[سحر البيان]

(25) The molarity of a solution is defined as:
(A) number of moles of solute per kilogram of solution.
(B) number of moles of solute per liter of solution.
(C) number of grams of solute per liter of solution.
(D) number of moles of solute per kilogram of solvent


(26) What volume, in mL, of a 0.38 M solution is required to provide 3.17 g of KBr?
(Atomic weights: K = 39.10, Br = 79.90).
(A) 60 mL
(B) 90 mL
(C) 70 mL
(D) 100 mL

M=n /V ,,,,,,,,,,,,,V =n/M
n= mass/ molar mass =3.17/119 = 0.027 mol

V=0.027/0.38 = 0.070 L >>>>>> 70 ml

(27) A nitride ion, N3- , has:
(A) 7 protons and 10 electrons
(B) 14 protons and 7 electrons
(C) 7 protons and 7 electrons
(D) 7 protons and 4 electrons


7 بروتونات ( عدد الالكترونات 7+3 =10 ) لأنه اكتسب 3 الكترونات

(28) What volume of 3.2 M K2CO3 is needed to prepare 250 mL of a 0.200 M K2CO3 solution?
(A) 86 mL
(B) 15.6

mL (C) 44.7 mL

(D) 10.0 mL

v=250 x 0.2/3.2 = 15.6 ml

(29) Which of the following represents the greatest mass?
(A) 2.0 x 102 mg
(B) 2.0 x 102 cg
(C) 1.0 x 105 xg
(D) 10.0 dg

نحولها لنفس الوحده حتى تصبح عملية المقارنه سهلة ...راح نحولها للجرام

2x10^2/1000 = 0.2g
2x10^2/100 = 2g
1x10^5/10^6 = 0.1\g

10/10 =1 g



(30) C + O2  CO2 this equation can be read as:
(A) 1 atom of carbon combines with 1 molecule of oxygen to form 1 molecule of
carbon dioxide.
(B) 1 mole of carbon combines with 1 mole of oxygen to form 1 mole of carbon
dioxide.
(C) both A and B are true.
(D) none of the above.