This is kind of tricky for me.

What os the empirical formula (lowest whole number ratio) of the compounds below?

A.

25.3% Cu, 12.9% S, 25.7% O, 36.1% water

How would i set this up? The water at the end is confusing me. I think I need to find the percentage of water inside the whole thing first, but I would be wrong. Can you help?

Cu = 25.3/63.54 = 0.398 (You have 3 places in 25.3 so don't throw anything away, at least not yet).

S = 12.9/32.064 = 0.402
O = 25.7/15.999 = 1.606
H2O = 36.1/18.015 = 2.00
Now we divide everything by the smallest, which is 0.398

Cu = 0.398/0.398 = 1.000
S = 0.402/0.398 = 1.01
O = 1.606/0.398 = 4.035
H2O = 2.00/0.398 = 5.025

So we round off to whole numbers now.
Cu 1.000 becomes 1.00
S 1.01 becomes 1.00
O 4.035 becomes 4.00
H2O 5.025 becomes 5.00
The formula is
Cu1S1O4*5H2O or since the 1s are not needed, the formula is CuSO4*5H2O

Do it just as you did the MgBr2.

25.3/atomic mass Cu =
12.9/atomc mass S =
25.7/atomc mass O =
36.1/molar mass H2O =
You already have the percent water in the entire molecule. The formula will come out
as CuxSyOz*WH2O
I don't know that this is the formula but it would look somthing like this.
CuSO4*5H2O

I'm still confused. Okay I solved everything but H20

25.3g Cu 1 mole/63.54 = .40
12.9g S 1 mole/32.064 = .40
25.7g O 1 mole/15.999 = 1.61

But what do i do with the H20? Can you work this part for me? I want to see how you did it

My teacher always told us to round to the hundreths place. How did you get 18.015 ??

aah wait i see how now.

I use a web site to do all my molar mass stuff. Here is a link if you want to use it. http://environmentalchemistry.com/yogi/reference/molar.html

Certainly! Let's break down the problem step by step.

To find the empirical formula of a compound, we need to determine the ratio of atoms present in the compound. In this case, we are given the percentage composition of copper (Cu), sulfur (S), oxygen (O), and water (H2O).

To find the empirical formula, we first need to consider the percentage composition by converting the percentages into grams. This will allow us to determine the number of moles of each element present in the compound.

For simplicity, let's assume we have 100 grams of the compound.

Step 1: Calculate the grams of each element:
- Copper (Cu): 25.3% of 100 grams = 25.3 grams
- Sulfur (S): 12.9% of 100 grams = 12.9 grams
- Oxygen (O): 25.7% of 100 grams = 25.7 grams

Now, here's where it gets a bit tricky since the composition includes water at the end.

To find the mass of water in the compound, we need to subtract the masses of copper, sulfur, and oxygen from the total mass of the compound. The remaining mass will be attributed to water.

Total mass of the compound = mass of copper + mass of sulfur + mass of oxygen + mass of water
100 grams = 25.3 grams + 12.9 grams + 25.7 grams + mass of water
mass of water = 100 grams - (25.3 grams + 12.9 grams + 25.7 grams)
mass of water = 36.1 grams

Now that we have the mass of water, we can calculate the number of moles of each element:

Step 2: Calculate the moles of each element:

- Moles of copper (Cu): mass of Cu / molar mass of Cu
- Moles of sulfur (S): mass of S / molar mass of S
- Moles of oxygen (O): mass of O / molar mass of O
- Moles of water (H2O): mass of H2O / molar mass of H2O

The molar masses are:
- Molar mass of Cu = 63.55 g/mol
- Molar mass of S = 32.07 g/mol
- Molar mass of O = 16.00 g/mol
- Molar mass of H2O = (2 x 1.01) + 16.00 = 18.02 g/mol

Using these values, we can now calculate the number of moles:

Moles of Cu = 25.3 grams / 63.55 g/mol
Moles of S = 12.9 grams / 32.07 g/mol
Moles of O = 25.7 grams / 16.00 g/mol
Moles of H2O = 36.1 grams / 18.02 g/mol

Step 3: Determine the simplest whole-number ratio:

To find the simplest whole-number ratio, we need to divide all the moles by the smallest value among them. We can round to the nearest whole number if needed.

Let's assume the smallest number of moles is for copper (Cu):

Moles of Cu: Moles of Cu / Moles of Cu = 1
Moles of S: (Moles of S / Moles of Cu) = (12.9 g / 32.07 g/mol) / (25.3 g / 63.55 g/mol) ≈ 0.4
Moles of O: (Moles of O / Moles of Cu) = (25.7 g / 16.00 g/mol) / (25.3 g / 63.55 g/mol) ≈ 1
Moles of H2O: (Moles of H2O / Moles of Cu) = (36.1 g / 18.02 g/mol) / (25.3 g / 63.55 g/mol) ≈ 1.8

Since we are looking for the empirical formula, we need to round the ratios to the nearest whole number:

The empirical formula of the compound is approximately CuSO2O9H5 or CuSO4.5H2O.

Note that there might be slight deviations from the whole number ratio due to rounding errors when using molar masses.

I hope this helps you understand how to approach this problem!