The presence of arsenic in a sample that may also contain...

The presence of arsenic in a sample that may also contain another Group 5 A element, antimony, can be confirmed by first precipitating the $\mathrm{As}^{3+}$ and $\mathrm{Sb}^{3+}$ ions as yellow solid $\mathrm{As}_{2} \mathrm{S}_{3}$ and orange solid $\mathrm{Sb}_{2} \mathrm{S}_{3} .$ If aqueous HCl is then added, only $\mathrm{Sb}_{2} \mathrm{S}_{3}$ dissolves, leaving behind solid $\mathrm{As}_{2} \mathrm{S}_{3} .$ The $\mathrm{As}_{2} \mathrm{S}_{3}$ can then be dissolved using aqueous HNO $_{3}$ $$\begin{aligned} 3 \mathrm{As}_{2} \mathrm{S}_{3}(\mathrm{s})+10 \mathrm{HNO}_{3}(\mathrm{aq})+4 \mathrm{H}_{2} \mathrm{O}(\ell) & \rightarrow \\ 6 \mathrm{H}_{3} \mathrm{AsO}_{4}(\mathrm{aq})+10 \mathrm{NO}(\mathrm{g})+9 \mathrm{S}(\mathrm{s}) \end{aligned}$$ Finally, the presence of arsenic is confirmed by adding $\mathrm{AgNO}_{3}$ to the solution of $\mathrm{H}_{3} \mathrm{AsO}_{4}$ to precipitate a reddish brown solid $\mathrm{Ag}_{x} \mathrm{AsO}_{y} .$ The composition of this solid is As, $16.199 \%$ and $\mathrm{Ag}, 69.964 \%$ (a) What are the oxidation numbers of As, $S,$ and $N$ in the reaction of $\mathrm{As}_{2} \mathrm{S}_{3}$ with nitric acid? (b) What is the formula of the reddish brown solid $\mathrm{Ag}_{\mathrm{x}} \mathrm{A} \mathrm{s} \mathrm{O}_{\mathrm{y}} ?$

Key Concepts

Empirical Formula Determination from Percent Composition

This concept is focused on calculating the simplest whole-number ratio of atoms in a compound based on its mass percent composition. It is a fundamental technique in analytical and inorganic chemistry for elucidating the stoichiometry of compounds by correlating experimental percentage data with the corresponding ratios of their constituent elements.

Precipitation Reactions and Selective Dissolution

Precipitation reactions are used to isolate specific ions or compounds from a solution by forming insoluble solids when two reacting species meet. The concept of selective dissolution plays a key role in qualitative analysis, where differential solubilities are exploited to separate and identify individual components in a mixture.

Oxidation Number Determination

This concept involves assigning formal charges to atoms in a molecule or ion according to set rules, which helps in balancing redox reactions and understanding electron transfer during chemical reactions. It allows chemists to trace how the oxidation state of an element changes through reaction pathways, an essential aspect in analyzing reaction mechanisms.

Transcript

00:01 Hello everyone, let us see the following question.

00:03 The presence of arisenic in a sample that may also contain another group 5 element, antimony.

00:09 So, they can be confirmed by first precipitating arisenic 3 plus with antimony.

00:14 So, arisenic is given as aas 3 plus ion.

00:18 It will be having an impurity of antimony 3 plus.

00:21 So, there will be precipitation of anti -aric sulfide, that is a yellow solid.

00:28 So, erysenic sulfide, as2, s3, which is a yellow ppt.

00:37 However, antimony sb2 s3 is a orange color, somewhat it is orange color solid.

00:48 Okay, now leaving, now if fql is added, only antimony dissolves.

00:55 This can be dissolved with the hcl.

00:56 However, this cannot be dissolved.

01:00 It leaves behind as a residue.

01:02 This is even with hcl, it is a yellow residue, loppt.

01:06 Now, the eryssinic sulfide can be then dissolved using equest nitric acid.

01:12 The equation given here as as2s3, okay, with nitric acid, that is hno3.

01:22 In the presence of water, that is h2o, it forms arisenate.

01:32 And no and sulfur.

01:38 So, this is also given that this is solid, this is acquiesce, this is liquid, this is equious, no is a gas, sulfur is a solid, so this is precipitative.

01:57 So we can also balance the equation as this is 3, this is 10 sulfuric acid, water is 4 unit, ericinate is 1, 6 unit, nitrogen monoxide is 10 unit, sulfur 9.

02:13 This is given already in the question.

02:15 Now, based on this, there is a question.

02:19 Finally, the presence of arisenic is confirmed by adding agno3 to the solution of h3aso4.

02:26 H3 aso4 to this we have to add a solution of ag no3.

02:34 So, we get the precipitate of something called agx, as1 unit and oxygen y.

02:47 So, the composition of this solid is so that in this, there is ag and ericinate the percentage is given.

02:57 Percentage of ag is given as 69 .964 percentage.

03:04 Eracinate is given as 16 .199 percentage.

03:10 Similarly, the remaining percentage should be oxygen, that is 13 .837.

03:18 Now we have to find out the formula of this particular compound.

03:21 So, it's given as only x, y...