Tag: chemistry

Questions Related to chemistry

The solubility of $Ag _{2}CO _{3}$ in water is $1.26 \times 10^{-4}$ mole/litre. What is solubility in 0.02 M $Na _{2}CO _{3}$ solution?
Note : Assume no hydrolysis of $CO _{3}^{2-}$ ion. (Take $\sqrt[3]{2} = 1.26$).

chemistry nature of things objects that float or sink substances that sink or float soluble and insoluble substances

  1. $5 \times 10^{-6}$M

  2. $\sqrt{50} \times 10^{-6}$M

  3. $10^{-5}$M

  4. $2 \times 10^{-5}$M

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Correct Option: C

$PbCl _2$ has maximum concentration of $1.0 \times 10^{-3}$ M in its saturated aq. solution at $25^0$C. Its solubility in $0.1$M NaCl solution will be : 

chemistry nature of things objects that float or sink substances that sink or float soluble and insoluble substances

  1. $4 \times 10^{-7}$M

  2. $4 \times 10^{-9}$M

  3. $2 \times 10^{-7}$M

  4. $2 \times 10^{-9}$M

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Correct Option: A
Explanation:

In saturated aqueous solution :
Maximum concentration in saturated aqueous solution is the solubility (S) of $\displaystyle PbCl _2$

$\displaystyle S=1.0 \times 10^{-3} \ M$

$\displaystyle [PbCl _2]=[Pb^{2+}]=S=1.0 \times 10^{-3} \ M$

$\displaystyle [Cl^-]=2 \times [PbCl _2]= 2 \times  S= 2 \times  1.0 \times 10^{-3} \ M=2.0 \times 10^{-3} \ M$

$\displaystyle K _{sp}=[Pb^{2+}] \times [Cl^-]^2$

$\displaystyle K _{sp}=1 .0 \times 10^{-3} \times [2.0 \times 10^{-3}]^2$

$\displaystyle K _{sp}=4.0 \times 10^{-9}$

In 0.1 M NaCl solution:

$\displaystyle [Cl^-]=[NaCl]=0.1 \ M$

Assuming $Cl^-$ ion from $PbCl _2$ is negligible

$\displaystyle K _{sp}=[Pb^{2+}] \times [Cl^-]^2$

$\displaystyle 4.0 \times 10^{-9}=[Pb^{2+}] \times [0.1]^2$

$\displaystyle [Pb^{2+}]=4.0 \times 10^{-7}  \ M$

While cooking, if the bottom of the vessel is getting blackened on the outside, it means that __________.

chemistry combustion and flame fuels fuel and effects of burning fuel study of combustion

  1. the food is not cooked completely

  2. the fuel is not burning completely

  3. the fuel is wet

  4. all of the above

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Correct Option: B
Explanation:

While cooking, if the bottom of the vessel is getting blackened on the outside, it means that the fuel is not burning completely. When the fuel burns completely giving a blue flame, the bottom of the vessel remains clean. 


When the fuel does not burn completely then a sooty flame appears which makes the bottom of the utensil black. It is due to the air holes, which are getting blocked and the fuel does not burn completely.

Which of the following is most harmful for human body?

chemistry combustion and flame fuels fuel and effects of burning fuel study of combustion

  1. CO

  2. $CO _2$

  3. Oxides of nitrogen

  4. Lead compounds

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Correct Option: D

Why is CNG a cleaner fuel?

chemistry combustion and flame fuels fuel and effects of burning fuel study of combustion

  1. No particulate emission

  2. Releases very less amounts of sulphur and nitrogen oxides

  3. No emission of ash

  4. All of the above

Show answer
Correct Option: D
Explanation:

C.N.G (compressed natural gas) is a cleaner fuel because it causes less pollution by emitting fewer pollutants like carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen dioxide, particulate matter, unburned hydrocarbons etc.

When a nail is added to acidic copper sulphate solution, the colour changes from _______.

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. blue to green

  2. green to blue

  3. blue to pink

  4. pink to green

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Correct Option: A
Explanation:

When a nail is added to acidic copper sulphate solution, the colour changes from blue to green.
Copper sulphate reacts with iron to form iron sulphate.

Which of the following is true?

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. Melting of ice is reversible change.

  2. Burning of magnesium is reversible change.

  3. Rusting of iron is reversible change.

  4. All of the above.

Show answer
Correct Option: A
Explanation:

The statement (A) is true.
Melting of ice is reversible change.
Burning of magnesium is irreversible change.
Rusting of iron is irreversible change.

Which of the following is true?

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. A physical change can never be reversible.

  2. A chemical change can never be reversible.

  3. Both of the above

  4. A physical change may be reversible.
    Also, a chemical change may be reversible.

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Correct Option: D
Explanation:

A physical change may be reversible. For example, melting of ice is a reversible change.
Also, a chemical change may be reversible. For example, the reaction between $\displaystyle N _2$ and $\displaystyle H _2$ to form $\displaystyle NH _3$ is a reversible chemical change.

Choose the incorrect statement(s).

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. Chemical reactions are characterized by the change in colour.

  2. Chemical reactions are not alone characterized by change in state.

  3. Physical changes are characterized by the change in colour of reacting substances.

  4. Physical changes are not reversible.

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Correct Option: D

When sugar is stirred with a spoon in a glass of water, more sugar is dissolved and faster. Why?

chemistry phenomena around us changes and its classification types of changes classification of changes

  1. Spoon acts as a catalyst

  2. On stirring, temperature increases

  3. Stirring increases the rate of interaction

  4. Spoon increases the attraction between the molecules of water and sugar

Show answer
Correct Option: B,C
Explanation:
Stirring, or agitation helps to disperse the particles of sugar throughout the water, which is another way of increasing the surface area of the sugar and accelerating the time it takes to dissolve. The stirring motion also increases kinetic energy, which increases the temperature of the solution – and that's the next way to make sugar dissolve more quickly. An increase in the kinetic energy of the constituent particle increases the rate of interaction as well as the temperature of the solution.

Hence, option (B) & (C)  are correct.