2 GC problems...help please!

[virtualmaster999]

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Hi all!

Could someone help me with two GC problems I got stuck on? (both from bootcamp, but Im still confused)

1) 100 mL of 0.50 M CaCl2(aq) is mixed with 100 mL of 0.25 M H2SO4(aq). What is the final concentration of [Ca2+] in this solution? CaSO4 is insoluble in solution.


2) A 1.0 L sample of an aqueous solution contains 0.20 mol of NaCl and 0.10 mol of MgCl2. What is the minimum amount of moles of AgNO3 that must be added to the solution to precipitate all of the Cl- ions as AgCl(s)?
-So I know how to get the 0.4 mols part..but in the explanation, I was confused where it said "Since there is only one silver atom in AgNO3, we will need 0.40 mol of Ag to react with all 0.40 mol of Cl–"
How do you get to this? What if there were 2 Ag atoms??

Anything helps, and I truly appreciate everything!!

Thanks in advance!!

 

[KyoPhan]

When placed in water, immediately how many mols of Ca+2 and how many mols of SO4-2 are there?
Ca+2 - 0.05mol from 100mL x 0.50M - remember to convert to liters
SO4-2 - 0.025mol

Limiting reagent is SO4-2, so use that to determine how much Ca+2 gets used up to make CaSO4(s) when they combine.
0.05mol - 0.025mol = 0.025mol of Ca+2 remaining
Total volume when mixed is 100mL+100mL = 200mL

Final concentration: [Ca+2] = #mol/#Liters
=0.025mol/200mL
= 0.025mol/0.2L
= 0.125M

I haven't touched chem in a while. Is that the correct answer?

 

[100%permwinner]

When placed in water, immediately how many mols of Ca+2 and how many mols of SO4-2 are there?
Ca+2 - 0.05mol from 100mL x 0.50M - remember to convert to liters
SO4-2 - 0.025mol

Limiting reagent is SO4-2, so use that to determine how muchol of Ca+2 remaining
Total volume when mixed is 100mL+100mL = 200mL

Ca+2 gets used up to make CaSO4(s) when they combine.
0.05mol - 0.025mol = 0.025m
Final concentration: [Ca+2] = #mol/#Liters
=0.025mol/200mL
= 0.025mol/0.2L
= 0.125M

I haven't touched chem in a while. Is that the correct answer?

Sulfuric acid will be completely consumed first and half of Ca2+ will be consumed at the same time. I agree with the calculations and answer.

 

[100%permwinner]

Hi all!

Could someone help me with two GC problems I got stuck on? (both from bootcamp, but Im still confused)

1) 100 mL of 0.50 M CaCl2(aq) is mixed with 100 mL of 0.25 M H2SO4(aq). What is the final concentration of [Ca2+] in this solution? CaSO4 is insoluble in solution.


2) A 1.0 L sample of an aqueous solution contains 0.20 mol of NaCl and 0.10 mol of MgCl2. What is the minimum amount of moles of AgNO3 that must be added to the solution to precipitate all of the Cl- ions as AgCl(s)?
-So I know how to get the 0.4 mols part..but in the explanation, I was confused where it said "Since there is only one silver atom in AgNO3, we will need 0.40 mol of Ag to react with all 0.40 mol of Cl–"
How do you get to this? What if there were 2 Ag atoms??

Anything helps, and I truly appreciate everything!!

Thanks in advance!!

1) Another person has correctly answered this question.
2) In the mixture, there are 0.4 moles of Cl- total. Na+, Mg2+, and nitrate are all spectator ions that don't precipitate. If you write out the net ionic equation, you will realize that the stoichimoetric ratio of Ag+ to Cl- to AgCl is 1:1:1. It makes sense that the moles of Ag+ added must equal to the total moles of Cl- present in the solution.

 

[virtualmaster999]

Thank you both so much!!

 

[KyoPhan]

Also, just make sure that the ratio at which they are combined is correct. In this case, it's 1:1 based on the equation.
Ca+2(aq) + SO4-2(aq) ---> CaSO4(s)

 

[virtualmaster999]

1) Another person has correctly answered this question.
2) In the mixture, there are 0.4 moles of Cl- total. Na+, Mg2+, and nitrate are all spectator ions that don't precipitate. If you write out the net ionic equation, you will realize that the stoichimoetric ratio of Ag+ to Cl- to AgCl is 1:1:1. It makes sense that the moles of Ag+ added must equal to the total moles of Cl- present in the solution.

Quick question about this...if the formula was like Ag2O, (rather than AgNO3) would you have 0.8 mol of Ag, since it is 0.4 mol Cl-/ Ag?

 

[100%permwinner]

Quick question about this...if the formula was like Ag2O, (rather than AgNO3) would you have 0.8 mol of Ag, since it is 0.4 mol Cl-/ Ag?

If that's the case, the equation would look like this Ag2O + 2Cl- -->2AgCl Still 0.4 moles of Ag2O is required as the ratio of Ag+ to Cl- is 1:1 (=2:2).
There is an analogous reaction under "Structure and Properties" https://en.wikipedia.org/wiki/Silver_oxide

 

[100%permwinner]

If that's the case, the equation would look like this Ag2O + 2Cl- -->2AgCl Still 0.4 moles of Ag2O is required as the ratio of Ag+ to Cl- is 1:1 (=2:2).
There is an analogous reaction under "Structure and Properties" https://en.wikipedia.org/wiki/Silver_oxide

Excuse me. Only 0.2 moles of Ag2O is needed. 0.4 moles of Ag+ is needed.

 

[virtualmaster999]

Excuse me. Only 0.2 moles of Ag2O is needed. 0.4 moles of Ag+ is needed.

I see I see. Thank you again!