nAn unknown compound was found to have the following chemical constituent percen

Question

nAn unknown compound was found to have the following chemical constituent percentage by weight A likely formula is ANaCIO4 B) NaCl o NaCIO3 Di NaCIO E NaC1202 How many grams of Oxygen are present in 1.2 x 10 molecules of MgSO4? [Gram Formula Wt = 120.4 gm] A 12.8 B) 16.2 c32.4 o,78.6 None of the above is not an electrolyte. 3) Of the species below, only A) HCI B) Rb2S04 C) Xe D) KOH E) NaCI 4) Aqueous potassium chloride will react with which one of the following in an exchange (replacement) reaction? A) calcium nitrate B) sodium bromide C) lead nitrate D) barium nitrate E) sodium chloride 5) Which of the following is insoluble in water at 25 °C? A) Ca3(PO4)2 B) Na2S C) (NH4)2CO3 D) Na(OH) E) Ba(C2H302)2

Explanation / Answer

1) To get the formula of the compound we will calculate the number of moles of these elements and then the molar ratio of these elements will give the formula of the compound .

Moles = given mass / molar mass of that element

*Given mass will be equal to the given percentage of that element.

Moles of Na = 30.90g/ 23.0 g/mol= 1.34 mol

Moles of O = 21.50g/ 16.0g/mol = 1.34 mol

Moles of Cl = 47.70 g/35.45 g/mol = 1.34 mol

Since the number of moles of the elements are same so the molar ratio is 1.34 : 1.34 : 1.34 that is 1:1:1

So the formula is NaClO

And the correct option is D

2) 1 molecule of MgSO4 has Oxygen atoms = 4

1.2×10^23 molecule has O atoms = 4×1.2×10^23

Mass of 1 mol (6.02×10^23 ) atoms of O = 16.0 g

So,

Mass of 4×1.2×10^23 atoms of O

= {16/(6.02×10^23)}×4×1.2×10^23 = 12.78 g ~ 12.8 g

So the correct option is A

3) Electrolyte are the species that can be ionised . Only nobel gas Xe can't be ionised.

So the correct option is C

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