TtWer every question. 9. 5.00 g each of unknown A and unknown B are analyzed and

Question

TtWer every question. 9. 5.00 g each of unknown A and unknown B are analyzed and found to be molecular compounds with identical empirical formulas. Which statement must be true (A) Unknown A and unknown B are the same compound. Unknown A and unknown B have the same molecular weight. (B) (C) There are the same number of atoms in equal masses of unknown A and unknown B. (D) There are the same number of molecules in equal masses of unknown A and unknown B. Which pair of elements both have chemical properties similar to those of sulfur? 10. (A) N, Br (B) N, O (C) P, CI (D) Se, Te 11. How many moles of potassium Molar Mass /g-mol- 212.3 ions are present in 53.0 g of K3PO4? (A) 1.36 mol K (C) 0.250 mol K Four samples of equal masses are present. Which sample (B) 0.749 mol K (D) 0.0832 mol K 12. contains the least number of atoms? (A) Clh(g) (B) Cu(s) (C) He(g) (D) Kr(g) 13. What is the mass of N atoms Molar Mass /g-mol1 14.01 present in 1.37x 101" molecules of N20? (A) 1.27×10-5 g (C) 6.37x 10" g (B) 1.00x10-Sg (D) 1.45x 107g

Explanation / Answer

answer: 9) C - there are the same number of atoms in equal masses of unknown A and unknown B

because the empirical formula for a chemical compound is the simplest positive integer ratio of atoms present in a compound

answer 10) D- Se,Te

because they belong to the same group of the periodic table

and Elements in the same group in the periodic table have similar chemical properties. This is because their atoms have the same number of electrons in the highest occupied energy level

answer 11) B - 0.749 mol K+

1 mole of K 3PO4 contains 3 moles of K+

moles of K3PO4 in 53.0 g = 53.0/212.3 = 0.249 mole

number of mole of K+ = 3*.249 = 0.749 mole

answer 12) D -Kr

number of atom = (mass/molar mass) * NA

where NA is Avogadro's number = 6.023*1023 atoms/mol

since mass is equal

so the number of atoms inversely proportional to the number of atom so higher molar mass least number of atoms present

molar mass of Cl2 = 70.906 g/mol

Cu = 63.5 g/mol

He = 4.00 g/mol

Kr = 83.798 g/mol

so Kr has least number of atoms

answer 13: C - 6.37*10-6

) mole of N2O = number of molecule / NA

= 1.37 * 1017 / 6.023 *1023

= 2.27 * 10-7 mole

1 mole of N2Ocontain 2 mole of N

so 2.27*10-7 mole contain = 2*2.27*10-7 mole of N = 4.54*10-7

mass of N = 4.54* 10-7 *14 =6.37*10-6 g of N

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