Phys Sc 430

Pretest 2.2 Solutions

 

1.†††††††† Avogadro was one of the first people to use the word "molecule".

††††††††††† What is the difference between a mole and a molecule?

†††††††††††

††††††††††† A molecule is two or more atoms chemically bonded to one another.

A mole consists of 6.02 X 1023 molecules or particles of anything.

Mole comes from a Latin word meaning lump. Molecule means little lump.

 

2.†††††††† Find the molar mass of Ö.

 

Rounded Rectangular Callout: Remember:
Iím a little furry animal that multiplies. If you have moles multiply by molar mass to get mass in grams.

a.†††††††† Ca(OH)2

 

††††††††††† 40 + 2(16) + 2(1) = 74 g/mole

 

b.†††††††† beryllium nitrate

 

††††††††††† Be(NO3)2

 


††††††††††† 9 + 2(14) + 6(16) = 133 g/mole††††††††††††††††††††††††††

 

3.†††††††† Convert the following:

 

a.†††††††† 300 g of Mg = __________moles

 

300 g (mole/24 g) = 12.5 moles

 

b.†††††††† 1 g of water = __________moles

 

 

††††††††††††††††††††††††††††††††††† 1 g(mole/18 g) = 0.056 moles

 

c.†††††††† 2 moles of O2 = ________grams

†††††††††††††††††††††††††††††††††††

††††††††††† 2 moles (32 g/mole) = 64 g

 

d.†††††††† 2 moles of O2 = ________molecules

 

††††††††††† 2 moles (6.02 X 1023 molecules/mole) = 1.2 X 1024 molecules

 

 

4.†††††††† Monty Mole found a mole of gold(Au). If gold sells for

$12 per gram, what is the value of Montyís mole of gold?

 

††††††††††† 1 moleAu = 197 g

 

††††††††††† 197 g($12/g) = $2364

 

5.†††††††† Two molecules is how many moles?

 

††††††††††† 2 molecule (mole/6.02 X 1023) = 3.33 X 10-24 moles

 

6.†††††††† Given:†††††††††††††† 4 NH3(g)††††††††††† +††††††††† 5 O2(g)†† ----->4 NO(g)††† +††††††††† 6 H2O(g)

 

A.††††††† How many moles of water will be produced if 5 moles of ammonia, NH3(g), react?

 

††††††††††† †††††††††††††††††††††††††††††††††††† or ††††††† 5 moles NH3 (5 O2/ 4 NH3(g)) = 7.5 moles O2

†††††††††††

††††††††††† x = 7.5 moles

 

B.†††††††† How many grams of oxygen reacted if only one mole of NO reacted?

 

†††††††††††

 

††††††††††† x = 1.25 moles of oxygen

 

††††††††††† 1.25 moles (32g/mole) = 40 g

 

 

 

C.†††††††† How many grams of ammonia will react with 2 grams of oxygen gas?

 

††††† 2 g (mole/32 g) = 0.0625 moles

 

†††††

 

††††† x = 0.05 moles NH3

 

††††† 0.05 moles NH3( 17g/mole) = 0.85 g

 

7.†††††† In the reduction of CuO experiment, why was mass seemingly "lost"?

 

††††††††† Cu O was turned into Cu, which is an element, so if itís weighed by itself, itíll weigh less than CuO. The oxygen is gone.

 

8.†††††† If 20% of an element has a mass of 260 units, and the rest has a mass of 263, what is atomic mass of that imaginary element?

 

††††† 0.20(260) + 0.80(263) = 262.4

 

9.†††††† Flash has a mole of red dye in his left hand and a mole of green dye in his right hand.

Trick question:

a.††††††††††† Which hand holds more molecules? Neither; each has an Avogadroís number of molecules.

b.††††††††††† Which hand holds more mass if the red stuff is selenium and the green stuff is bismuth? Bi (larger molar mass)

 

Donít dye your hair with that stuff!!!†††††

 

 

10.†††† Balance:

 

a.†††† 2 Al(s)††††††† +††††† Fe2O3(s)††††††††††††† ŗ†††† Al2O3(s)††††† +††††† 2 Fe(l)

 

b.†††† 4 K††† +††††† O2†††††††††††††††††††† ŗ†††† 2 K2O

 

c.††††† C11H24††††††† +††††† 17 O2††††††††††††††† ŗ†††† 11 CO2†††††† +††††† 12 H2O

 

d.†††† 6 Ca(NO3)2+††††† 2 Na3PO4††††††††††† ŗ†††† 2 Ca3(PO4)2††††††† + 6 NaNO3

 

e.†††† CuS†† +††††† 2 NaOH††††††††††††††††††††† ŗ†††† Cu(OH)2†††† +††††† Na2S

 

 

extra.††† Complete the table, given the fact that the average atomic mass of Z = 301.5.

 

Isotope

Mass number

Percent Abundance

 

299Z

 

 

 

299

 

20

301Z

 

 

301

 

50

 

???Z

 

 

 

???

 

???

 

 

††††††††††† 0.20*299 + 0.50*301 + 0.30*x = 301.5

 

††††††††††††††††††††††† x = 304 u

Review Section

 

11.††††††† Which are covalent compounds (two types of atoms bonded together)?

 

a.       BF3_____

b.       H2O2____

c.       O3_________

d.       Ca(OH)2_________

e.       air______

 

 

12.††††††† What is the difference between a compound and an element?

 

A compound consists of two or more types of elements bonded to another. An element only has one type of atom.

 

13.††††††† Recopy and complete the following table.

 

Family

Common Charge

3 examples

Reacts withÖ(give 1 example)

 

Alkali metals

+1

Li,Na,K

halogens

Alkaline earth metals

 

+2

Be,Mg,Ca

water

Halogens

-1

 

F,Cl,Br

Most metals

Noble or Inert gases

 

0

He,Ne,Ar

Almost nothing

 

14.††††††† Name the following:

 

a.                   MgS†††† magnesium sulfide

 

b.                   KOH††† potassium hydroxide

 

c.                   O2†††††††††† (diatomic)oxygen

 

d.                  Ga2(SO4)3†††††††† gallium sulfate