Question

Help with chemistry lab please asap? I need to determine the formula of a sample of copper sulfate hydrate.?

Crucible Crucible & hydrate Dehydrate
20.500 g 21.255 g 2 0.983 g

This is what I did so far:
An empty crucible has a mass of 20.500g. A sample of copper sulfate hydrate is added to the crucible, making the total mass of the crucible and hydrate 21.255 g. Subtraction of the mass of the empty crucible from the mass of the hydrate and crucible gives the mass of the hydrate. (21.255 g- 20.500 g = 0.755 g hydrate).

Answer 1

continued: Step 2: Subtract the mass of the dehydrated compound from the mass of the hydrate to determine the mass of water that was present in the hydrate.
20.983 g - 0.755 g = 20.228 g H2O present in the sample of hydrate

Answer 2

please show work. thanks

Answer 3

@ganeshie8

Answer 4

@chmvijay

Answer 5

I only have the text version of the lab, which is this:

Answer 6

Molar Mass of Compounds: Determining the Formula of a Hydrate—Text Version

When hydrates are heated, the water of hydration evaporates and is released as vapor. The remaining solid is known as the anhydrous salt, which is the compound same compound without the water molecules trapped inside.

Purpose:

To determine the formula of a hydrate.

Materials:
• crucible
•Bunsen burner
•balance
•CuSO4 hydrate

Procedure:
1.Measure the mass of the clean, empty crucible, record the mass.
2.Add one or two scoops of the hydrate to the crucible, record the mass.
3.Heat the crucible and hydrate above a Bunsen burner for at least ten minutes to make sure that all of the water evaporates.
4.Let the crucible cool and then mass the crucible with dehydrated solid inside, record the mass.
5.Calculate the formula of the hydrate.

Answer 7

I basically need to know how to find the empiricial formula

Answer 8

convert the masses (of the dehydrated compound and the water) you found to moles and compare them.

Answer 9

I know that, but idk how

Answer 10

have you found the moles?

Answer 11

I'm not good with moles convertion

Answer 12

no

Answer 13

I need someone to explain it to me

Answer 14

use this formula: \(n=\dfrac{m}{M}\rightarrow n_{CuSO_4}=\dfrac{0.983g}{159.62g/mol} \)
do the same for the water

Answer 15

n=moles, m=mass, M=molar mass

Answer 16

idk what the molas mass is tho

Answer 17

you can find it on a periodic table, just add up the molar masses of each individual atom in the compound

Answer 18

I don't really know how to do that

Answer 19

heres a periodic table http://ptable.com

the molar masses are given at the bottom of each square for that element.

Answer 20

so I add up the one from C, S, and O and it will be one number?

Answer 21

ones*

Answer 22

i already did the CuSO4 one. (i wrote it above), you can do the one for water

Answer 23

I mean Cu

Answer 24

oh

Answer 25

but how did u get 2 numbers

Answer 26

wait, so for H its 1.008 and for O its 15.999

Answer 27

the number at the top was the mass of the dehydrated substance, which is \(CuSO_4\). The hydrate is \(CuSO_4xH_2O\) so now you're finding how many moles of water there are

Answer 28

okay, but there are 2 hydrogens, so you need to add that 2 times

Answer 29

oh ok

Answer 30

1.008 * 2= 2.016

Answer 31

+ the oxygen

Answer 32

ok

Answer 33

18.015

Answer 34

good stuff. now, can you find the mass of the water?

Answer 35

does 18.015 go on the top of the fraction

Answer 36

it goes where the uppercase M is, so at the bottom.

Answer 37

ok how do i find the mass of H2o

Answer 38

you can find it with the data given in the question

Crucible Crucible & hydrate Dehydrate
20.500 g 21.255 g 2 0.983 g

mass of hydrate - mass of dehydrate = mass of water

Answer 39

wait hello we arent done??

Answer 40

@aaronq now what.. i need the formula

Answer 41

have you found the mass of the water?

Answer 42

yes

Answer 43

0.272 g

Answer 44

now find the moles by diving by the molar mass

Answer 45

so its n H2O= 0.272 g/18.015 g/mol

Answer 46

okay good. so what are the moles of each

Answer 47

So I divide? do i also do it to CuSO4?

Answer 48

yes

Answer 49

ok hold on

Answer 50

for water, its a long decimal

Answer 51

0.0150985...

Answer 52

0.015 is fine

Answer 53

the next one is 0.0061..

Answer 54

0.006158...

Answer 55

okay. so now that we know the amount of moles (which correlates to the number of atoms) we can compare the 2 to see in what ratio the hydrate is made of.

so divide the moles of water by the moles of the CuSO4: \(\dfrac{n_{H_2O}}{n_{CUSO_4}}\)

Answer 56

wait hold on, i forgot to say that in the data table we only have the mass of the Crucible and hydrate together, but i also calulated the mass of ONLY the hydrate, which is 0.755 g. do we need to use that?

Answer 57

nope. we only need the mass of the dehydrate and the water

Answer 58

ok

Answer 59

its 0.05514...

Answer 60

you divided incorrectly: 0.0150985/0.0061= 2.47

Answer 61

oh

Answer 62

because i didnt do the whole decimal

Answer 63

wait but the full decimal for CUSO4 isn't 0.0061

Answer 64

its 0.006158 and it continues.. i dnt remember the rest

Answer 65

i can divide again

Answer 66

do we need to use the wholeee decimal to divide?

Answer 67

i'm checking your calculations and the mass of the water you found is incorrect.

0.983 -( 21.255-20.500) = 0.228 g

the moles of water are 0.0126666

the moles of the dehydrate are 0.0061583

so the ratio is: 0.0126666/0.0061583=2.05683386

Answer 68

no you don't, but you placed the numbers in the wrong places.

Answer 69

oh

Answer 70

so, you have 2 water molecules for every molecules of copper sulfate, so the formula is \(CuSO_4*2H_2O\)

Answer 71

so for moles of water is this right? N= m/M  n H2O= 0.272 g/18.015 g/mol= 0.0126666

Answer 72

yes that's right

Answer 73

ok

Answer 74

do you understand that last part?

Answer 75

yes

Answer 76

okay cool.

Answer 77

oh my god u are a lifesaver . thanks

Answer 78

no problem !