Tag: introduction to mole

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Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

Which of the following molecules specie has the minimum number of lone pairs ? 

  1. $ X _eF _4 $
  2. $ BF^- _4 $
  3. $ ICI _3 $
  4. $ BeF _2 $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

BeF2 has a linear structure with no lone pairs on the central Beryllium atom. XeF4 has 2, BF4- has 0 (but is an ion), and ICl3 has 2. However, BeF2 is the neutral molecule with zero lone pairs on the central atom.

Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

A quantity of $2.0\ g$ of a triatomic gaseous element was found to occupy a volume of $448\ ml$ at $76\ cm$ of $Hg$ and $273\ K$.

The mass of its each atom is _______________.

  1. $100\ amu$
  2. $5.53\times 10^{-23}\ g$
  3. $33.3\ g$
  4. $5.53\ amu$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Given that
$P=76\ cm$ of $Hg =1\ atm$
$V=448\ ml=0.448\ L$
$T=273\ K$

Now,
$PV=nRT$

$n=\dfrac{PV}{RT}=\dfrac{1\times 0.448}{0.082\times 273}=0.02\ moles$

No. of moles $=\dfrac{mass}{molar\ mass}$

Molar mass $=\dfrac{mass}{mole}$

$3\times$ atomic mass $=\dfrac{2}{0.02}$

Atomic mass $=33.3\ g$

$\therefore$ mass of $1\ atom=\dfrac{33.3}{6.022\times 10^{23}}=5.53\times 10^{-23}\ g$
Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

Which of the following gas molecule has the longest mean free path at the same pressure and temperature?

  1. $H _2$
  2. $N _2$
  3. $O _2$
  4. $Cl _2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Mean free path is inversely proportional to the collision cross-section. Smaller molecules like H2 have a smaller cross-section, leading to a longer mean free path compared to larger molecules like N2, O2, or Cl2.

Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

Two gases X and Y have their molecular speed in ratio of $3:1$ at certain temperature. The ratio of their molecular masses $M _x:M _y$ is?

  1. $1:3$
  2. $3:1$
  3. $1:9$
  4. $9:1$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Molecular speed v is proportional to 1/sqrt(M). If v_x/v_y = 3/1, then sqrt(M_y/M_x) = 3/1, so M_y/M_x = 9/1. Thus, M_x/M_y = 1/9.

Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

A gaseous mixture of three gases A, B and C has a pressure of $10$ atm. The total number of moles of all the gases is $10$. If the partial pressures of A and B are $3.0$ and $1.0$ atm, respectively, and if C has molecular mass of $2.0$, what is the mass of C, in g, present in the mixture?

  1. $6$
  2. $8$
  3. $12$
  4. $3$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Dalton's law of partial pressures, the partial pressure of a gas is proportional to its mole fraction. The mole fraction of gas C is calculated from total moles (10) and total pressure (10 atm), where the sum of partial pressures of A and B is 3.0 + 1.0 = 4.0 atm, leaving the partial pressure of C as 10 - 4 = 6 atm. Thus, the moles of C equal (6/10) * 10 = 6 moles. With a molecular mass of 2.0 g/mol, the mass of C is 6 moles * 2.0 g/mol = 12 g.

Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

A protein, isolated from a bovine preparation, was subjected to amino acid analysis. The amino acid present in the smallest amount was lysine, $C _6H _{14}N _2O _2$ and the amount of lysine was found to be $365\ mg$ per $100\ g$ protein. What is the minimum molecular mass of the protein?   

  1. $40,000,000$
  2. $40, 000$
  3. $40$
  4. $4, 00,000$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The minimum molecular mass of a protein is calculated based on the assumption that there is at least one molecule or residue of the least abundant component per protein molecule. Since 365 mg (0.365 g) of lysine is present in 100 g of protein, the minimum molecular mass M satisfies (Mass of lysine in 1 mol / M) = (0.365 g / 100 g). Specifically, taking one lysine molecule per protein molecule, M = (Molecular weight of lysine * 100 g) / 0.365 g. The molecular formula of lysine C6H14N2O2 has a molar mass of 146 g/mol. Thus, M = (146 * 100) / 0.365 = 40,000 g/mol.

Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

A mixture contains $NaCl$ and unknown chloride $MCl$. When $1\ g$ of this mixture is dissolved in water and excess of $AgNO _{3}$ Solution is added to it, $2.567\ g$ of white precipitate is obtained. In another experiment, $1\ g$ of the same original mixture is heated to $300^{o}C$. Some vapour come out which are absorbed in acidified $AgNO _{3}$ solution by which $1.341\ g$ of white precipitate is formed. The molecular mass of unknown chloride is

  1. $53.4$
  2. $58.5$
  3. $44.5$
  4. $74.4$
Reveal answer Fill a bubble to check yourself
A,B Correct answer