Help on a chemistry A level question

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Miakat1602
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#1
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#1
Magnesium nitrate is used in fertilisers as a source of nitrogen.
(a)* A student plans to prepare 250.0cm3 of a 0.4000moldm–3 solution of magnesium nitrate, starting from magnesium nitrate crystals, Mg(NO3)2•6H2O.
Describe how the student would prepare the solution, giving full details of quantities, apparatus and method. [6 marks]
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MadisonH2018
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#2
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#2
Hi, I'm struggling with this question too, did you get the answer?
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Ben-Hassen
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#3
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#3
(Original post by Miakat1602)
Magnesium nitrate is used in fertilisers as a source of nitrogen.
(a)* A student plans to prepare 250.0cm3 of a 0.4000moldm–3 solution of magnesium nitrate, starting from magnesium nitrate crystals, Mg(NO3)2•6H2O.
Describe how the student would prepare the solution, giving full details of quantities, apparatus and method. [6 marks]
I'll answer the part on the quantity, you should already have an understanding of the method, just don't forget to add the thing you're doing the method with. E.g. Step one would be to measure the solid accurately [with a mass balance].
But as for what to do with the numbers. Basically, you want to find out what mass you're starting with. To do that you have a volume (250.0 cm3) and a concentration (0.4 moldm-3). The equation you should know is moles= conc. x volume. The volume needs to be in dm3 though so:
250/1000 x 0.4 = 0.1 mol.
Then you multiply the moles(0.1) by the Mr of the solid which should be 148.3. The final answer should be you need to start with 14.83g of solid Magnesium Nitrate.
Hope that helped any others who had this homework as well. It took a bit to realise it for me as well lol.
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gg170
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#4
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#4
(Original post by Miakat1602)
Magnesium nitrate is used in fertilisers as a source of nitrogen.
(a)* A student plans to prepare 250.0cm3 of a 0.4000moldm–3 solution of magnesium nitrate, starting from magnesium nitrate crystals, Mg(NO3)2•6H2O.
Describe how the student would prepare the solution, giving full details of quantities, apparatus and method. [6 marks]
Where did u get the 2019 paper from ?
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Davies Chemistry
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#5
Report 1 year ago
#5
(Original post by Ben-Hassen)
I'll answer the part on the quantity, you should already have an understanding of the method, just don't forget to add the thing you're doing the method with. E.g. Step one would be to measure the solid accurately [with a mass balance].
But as for what to do with the numbers. Basically, you want to find out what mass you're starting with. To do that you have a volume (250.0 cm3) and a concentration (0.4 moldm-3). The equation you should know is moles= conc. x volume. The volume needs to be in dm3 though so:
250/1000 x 0.4 = 0.1 mol.
Then you multiply the moles(0.1) by the Mr of the solid which should be 148.3. The final answer should be you need to start with 14.83g of solid Magnesium Nitrate.
Hope that helped any others who had this homework as well. It took a bit to realise it for me as well lol.
Be careful. The Mr of Mg(NO3)2 is 148.3 but you are dealing with the hydrated solid Mg(NO3)2.6H2O so the Mr is 148.3 + (6 x 18) =256.2
So you need to add 25.6 g of the solid.
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billijean0419
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#6
Report 7 months ago
#6
could you explain the method please?
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