Download App

Solutions — Chemistry STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceChemistrySolutions5 Marks
Question
  1. Differentiate between molarity and molality for a solution. How does a change in temperature influence their values?
  2. Calculate the freezing point of an aqueous solution containing $10.50g$ of $\ce{MgBr_2}$ in $200 g$ of water. (Molar mass of $\ce{MgBr_2 = 184 g})$
$(K_f$​​​​​​​ for water $= 1.86 K \ kg \ mol^{–1})$
✓

Answer

  1. Molality $(m)$ is the number of moles of the solute per kilogram $(kg)$ of the solvent whereas Molarity is the number of moles of solute present in one litre $($or one cubic decimeter$)$ of solution at a particular temperature.
Molality is independent of temperature whereas Molarity is function. of temperature because volume depends on temperature and the mass does not or Molarity decreases with increase of temperature.
  1. $\Delta\text{T}_{f}=7.5^{o}C$
$\Delta\text{T}_{f}=\text{iK}_{f}\text{m}$
$\text{T}_{f}^{0}-\text{T}_{f}=3\times1.86^0\text{C \ kg mol}^{-1}\times\frac{10.50g}{\text{184 gmol}^{-1}}\times\frac{\text{1000}}{\text{200 \ kg}}$
$0^\circ \ C-T_f = 1.59^\circ \ C$
$T_f = –1.59^\circ \ C$ or $271.41 K.$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "5 Marks Questions" from Solutions→Solutions — all question types→Chemistry STD 12 Science question papers→Rajasthan Board STD 12 Science question papers→Rajasthan Board question paper generator→

Similar questions

$\ce{COSO_4Cl._5NH_3}$ exists in two isomeric forms $'A\ '$ and $'B\ '.$ Isomer $'A\ '$ reacts with $AgNO_3$ to give white precipitate but does not react with $BaCl_2.$ Isomer $'B\ '$ gives a white precipitate with $BaCl_2$ but does not react with $AgNO_3.$ Answer the following questions.
i. Identify $'A\ '$ and $'B\ '$ and write their structural formulas.
ii. Name the type of isomerism involved.
iii. Give the $\text{IUPAC}$ name of $'A\ '$ and $'B\ '.$
→
Explain different types of isomerism in amines.
→
  1. Complete the following chemical equations:
  1. $ \text{MnO}_{4}^{-}\text{(aq)}+\text{S}_{2}\text{O}_{4}\text{(aq)}+\text{H}_{2}\text{O}\text{(l)}\rightarrow$
  2. $\text{Cr}_{2}\text{O}_{4}^{2-}\text{(aq)}+\text{Fe}^{2+}\text{(aq)}+\text{H}^{+}\text{(aq)}\rightarrow$
  1. Explain the following observations:
  1. $La^{3+} (Z = 57)$ and $Lu^{3+} (Z = 71)$ do not show any colour in solutions.
  2. Among the divalent cations in the first series of transition elements, manganese exhibits the maximum paramagnetism.
  3. $Cu^+$ ion is not known in aqueous solutions.
→
Derive a formula to determine the molar mass of a solute by depression of freezing point.
→
  1. Account for the following:
    1. Mn shows the highest oxidation state of $+7$ with oxygen but with fluorine it shows the highest oxidation state of $+4.$
    2. $Cr^{2+}$ is a strong reducing agent.
    3. $Cu^{2+}$ salts are coloured while $Zn^{2+}$ salts are white.
  2. Complete the following equations:
    1. $2\text{MnO}_{2} + 4\text{KOH} + \text{O}_{2} \xrightarrow{\Delta}$
    2. $\text{Cr}_{2}\text{O}^{2-}_{7}+ 14\text{H}^{+} + 6\text{I}^{-}\rightarrow.$
→
What do you mean by elevation of boiling point and molal elevation constant? Give the formula or equation to determine the molar mass from elevation of boiling point.
→
Explain the structure of fructose.
→
Write only the principle for the manufacturing of sulphuric acid by contact process?
→
Discuss in detail DNA and RNA.
→
$\ce{COSO_4Cl.5NH_3}$ exists in two isomeric forms $‘A’$ and $‘B’$. Isomer $‘A’$ reacts with $\ce{AgNO_3}$ to give white precipitate, but does not react with $\ce{BaCl_2.}$ Isomer $‘B’$ gives white precipitate with $\ce{BaCl_2} $ but does not react with $\ce{AgNO_3}$. Answer the following questions.
  1. Identify $‘A’$ and $‘B’$ and write their structural formulas.
  2. Name the type of isomerism involved.
  3. Give the $\text{IUPAC}$ name of $‘A’$ and $‘B’.$
→