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]
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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]
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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)
Kuch bhi 😂
chutiyo
Is the bits given in mains till 2018…Need some more bits try to update
Try to give more questions from every lesson it’s may help full to cover all models
why r there only 2 questions??