I am a bit lost as to how to go about answering this question. Any help will be appreciated.

When 1.40g of hydrated magnesium sulphate is heated to constant mass, 0.68g of the anhydrous salt remains. Find the formula for the hydrated magnesium sulphate.

Write the balanced equation:

MgSO4xH2O >> MgSO4 + x H2O

so the question is , what it the value of x?

You have .68g of MgSO4, calculate the number of moles that is. That will also be the number of moles of MgSO4 of the hydrated salt.

Now you have
N MgSO4.xH2O and you know N.

But you also know that there are 1.40-.68g water, so calculate the number of mole of water that is. Call that number M.

Nx= M
solve for x

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To find the formula for the hydrated magnesium sulphate, you need to determine the value of x in the formula MgSO4⋅xH2O. Here's how you can approach the problem:

1. Calculate the number of moles of anhydrous magnesium sulfate (MgSO4) using its molar mass. The molar mass of MgSO4 is 120.37 g/mol.

Number of moles of MgSO4 = mass of MgSO4 / molar mass of MgSO4
= 0.68 g / 120.37 g/mol

2. Since the number of moles of anhydrous magnesium sulfate is the same as the number of moles of the hydrated salt (MgSO4⋅xH2O), x moles of water are associated with each mole of MgSO4.

3. Calculate the number of moles of water (H2O) using the given mass of water.

Mass of water = mass of hydrated salt - mass of anhydrous salt
= 1.40 g - 0.68 g

Number of moles of water = mass of water / molar mass of water
= (1.40 g - 0.68 g) / molar mass of water

4. Now equate the mole ratios of MgSO4 and H2O in the formula MgSO4⋅xH2O:

Number of moles of MgSO4 = x × number of moles of water

Substitute the values you have calculated to solve for x:

In step 1, you found the number of moles of MgSO4.
In step 3, you found the number of moles of water.

Nx = M

Substituting the values:
N (number of moles of MgSO4) = 0.68 g / 120.37 g/mol
M (number of moles of water) = (1.40 g - 0.68 g) / molar mass of water

Solve for x: 0.68 g / 120.37 g/mol = [(1.40 g - 0.68 g) / molar mass of water] × x

Simplifying, you'll find the value of x, which represents the number of moles of water associated with each mole of MgSO4.

x = [(1.40 g - 0.68 g) / molar mass of water] × [120.37 g/mol / 0.68 g]

By substituting the values correctly and performing the necessary calculations, you will obtain the value of x. This value represents the number of moles of water (H2O) in the formula for hydrated magnesium sulphate (MgSO4⋅xH2O).