Tag: chemistry

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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

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

Iron pyrites has formula $FeS _2. (Fe = 56; S = 32)$. What is the mass of sulfur contained in 30 grams of pyrites?

  1. 16 g

  2. 32 g

  3. 20 g

  4. 24 g
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Molecular weight of $ \displaystyle FeS _2 =  56+2(32)=120$ g/mol.

One mole (120 g) of $ \displaystyle FeS _2$ will contain $ \displaystyle 2 \times 32 = 64$ g of $S$
30 g of $ \displaystyle FeS _2$ will contain $ \displaystyle \dfrac {30}{120} \times  64=16$ g of $S$.
Hence, the mass of sulfur contained in 30 grams of pyrites is 16 g.

Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept
An organic compound contains 69% carbon, 4.8% hydrogen and the remaining is oxygen. calculate the masses of carbon dioxide produced when 0.20g of substance is subjected to combustion.

  1. 0.40 g

  2. 0.50 g

  3. 0.60 g

  4. 0.70 g
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Percentage of carbon in organic compound $= 69 \%$

So, 100 g of organic compound contains 69 g of carbon.

∴ 0.2 g of organic compound will contain $=\dfrac{ 69 \times 0.2}{ 100} = 0.138$ g of carbon

The molecular mass of carbon dioxide, $CO _2 = 44$ g

So, 12 g of carbon is contained in 44 g of $CO _2$.

0.138 g of carbon will be contained $= \dfrac{44 \times 0.138}{12} = 0.506$ g of carbon.

Thus, 0.506 g of $CO _2$ will be produced on complete combustion of 0.2 g of an organic compound.
Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

The mass of one molecule of water is approximately:

  1. $1\ g$
  2. $0.5\ g$
  3. $1.66 \times 10^{-24}\, g $
  4. $ 3 \times 10^{-23}\, g $
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Mass of $6.0 \times 10^{23}$ molecules of water is 18 g.

Mass of 1 molecule of water $=\dfrac{M}{N _A}=\dfrac{18}{6.0\times 10^{23}}$

Mass of 1 molecule of water $=3. \times$ $10^{-23}$ g 
Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

In an experiment, the following four gases were produced. 11.2 L of which two gases at STP will weigh 14 g ?

  1. $N _2O$
  2. $NO _2$
  3. $N _2$
  4. $CO$
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation
22.4 L of  a gas at STP$=$ 1 mole.
11.2 L of  a gas at STP$=$ 0.5 mole.
11.2 L of a gas at STP will weigh 14 g.
0.5 moles of a gas at STP will weigh 14 g.
1 mole of a gas at STP will weigh $\dfrac {1}{0.5} \times 14=28$ g.
The molecular weight of the gas is 28 g/mol.
Molecular weight of  $N _2O = 2 (14)+16=44$ g/mol.
Molecular weight of  $NO _2 =14+ 2 (16)=46$ g/mol.
Molecular weight of  $N _2 = 2 (14)=28$ g/mol.
Molecular weight of  $CO = 12+16=28$ g/mol.
Hence, 11.2 L of $N _2$ and $CO$ at STP will weigh 14 g.
Multiple choice introduction to mole gas laws and mole concept atoms and molecules chemistry mole concept chemical formula and mole concept

If of conservation of mass was to hold true, then 20.8 g of ${ BaCl } _{ 2 }$ on reaction with 9.8 g of ${ H } _{ 2 }{ SO } _{ 4 }$ will produce 7.3 g of $HCl$ and ${ BaSO } _{ 4 }$ equal to :

  1. 11.65 g

  2. 23.3 g

  3. 25.5 g

  4. 30.6 g
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$BaCl _2+H _2SO _4 \longrightarrow BaSO _4+2HCl$


$1$ mole of $BaCl _2$ reacts with $1$ mole of $H _2SO _4$ to give $1$ mole of $BaSO _4$ and $2$ moles of $HCl$.


Here, moles of $BaCl _2=\dfrac{20.8}{208}=$ moles of $H _2SO _4= \dfrac{9.8}{98}=0.1$

$\therefore$ Moles of $BaSO _4$ formed $=0.1$

$\therefore$ Mass of $BaSO _4$ formed $=0.1 \times 233= 23.3 g$


i.e. $20.8+9.8=7.3+23.3=30.6$

Hence the correct option is B.