I don’t understand these questions please help

Explanation:

#3 Here basically you have to convert the mg to g first because we want to know the number of g of calcium per glass. That comes out to be 305/1000= 0.305g. So then, now you have to set up a algebraic equation

0.305x=1.3 (basically x refers to number of glasses)

x= 4.26 (now we know the kid needs to drink about 4 glasses/cups per day)

#4

Here convert moles to grams using molar mass of NaCl.

12.5molesx58.44g/mol > 730.5g NaCl

#5

So any gas at STP occupies 22.4 liters/1mol of gas.

110L x 1mol/22.4L = 4.91 moles N2

#6

So here basically do the same thing as 5 to find the moles. Then multiply that moles with 6.022x10^23 molecules (because 1 mol has 6.022x10^23 molecules) to find the number of molecules.

You should get 1.21x10^25 molecules

#7

Here basically find the moles first then convert the moles to grams using molar mass of H3PO4.

Molarity=moles/volume

1.7= x/0.550 (here we converted ml to L because volume is in liters for molarity)

x= 0.935 moles

Then, 0.935mol x 97.994g/1mol = 91.6g H3PO4

#8

Here convert the grams to moles using molar mass first (divide the grams by the molar mass) then multiply the number which is moles by 6.022x10^23 molecules (because 1 mol has 6.022x10^23 molecules) to find the number of molecules.

You should get 2.77x10^24 molecules

Hopefully everything makes sense lmk if it doesn't...I have tried my best to do these quickly I am sorry for any errors.

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%

c, liquids evaporate, creating a gas