Calculate the percent composition of silicon dioxide...?

Question

Okay, these questions are on something I have to turn in tommorow, so I'm pretty desperate for answers. If you help me answer these and explain the process (as thoroughly and on my level (11th grade) as possible) I'll choose your answer as the best.

After calculating the percent composition of silicon dioxide, answer these questions:

1. What mass of silicon dioxide would contain 25g oxygen?

2. How many moles of silicon dioxide would contain 25g oxygen?

3. How many molecules of silicon dioxide would contain 25 g of oxygen?


I'm concerned about getting the answers, but EVEN MORE concerned about understanding HOW to get the answers!

Thanks!

Answer 1

% mass composition is the mass of 1 component of a system divided by the total mass x 100%. In the case of compounds, it is the mass of one element divided by the total mass of the compound.

%mass O = mass of Oxygen/mass of SiO2 x 100%

To calculate the %mass, you assume you have 1 mole of the compound:

1 mole SiO2 = 60.1 g

1 mole SiO2 contains 2 mole O

2 mole O = 32.00 g

% mass O = 32.00 g/ 60.1 g x 100% = 53.2%

Now, to calculate different quantities of Oxygen, you know the compound must maintain the 53.2% composition.

1. 0.532 = 25 g Oxygen/ mass of SiO2
mass of SiO2 = 25 g / 0.532 = 47.0 g SiO2

2. 47.0 g SiO2 ( 1 mole SiO2 / 60.1 g) = 0.781 mole SiO2

3. 0.781 mole SiO2 (6.022 x 10^(23) molecules / mole SiO2) = 4.70 x 10^(23) molecules of SiO2

I hope that helps.

Answer 2

Molecular Weight Of Silicon Dioxide

Answer 3

First step is to get atomic weights (the atomic weight is how much one mole of an atom or molecule weighs in grams) from a periodic table.
for Si: 28.0855, for O: 15.9994.
Then one SiO2 ( silicon dioxide) molecule weighs
28.0855+2*15.9994=60.0843
Second step: (weigth of sillicon/weight of silicon dioxide)*100
so (28.0855/60.0843)*100=46.74 % Si

For oxygen you do (2*weight of oxygen/weight of silicon dioxide)*100 because there are two oxygen atoms in the molecule
so (2*15.9994/60.0843)*100=53.26% O this means there are 53.26 g of oxygen for every 100g of sillicon dioxide or 100g SiO2/53.26g O

Question 1: 25g O*(100g SiO2/53.26g O)=46.94g SiO2.
The g O cancel leaving you with g SiO2 as your units. Also store the numbers you use in your calculaters memory for maximum accuarcy.

Question 2: 25g O*(1 mole of O/15.9994g O)*
(1 mole ofSiO2/2 moles of O)=0.7813 moles of SiO2.

Hope that helps.

Answer 4

Atomic weights: Si=28 O=16 SiO2=60

28/60 x 100% = 46.6% Si

32/60 x 100% = 53.3% O

25gO x 1molO/16gO x 1molSiO2/2molO x 60gSiO2/1molSiO2 = 47g SiO2 to two significant figures

25gO x 1molO/16gO x 1molSiO2/2molO = 0.78 moles SiO2

0.78molSiO2 x 6.02x10^23moleculesSiO2/1molSiO2 = 4.7 x 10^23 molecules SiO2