Environmental Chemistry – JEE Main Previous Year Questions with Solutions

JEE Main Previous Year Papers Questions of Chemistry With Solutions are available at eSaral.

 

Simulator

Previous Years AIEEE/JEE Mains Questions

Q. 29.5 mg of an organic compound containing nitrogen was digested according to Kjeldahl’s method and the evolved ammonia was absorbed in 20 mL of 0.1 M HCl solution. The excess of the acid required 15 mL of 0.1 M NaOH solution for complete neutralization. The percentage of nitrogen in the compound is :-

(1) 29.5          (2) 59.0          (3) 47.4            (4) 23.7

[AIEEE-2010]

Sol. (4)

Equation of $\mathrm{NH}_{3}$

$=(0.1 \times 20)-(0.1 \times 15)=0.5$

wt. of $\mathrm{NH}_{3}$

$=0.5 \times 17=8.5 \mathrm{mg}$

wt. of $^{\prime} N^{\prime}$

$=\frac{14}{17} \times 8.5 \mathrm{mg}=7 \mathrm{mg}$

$\%$ of $^{\prime} \mathrm{N}^{\prime}=\frac{7}{29.5} \times 100=23.7$


Q. The recommended concentration of fluoride ion in drinking water is up to 1 ppm as fluoride ion is required to make teeth enamel harder by converting $\left[3 \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2} \cdot \mathrm{Ca}(\mathrm{OH})_{2}\right]$ to :

(1) $\left[3\left(\mathrm{CaF}_{2}\right) \cdot \mathrm{Ca}(\mathrm{OH})_{2}\right]$

(2) $\left[3\left(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2} \cdot \mathrm{CaF}_{2}\right]\right.$

(3) $\left[3\left(\mathrm{Ca}(\mathrm{OH})_{2}\right] \cdot \mathrm{CaF}_{2}\right]$

(4) $\left[\mathrm{CaF}_{2}\right]$

[JEE-Mains -2018]

Sol. (2)

$\left[3 \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2} \cdot \mathrm{Ca}(\mathrm{OH})_{2}\right]+2 \mathrm{F}^{\ominus} \longrightarrow$

(drinking water upto $1 \text { ppm })$

$\left[3 \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2} \cdot \mathrm{CaF}_{2}\right]+2 \mathrm{OH}^{\ominus}$

(Harder teeth enamel)


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Comments
  • May 15, 2020 at 7:26 pm

    Try to give more questions from every lesson it’s may help full to cover all models

  • May 3, 2020 at 3:45 pm

    why r there only 2 questions??