HW E9 Part B

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005388369
Posts: 73
Joined: Sat Sep 28, 2019 12:16 am

HW E9 Part B

Postby 005388369 » Tue Oct 01, 2019 5:22 pm

Part B of question E9 asks to find how many formula units of the compound (magnesium sulfate heptahydrate) are present in 5.15g. How would I solve this?

AlyshaP_2B
Posts: 112
Joined: Wed Sep 18, 2019 12:19 am

Re: HW E9 Part B

Postby AlyshaP_2B » Tue Oct 01, 2019 5:27 pm

First, you need to determine the number of moles in 5.51 grams, so you need to find the molar mass of MgSO4.7H2O and divide (5.15/24.48). Then, multiply that number by Avogadro's constant to find the number of formula units!

Vincent Leong 2B
Posts: 207
Joined: Fri Aug 09, 2019 12:15 am

Re: HW E9 Part B

Postby Vincent Leong 2B » Tue Oct 01, 2019 5:29 pm

Use avogrado's number (6.022x10^23 molecules/atoms per mol) to solve for the amount of formula units.
1) Convert the grams of magnesium sulfate into moles using the compounds molar mass
2) multiply the amount of moles you calculated with 6.022 x 10^23
3) you have your answer

*make sure to include the mass of 7 water molecules (18 g/mol * 7) when calculating the molar mass of magnesium sulfate.

Megan Ngai- 3B
Posts: 50
Joined: Fri Aug 09, 2019 12:17 am

Re: HW E9 Part B

Postby Megan Ngai- 3B » Tue Oct 01, 2019 11:08 pm

1. you need to find the amount of moles in 5.51g.
- you divide 5.51g by the molar mass of the compound, 24.48
2. multiply by Avogadro's constant (6.022 x 10^23)
- the units of moles will cancel out and you are left with formula units!

Katie Kyan 2K
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Re: HW E9 Part B

Postby Katie Kyan 2K » Wed Oct 02, 2019 12:41 am

First convert 5.15 grams of magnesium sulfate heptahydrate to moles using its molar mass (246.46 grams/mole). From there using dimensional analysis multiply the number of moles of magnesium sulfate heptahydrate by 11 since there are 11 moles of oxygen per one mole of magnesium sulfate heptahydrate. Then using Avogadro's number multiple the moles of oxygen by 6.022x10^23 atoms of O per one mole of oxygen. This should give you the answer 1.38x10^23 atoms of Oxygen.


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