Molar volume

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problem# h2chefor1          →  Molar volume

Atomic mass H =1     B = 11     C = 12     N = 14     O = 16 Na =23     Mg = 24     P = 31     S = 32     Cl = 35.5 K =39     Ca = 40     Br = 80     Ba = 137     Pb = 207

14. Consider the following gas at (STP)standard condition for temperature and pressure.        i) Gas HCL       2.8 dm3        ii) Gas NO       6.02 x 1022 molecules.        iii) Gas CO       weight 3.5 g.        iv) Gas NH3       11.2 dm3 Which one of the folllowing is incorrect? 1. The number of moles of gas HCL equals the number of moles of gas CO. 2. The number of molecules of gas NO is the least. 3. Volume of gas CO is 1.25 times of the volume of gas NO. 4. Gas NH3 occupies the least minimum pressure.

(Problem credited by -- Thailand Entrance High School-Chemistry)

Photos credited bt Ratchamongkol

Strategy the rule "Must have" of Mr.Zhang ® Find the number of moles; PV=nRT , and V,R,T are constant. P ∝ n ( n = the number of moles)

V = nRT/p   →  (1)

V = (1.00 mol)(0.0821 L atm/mol K)(273.15 K) / (1.00 atm)

Therefore; V = 22.4 L

Solution
From equation(1); we give A is the number of moles of HCl
1 mole 22.4 x 10-3 m3	=	A 2.8 x 10-3 m3
1 mole x 2.8 x 10-3 m3 22.4 x 10-3 m3	=	A
A	=	0.125 mole
(i) the number of moles of gas HCl in 2.8 dm3	=	0.125 mole
(ii) the number of moles of gas NO	=	the number of molecule of gas NO NA (Avogadro's number)
⇒	=	6.02 x 1022 6.02 x 1023	=	0.1 mole

(iii) the number of moles of gas CO

=

mass(in grams)

mass of 1 mole of the compound(CO)

                                       ⇒           =  3.5/28
                                                      = 0.125 mole

(iv) the number of moles of gas NH3 11.2 dm3;
1 mole 22.4 x 10-3 m3	=	B 11.2 x 10-3 m3
1 mole x 11.2 x 10-3 m3 22.4 x 10-3 m3	=	B
B	=	0.5 mole
(iv) the number of moles of gas NH3 11.2 dm3 is 0.5 mole

Comparing the volume of NO=0.1 mole and CO=0.125 mole
Find the volume of NO=0.1 mole;
1 mole 22.4 L	=	0.1 C
C	=	0.1 x 22.4 L

Find the volume of CO=0.125 mole;
1 mole 22.4 L	=	0.125 D
D	=	0.125 x 22.4 L

Volume of gas CO is 1.25 times of the volume of gas NO.
∴no. 3 is correct.

Ans.  no. 4 is incorrect.  ∴we have the maximum number of moles of gas NH3 therefore,we can concluded that gas NH3  have the most pressure as well.

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Chemistry Bonding & Chemical compound formula

	Mr.Rittichai   Sae Tia     Cell phone : +66843315969 / 0843315969     Home phone : +6624769832/ 024769832     23/14 Moo5, Soi Suksawad14,     Suksawad Rd.,Jomtong,     Bangkok - Thailand
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# h3chefor1          →  Molecule Formulae
Element		reacts with		, and will get the compound molecule.
What is the mass of this molecular compound?

1. 168		2. 248
3. 256		4. 328

(Problem credited by -- Thailand Entrance High School)

Strategy the rule "Must have" of Mr.Zhang ® Find the molecular formula , and later calculate the mass.

Solution

Element A; configuration atomic no=38 Energy level  →   2, 8, 18, 8, 2 A is an ion,lose 2 electrons,is in group 2, 5 shells outermost shell of A,there is 2 electrons 1s² 2s²2p⁶ 3s²3p⁶3d¹⁰ 4s²4p⁶ 5s² Energy level  →   2, 8, 18, 8, 2 5th period,group 2

Element B; configuration atomic no=35 atomic no=35 1s² 2s²2p⁶ 3s²3p⁶3d¹⁰ 4s²4p5 Energy level  →   2, 8, 18, 7 4th period,group 7

Empirical formula of the molecular compound, A has a +2 charge and B has a -1 charge , therefore 1A2+ ion is required to balance 2 B-

Now how to balance take the two ions... in this case A and B. That makes group IIA and group VIIA. Therefore A is +2 and B is -1. Now reverse the numbers of the charges... A now has 1 and B is now 2. Therefore...two atoms of B and one atom of A has the chemical equation; A + B2    →   AB2

Hence the Molecule Compound Mass is  88+2(80) = 248

Ans.  no. 3 - 248 is the answer

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