State with equations what happens when borax is heated on a platinum wire Ioop and to the resulting transparent mass, a minute amount of `CuO` is adde

Monjur Alahi

State with equations what happens when borax is heated on a platinum wire Ioop and to the resulting transparent mass, a minute amount of `CuO` is added and the mixture is again heated first in the oxidising flame and then in the reducing flame of a Bunsen burner?


0 like 0 dislike
1 views
Share with your friends

1 Answers

Salim Ahmed Kawsar

Call

Correct Answer - When a borax is heated on a platinum wire loop, a transparent glassy beat called the borax bead is formed.
`Na_(2)B_(4)O_(7) . 10H_(2)Ounderset(-10H_(2)O)overset(Delta)toNa_(2)B_(4)O_(7)overset(740^(@)C)to ubrace(2NaBO_(2)+B_(2)O_(3))_("glassy mass");`
When this transparent glassy bead is heated with `CuO` in the oxidising flame, it imparts blue colour to the bead due to the formation of cupric metaborate.
`CuO + B_(2)O_(3) overset("oxidising flame")to Cu(BO_(2))_(2)`(blue bead)
However, when cupric metaborate is heated in the reducing flame of the Bunsen burner, the blue cupric metaborate is reduced by carbon present in the flame first to colourless coprous metaborate and then to metal which produces red scales.
`underset("Cupric metaborate")(2Cu(BO_(2))_(2))+C to underset("Cuprous metaborate")(2CuBO_(2)+B_(2)O_(3))+CO`
`overset(("blue"))(2CuBO_(2))+C to undersetunderset(("red"))("Copper metal")(2Cu overset(("Colourless"))(+)B_(2)O_(3))+CO`

0 like 0 dislike
1 views
Talk Doctor Online in Bissoy App
A car moves at a velocity 2.24 `km h^(-1)` in first minute, at 3.60 `km h^(-1)` in the second minute and at 5.18 `km h^(-1)` in the third minute. Calc

Displacement in first minute `s_(1)=v_(1)xxt_(1)=2.24xx(1)/(60)km` Displacement in second minute `s_(2)=v_(2)xxt_(2)=3.60xx(1)/(60)km` Displacement in third minute `s_(3)=v_(3)xxt_(3)=5.18xx(1)/(60)km` Total Displacement, `s=s_(1)+s_(2)+s_(3)=(2.24)/(60)+(3.60)/(60)+(5.18)/(60)=(11.02)/(60)km`. Total time taken, `t=1+1+1=3 "min"=(1)/(20)h` `therefore "average velocity",=(s)/(t)=(11.02)/(60)xx(20)/(1)=3.67 kmh^(-1)`

2 Answers 4 views
Given that: `DeltaG_(F)^(@)(CuO) =-30.4 "Kcal"//"mole"` `DeltaG_(f)^(@)(Cu_(2)O)=-34.98 Kcal//"mole" " "T=298K` Now on the basis of above data which o

Correct Answer - B `(2) Cu_(2)O(s) +(1)/(2)O_(2)(g) hArr 2CuO(s)` `DeltaG_("reaction")^(@) =[2xx(-30.4)]-[-34.98]=-25.82 `Kcal and `-25.82 xx 10^(3) =2.303 xx 2xx 298 `logK `therefore K~~10^(19), ` a very high value, hence reaction will...

2 Answers 1 views
Two boys are holding a wire, standing 4 m apart. The wire sags in the shape of a circular arc with a sag of 1.0 m. The students rotate the wire about

Correct Answer - 0.97mV

2 Answers 2 views
Two radioactive elements A and B are present in a mixture. Both are beta active. Half lives of A and B are 30 minute and 60 minute respectively. The i

Correct Answer - (a) `(1)/(2)` (b) `5.2xx10^(-11)`

2 Answers 1 views
A magnetic needle performs `20` oscillations per minute in a horizontal plane. If the angle of dip be `30^@`, then how many oscillation per minute wil

Correct Answer - `[21.5 min^(-1),15.2 min^(-1)]`

2 Answers 11 views
A steady e,.m .f of 1.72 is maintaied across two platinum electrodes placed in a solution of `CuCl_(2)` At the end o f510 s, the mass of copper deposi

Correct Answer - `0.0063 Omega`

2 Answers 1 views
For a given sample, the count rate is `47.5alpha` particle per minute. After 5 minutes, the count is reduced to `27 alpha` particles per minute. Find

Correct Answer - `0.0019 s^(-1) 368.12 s`

2 Answers 3 views
(i) What happens when: (a) Borax is heated strongly (b) Boric acid is added to water ( c) Aluminium is treated with dilute `NaOH`. (d) `BF_(3)` is rea

Correct Answer - (i)(a)When borax is heated strongly, a transparent glassy bead which consists of sodium metaborate `(NaBO_(2))` and boric anhydride is formed. `Na_(2)B_(4)O_(7). 10H_(2)Ooverset(Delta)toNa_(2)B_(4)O_(7)+10H_(2)O uar r` `Na_(2)B_(4)O_(7)overset(740^(@)C)to 2NaBO_(2)+underset("borax bead")(B_(2)O_(3))`...

2 Answers 1 views
A copper wire has a resistance of \( 0.60 hm \). Anozner copper wire of the samemass as the first one is dou ble in length of the first. Find the resistance of the second wire.

We know that R = ρl/A R ∝ l R1/R2 = l1/l2 Given ∵ l2 = 2l1 R1 = 0.60 hm R2/R1 = l2/l1 R2/R1 = 2l1/l1 R2 = 2 R1 R2 = 2 x 0.60 R2 = 1.2 hm

2 Answers 3 views
A steel wire is acted upon by a load of 10 N. Calculate the extension produced in the wire, if the strain energy stored in the wire is 1.1 × 10^-3 J.

Given: F = 10 N, Strain energy = 1.1 × 10-3 J, To find: Extension (l) Formula: W = \(\frac{1}{2}\) × F × l Calculation: From formula, l = \(\frac{2\,W}{F}=\frac{2\times1.1\times10^{-3}}{10}\) = 2.2 × 10-4 m. The extension produced in the wire is...

2 Answers 4 views
X