysis electroplating extraction of metals by electrolysis

Zn metal reduces ${SO _{3}}^{2-}$ ions into $H _{2}S$in presence of concentrated $H _{2}SO _{4}$ What weight of Zn is required for
reduction of 6.3 g $Na _{2}SO _{3}$ in presence of concentrated acid.

  1. 9.75 g

  2. 13 g

  3. 130 g

  4. 23 g
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

eq. of $Zn=$ eq.of ${SO _{3}}^{2-}$
$\frac{w}{65}\times 2 =\frac{6.3}{126}\times 6\Rightarrow w=\frac{6.3}{126}\times \frac{6\times 65}{2}=9.75 g$


Multiple choice chemistry occurrence of carbon compounds in nature substances, objects and energy alternative fuels and energy sources alternative sources of energy

How many carbon atoms are there in the hydrocarbon molecules of diesel ?

  1. 18 to 30

  2. 14 to 30

  3. 18 to 25

  4. 14 to 20
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Petroleum-derived diesel is composed of about 75% saturated hydrocarbons (primarily paraffin including n, iso, and cycloparaffins), and 25% aromatic hydrocarbons (including naphthalenes and alkylbenzenes). The average chemical formula for common diesel fuel is $C _{12}H _{24}$, ranging approximately from $C _{10}H _{20} ....... C _{15}H _{28}$.

Multiple choice chemistry further aspects of equilibria dissociation constants ionisation of weak acids and weak bases ionization constants of weak acids and weak bases

The value of observed and calculated molecular weight of silver nitrate are $92.64$ and 170 respectively. The degree of dissociation of silver nitrate is :

  1. $60\%$
  2. $83.5\%$
  3. $46.7\%$
  4. $60.23\%$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The van't Hoff factor i = (Calculated MW) / (Observed MW) = 170 / 92.64 = 1.835. For AgNO3, i = 1 + alpha(n-1). Since n=2, i = 1 + alpha. Thus, alpha = 0.835 or 83.5%.

Multiple choice group 17 elements - trends in chemical properties group 17 elements - properties p- block elements-ii p-block elements chemistry

Iodide of MilIon's base is :

  1. $HIO _3$
  2. $K _2Hgl _4$
  3. $NH _2HgO.HgI $
  4. $Hg(NH _2)I$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Iodide of MilIon's base is $\displaystyle NH _2HgO.HgI$
It is formed when Nessler's reagent (alkaline solution of $\displaystyle K _2[HgI _4]$) reacts with $NH _3$. 

Iodide of MilIon's base is a reddish brown ppt.

Multiple choice physics upthrust in fluids, archimedes' principle and floatation applications of floatation principle of floatation and its applications when do objects float on water?

A beaker containing water weighs $100$ g. It is placed on the pan of a balance and a piece of metal  weighing 70 g and having a volume of $10c{m^3}$ is placed inside the water in beaker. The weight of the beaker and the metal would be:

  1. $170g$
  2. $160$g
  3. $100$g
  4. $30g$
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice chemistry energy rocks and minerals petroleum and natural gas fossil fuels

What is the octane number of triptane?

  1. 45

  2. 25

  3. 100

  4. 125
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Octane number is the percentage by volume of iso-octane present in a mixture of iso-octane and heptane which has the same knocking performance as the sample fuel. For eg - octane number of triptane is 125. Hence, the answer is D.

Multiple choice chemistry energy rocks and minerals petroleum and natural gas fossil fuels

The RON/MON values of $n$-heptane is:

  1. $0$
  2. $100$
  3. $1000$
  4. $50$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Octane number can be determined by RON, MON and AKI. The most common method used for the measurement is RON. RON is determined by running the fuel in a test engine and comparing the results with those for mixtures of iso- octane and $n$- heptane. The RON/MON value for $n$- heptane is 0.