A 6.25 gram sample of copper(II) chloride hydrate was heated until all the water was liberated. The residue massed 4.45 grams. How many water molecules are present for every formula unit of copper(II) chloride?
First, we get the molar masses to the CuCl2 and H2O. Just get a periodic table and add the individual masses of elements in the chemical formula:
CuCl2: 63.55 + 2*35.45 = 134.45
H2O: 2*1 + 1*16 = 18
Then we get their moles. We divide the mass by the molar mass to get the moles. Note that the 4.45 grams is for anhydrous CuCl2 (or the one without water):
4.45 g / 134.45 g/mol = 0.033 mol
For water, we first subtract 6.25 by 4.45 grams, because the difference is the mass of the released H2O. Then divide by the molar mass:
(6.25 - 4.45) / 18 = 0.1 mol
Finally, we get the ratio of moles:
CuCl2 : H2O
0.033:0.1 = 1:n
n = 3.03 or approximately equal to 3
Thus, the formula of the hydrate is CuCl2 * 3H2O
Hope this helps~ :3
Thank you! I really love how you took the time to help me out!
To find the number of water molecules present for every formula unit of copper(II) chloride, we need to calculate the difference in mass between the hydrate and the residue.
1. Find the mass of water lost:
Mass of hydrate - Mass of residue = Mass of water lost
6.25 g - 4.45 g = 1.8 g
2. Convert the mass of water lost to moles:
Moles of water = Mass of water lost / molar mass of water
The molar mass of water (H2O) is approximately 18.015 g/mol.
Moles of water = 1.8 g / 18.015 g/mol ≈ 0.0998 mol
3. Find the number of water molecules using Avogadro's number:
1 mol of water contains 6.022 × 10^23 molecules (Avogadro's number).
Number of water molecules = Moles of water × Avogadro's number
Number of water molecules = 0.0998 mol × 6.022 × 10^23 molecules/mol ≈ 6.006 × 10^22 molecules
Therefore, there are approximately 6.006 × 10^22 water molecules present for every formula unit of copper(II) chloride.
To determine the number of water molecules present for every formula unit of copper(II) chloride, we need to use the information about the mass of the hydrate before and after heating.
Let's start by finding the mass of water that was liberated during heating. We can subtract the mass of the residue from the mass of the original sample:
Mass of water liberated = Mass of hydrate before heating - Mass of residue
= 6.25 grams - 4.45 grams
= 1.80 grams
Next, we need to convert the mass of water liberated into moles of water. To do this, we can use the molar mass of water, which is approximately 18 grams/mol:
Moles of water = Mass of water / Molar mass of water
= 1.80 grams / 18 grams/mol
= 0.10 moles
Since 1 mole of water contains 6.022 x 10^23 molecules (Avogadro's number), we can calculate the number of water molecules:
Number of water molecules = Moles of water * Avogadro's number
= 0.10 moles * 6.022 x 10^23 molecules/mol
= 6.022 x 10^22 molecules
Now, we need to determine the number of formula units of copper(II) chloride present in the sample. To do this, we first need to calculate the number of moles of copper(II) chloride based on the mass of the residue:
Moles of copper(II) chloride = Mass of residue / Molar mass of copper(II) chloride
The molar mass of copper(II) chloride can be calculated by adding the atomic masses of its constituent elements:
Molar mass of copper(II) chloride = Atomic mass of Cu + (2 * Atomic mass of Cl)
Using the atomic masses from the periodic table, the molar mass of copper(II) chloride is:
Molar mass of copper(II) chloride = 63.55 g/mol + (2 * 35.45 g/mol)
= 63.55 g/mol + 70.90 g/mol
= 134.45 g/mol
Substituting the values into the formula, we can find the moles of copper(II) chloride:
Moles of copper(II) chloride = 4.45 grams / 134.45 g/mol
= 0.0331 moles
Finally, we can determine the ratio of water molecules to formula units of copper(II) chloride:
Ratio = Number of water molecules / Moles of copper(II) chloride
= 6.022 x 10^22 molecules / 0.0331 moles
= 1.82 x 10^24 molecules/mol
Therefore, for every formula unit of copper(II) chloride, there are approximately 1.82 x 10^24 water molecules present.