<u><em>Question 1</em></u>
The average atomic mass of element is 84.66
<u>calculation</u>
Average atomic mass is of an element is the sum of masses of its isotope each multiplied by its natural abundance.
that is.
[(50.50 x 83.75) /100] + [( 30.25 x 84.45)/100] + [(,9.25 x 87.40)/100]
= 42.29 +25.55 +16.82= 84.66
<u><em>Question 2</em></u>
fill the table
symbol element protons neutrons Electrons mass No Atomic No
Cs-133 cesium 55 78 55 133 55
Na-23 sodium 11 12 11 23 11
Ne 22 Neon 10 12 1 0 22 10
Au -197 Gold 79 118 79 197 79
<u><em>Question 3</em></u>
The moles of tungsten that are in 93.50 grams are 0.509 moles
moles= mass/molar mass
molar mass of tungsten = 183.84 g/mol
moles is therefore= 93.50 g/ 183.84 g/mol= 0.509 moles
<em><u>question 4</u></em>
CO2 molecules at STP are 1.547 x10^23 molecules
Step 1: find the moles of CO2
At STP 1 mole of a gas= 22.4 l
? =5.75 L
by cross multiplication
= (5.75 L x 1 mole)/ 22.4 L= 0.257 moles
Step 2: use the Avogadro's constant to calculate the number of molecule
that is 1 moles = 6.02 x10^23 molecules
0.257 moles= ? molecules
by cross multiplication
=(0.257 moles x 6.02 x 10^23) / 1 mole = 1.547 x10^23 molecules
<u><em>question 5</em></u>
The number of calcium atoms is 3.82 x10^24 atoms
Step 1: find the moles of calcium
= 253.50 g /40 g/mol= 6.34 moles
Step 2: use the Avogadro's law to calculate the number of atoms.
that is 1 mole= 6.02 x 10^23 atoms
6.34 moles= ? atoms
=6.34 x 6.02 x10^23 = 3.82 x10^24 atoms
<u><em>Question 6</em></u>
mass in grams of NiBr2 is 126.97 grams
Step 1: by use of Avogadro's law constant calculate the number of moles
that is 1 mole = 6.02 x 10^23
? = 3.50 x 10^23
by cross multiplication
= (1 mole x 3.50 x10^23) / 6.02 x10^23 =0.581 moles
step 2: calculate the mass
mass =moles x molar mass
= 0.581 moles x218.53 g/mol = 126.97 grams
<u><em>Bonus question</em></u>
The molecules of water= 1.00 x10^26 molecules
calculation
convert liters into ml
= 3 x 1000 = 3000 ml
find the mass of water
= density x volume
=3000 x0.998 2994 grams
find the moles of water=mass/molar mass
= 2994 g/ 18 g/mol= 166.33 moles
Use Avogadro's constant to calculate the molecules of water
that is 1 mole= 6.02 x10^23 molecules
166.33 moles= ? molecules
= (166.33 moles x6.02 x10^23 molecules) / 1 mole = 1.00 x10^26 molecules
