Tag: chemistry

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Questions Related to chemistry

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

$PbCl _2$ 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 : 

  1. $4 \times 10^{-7}$M
  2. $4 \times 10^{-9}$M
  3. $2 \times 10^{-7}$M
  4. $2 \times 10^{-9}$M
Reveal answer Fill a bubble to check yourself
A Correct answer
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

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

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

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

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

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

  1. the food is not cooked completely

  2. the fuel is not burning completely

  3. the fuel is wet

  4. all of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

Which of the following is most harmful for human body?

  1. CO
  2. $CO _2$

  3. Oxides of nitrogen

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

Lead compounds are heavy metal toxins that cause severe, long-term damage to the nervous system, kidneys, and blood, making them significantly more harmful than common atmospheric pollutants like CO or CO2 in terms of cumulative toxicity. While CO is acutely toxic, lead compounds are persistent environmental poisons.

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

Why is CNG a cleaner fuel?

  1. No particulate emission

  2. Releases very less amounts of sulphur and nitrogen oxides

  3. No emission of ash

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

Which of the following is true?

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

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

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

Which of the following is true?

  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.
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

Choose the incorrect statement(s).

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

Physical changes are generally reversible (e.g., melting ice), whereas chemical changes are generally irreversible. Therefore, the statement that physical changes are not reversible is incorrect.

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

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

  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
Reveal answer Fill a bubble to check yourself
B,C Correct answer
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.