Chemistry

Mole Concept and Stoichiometry

354 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 evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

The mass of residue left after strongly heating 1.38 g of silver carbonate will be: 

  1. 1.16 g

  2. 1.33 g

  3. 2.66 g

  4. 1.08 g
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$Ag _2CO _3\rightarrow Ag _2O+CO _2(g)$
I mole of $Ag _2CO _3$ (275.74) grams  on decomposition gives a mass residue of 231.73 grams of $Ag _2O$ remaning mass is liberated as $CO _2$ gas.
If 1.38 grams $Ag _2CO _3$ is hetaed it produces X grams of mass residue of  $Ag _2O$
$X=\frac{1.38\times 231.739}{275.745}=1.16$ grams
Hence option A is correct.

Multiple choice chemistry biomolecules enzymes and hormones hormones coordination in human beings- chemical control

The total number of amino acids in a molecule of the Hypoglycemic hormone is:

  1. 30

  2. 21

  3. 51

  4. 27
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The total number of amino acids in a molecule of the Hypoglycemic hormone is 51. The human hormone insulin is composed of 51 amino acids. It is a dimer of an A-chain consisting of 21 amino acids, and a B-chain consisting of 30 amino acids, which are linked together by disulphide bonds.

Multiple choice zoology physical resources carbon cycle ozone layer depletion and causes depletion of ozone layer

Correct percentage of two green house gases is

  1. $N _2O-6\%, CO _2-86\%$
  2. $CH _4-20\%, N _2O-18\%$
  3. $CO _2-40\%, CFC-30\%$
  4. $CFC-14\%, CH _4-20\%$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The warming of earth's surface when sun radiations are absorbed and trapped in earth's atmosphere, is called greenhouse effect. The gases responsible for green house effect are called green house gases which trap the radiations and don't let them reflect back from the earth's surface. The green house gases are Chlorofluorocarbons (CFC's), Carbon dioxide (CO2), Methane (CH4) and Nitrous Oxide (N2O). 
The approximate percentage of different greenhouse gases in the atmosphere is:
CFCs - 14%
CO2 - 60%
‎CH4 - 20%
N2O - 6%
So, the correct answer is 'CFC−14%, CH4 - 20%

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 biology protectors of biosphere structure of chloroplast plastids photosynthetic pigments

If 24 G-3-P molecule are formed in $C _3$ plants. Calculate 
a) the number of $CO _2$ used and 
b) the number of $G3P$ used for regeneration $RuBP$ molecule.

  1. a=12, b=20

  2. a=24, b=48

  3. a=12, b=24

  4. a=20, b=12
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
All together for one G3P to leave the cycle (and go towards glucose blend), three CO2 particles must enter the cycle, giving three new molecules of settled carbon. At the point when three CO2 particles enter the cycle, six G3P atoms are made. One leaves the cycle and is utilized to make glucose, while the other five must be reused to recover three atoms of the RuBP acceptor. 
3 CO2 joins with 3 RuBP acceptors, making 6 atoms of (G3P). 
1 G3P particle leaves the cycle and goes towards making glucose. 
5 G3P particles are reused, recovering 3 RuBP acceptor atoms.
So, the correct option is 'a=12, b=24'.
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

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 $C _{10}H _{20} ....... C _{15}H _{28}$.