Tag: chemistry

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Multiple choice chemistry substances in common use salts and their properties study of some important salts salts used in daily life

The type of bonding present in a substance can be determined from experimental data.
Based on the information in the table below, which of the following substances is most likely to represent the identity of the solid?

Melting Point Density Conductivity Alone Conductivity in Aqueous Solution
$801^{\circ}C$ $2.17\ g/cc$ None Excellent
  1. Platinum, $Pt$
  2. Sodium chloride, $NaCl$
  3. Glucose, $C _{6}H _{12}O _{6}$
  4. Quartz, $SiO _{2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The high melting point (801 C) and excellent conductivity in aqueous solution are characteristic of an ionic compound. Sodium chloride (NaCl) is a classic ionic solid that fits these properties perfectly.

Multiple choice chemistry substances in common use salts and their properties study of some important salts salts used in daily life

Which of the following materials conducts electricity?

  1. Crystalline potassium chloride

  2. Fused sulphur

  3. Molten sodium chloride

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

In crystalline solids, the ions are tightly bound by strong coulombic force of attraction having greater interatomic interaction and less interparticle space. $ { Na }^{ + }$ and ${ Cl }^{ - } $ ions are free to move only in molten state or aqueous solution. Hence, they show electrical conductivity in molten state.

Multiple choice chemistry substances in common use salts and their properties study of some important salts salts used in daily life

Crude common salt is hygroscopic because of impurities of:

  1. $CaSO _{4}$ and $MgSO _{4}$
  2. $CaCl _{2}$ and $MgCl _{2}$
  3. $CaBr _{2}$ and $MgBr _{2}$
  4. $Ca\left ( HCO _{3} \right ) _{2}$ and $Mg\left ( HCO _{3} \right ) _{2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Crude common salt contains impurities such as $ CaSO _{ 4 },   CaCl _{ 2 } ,   MgCl _{ 2} $. Hence it is deliquescent (hygroscopic).

Hence option B is correct.

Multiple choice chemistry substances in common use salts and their properties study of some important salts salts used in daily life

Molten sodium chloride conducts electric current due to the presence of:

  1. free electrons

  2. free mobile ions

  3. immobile ions

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Current is the rate of flow of charge. NaCl is an ionic solid. An ionic solid consists of a lattice of ${ Na }^{ + }$ and ${ Cl }^{ - }$ ions in which these ions are fixed in their places. Solid NaCl does not contain any mobile charge carriers that can facilitate the flow of charge. But molten NaCl contains free mobile ions ${ Na }^{ + }$ and ${ Cl }^{ - }$ ions which allow the passage of current.


Thus, molten NaCl conducts electric current due to the presence of free mobile ions.

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

When a chemical reaction takes place, during the course of the reaction the rate of reaction?

  1. Keeps on increasing with time

  2. Remains constant with time

  3. Keeps on decreasing with time

  4. Shows irregular trend with time
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Rate of reaction $\propto$ conc. of reactants
As the reaction proceeds, concentration of the reactants decreases hence the rate also keeps on decreasing with time.

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

In a reaction $2HI \rightarrow H _{2} + I _{2}$, the concentration of $HI$ decreases from $0.5\ mol\ L^{-1}$ to $0.4\ mol\ L^{-1}$ in $10$ minutes. What is the rate of reaction during this interval?

  1. $5\times 10^{-3} M\ min^{-1}$
  2. $2.5\times 10^{-3} M\ min^{-1}$
  3. $5\times 10^{-2} M\ min^{-1}$
  4. $2.5\times 10^{-2} M\ min^{-1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Average rate $= -\dfrac {1}{2} \dfrac {\triangle [R]}{\triangle t} = -\dfrac {1}{2}\times \dfrac {0.4 - 0.5}{10}$


$= \dfrac {1}{2}\times \dfrac {0.1}{10} = 5\times 10^{-3}M\ min^{-1}$.

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

Which of the following statements is correct?

  1. The rate of a reaction decreases with passage of time as the concentration of reactants decreases.

  2. The rate of a reaction is same at any time during the reaction.

  3. The rate of a reaction is independent of temperature change.

  4. The rate of a reaction decreases with increase in concentration of reaction(s).
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to rate law expression,
$Rate \propto [R]$
Thus, rate of a reaction decreases with passage of time as the concentration of reactants decreases.