During the borax bead test with CuSO4, a blue-green colour of the bead was observed in oxidizing flame due to the formation of
Show Hint
For borax bead test:
• In the oxidizing flame, metal ions form metaborates, which produce characteristic colours.
• The observed colour is a key indicator of the specific metal ion present.
- CuO
\(Cu(BO_2)_2\)
\(Cu_3B_2\)
- Cu
The Correct Option is B
Solution and Explanation
Borax Bead Test:
1. Definition: The borax bead test is a qualitative test used to identify metal ions based on the colour imparted to the bead in the oxidizing or reducing flame.
In this test, borax (\(\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}\)) decomposes to form sodium metaborate (\(\text{NaBO}_2\)) and boric anhydride (\(\text{B}_2\text{O}_3\)) when heated:
\[\text{Na}_2\text{B}_4\text{O}_7 \xrightarrow{\Delta} 2\text{NaBO}_2 + \text{B}_2\text{O}_3.\]
2. Reaction with \(\text{CuSO}_4\): Copper ions react with boric anhydride (\(\text{B}_2\text{O}_3\)) to form copper metaborate (\(\text{Cu(BO}_2)_2\)) in the oxidizing flame:
\[\text{CuSO}_4 + \text{B}_2\text{O}_3 \rightarrow \text{Cu(BO}_2)_2 + \text{SO}_3.\]
3.Observation: \(\text{Cu(BO}_2)_2\) is responsible for the blue-green colour observed in the oxidizing flame.
Final Answer: \((3)\) \(\mathbf{Cu(BO}_2)_2\).
Top Questions on Solutions
A substance 'X' (1.5 g) dissolved in 150 g of a solvent 'Y' (molar mass = 300 g mol$^{-1}$) led to an elevation of the boiling point by 0.5 K. The relative lowering in the vapour pressure of the solvent 'Y' is $____________ \(\times 10^{-2}\). (nearest integer)
[Given : $K_{b}$ of the solvent = 5.0 K kg mol$^{-1}$]
Assume the solution to be dilute and no association or dissociation of X takes place in solution.- The crystal field splitting energy of $[Co(oxalate)_3]^3-$ complex is 'n' times that of the $[Cr(oxalate)_3]^3-$ complex. Here 'n' is_______ (Assume $\Delta_0 > P$)}
- Calculate the boiling point of a solution containing 0.61 g of benzoic acid (122 \( g mol^{-1} \)) in 5 g of \( CS_2 \) in which it dimerises to 88%. \( T_b^\circ(CS_2) = 46.2^\circ C, K_b = 2.3 K kg mol^{-1} \).
- State Raoult’s Law for volatile solutes and explain its deviations.
- Define Colligative Properties and provide two examples.
Questions Asked in JEE Main exam
- Let $\vec{a}=2\hat{i}-\hat{j}-\hat{k}$, $\vec{b}=\hat{i}+3\hat{j}-\hat{k}$ and $\vec{c}=2\hat{i}+\hat{j}+3\hat{k}$. Let $\vec{v}$ be the vector in the plane of $\vec{a}$ and $\vec{b}$, such that the length of its projection on the vector $\vec{c}$ is $\dfrac{1}{\sqrt{14}}$. Then $|\vec{v}|$ is equal to
- JEE Main - 2026
- Vector Algebra
- The wavelength of photon 'A' is 400 nm. The frequency of photon 'B' is \(10^{16}\,\text{s}^{-1}\). The wave number of photon 'C' is \(10^{5}\,\text{cm}^{-1}\). The correct order of energy of these photons is:
- JEE Main - 2026
- General Chemistry
- Given below are two statements: Statement I: The increasing order of boiling point of hydrogen halides is HCl<HBr<HI<HF. Statement II: The increasing order of melting point of hydrogen halides is HCl<HBr<HF<HI. In the light of the above statements, choose the correct answer from the options given below:
- JEE Main - 2026
- General Chemistry
Inductance of a coil with \(10^4\) turns is \(10\,\text{mH}\) and it is connected to a DC source of \(10\,\text{V}\) with internal resistance \(10\,\Omega\). The energy density in the inductor when the current reaches \( \left(\frac{1}{e}\right) \) of its maximum value is \[ \alpha \pi \times \frac{1}{e^2}\ \text{J m}^{-3}. \] The value of \( \alpha \) is _________.
\[ (\mu_0 = 4\pi \times 10^{-7}\ \text{TmA}^{-1}) \]- JEE Main - 2026
- Ray optics and optical instruments
A small block of mass \(m\) slides down from the top of a frictionless inclined surface, while the inclined plane is moving towards left with constant acceleration \(a_0\). The angle between the inclined plane and ground is \(\theta\) and its base length is \(L\). Assuming that initially the small block is at the top of the inclined plane, the time it takes to reach the lowest point of the inclined plane is _______.
- JEE Main - 2026
- General Physics