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Question
The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.
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Solution 1
\[\begin{array}{cc}
\ce{H}\phantom{..............}\ce{Cl}\phantom{................}\ce{F}\phantom{........}\\
\backslash\phantom{...............}\backslash\phantom{................}\backslash\phantom{......}\\
\ce{H - C - COOH Cl - C - COOH F - C - COOH}\\
/\phantom{...............}/\phantom{................}/\phantom{.......}\\
\phantom{.}\ce{\underset{acid}{\underset{Acetic}{H}}}\phantom{.....}\ce{\underset{acid}{\underset{Trichloroacetic}{Cl}}}\phantom{..}\ce{\underset{acid}{\underset{Trifluoroacetic}{F}}}\phantom{......}\end{array}\]
Among H, Cl, and F, H is the least electronegative, while F is the most electronegative. Then, F can withdraw electrons towards itself more than Cl and H. Thus, trifluoroacetic acid can easily lose H+ ions, i.e., trifluoroacetic acid ionizes to the largest extent. Now, the more ions produced, the greater is the depression of the freezing point. Hence, the depression in the freezing point increases in the order:
Acetic acid < trichloroacetic acid < trifluoroacetic acid
Solution 2
The depression in freezing point for acetic acid, trichloroacetic acid and trifluoroacetic acid is in the order.
\[\begin{array}{cc}
\phantom{.........}\ce{Cl}\phantom{...................}\ce{F}\\
\phantom{.........}|\phantom{.....................}|\\
\ce{CH3COOH < Cl - C - COOH < F - C - COOH}\\
\phantom{.........}|\phantom{.....................}|\\
\phantom{.........}\ce{Cl}\phantom{...................}\ce{F}\\
\end{array}\]
In freezing points, trifluoroacetic acid records the greatest depression. This is because fluorine has the greatest effect, leading to the largest ionisation of the acid due to its high electronegativity. It exhibits the greatest freezing point depression because of the maximum amount of ions present (depression in F.P. is a colliding property that depends upon the number of particles present in the solution). Chlorine has a smaller effect and is less electronegative. Consequently, there is less trichloroacetic acid ionisation. Acetic acid is the least ionised and shows the slightest decrease in freezing point because it lacks an electronegative group bonded to its carbon atom.
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| Henna is investigating the melting point of different salt solutions. She makes a salt solution using 10 mL of water with a known mass of NaCl salt. She puts the salt solution into a freezer and leaves it to freeze. She takes the frozen salt solution out of the freezer and measures the temperature when the frozen salt solution melts. She repeats each experiment. |
| S.No | Mass of the salt used in g |
Melting point in °C | |
| Readings Set 1 | Reading Set 2 | ||
| 1 | 0.3 | -1.9 | -1.9 |
| 2 | 0.4 | -2.5 | -2.6 |
| 3 | 0.5 | -3.0 | -5.5 |
| 4 | 0.6 | -3.8 | -3.8 |
| 5 | 0.8 | -5.1 | -5.0 |
| 6 | 1.0 | -6.4 | -6.3 |
Assuming the melting point of pure water as 0°C, answer the following questions:
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- Why did Henna collect two sets of results?
- In place of NaCl, if Henna had used glucose, what would have been the melting point of the solution with 0.6 g glucose in it?
OR
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- 0.10 M Ba3 (PO4)2
- 0.10 M Na2 SO4
- 0.10 M KCl
- 0.10 M Li3 PO4
Ibrahim collected 10 mL each of fresh water and ocean water. He observed that one sample labeled “P” froze at 0° C while the other “Q” at -1.3° C. Ibrahim forgot which of the two, “P” or “Q” was ocean water. Help him identify which container contains ocean water, giving rationalization for your answer.
The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.
The depression in the freezing point of water observed for the same amount of acetic acid, trichloroacetic acid, and trifluoroacetic acid increases in the order given above. Explain briefly.
The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.
The depression in the freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.
The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.
The depression in freezing point of water observed for the same amount of acetic acid, trichloroacetic acid and trifluoroacetic acid increases in the order given above. Explain briefly.
