Calculating Ca2+ Ions in 0.05 Moles of Ca(NO3)2 | Homework Equations

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In summary, the question asks for the number of Ca2+ ions in 0.05 moles of Ca(NO3)2. The correct approach is to use the molar mass of Ca(NO3)2 to convert moles to grams, then use the stoichiometric ratio of 1 mole Ca(NO3)2 to 1 mole Ca2+ to find the number of Ca2+ ions. It is important to keep track of units and stoichiometric ratios in order to get the correct answer.
  • #1
chawki
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Homework Statement




Homework Equations


How many Ca2+ ions are there in 0.05 moles of Ca(NO3)2?

The Attempt at a Solution


how do we calculate the number of ions?
 
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  • #2
(0.05/molar mass) * 6.022*10e23 ?
 
  • #3
Correct, although you should include one more factor:
Each mole of Ca(NO3)[/sub]2[/sub] contains 1 mole of Ca2+ ions.

Since it's a 1:1 ratio, it won't affect the numerical value of your answer...but you don't want to start the habit of omitting that factor, since it would be a different story if you had been asked how many oxygen or nitrogen atoms were present.
 
  • #4
can you tell me how it would be different. or what are the steps to approach these kind of questions!
because i have that habit of doing (number of moles/molar mass)*6.022*10e23
 
  • #5
When I was a TA, I told my students to always keep track of units during calculations. This includes keeping track of which ions, atoms, or molecules you're measuring amounts of. That way you can tell at a glance whether you've inadvertently left out any stoichiometric ratios or conversion factors.

[tex]0.05g Ca(NO_{3}){_2}*\frac{1 mole Ca(NO_{3}){_2}}{molar mass Ca(NO_{3}){_2}}*\frac{1 mole Ca^{2+}}{1 mole Ca(NO_{3}){_2}}*6.022*10^{23}\frac{atoms}{mole}[/tex]

The units for molar mass are obviously grams/mole.
 
  • #6
how would it be if we have been asked to find how many oxygen atoms were present in 2 moles.
is it: 2/(2*3*16)*6.022*10e23
or 2/16 * 6.022*10e23 ?
 
  • #7
The stoichiometric ratio
[tex]\frac{1 mole Ca^{2+}}{1 mole Ca(NO_{3}){_2}}[/tex]
would be replaced with
[tex]\frac{6 moles O}{1 mole Ca(NO_{3}){_2}}[/tex]
 
  • #8
so it would be:
(2*6/164.1)*6.022*10e23
and that's 4.403*10e22 ?
 
  • #9
Where is the 2 coming from, and why aren't you using the mass of calcium nitrate?
 
  • #10
2 came from (NO3)2 , we have 2N
and i used the mass which is 164.1
 
  • #11
There are several problems with this.
1. You stated you were looking for oxygen atoms, not nitrogen atoms.
2. Suppose you had been given 0.30 moles of the salt instead of 0.05 moles. How would your calculations have been different?
 
  • #12
PhaseShifter said:
Where is the 2 coming from, and why aren't you using the mass of calcium nitrate?

Why do you need the mass of calcium nitrate? The question asks for 0.05 mol, not 0.05 g.:confused:
 

1. How do you calculate the number of Ca2+ ions in 0.05 moles of Ca(NO3)2?

To calculate the number of Ca2+ ions in 0.05 moles of Ca(NO3)2, you first need to determine the molar mass of Ca(NO3)2, which is 164.09 g/mol. Next, multiply the number of moles (0.05) by Avogadro's number (6.02 x 10^23) to get the total number of molecules. Since Ca(NO3)2 contains two Ca2+ ions per molecule, you can then multiply the total number of molecules by 2 to get the number of Ca2+ ions, which in this case would be 6.02 x 10^23 x 2 = 1.204 x 10^24 Ca2+ ions.

2. What are the units for the concentration of Ca2+ ions in 0.05 moles of Ca(NO3)2?

The units for the concentration of Ca2+ ions in 0.05 moles of Ca(NO3)2 would be moles per liter (mol/L). This is because concentration is typically expressed as the amount of solute (in this case, Ca2+ ions) per unit volume of solution (in this case, 1 liter).

3. Can you use the formula for calculating Ca2+ ions in 0.05 moles of Ca(NO3)2 for other compounds?

No, the formula for calculating the number of Ca2+ ions in 0.05 moles of Ca(NO3)2 is specific to this compound. Other compounds will have different formulas for calculating the number of ions present.

4. Is it necessary to know the molar mass of Ca(NO3)2 to calculate the number of Ca2+ ions in 0.05 moles of Ca(NO3)2?

Yes, knowing the molar mass of Ca(NO3)2 is necessary in order to calculate the number of Ca2+ ions in 0.05 moles of Ca(NO3)2. This is because the molar mass is used to convert moles of the compound to molecules, which is a necessary step in the calculation.

5. Can the same formula be used to calculate the number of Ca2+ ions in other concentrations of Ca(NO3)2?

Yes, the same formula can be used to calculate the number of Ca2+ ions in other concentrations of Ca(NO3)2 as long as you know the concentration (in moles) and the molar mass of the compound. The only change would be the number of moles of Ca(NO3)2 used in the calculation, depending on the concentration given.

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