Question

The pH of $0.5M$ aqueous solution of $HF$ $({K_a} = 2 \times {10^{ - 4}})$ is:
(A) 2
(B) 4
(C) 6
(D) 10

Answer 1

Hydrogen fluoride is a valuable dissolvable in which to plan metallic fluorides. We have seen that solvolysis by fluid hydrogen fluoride produces numerous fluorides wherein the metals are in their unique oxidation state. It is conceivable, by the utilization of suitable oxidizing specialists, to deliver components in a higher oxidation state. Basic fluorine weakened with vaporous nitrogen will oxidize thallium(I) to thallium (III).

Complete step-by-step solution: As we know,
${K_a} = c \times {\alpha ^2}$
Let us now substitute the values in the equation;
$2 \times {10^{ - 4}} = 0.5 \times {\alpha ^2}$
$\alpha = 2 \times {10^{ - 2}}$
$\Rightarrow [{H^ + }] = c \times \alpha$
Now, let us substitute the values then we get;
$[{H^ + }] = 0.5 \times 2 \times {10^{ - 2}}$ $= {10^{ - 2}}$
As we got the value of $[{H^ + }]$ let us find out the $pH$ as:
$pH = - \log [{H^ + }]$
$\Rightarrow pH = - \log [{10^{ - 2}}]$
$\Rightarrow pH = 2 \times (\log 10)$
That leaves us with the value of
$pH = 2$

Additional Information: What are the uses of $HF$?
When all is said in done, the anhydrous compound hydrogen fluoride is more normal modernly than its fluid arrangement, hydrofluoric corrosive. Its primary uses, on a weight premise, are as a forerunner to organofluorine mixes and an antecedent to cryolite for the electrolysis of aluminum.
1.Precursor to organofluorine mixes : HF responds with chlorocarbons to give fluorocarbons. A significant use of this response is the creation of tetrafluoroethylene, antecedent to Teflon. Chloroform is fluorinated by $HF$ to deliver chlorodifluoromethane. Pyrolysis of chlorodifluoromethane yields TFE. $HF$ is a receptive dissolvable in the electrochemical fluorination of natural mixes. In this methodology, HF is oxidized within the sight of a hydrocarbon and the fluorine replaces C–H bonds with C–F bonds. Perfluorinated carboxylic acids and sulfonic acids are delivered in this way. 1,1-Difluoroethane is delivered by adding HF to acetylene utilizing mercury as an impetus.
2.Precursor to metal fluorides and fluorine:The electrowinning of aluminum depends on the electrolysis of aluminum fluoride in liquid cryolite. A few kilograms of HF are burned-through per ton of Al delivered. Other metal fluorides are delivered utilizing HF, including uranium hexafluoride. $HF$ is the forerunner to natural fluorine by electrolysis of an answer of $HF$ and potassium bifluoride. The potassium bifluoride is required in light of the fact that anhydrous $HF$ doesn't lead power. A few thousand tons of Fluorine are created every year.

3.Catalyst:$HF$ fills in as an impetus in alkylation measures in treatment facilities. It is utilized in most of the introduced straight alkyl benzene creation offices on the planet. The cycle includes dehydrogenation of n-paraffins to olefins, and resulting response with benzene utilizing $HF$as impetus.

4.Solvent:Hydrogen fluoride is a fantastic dissolvable. Mirroring the capacity of $HF$ to partake in hydrogen holding, even proteins and sugars disintegrate in $HF$ and can be recuperated from it. Interestingly, most non-fluoride inorganic synthetic compounds respond with $HF$ instead of dissolving.

Hence, the correct option is B.

Note: Upon contact with dampness, including tissue, hydrogen fluoride quickly converts to hydrofluoric corrosive, which is profoundly destructive and poisonous. Presentation requires quick clinical attention. It can cause visual deficiency by fast decimation of the corneas. Taking in hydrogen fluoride at significant levels or in mix with skin contact can cause passing from a sporadic heartbeat or from liquid development in the lungs.